This document summarizes a study that investigated the temperature-induced changes in microstructure and dynamics of MEH-PPV films using various techniques. Solid-state NMR was used to characterize polymer chain motions as a function of temperature, finding differences in activation energy between films cast from toluene versus chloroform. WAXS experiments revealed that the interchain spacing in molecular aggregates increases with temperature, particularly where molecular relaxations occur. Fluorescence spectroscopy showed modifications upon temperature treatment that correlated with changes observed using WAXS.
Dear Customer,
Stabicon has helped needs of customers in specific areas of the pharmaceutical Analytical Method Development, Validation and Stability study. As the expansion of our analytical services in new technologies and testing methods to help our clients in characterizing future medicines. We understand biology at each of these levels to advance an integrated view of life processes for Biopharmaceuticals. We realize that future medicines (Biopharma) success requires ability to integrate protein testing capabilities which will provide strategic time and cost advantage for Biopharmaceutical sector.
We would like to share our presentation on Biopharma solution, to download the presentation please click on the below link
https://www.box.net/shared/aboumapp9h9gftunenja/1f7c7a6ef1/rss.xml
If you are interested in our Biopharma services, it will be a good idea to interact with our technical team/ commercial team for further clarification, looking forward to your response.
Thanking you and assuring our best service at all time
Regards
Vijay
Project Director
Stabicon Life Sciences Pvt Ltd
Mobile: +919591974355/080-41714280
www.stabicon.com
Jan Jensen's presentation at WATOC 2011molmodbasics
The document describes the Effective Fragment Molecular Orbital (EFMO) method, which blurs the boundary between quantum mechanical and molecular mechanical approaches. EFMO extracts multipoles and polarizabilities from monomer quantum calculations to model polarization effects classically. It also performs dimer quantum calculations to model covalent and non-Coulomb interactions directly. EFMO has been implemented in GAMESS and shows improved accuracy over the Fragment Molecular Orbital method for modeling the 20-residue Trp cage peptide.
Blurring the boundary between linear scaling QM, QM/MM and polarizable force ...molmodbasics
The document describes the Effective Fragment Molecular Orbital (EFMO) method, which blurs the boundary between linear scaling quantum mechanics, quantum mechanics/molecular mechanics, and polarizable force fields. EFMO extracts properties from monomer self-consistent field calculations and then computes many-body polarization and Coulomb interactions classically. It has been implemented in GAMESS and shown to provide more accurate energies and gradients than the Fragment Molecular Orbital method for a test case of the Trp cage protein. EFMO is presented as a promising method for efficiently treating large biomolecular systems through a quantum-mechanics-like treatment of short-range effects combined with a classical treatment of long-range interactions.
This document summarizes key concepts about enzymes, energy, and metabolism from Chapter 8.
It defines energy and explains that energy transformations are linked to chemical reactions in cells. It also describes the two main types of energy - potential and kinetic energy.
It then discusses metabolism, anabolic and catabolic reactions, and how enzymes are involved in catalyzing biochemical reactions. The laws of thermodynamics are also summarized, especially how free energy is related to work and how ATP is used to transport energy in cells.
Metabolic pathways are organized networks of chemical reactions that are interconnected and regulated by enzymes and feedback inhibition to maintain homeostasis.
This study investigated the structural, thermodynamic and unfolding properties of the kappa class glutathione transferase (CdGSTK1-1) from Camelus dromedarius. The key findings were:
1) CdGSTK1-1 was expressed in E. coli and purified. Analytical gel filtration showed it has a unique trimeric structure.
2) CdGSTK1-1 exhibited low thermal stability and unfolded through three states with intermediate species formation. The first transition melting point was 40.3°C and the second was 49.1°C.
3) Intrinsic fluorescence and near-UV CD studies indicated that substrate binding did not cause major conformational changes in
This document summarizes a study that investigated how the nanostructure and microstructure of poly(L-lactic acid)/layered silicate hybrids affects their morphological and thermomechanical properties. Nanocomposites and microcomposites with various loadings of natural and organically-modified montmorillonite clay were produced by solution casting. Characterization techniques like XRD, TEM, AFM, and DSC were used to analyze the structure and properties. The results showed that at low clay content, exfoliation dominates, but at higher loadings both exfoliation and intercalation occur. The addition of organoclay improved thermal stability and the polymer's thermal behavior depended on the clay nature and
International Journal of Polymer Science & Engineering
is a peer-reviewed journal that covers all aspects of polymer science and engineering. Journal mainly focuses on polymerization techniques and recent advances of plastic engineering. It accepts both original research papers as well as comprehensive review articles.
This document summarizes research on synthesizing polylactide/clay nanocomposites by in situ polymerization of D,L-lactide monomer in supercritical carbon dioxide. Polylactide chains were grafted onto clay surfaces, leading to exfoliated nanocomposite morphologies. High clay content "masterbatches" of 30-50% clay were produced and used to create commercial polylactide nanocomposites with 3% clay by melt blending. The resulting nanocomposites showed improved stiffness, toughness, and impact resistance compared to pure polylactide.
Dear Customer,
Stabicon has helped needs of customers in specific areas of the pharmaceutical Analytical Method Development, Validation and Stability study. As the expansion of our analytical services in new technologies and testing methods to help our clients in characterizing future medicines. We understand biology at each of these levels to advance an integrated view of life processes for Biopharmaceuticals. We realize that future medicines (Biopharma) success requires ability to integrate protein testing capabilities which will provide strategic time and cost advantage for Biopharmaceutical sector.
We would like to share our presentation on Biopharma solution, to download the presentation please click on the below link
https://www.box.net/shared/aboumapp9h9gftunenja/1f7c7a6ef1/rss.xml
If you are interested in our Biopharma services, it will be a good idea to interact with our technical team/ commercial team for further clarification, looking forward to your response.
Thanking you and assuring our best service at all time
Regards
Vijay
Project Director
Stabicon Life Sciences Pvt Ltd
Mobile: +919591974355/080-41714280
www.stabicon.com
Jan Jensen's presentation at WATOC 2011molmodbasics
The document describes the Effective Fragment Molecular Orbital (EFMO) method, which blurs the boundary between quantum mechanical and molecular mechanical approaches. EFMO extracts multipoles and polarizabilities from monomer quantum calculations to model polarization effects classically. It also performs dimer quantum calculations to model covalent and non-Coulomb interactions directly. EFMO has been implemented in GAMESS and shows improved accuracy over the Fragment Molecular Orbital method for modeling the 20-residue Trp cage peptide.
Blurring the boundary between linear scaling QM, QM/MM and polarizable force ...molmodbasics
The document describes the Effective Fragment Molecular Orbital (EFMO) method, which blurs the boundary between linear scaling quantum mechanics, quantum mechanics/molecular mechanics, and polarizable force fields. EFMO extracts properties from monomer self-consistent field calculations and then computes many-body polarization and Coulomb interactions classically. It has been implemented in GAMESS and shown to provide more accurate energies and gradients than the Fragment Molecular Orbital method for a test case of the Trp cage protein. EFMO is presented as a promising method for efficiently treating large biomolecular systems through a quantum-mechanics-like treatment of short-range effects combined with a classical treatment of long-range interactions.
This document summarizes key concepts about enzymes, energy, and metabolism from Chapter 8.
It defines energy and explains that energy transformations are linked to chemical reactions in cells. It also describes the two main types of energy - potential and kinetic energy.
It then discusses metabolism, anabolic and catabolic reactions, and how enzymes are involved in catalyzing biochemical reactions. The laws of thermodynamics are also summarized, especially how free energy is related to work and how ATP is used to transport energy in cells.
Metabolic pathways are organized networks of chemical reactions that are interconnected and regulated by enzymes and feedback inhibition to maintain homeostasis.
This study investigated the structural, thermodynamic and unfolding properties of the kappa class glutathione transferase (CdGSTK1-1) from Camelus dromedarius. The key findings were:
1) CdGSTK1-1 was expressed in E. coli and purified. Analytical gel filtration showed it has a unique trimeric structure.
2) CdGSTK1-1 exhibited low thermal stability and unfolded through three states with intermediate species formation. The first transition melting point was 40.3°C and the second was 49.1°C.
3) Intrinsic fluorescence and near-UV CD studies indicated that substrate binding did not cause major conformational changes in
This document summarizes a study that investigated how the nanostructure and microstructure of poly(L-lactic acid)/layered silicate hybrids affects their morphological and thermomechanical properties. Nanocomposites and microcomposites with various loadings of natural and organically-modified montmorillonite clay were produced by solution casting. Characterization techniques like XRD, TEM, AFM, and DSC were used to analyze the structure and properties. The results showed that at low clay content, exfoliation dominates, but at higher loadings both exfoliation and intercalation occur. The addition of organoclay improved thermal stability and the polymer's thermal behavior depended on the clay nature and
International Journal of Polymer Science & Engineering
is a peer-reviewed journal that covers all aspects of polymer science and engineering. Journal mainly focuses on polymerization techniques and recent advances of plastic engineering. It accepts both original research papers as well as comprehensive review articles.
This document summarizes research on synthesizing polylactide/clay nanocomposites by in situ polymerization of D,L-lactide monomer in supercritical carbon dioxide. Polylactide chains were grafted onto clay surfaces, leading to exfoliated nanocomposite morphologies. High clay content "masterbatches" of 30-50% clay were produced and used to create commercial polylactide nanocomposites with 3% clay by melt blending. The resulting nanocomposites showed improved stiffness, toughness, and impact resistance compared to pure polylactide.
This document summarizes a study of the photoluminescence and relaxation processes in MEH-PPV (poly(2-methoxy-5-(2-ethylhexyloxy)-p-phenylene-vinylene)). The study found two main thermal relaxation transitions in MEH-PPV: a glass transition around 340 K and a β-relaxation between 200-220 K. The glass transition is strongly correlated with the dissociation of fluorescent emissive interchain complexes, while the β-relaxation involves movements of the lateral substituents and CH2 groups along the polymer backbone. NMR experiments showed increasing mobility through the side chains, with carbons closer to the aromatic ring being more rigid. A kinetic
This document summarizes a solid-state nuclear magnetic resonance study of molecular dynamics in the polymer MEH-PPV. The main findings are:
1) Slow motions (1 Hz-1 kHz) in the polymer backbone involve small angle librations over a temperature range of 213-323 K.
2) Two motional regimes were identified in the side chains: intermediate motions (1-50 kHz) for all chemical groups, and additional fast rotation (100 MHz) for terminal CH3 groups.
3) A correlation was observed between motional parameters determined from NMR and changes in photoluminescence behavior with temperature.
This document summarizes femtosecond-resolved experiments on the primary photochemistry of 9-nitroanthracene. The experiments observed the ultrafast decay of the initially excited singlet state through time-resolved fluorescence, and detected the accumulation of the anthryloxy radical and formation of the relaxed phosphorescent T1 state through transient absorption experiments. The experiments provide timescales for the formation of the primary photoproducts, the anthryloxy radical and the T1 state, which both occur within a few picoseconds. Calculations were also performed to understand the molecular orbitals responsible for intersystem crossing between the singlet and triplet manifolds.
Role of αc–relaxation in high-temperature polymer deformation.
Proceedings of the American Society for Composites 2009-Twenty-Fourth Technical ConferenceWith the Canadian Association for Composite Structures and Materials (Joint Canadian-American International Conference), September 15-17, Newark, DE
This article discusses the solvent-conjugated polymer interactions of MEH-PPV and PF in various solvent solutions and thin films. Absorption and emission spectra were measured for polymer solutions, and thin films were prepared by dip or spin coating. The results show that MEH-PPV and PF exhibit different behaviors in solutions and films based on solvent quality and chain conformation. Specifically, dispersive forces were found to influence the effective conjugation of MEH-PPV chains, while energy transfer processes differed for the a and b chains of PF based on solvent. The memory effect, where chain conformations are maintained from solution to film, also varied between the two polymers and based on solvent used.
RELATIVISTIC MEAN FIELD STUDY OF SM ISOTOPES WITH FTBCS APPROACHijrap
A theoretical study of the thermal pairing correlation as a function of temperature is performed for eveneven
148-154Sm isotopes using Finite Temperature Bardeen-Cooper-Schrieffer (FTBCS) approach within the
Relativistic Mean Field (RMF) model. Numerical results obtained at T=0 are found to be consistent with
the available experimental values. Further, results show the thermal dependency of various nuclear
parameters like gap parameter, pairing energy, binding energy, deformation and density. At T≠0.0 MeV,
the destruction of Cooper pairs and the pairing phase transition as well as shape transition is observed in
148-154Sm nuclei at critical temperature Tc≠0.
On the-mechanism-of-proton-conductivity-in-h-sub3sub o-sbteo-sub6sub_2012_jou...Javier Lemus Godoy
This document summarizes a study investigating the proton conductivity mechanism in H3OSbTeO6 using neutron diffraction, quasielastic neutron scattering, and NMR experiments at various temperatures. H3OSbTeO6 has an outstanding proton conductivity even at room temperature. It consists of a three-dimensional framework of corner-sharing SbO6 and TeO6 octahedra forming cages where H3O+ ions are located. Three types of ion motion were observed: rotations of the H3O group, jumps between equivalent positions within cages, and long-range translational diffusion between cages. Structural changes reflected the onset of ionic conductivity. Details of the complex diffusion mechanism are provided.
Thermally Stimulated Discharge Current study of PMMA:PVP blendsinventionjournals
International Journal of Pharmaceutical Science Invention (IJPSI) is an international journal intended for professionals and researchers in all fields of Pahrmaceutical Science. IJPSI publishes research articles and reviews within the whole field Pharmacy and Pharmaceutical Science, new teaching methods, assessment, validation and the impact of new technologies and it will continue to provide information on the latest trends and developments in this ever-expanding subject. The publications of papers are selected through double peer reviewed to ensure originality, relevance, and readability. The articles published in our journal can be accessed online.
Coulomb Screening and Coherent Phonon in Methylammonium Lead Iodide PerovskitesLexi Cao
This document reports on a study of exciton and carrier dynamics in methylammonium lead iodide perovskite (CH3NH3PbI3) in the tetragonal and orthorhombic phases using transient absorption spectroscopy. The authors observe stronger saturation of free carrier concentration under high light intensity in the orthorhombic phase compared to the tetragonal phase. They attribute this to weaker Coulomb screening and more difficult exciton dissociation in the orthorhombic phase due to its smaller dielectric constant and larger exciton binding energy. At high excitation intensities and low temperature, they also observe a coherent phonon oscillation with a frequency of 23.4 cm-1 that may contribute
Relativistic Mean Field Study of SM Isotopes with FTBCS Approach ijrap
This document summarizes a study that uses the Relativistic Mean Field (RMF) model combined with the Finite Temperature Bardeen-Cooper-Schrieffer (FTBCS) approach to study pairing correlations in even-even 148-154Sm isotopes as a function of temperature. At zero temperature, results for various nuclear properties are consistent with experimental data. As temperature increases from zero, pairing is destroyed and a pairing phase transition is observed in the Sm isotopes at a critical non-zero temperature. The document outlines the RMF and FTBCS formalisms used and discusses numerical calculations of properties like binding energy, deformation, and density as temperature varies.
The document summarizes research investigating the interface phenomena of poly(o-ethoxyaniline) (POEA) films using atomic force spectroscopy. The study found that POEA films consist of conducting islands surrounded by a less conductive matrix. The conducting islands were characterized by the presence of double-layer forces and visualized using transmission electron microscopy. The conducting islands were only 15 nm in diameter and could only be identified using adhesion mapping, not contact mode atomic force microscopy which showed larger aggregates. The degree of doping and pH affected the morphology and interactions observed, with fully dedoped POEA at pH 5 and partially conducting polyaniline.
This document discusses a method for predicting stereochemical reaction paths using orbital interactions between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of reacting species. The method involves identifying the HOMO and LUMO regions of the reacting molecules and determining which orientation leads to maximum overlap between the HOMO of one species and LUMO of the other. Several examples of intramolecular reactions are analyzed using this approach. The method is presented as a simple and practical way to interpret and predict favorable reaction stereochemistry.
This document summarizes a study on the effects of solvent and molecular weight on the fluorescence emission of MEH-PPV. Three MEH-PPV samples with molecular weights of 51 kg/mol, 86 kg/mol, and 125 kg/mol were dissolved in two solvents, chloroform and toluene, at concentrations ranging from 10-8 mol/L to 10-4 mol/L. Films were produced from these solutions. The fluorescence spectra of the solutions and films showed differences due to how the solvents solvate the polymer chains. A red shift in fluorescence was observed at higher concentrations, which can be explained by Kasha's rule. Conformations observed in solution are partially retained in the solid films
This document describes a study of the effects of solvent and molecular weight on the fluorescence emission of MEH-PPV. MEH-PPV samples with three different molecular weights were dissolved in two solvents, chloroform and toluene, at various concentrations. Fluorescence spectra were recorded for the solutions and films cast from the solutions. The films cast from chloroform solutions exhibited lower crystallinity than those from toluene solutions. A red shift in the fluorescence spectra was observed at higher concentrations, which can be explained by Kasha's rule regarding chromophore orientation. The conformations observed in solution are partially retained in the solid films. Annealing films eliminates stressed conformations and leads to sharper fluorescence spectra.
Research Inventy : International Journal of Engineering and Scienceresearchinventy
This document summarizes a research study on the thermoluminescence properties of nanocrystalline europium-doped barium sulfate (BaSO4:Eu) phosphor. Key findings include:
1) Nanocrystalline BaSO4:Eu powder was successfully synthesized via a chemical co-precipitation technique and characterized using XRD and TEM analysis.
2) TL measurements showed a single prominent dosimetric peak around 456 K, above room temperature, making the material suitable for radiation dosimetry.
3) The material exhibited a linear dose response up to 100 Gy. Deconvolution of the TL glow curve identified two trap centers responsible for the observed luminescence
This document summarizes a study on how geometric confinement of building blocks controls the mechanical properties of poly(urethane−urea) copolymer films. The researchers prepared copolymer films using poly(ethylene oxide) soft segments of different molecular weights and dried the films at different temperatures. They found that films dried at higher temperatures exhibited a hierarchical structure with tightly packed helical and sheet-like secondary structures. These films demonstrated an unusual combination of stiffness, strength, extensibility, and toughness due to confinement of soft segment crystallization within hard segment channels. The confinement is driven by interactions not previously observed in polyurethane copolymers and results in a structural hierarchy that mimics protein structures.
This document summarizes a study on how geometric confinement of building blocks controls the mechanical properties of poly(urethane−urea) copolymer films. The researchers prepared copolymer films using poly(ethylene oxide) soft segments of different molecular weights and dried the films at different temperatures. They found that films dried at higher temperatures exhibited a hierarchical structure with tightly packed helical and sheet-like secondary structures. These films demonstrated an unusual combination of stiffness, strength, extensibility, and toughness due to confinement of soft segment crystallization within hard segment channels. The severity of confinement could be tuned through soft segment molecular weight and drying temperature, offering a way to control material properties.
Roman Boulatov and colleagues developed a new approach to force spectroscopy using small molecule probes to apply mechanical forces to reactive groups and study chemomechanical phenomena. They designed a cyclic molecule, stilbene, that can be switched between a relatively unstrained and highly strained state using light, applying forces in the range of tens to hundreds of piconewtons. They observed the rate of dissociation of a carbon-carbon bond increase by a factor of 106 under the highest forces. This new approach miniaturizes force spectroscopy to the nanoscale and allows reactions to be monitored using conventional spectroscopy tools, providing insights into mechanically assisted chemistry not visible to other methods.
Bridging length and time scales in biomolecular systemsuvacolloquium
Speaker: prof. dr. Peter Bolhuis
Date: 27-11-2015
Abstract: Biomolecular systems, whether in living cells or in complex biomaterials, often undergo rare but important conformational changes; for instance, proteins can fold and (partially) unfold, bind and dissociate again, lipid membranes can phase separate, or transform shape and topology, DNA can hybridize, supercoil, and so on. Molecular dynamics simulation can in principle provide useful predictions of such processes on an atomistic level that are complementary to experiment. However, in practice, molecular dynamics is far from fulfilling this promise due to the large size of a cellular system (billions of atoms) and the long times involved (at least on the order of seconds). The multiscale modeling framework aims to circumvent this problem by envisioning hierarchical levels of description, each appropriate for certain length and time scales of a biophysical system. The challenge for the computer simulator is to develop the right description for each length or time sc!
ales, to link different scales together and to develop efficient sampling algorithms. One approach is to start with the atomistic level molecular dynamics description and use this to define a coarser grained description. Another approach is to realize that many processes such as (un)folding and other conformational changes in proteins in fact are rare events caused by high free energy barriers between stable states. To overcome such barriers, many techniques have been developed, e.g. replica exchange, metadynamics, and transition path sampling. In this presentation I will focus on the need for such simulation methods, and exemplify these methods on interesting applications such as proton transfer in a protein environment, conformational changes in (signalling) proteins, chaperone function, protein and fibril self-assembly, cooperativity in G-coupled receptors. In each case, we can gain novel insight from these simulations.
This document is the thesis of Qi Chen on the topic of using block copolymer vesicles as nanocontainers to study enzymatic reactions under confinement. The thesis introduces block copolymer vesicles as biomimetic containment systems that have better mechanical stability than liposomes. It discusses using these vesicles to encapsulate enzymes and study their reaction kinetics under nanoscale confinement, which has received little attention due to the instability of liposome membranes. The thesis aims to control the size and morphology of the block copolymer vesicles and study enzymatic reactions encapsulated within the vesicles to gain insights into reaction kinetics at small volumes comparable to cellular compartments.
This document reports on a study of the photophysical and electroluminescent properties of a conjugated-nonconjugated multi-block copolymer. Time-resolved fluorescence experiments and comparisons of solution and solid state fluorescence indicate that in the solid state, emission comes from associated species like ground state dimers or excimers, rather than isolated chromophores. Absorption, fluorescence, FTIR and NMR spectroscopy were used to characterize the materials. Light-emitting diodes were fabricated using the copolymer to study its electroluminescent properties.
Este documento apresenta uma revisão sobre dispositivos poliméricos eletroluminescentes. Em três frases:
1) É apresentada uma visão geral sobre dispositivos que utilizam polímeros conjugados como meio ativo e descreve seus principais componentes.
2) São mostrados exemplos de polímeros e copolímeros conjugados comumente empregados em dispositivos poliméricos emissores de luz, como poli(fluorenos).
3) Alguns aspectos das propriedades de foto e eletroluminescência
This document summarizes a study of the photoluminescence and relaxation processes in MEH-PPV (poly(2-methoxy-5-(2-ethylhexyloxy)-p-phenylene-vinylene)). The study found two main thermal relaxation transitions in MEH-PPV: a glass transition around 340 K and a β-relaxation between 200-220 K. The glass transition is strongly correlated with the dissociation of fluorescent emissive interchain complexes, while the β-relaxation involves movements of the lateral substituents and CH2 groups along the polymer backbone. NMR experiments showed increasing mobility through the side chains, with carbons closer to the aromatic ring being more rigid. A kinetic
This document summarizes a solid-state nuclear magnetic resonance study of molecular dynamics in the polymer MEH-PPV. The main findings are:
1) Slow motions (1 Hz-1 kHz) in the polymer backbone involve small angle librations over a temperature range of 213-323 K.
2) Two motional regimes were identified in the side chains: intermediate motions (1-50 kHz) for all chemical groups, and additional fast rotation (100 MHz) for terminal CH3 groups.
3) A correlation was observed between motional parameters determined from NMR and changes in photoluminescence behavior with temperature.
This document summarizes femtosecond-resolved experiments on the primary photochemistry of 9-nitroanthracene. The experiments observed the ultrafast decay of the initially excited singlet state through time-resolved fluorescence, and detected the accumulation of the anthryloxy radical and formation of the relaxed phosphorescent T1 state through transient absorption experiments. The experiments provide timescales for the formation of the primary photoproducts, the anthryloxy radical and the T1 state, which both occur within a few picoseconds. Calculations were also performed to understand the molecular orbitals responsible for intersystem crossing between the singlet and triplet manifolds.
Role of αc–relaxation in high-temperature polymer deformation.
Proceedings of the American Society for Composites 2009-Twenty-Fourth Technical ConferenceWith the Canadian Association for Composite Structures and Materials (Joint Canadian-American International Conference), September 15-17, Newark, DE
This article discusses the solvent-conjugated polymer interactions of MEH-PPV and PF in various solvent solutions and thin films. Absorption and emission spectra were measured for polymer solutions, and thin films were prepared by dip or spin coating. The results show that MEH-PPV and PF exhibit different behaviors in solutions and films based on solvent quality and chain conformation. Specifically, dispersive forces were found to influence the effective conjugation of MEH-PPV chains, while energy transfer processes differed for the a and b chains of PF based on solvent. The memory effect, where chain conformations are maintained from solution to film, also varied between the two polymers and based on solvent used.
RELATIVISTIC MEAN FIELD STUDY OF SM ISOTOPES WITH FTBCS APPROACHijrap
A theoretical study of the thermal pairing correlation as a function of temperature is performed for eveneven
148-154Sm isotopes using Finite Temperature Bardeen-Cooper-Schrieffer (FTBCS) approach within the
Relativistic Mean Field (RMF) model. Numerical results obtained at T=0 are found to be consistent with
the available experimental values. Further, results show the thermal dependency of various nuclear
parameters like gap parameter, pairing energy, binding energy, deformation and density. At T≠0.0 MeV,
the destruction of Cooper pairs and the pairing phase transition as well as shape transition is observed in
148-154Sm nuclei at critical temperature Tc≠0.
On the-mechanism-of-proton-conductivity-in-h-sub3sub o-sbteo-sub6sub_2012_jou...Javier Lemus Godoy
This document summarizes a study investigating the proton conductivity mechanism in H3OSbTeO6 using neutron diffraction, quasielastic neutron scattering, and NMR experiments at various temperatures. H3OSbTeO6 has an outstanding proton conductivity even at room temperature. It consists of a three-dimensional framework of corner-sharing SbO6 and TeO6 octahedra forming cages where H3O+ ions are located. Three types of ion motion were observed: rotations of the H3O group, jumps between equivalent positions within cages, and long-range translational diffusion between cages. Structural changes reflected the onset of ionic conductivity. Details of the complex diffusion mechanism are provided.
Thermally Stimulated Discharge Current study of PMMA:PVP blendsinventionjournals
International Journal of Pharmaceutical Science Invention (IJPSI) is an international journal intended for professionals and researchers in all fields of Pahrmaceutical Science. IJPSI publishes research articles and reviews within the whole field Pharmacy and Pharmaceutical Science, new teaching methods, assessment, validation and the impact of new technologies and it will continue to provide information on the latest trends and developments in this ever-expanding subject. The publications of papers are selected through double peer reviewed to ensure originality, relevance, and readability. The articles published in our journal can be accessed online.
Coulomb Screening and Coherent Phonon in Methylammonium Lead Iodide PerovskitesLexi Cao
This document reports on a study of exciton and carrier dynamics in methylammonium lead iodide perovskite (CH3NH3PbI3) in the tetragonal and orthorhombic phases using transient absorption spectroscopy. The authors observe stronger saturation of free carrier concentration under high light intensity in the orthorhombic phase compared to the tetragonal phase. They attribute this to weaker Coulomb screening and more difficult exciton dissociation in the orthorhombic phase due to its smaller dielectric constant and larger exciton binding energy. At high excitation intensities and low temperature, they also observe a coherent phonon oscillation with a frequency of 23.4 cm-1 that may contribute
Relativistic Mean Field Study of SM Isotopes with FTBCS Approach ijrap
This document summarizes a study that uses the Relativistic Mean Field (RMF) model combined with the Finite Temperature Bardeen-Cooper-Schrieffer (FTBCS) approach to study pairing correlations in even-even 148-154Sm isotopes as a function of temperature. At zero temperature, results for various nuclear properties are consistent with experimental data. As temperature increases from zero, pairing is destroyed and a pairing phase transition is observed in the Sm isotopes at a critical non-zero temperature. The document outlines the RMF and FTBCS formalisms used and discusses numerical calculations of properties like binding energy, deformation, and density as temperature varies.
The document summarizes research investigating the interface phenomena of poly(o-ethoxyaniline) (POEA) films using atomic force spectroscopy. The study found that POEA films consist of conducting islands surrounded by a less conductive matrix. The conducting islands were characterized by the presence of double-layer forces and visualized using transmission electron microscopy. The conducting islands were only 15 nm in diameter and could only be identified using adhesion mapping, not contact mode atomic force microscopy which showed larger aggregates. The degree of doping and pH affected the morphology and interactions observed, with fully dedoped POEA at pH 5 and partially conducting polyaniline.
This document discusses a method for predicting stereochemical reaction paths using orbital interactions between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of reacting species. The method involves identifying the HOMO and LUMO regions of the reacting molecules and determining which orientation leads to maximum overlap between the HOMO of one species and LUMO of the other. Several examples of intramolecular reactions are analyzed using this approach. The method is presented as a simple and practical way to interpret and predict favorable reaction stereochemistry.
This document summarizes a study on the effects of solvent and molecular weight on the fluorescence emission of MEH-PPV. Three MEH-PPV samples with molecular weights of 51 kg/mol, 86 kg/mol, and 125 kg/mol were dissolved in two solvents, chloroform and toluene, at concentrations ranging from 10-8 mol/L to 10-4 mol/L. Films were produced from these solutions. The fluorescence spectra of the solutions and films showed differences due to how the solvents solvate the polymer chains. A red shift in fluorescence was observed at higher concentrations, which can be explained by Kasha's rule. Conformations observed in solution are partially retained in the solid films
This document describes a study of the effects of solvent and molecular weight on the fluorescence emission of MEH-PPV. MEH-PPV samples with three different molecular weights were dissolved in two solvents, chloroform and toluene, at various concentrations. Fluorescence spectra were recorded for the solutions and films cast from the solutions. The films cast from chloroform solutions exhibited lower crystallinity than those from toluene solutions. A red shift in the fluorescence spectra was observed at higher concentrations, which can be explained by Kasha's rule regarding chromophore orientation. The conformations observed in solution are partially retained in the solid films. Annealing films eliminates stressed conformations and leads to sharper fluorescence spectra.
Research Inventy : International Journal of Engineering and Scienceresearchinventy
This document summarizes a research study on the thermoluminescence properties of nanocrystalline europium-doped barium sulfate (BaSO4:Eu) phosphor. Key findings include:
1) Nanocrystalline BaSO4:Eu powder was successfully synthesized via a chemical co-precipitation technique and characterized using XRD and TEM analysis.
2) TL measurements showed a single prominent dosimetric peak around 456 K, above room temperature, making the material suitable for radiation dosimetry.
3) The material exhibited a linear dose response up to 100 Gy. Deconvolution of the TL glow curve identified two trap centers responsible for the observed luminescence
This document summarizes a study on how geometric confinement of building blocks controls the mechanical properties of poly(urethane−urea) copolymer films. The researchers prepared copolymer films using poly(ethylene oxide) soft segments of different molecular weights and dried the films at different temperatures. They found that films dried at higher temperatures exhibited a hierarchical structure with tightly packed helical and sheet-like secondary structures. These films demonstrated an unusual combination of stiffness, strength, extensibility, and toughness due to confinement of soft segment crystallization within hard segment channels. The confinement is driven by interactions not previously observed in polyurethane copolymers and results in a structural hierarchy that mimics protein structures.
This document summarizes a study on how geometric confinement of building blocks controls the mechanical properties of poly(urethane−urea) copolymer films. The researchers prepared copolymer films using poly(ethylene oxide) soft segments of different molecular weights and dried the films at different temperatures. They found that films dried at higher temperatures exhibited a hierarchical structure with tightly packed helical and sheet-like secondary structures. These films demonstrated an unusual combination of stiffness, strength, extensibility, and toughness due to confinement of soft segment crystallization within hard segment channels. The severity of confinement could be tuned through soft segment molecular weight and drying temperature, offering a way to control material properties.
Roman Boulatov and colleagues developed a new approach to force spectroscopy using small molecule probes to apply mechanical forces to reactive groups and study chemomechanical phenomena. They designed a cyclic molecule, stilbene, that can be switched between a relatively unstrained and highly strained state using light, applying forces in the range of tens to hundreds of piconewtons. They observed the rate of dissociation of a carbon-carbon bond increase by a factor of 106 under the highest forces. This new approach miniaturizes force spectroscopy to the nanoscale and allows reactions to be monitored using conventional spectroscopy tools, providing insights into mechanically assisted chemistry not visible to other methods.
Bridging length and time scales in biomolecular systemsuvacolloquium
Speaker: prof. dr. Peter Bolhuis
Date: 27-11-2015
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This document is the thesis of Qi Chen on the topic of using block copolymer vesicles as nanocontainers to study enzymatic reactions under confinement. The thesis introduces block copolymer vesicles as biomimetic containment systems that have better mechanical stability than liposomes. It discusses using these vesicles to encapsulate enzymes and study their reaction kinetics under nanoscale confinement, which has received little attention due to the instability of liposome membranes. The thesis aims to control the size and morphology of the block copolymer vesicles and study enzymatic reactions encapsulated within the vesicles to gain insights into reaction kinetics at small volumes comparable to cellular compartments.
This document reports on a study of the photophysical and electroluminescent properties of a conjugated-nonconjugated multi-block copolymer. Time-resolved fluorescence experiments and comparisons of solution and solid state fluorescence indicate that in the solid state, emission comes from associated species like ground state dimers or excimers, rather than isolated chromophores. Absorption, fluorescence, FTIR and NMR spectroscopy were used to characterize the materials. Light-emitting diodes were fabricated using the copolymer to study its electroluminescent properties.
Este documento apresenta uma revisão sobre dispositivos poliméricos eletroluminescentes. Em três frases:
1) É apresentada uma visão geral sobre dispositivos que utilizam polímeros conjugados como meio ativo e descreve seus principais componentes.
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3) Alguns aspectos das propriedades de foto e eletroluminescência
O documento discute a eletrônica de polímeros como uma área promissora de pesquisa que pode levar a aplicações comerciais de baixo custo. Ele descreve o desenvolvimento de polímeros condutores e dispositivos orgânicos como OLEDs. Também destaca o potencial de mercado para aplicações como etiquetas RFID de baixo custo e displays flexíveis.
[SUMMARY] The ionic copolymer SAA (poly(styrene-co-acrylic acid-co-1-
pyrenylmethyl methacrylate)) was synthesized via radical polymerization in water and
characterized by thermal (DSC, TGA), spectroscopic (13C and 1H NMR, UV-VIS, FTIR,
steady-state and time-resolved fluorescence) and electrical (electroluminescence) analyses.
Blends with poly[2-methoxy-5-(2'-ethylhexyloxy)-p-phenylenevinylene] MEH-PPV were
studied from 0.01; 0.05; 0.10
O documento discute a pesquisa de um químico sobre polímeros condutores, conhecidos como polímeros eletrônicos ou OLED. O pesquisador aumentou a eficiência de luz e corrente elétrica desses materiais através da mistura com um co-polímero. A tecnologia OLED pode substituir LCDs e plasmas em telas mais finas e flexíveis, mas ainda enfrenta desafios como instabilidade do material.
This article discusses electroluminescence of MEH-PPV and poly(styrene-co-acrylic acid-co-1-pyrenylmethyl methacrylate) (SAA) blends. The SAA copolymer contains 3 mol% acrylic acid units and a small amount of pyrenyl groups. Blend films with various MEH-PPV/SAA ratios were prepared and their morphology was studied using microscopy. Devices using MEH-PPV alone had a turn-on voltage of 3.5 V and luminance of 500 cd/m2 at 5 V, while a 50/50 blend showed a turn-on of 2.5 V and luminance of 2300 cd
A tale of scale & speed: How the US Navy is enabling software delivery from l...sonjaschweigert1
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Encryption in Microsoft 365 - ExpertsLive Netherlands 2024Albert Hoitingh
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European Polymer Journal
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1
Contents lists available at ScienceDirect
European Polymer Journal
journal homepage: www.elsevier.com/locate/europolj
2 Temperature dependence of molecular dynamics and supramolecular
F
3 aggregation in MEH-PPV films: A solid-state NMR, X-ray and fluorescence
OO
4 spectroscopy study
5 A.A. Souza a, R.F. Cossiello b, T.S. Plivelic c, G.L. Mantovani a, G.C. Faria a, T.D.Z. Atvars b,
6 I.L. Torriani c,d, T.J. Bonagamba a, E.R. deAzevedo a,*
7 a
Instituto de Física de São Carlos, Universidade de São Paulo, Caixa Postal 369, 13560-970 São Carlos, SP, Brazil
PR
8 b
Instituto de Química, Universidade Estadual de Campinas, Caixa Postal 6154, 13084-971 Campinas, SP, Brazil
9 c
Laboratório Nacional de Luz Síncrotron, Caixa Postal 6192, 13083-970 Campinas, SP, Brazil
10 d
Instituto de Física, Universidade Estadual de Campinas, Caixa Postal 6165, 13084-971 Campinas, SP, Brazil
11
a r t i c l e i n f o a b s t r a c t
1 3
2 8
14
15
16
Article history:
Received 29 June 2008
Received in revised form 23 August 2008
D
This article presents an investigation of the temperature induced modification in the
microstructure and dynamics of poly[2-methoxy-5-(20 -ethylhexyloxy)-1,4-phenylenevin-
ylene] (MEH-PPV) cast films using Wide-Angle X-ray Scattering (WAXS), solid-state
29
30
31
TE
17 Accepted 16 September 2008
Nuclear Magnetic Resonance (NMR), and Fluorescence Spectroscopy (PL). MEH-PPV chain 32
18 Available online xxxx
19 motions were characterized as a function of temperature by NMR. The results indicated 33
that the solvent used to cast the films influences the activation energy of the side-chain 34
motions. This was concluded from the comparison of the activation energy of the toluene 35
20 Keywords:
21 MEH-PPV films
cast film, Ea = (54 ± 8) kJ/mol, and chloroform cast film, Ea = (69 ± 5) kJ/mol, and could be 36
EC
22 NMR attributed to the higher side-chain packing provided by chloroform that preferentially sol- 37
23 DIPSHIFT vates the side chain in contrast to toluene that solvates mainly the backbone. Concerning 38
24 WAXS the backbone mobility, it was observed that the torsional motions in the MEH-PPV have 39
25 Molecular aggregation average amplitude of $10° at 300 K, which was found to be independent of the solvent 40
26 Fluorescence used to cast the films. In order to correlate the molecular dynamics processes with the 41
27
changes in the microstructure of the polymer, in situ WAXS experiments as a function of 42
RR
temperature were performed and revealed that the interchain spacing in the MEH-PPV 43
molecular aggregates increases as a function of temperature, particularly at temperatures 44
where molecular relaxations occur. It was also observed that the WAXS peak associated 45
with the bilayer spacing, narrows and their by increases intensity whereas the peak asso- 46
ciated with the interbackbone planes reduces its intensity for higher temperatures. This 47
last result could be interpreted as a decrease in the number of aggregates and the reduction 48
CO
of the interchain species during the MEH-PPV relaxation processes. These WAXS results 49
were correlated with PL spectra modifications observed upon temperature treatments. 50
Ó 2008 Elsevier Ltd. All rights reserved. 51
52
53
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54 1. Introduction tron and hole transport properties [1–4]. The large-scale 58
electroluminescent devices can be feasible due to their 59
55 Conjugated polymers have potential to be employed in simple production. However, the efficiency of the electro- 60
56 several applications such as materials for light-emitting luminescence (EL) and photoluminescence (PL) is reduced 61
57 diodes, lasers and thin-film transistors due to their elec- when the conjugated polymers form interchain species 62
that arise as a result of molecular aggregation [5,6]. Molec- 63
ular aggregation and, consequently, the electro- and 64
* Corresponding author. Tel.: +55 16 33738086; fax: +55 1633739876.
E-mail address: azevedo@ifsc.usp.br (E.R. deAzevedo). photo-luminescence emissions and charge transport 65
0014-3057/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.eurpolymj.2008.09.030
Please cite this article in press as: Souza AA et al., Temperature dependence of molecular dynamics and supramolecular ...,
Eur Poly J (2008), doi:10.1016/j.eurpolymj.2008.09.030
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66 properties may be partially controlled by the processing 2. Experimental 126
67 conditions which change the polymer microstructure and
68 morphology [7–9]. MEH-PPV with average molar weight Mn = 86 kg/mol 127
69 Photoluminescence and electroluminescence are corre- and polydispersity Mn/Mw = 4.9 was obtained from 128
70 lated phenomena not only strongly dependent on the Sigma–Aldrich Co. Toluene and chloroform solvents with 129
71 microstructure of the material but also on the dynamics spectrophotometric grade were purchased from Acros. All 130
72 of the polymer chains [7–9]. For example, the temperature materials were used as received. 131
73 dependence of the electroluminescent devices with MEH- MEH-PPV solutions were prepared by dissolving the 132
74 PPV showed changes [10–12] associated with specific polymer samples in each solvent. After that, the solutions 133
75 movements of the polymer chain such as motions of the were maintained in the dark in a sealed flask. Films were 134
76 lateral groups at 220 K and related with the glass transition prepared by casting the solutions in a Petri dish, with slow 135
77 (Tg) at 330 K [13,14]. In our previous reports [13,14] it was evaporation under a saturated solvent atmosphere, at
F
136
78 postulated that the blue shift of the PL spectra at temper- room temperature, for 30 h. Later, the films were dried in 137
79 atures above the glass transition could be explained by an oven under dynamic vacuum at a temperature of ca. 138
OO
80 the interchain dissociation induced by thermal motions, 323 K for 24 h. Film thicknesses were approximately 139
81 although no further experimental evidence have been 30–40 lm. For WAXS experiments, multilayer samples of 140
82 given. up to 400 lm thicknesses were prepared by stacking 141
83 Wide-Angle X-ray Scattering (WAXS) and Transmis- pieces cut from a single film. 142
84 sion Electron Microscopy (TEM) showed that MEH-PPV Steady-state fluorescence spectra of MEH-PPV films 143
85 films form molecular aggregates that present local nano- were recorded using a PC1TM Photon Counting Spectroflu- 144
PR
86 scopic order with structural anisotropy [15,16]. The dif- orimeter from ISS Inc. The spectral range was from 600 to 145
87 fraction patterns obtained in stretched films were 800 nm for the emission spectra. Slits were selected for a 146
88 indexed proposing an orthorhombic unit cell with spectral resolution of ±0.5 nm. Excitation wavelength was 147
89 parameters a = 7.12 Å, b = 16.05 Å and c = 6.47 Å [16]. A kex = 490 nm. 148
90 further description of the molecular aggregates was pre- WAXS experiments were performed at the D11A-SAXS 149
91 sented recently [2], where it was shown that MEH-PPV beamline of the LNLS (Brazilian Synchrotron Light Labora- 150
92
93
94
chains are locally ordered with phenyl rings partially or-
ganized parallel to each other and also parallel to the
film plane. This molecular packing was described as a
D
tory). The wavelength used was 1.608 Å and the sample
detector distance was approximately 182 mm in all cases.
The films were set-up in two configurations: with the inci-
151
152
153
TE
95 superstructure unit cell consisting of a bilayer arrange- dent X-ray beam perpendicular () and near-parallel (||) to 154
96 ment with repeating distance of 24.2 Å along the b-axis, the film plane. 155
97 a characteristic distance of 6.3 Å assigned to repeated The samples were first examined at room temperature 156
98 unit along the backbone (c-axis), and the regular spacing for two-dimensional (2D) patterns. Data were recorded in 157
99 between the backbones of the coplanar phenylene rings Fuji film image plates and 30 min exposures were taken 158
EC
100 (a = 4.3 Å). Moreover, the size of the chain-packed in all cases. Average radial intensity profiles were obtained 159
101 MEH-PPV nanostructured domain was estimated from integrating an arbitrary 30° angular sector in the case of 160
102 the diffraction line profile and assumed to consist of no the isotropic scattering pattern ( incidence) and a similar 161
103 more than 4d-spacings in each crystallographic direction. sector centered around the maximum in the oriented scat- 162
104 Although the structure of MEH-PPV films and the con- tering ring (|| incidence). Intensities were normalized by 163
RR
105 formation of the polymer chains have been well de- the integrated intensity incident on the sample during 164
106 scribed in the literature and their influence on the PL the exposure and by sample absorption. Parasitic scatter- 165
107 and EL were also well understood, the relationship be- ing was subtracted from each pattern. 166
108 tween structure and dynamics of the polymer chains Afterwards, one-dimensional (1D) patterns for the 167
109 are not well known [16]. Therefore, the aim of this re- in situ thermal treatment were recorded using a linear po- 168
110 port is the study of the temperature dependence of the sition sensitive detector (PSD). The samples were placed in 169
CO
111 dynamics, supramolecular organization, and short-range a hot stage cell specially designed for X-ray scattering mea- 170
112 chain ordering of MEH-PPV films, when the film is cast surements (THM 600, Linkam Ltda [25]). For each of the 171
113 from two solvents, chloroform and toluene, with distinct experimental geometries ( and || incidences) the films 172
114 solvation abilities. The polymer chains dynamics was were placed in a sample support adapted to the hot stage. 173
115 studied by a set of very convenient solid-state NMR tech- The difference between the values of the temperature on 174
UN
116 niques to detect possible differences in the molecular the sample and the values set on the controller was less 175
117 dynamics due to molecular aggregation: DIPSHIFT than 5 K for all scans in the range 123–423 K, allowing a 176
118 (DIPolar-chemical SHIFT correlation) [17–20] and CODEX fairly precise determination of the thermal state of the 177
119 (Centerband-Only Detection of EXchange) [21–24]. Tem- sample. The in situ measurements were performed allow- 178
120 perature evolution of the supramolecular and the ing 5 min of stabilization and 15-min data acquisition for 179
121 short-range structures was studied by WAXS as well as each desired temperature. From room temperature the 180
122 Steady-state Fluorescence Spectroscopy allows to check samples were rapidly quenched (60 K/min) down to 181
123 whether structural changes had happen (due to its sensi- 123 K. Next, after each step of a heating ramp (10 K/min), 182
124 tivity to short range interaction among the polymer WAXS patterns were obtained for the temperatures 198, 183
125 chains). 273, 313, 348 and 423 K. The samples were kept at the 184
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185 highest temperature during 1 h. After this isothermal treat-
186 ment, additional data were taken. Finally, the samples
187 were cooled down to 348 and 293 K at the rate of
188 10 K/min, with additional exposures being obtained at
189 these temperatures. The 1 h annealing at 423 K, was
190 chosen well above the MEH-PPV glass transition tempera-
191 ture (Tg = 330 K) [13].
192 NMR experiments were performed using a VARIAN
193 INOVA spectrometer at 13C and 1H frequencies of 100.5
194 and 400.0 MHz, respectively. A VARIAN 7-mm MAS dou-
195 ble-resonance probe head with variable temperature (VT)
196 was used. The spinning speeds, varying between 4 and
F
197 6 kHz, were controlled by a VARIAN pneumatic system that
198 ensures a rotation stability of ±2 Hz. Typical p/2 pulses
OO
199 lengths of 3.5 and 4.5 ls were applied for 13C and 1H,
200 respectively. Time Proportional Phase Modulated (TPPM)
201 proton decoupling with field strength of 70 kHz, cross-
202 polarization time of 1 ms and recycle delays varying be-
203 tween 3 and 5 s were used. Amplitude of slow molecular
204 motions were investigated using CODEX technique
PR
205 [21,22] with mixing time tm of 200 ms and evolution times
206 (Ntr) ranging from 333 to 2500 ls. The temperature depen-
207 dence of 13C–1H dipolar coupling were measured using
208 DIPSHIFT technique [18], where 1H–1H homonuclear
209 decoupling was achieved by the Phase-Modulated-Lee-
210 Goldburg (PMLG) sequence [26,27], using field strengths
211
212
of approximately 80 kHz.
3. Results and discussions
D
TE
213 This article is organized as follow. The room tempera-
214 ture photoluminescence spectra of MEH-PPV films cast
215 form toluene and chloroform is presented and compared
together with a short discussion about the temperature
EC
216
Fig. 1. Steady-state fluorescence spectra of MEH-PPV films. (a) Room
217 dependence of the PL. In sequence, WAXS are analyzed as
temperature spectra of chloroform (square symbols) and toluene (circle
218 a function of temperature in order to give some insight symbols) cast films before and after annealing by 12 h at 363 K (full or
219 about the temperature dependence of the microstructure empty symbols, respectively). The arrow stands for the blue shift
220 of the MEH-PPV aggregates. Then, to elucidate the charac- observed as a function of temperature. (b) Steady-state fluorescence
221 teristics of the molecular dynamics processes in the poly- spectra of MEH-PPV films cast from chloroform as a function of
RR
temperature from 53 to 393 K. The inset show the integrated intensity
222 mer chains, solid-state NMR measurements are of the corresponding spectra of MEH-PPV films cast from chloroform as a
223 presented. Finally, a correlation between the strucutural function of temperature.
224 and dynamics results are presented and discussed in the
225 context of the change in the PL spectra.
range of 2000 cmÀ1 which are orders of magnitude larger 241
CO
226 3.1. Photoluminescence spectroscopy than expected for homogeneous broadening [33]. As it 242
can be observed in Fig. 1a, there is a slightly difference in 243
227 Steady-state fluorescence spectra (PL) of MEH-PPV films the intensity of the band assigned to the excimeric/inter- 244
228 cast from toluene and chloroform solutions before and chain species upon the different solvents, which are mostly 245
229 after annealing at 363 K for 12 h are shown in Fig. 1a. In erased with thermal annealing. We also noticed that there 246
UN
230 general, these spectra are composed by a higher intensity is an increase of the FWHM with the annealing, which can 247
231 band around 650 nm and a second overlapped band be attributed to the increase of the relative amount of 248
232 around 700 nm (Fig. 1). This spectrum, usually observed aggregates compared with the non-annealed sample. 249
233 for the MEH-PPV films, is assigned to the interchain species In order to provide information about the tempera- 250
234 separated by a backbone interplanar distance of $4.05 Å ture dependence of the photoluminescence, the PL spec- 251
235 [28–31]. The longer red-edge tail is also observed which tra was also recorded from 53 to 393 K for MEH-PPV 252
236 results from the overlap of two contributions, the vibronic films cast from chloroform, Fig. 1b. The behavior of the 253
237 progression of the aggregate emission and from the emis- spectra as a function of temperature is similar to the 254
238 sion of excimeric/interchain species [32]. Spectral broad- one reported in Ref. [13], i.e., at temperatures below 255
239 ening was estimated and the full-width at the half- 150 K little variation is observed either in the integrated 256
240 maximum (FWHM) showed that those values are in the intensity (see figure inset) or in the position of the PL 257
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258 bands. Between 150 and 300 K there is an increase in the For the interpretation of the structural changes, the 280
259 integrated intensity, which is accompanied by a blue curves were fitted using Gaussian functions for the peaks 281
260 shift. Above 300 K a stronger intensification and also a and a logarithmic baseline for the background. The individ- 282
261 blue shift is observed. Toluene cast films presents a sim- ually fitted contribution of each peak is plotted on the bot- 283
262 ilar behavior [13]. tom of the Fig. 2a and b whereas the total fit is represented 284
as a continuous red line in the same plots. The most impor- 285
263 3.2. Wide-Angle X-Ray Scattering (WAXS) tant wide angle peaks were referred to the molecular pack- 286
ing parameters proposed by Jeng et al. [2]. The first 287
264 The microstructure of the MEH-PPV films as well as reflection observed for q = 0.27 ÅÀ1 (d1 = 2p/q = 23.2 Å) is 288
265 the modifications induced by temperature was studied assumed to represent the bilayer chain packing distance. 289
266 by WAXS. Fig. 2 shows integrated intensity scans (left) The next important characteristic length observed for 290
267 from the 2D-WAXS images (right) for as cast MEH-PPV q = 1.03 ÅÀ1 (d2 = 6.1 Å) corresponds to the monomeric re- 291
F
268 free-standing films obtained from chloroform solution peat unit. These two parameters define the chain packed 292
269 using perpendicular and parallel incidences, at 293 K. planar layers of the MEH-PPV films. Finally, the peak in 293
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270 The anisotropy features of these films are already con- our patterns located at q = 1.49 ÅÀ1 (d3 = 4.2 Å) would cor- 294
271 firmed comparing the 2D patterns. These patterns are respond to the inter-backbone distance, in the direction 295
272 similar in shape, showing differences in relative peak normal to the coplanar phenylene rings, as reported by 296
273 intensities and scattering contributions according to the Jeng et al. [2]. It is worth mentioning that, due to the exist- 297
274 geometry of the experiment. Similar to Ref. [2], preferen- ing disorder, the scattering peaks are quite broad, but their 298
275 tial orientation of the ordered domains can be clearly positions could be well determined from the fittings. From 299
PR
276 noted in the 2D images of the parallel (||) incidence pat- the aforementioned results, is possible to conclude that the 300
277 terns, in which the reflections corresponding to q values major difference with the data reported in the literature 301
278 $0.27 ÅÀ1 and $1.5 ÅÀ1 present arcs of stronger [2,16] is that corresponding to the d1 parameter. Nonethe- 302
279 intensity. less, discrepancies in the bilayer packing parameter are not 303
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Fig. 2. MEH-PPV films cast from chloroform: WAXS intensity profiles obtained from the corresponding 2D patterns (shown at right). (a and b)
Perpendicular and (c and d) parallel incidence to the film plane. Red line: fit of the experimental data using Gaussian functions for the peaks and a
logarithmic baseline for the background.
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304 surprising, since more than one type of chain packing may also observed (see also Fig. 3b), indicating a decrease in 332
305 coexist for the as-cast films. the number of the scattering objects or chain dissocia- 333
306 Fig. 3 shows the WAXS intensity profiles at some se- tion in the perpendicular direction to the ring planes. 334
307 lected temperatures, below and above Tg, obtained for Finally, the behavior of the d2 parameter can only 335
308 MEH-PPV films cast from chloroform at parallel and per- be clearly followed in the perpendicular incidence pat- 336
309 pendicular incidences. All the intensity profiles were nor- terns (see Fig. 3b and d). Its value of (approximately 337
310 malized by an arbitrary scale factor to observe more 6.0 Å) for all temperatures ranging from 123 to 423 K, 338
311 clearly the changes in intensity and peak positions. The confirms the stability of this molecular packing param- 339
312 main modifications of the first diffraction maximum are eter. Note that this parameter represents the distance 340
313 better seen in the parallel incidence geometry (Fig. 3a). between two benzene units and is only related to bond 341
314 A shift in the peak position of this reflection, associated lengths. 342
315 with the bilayer spacing d1, and a narrowing of the line The explicit dependence of d1, d2 and d3 parameters 343
F
316 width as a function of increasing temperature is ob- with the temperature and the annealing time is shown in 344
317 served. The d1 values varied from 19.3 to 21.3 Å. A shoul- Fig. 4a for the chloroform cast film. The most noticeable ef- 345
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318 der in this peak is hardly noticed at the lower fect is observed for d1 parameter. It increases continuously 346
319 temperatures, but becomes more evident for 423 K. The as the temperature is raised from 123 to 318 K. Such 347
320 maximum intensity values and narrowest line profiles behavior is in good agreement with the increase in side- 348
321 were obtained for 423 K and after the samples were kept chain mobility, as we are going to show in sequence. The 349
322 at that temperature for 1 h (see Fig. 3c). The peak area subsequent increase in d1 values from $20.5 to $21.5 Å 350
323 increases as a function of thermal treatment (tempera- when the temperature reaches 348 K, can be correlated 351
PR
324 ture and annealing time). This result indicates an in- with the onset of the polymer glass transition at 323 K, 352
325 crease in the number of molecular aggregates in the that produces higher free volume for the relaxation of 353
326 bilayer normal direction. the aggregate supramolecular structures. From 348 to 354
327 Furthermore, in Fig. 3a, the peak associated with the 423 K and after 1 h annealing at 423 K, the d1 parameter 355
328 d3 parameter seems to shift to lower q values, which decreases slightly. After cooling to room temperature, a va- 356
329 would indicate an increase in the inter-backbone spacing lue of $20.9 Å is obtained. Thus, the overall increase of this 357
330
331
perpendicular to the plane of the phenylene rings. As a
reduction in the peak intensity with the temperature is
D
parameter is $0.4 Å. A similar behavior in the WAXS
profiles and d1, d2 and d3 parameters was observed for
358
359
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Fig. 3. WAXS intensity curves of MEH-PPV film cast from chloroform for in situ thermal treatment. (a) Parallel and (b) perpendicular incidence scattering
curves for temperatures from 123 to 423 K before annealing. (c) Parallel and (d) perpendicular incidence scattering curves at 423 K before and after 1 h
annealing and for 293 K at the end of the temperature cycle.
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Fig. 4. Temperature dependence of the structural parameters d1, d2 and d3 for MEH-PPV: (a) cast from chloroform, (b) cast from toluene. (c) Average size hDi
of the ordered domains in the bilayer normal direction. Dotted lines: visual guide of the behavior.
360 the toluene cast films except for the higher d1 variation at form casting, but bigger values (around 100 Å) are attained 372
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361 higher temperatures (see Fig. 4b). after the temperature of 423 K is reached. 373
362 Using Scherrer equation [34], the average size of the or-
363 dered domains <D> in the bilayer normal direction could 3.3. Solid-state NMR 374
364 be roughly estimated from the line width (FWHM) of the
365 d1 diffraction profile. As shown in Fig. 4c for chloroform Fig. 5 shows the repeat unit, the orientation of the 375
366 cast samples, almost constant values of <D> (around principal values of the CSA tensor, and typical 13C CP/ 376
367 60 Å) are found for temperatures up to 348 K. An increase MAS spectra of MEH-PPV at 303 K from chloroform and 377
368 of 20% is obtained for 423 K and a maximum value is toluene cast films. The line assignments are also shown. 378
369 reached after 1 h of annealing (90 Å). For the films obtained All the spectra are basically identical (including those at 379
370 from toluene solution, initially lower <D> values are low temperatures, 233 K), showing that there are no 380
371 achieved compared with the films obtained from chloro- drastic different in the chemical conformational state of 381
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Fig. 5. (a) MEH-PPV chemical structure; (b) chemical shift tensor principal axis orientation and typical C CP/MAS spectra of MEH-PPV at 303 K for films
cast from (c) chloroform, and (d) toluene. *denotes the spinning sidebands.
382 the polymer chains the films prepared with the different Fig. 7. It is possible to observe that the effective 417
383
384
solvents.
NMR can provide specific information about the side-
D
hmdip ðTÞi=mrigid is smaller for films where toluene was used
dip
as solvent, confirming the higher degree of side-chain
418
419
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385 chain molecular dynamics in MEH-PPV [14]. The degree mobility in films cast from toluene. Comparing the CH 420
386 of molecular dynamics of a particular molecular group in and CH2 DIPSHIFT curves (Fig. 6a–b), it is also seen that 421
387 the side-chain can be characterized by measuring the there is a clear difference for chloroform than for toluene 422
388 strength of the effective 13C–1H dipolar coupling for that cast films. This also indicates a more loosely packed side- 423
389 segment, which can be provided by DIPSHIFT technique chain in the toluene cast films. This feature can be better 424
EC
390 [17,20]. Such experiments, performed under Magic-An- observed in Fig. 7 that shows the temperature behavior 425
391 gle-Spinning (MAS), provide a measurement of the of the CH and CH2 hmdip ðTÞi=mrigid parameters for both films.
dip
426
13
392 C–1H magnetic dipolar coupling for each chemical group. For films cast from chloroform the CH group S parameter is 427
393 This is done by measuring the dependence of the signal higher than for CH2 in the whole temperature range, indi- 428
394 amplitude with the evolution period (t1), used for codifying cating a significant difference in the degree of mobility be- 429
the 13C–1H dipolar coupling, which produces a typical tween the head and the tail of the side-chain. In contrast,
RR
395 430
396 curve that depends on the strength of the averaged dipolar for the film cast from toluene the S parameters for the 431
397 coupling, hmdip i. Since motions with correlation times CH and CH2 are mostly identical in the temperature range, 432
398 shorter than $100 ls average the dipolar coupling be- suggesting that the mobility in the head and tail of the 433
399 tween 1H and 13C, from the measurement of this parameter side-chain are much similar. This corroborates the above 434
400 it is possible to distinguish rigid from mobile segments and findings that point to a looser packing in the side-chain 435
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401 estimate the amplitude of the molecular rotation. Molecu- in films cast from toluene. Note that the packing of the 436
402 lar order parameters S for each chemical group can also be side-chain would avoid motion of the whole side-chain, 437
403 obtained as the ratio between this averaged dipolar cou- but not anisotropic motion of specific segments in the 438
404 pling and its respective rigid-lattice value S ¼ hmdip i=mrigid .
dip side-chain. Moreover, the fact that the effective S parame- 439
405 Besides, measuring the ratio hmdip ðTÞi=mrigid versus temper-
dip ters tend to a plateau different from zero at higher temper- 440
406 ature allows qualitatively monitoring the increase of the atures is due to the presence of a residual dipolar coupling, 441
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407 molecular dynamic rate as a function of T. Typical DIPSHIFT indicating that the side-chains in MEH-PPV do not rotate 442
408 curves for the CH (labeled 11 in Fig. 5a) and CH2 (labeled isotropically, but execute rotations around a local axis. This 443
409 14 and 15 in Fig. 5a) side-chain groups of MEH-PPV films residual coupling is observed as a plateau even at temper- 444
410 at 293 K cast from chloroform and toluene are shown in atures well above Tg, which indicates that the motions ob- 445
411 Fig. 6. These chemical groups were chosen as probes to served are not really associated with free side-chains in the 446
412 the molecular dynamics because they are placed in the amorphous region of the polymer, but with ‘‘trapped” side- 447
413 head (close to the backbone) and tail (at the end) of the chains in the aggregated regions of the polymer. To con- 448
414 side-chain, respectively, allowing detecting possible differ- firm that this effect is really solvent related we performed 449
415 ences in the dynamics at different side-chain positions. The thermal annealing of the samples at 363 K during 12 h un- 450
416 corresponding hmdip ðTÞi=mrigid parameters are also shown in
dip der dynamic vacuum. As it can be observed in Fig. 7b and d, 451
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characteristics, which can be easily erased by thermal 457
annealing. However, this was only a qualitative discussion 458
and it would be worth to quantify the change in the kinetic 459
parameter that characterizes the molecular dynamics. 460
Concerning the geometry of the motions, the fact that the 461
S parameter does not go to zero at high temperatures (fast 462
motion limit) indicates that the motion is anisotropic, i.e., 463
occurs about a specific axis or only part of the segments 464
take part of the motion in the DIPSHIFt time scale. How- 465
ever, the DIPSHIFT data of the CH2 group attached to the 466
backbone (labeled 10 in Fig. 5a) shows that this group is 467
rather rigid (no temperature dependence were detected 468
F
in the DIPSHIFT curves of this group from 213 to 353 K). 469
This is largely consistent with a motional model where 470
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the CH group executes n-site jumps around the 471
H2C10AC11H bond, i.e., n-site jumps on a cone with an 472
opening defined by the relative orientation of the CH bond 473
with respect to the CAC bond (ideally 109°). As described 474
in Ref. [35], using this previous knowledge of the motional 475
geometry one can use a spin dynamics simulation program 476
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[36] to simulate the experimental DIPSHIFT curves for car- 477
bon 11 and extract the correlation times as a function of 478
temperature. Besides, the shape of the DIPSHIFT curve 479
can also be related with the non-exponentiality of the mo- 480
tion correlation function, which in some cases can be 481
translated as a distribution of correlation times. In Fig. 6a 482
D
we show the temperature dependence of DIPSHIFT curves
for the MEH-PPV CH group in films cast from toluene and
chloroform with the corresponding simulations. The corre-
483
484
485
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sponding correlation times as a function of temperature 486
are shown in the Arrhenius plot of Fig. 6c. The activation 487
energy was evaluated as (69 ± 5) kJ/mol for films cast from 488
chloroform and (54 ± 8) kJ/mol for films cast from toluene. 489
Thus, the results show that the energy barrier for the onset 490
EC
of side-chain motion is higher for chloroform than for tol- 491
uene cast films. This seems the only effect of the solvent 492
memory interferes only on the local side-chain motion, 493
since the results do not point to a modification on the 494
geometry of the motion (same S parameter at high temper- 495
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ature and rigid CH2 attached to the backbone). 496
Despite DIPSHIFT experiments are sensitive to motions 497
in the kHz frequency range, the presence of molecular mo- 498
tions that occur with rates beyond the detection limit of 499
these experiments cannot be ruled out. Thus, to better 500
characterize the dynamics of these systems it is attractive 501
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to perform experiments capable of providing information 502
about motions in other frequency ranges. One of such 503
experiments is the CODEX [21,22] technique that makes 504
possible to characterize the slow motion (with rates in 505
the Hz scale) of different chemical groups with a consider- 506
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able degree of details. Essentially, the experiment detects 507
Fig. 6. (a) and (b) Typical 13C DIPSHIFT curves for the CH and CH2 side- the signal reduction resulting from changes in the orienta- 508
chain groups of MEH-PPV films cast from chloroform and toluene at tion-dependent chemical-shift frequencies due to segmen- 509
293 K, respectively. (c) Arrhenius plot of the correlation time (sc)
tal reorientations during a waiting time also denoted as 510
extracted from the CH DIPSHIFT curves for the samples cast from
chloroform and toluene. mixing time tm. Information about the amplitude (mean 511
reorientation angles) of the motion is obtained by the 512
452 the behavior of both films becomes much similar, confirm- dependence of E(tm, Ntr), as a function of Ntr. 513
453 ing that the differences observed are associated with mem- In previous work, it was observed the presence of slow 514
454 ory effect due to the solvent. molecular motions in the backbone of MEH-PPV at 293 K 515
455 The above statements reveal that the side-chain [13,14]. These motions were assigned as small angle ring 516
456 dynamics of MEH-PPV films can be affected by the solvent rotations around the 1–4 axis. Fig. 8 shows E(tm, Ntr) as a 517
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Fig. 7. Thermal behavior of the order parameter S for CH and CH2 side-chain groups in MEH-PPV cast from (a) chloroform before annealing, (b) chloroform
after annealing at 363 K by 12 h, (c) toluene before annealing, and (d) toluene after annealing at 363 K by 12 h.
EC
518 function of Ntr for the para-carbons (labeled 1 and 4 in served. The fact that no solvent effects were observed in 542
519 Fig. 5a) of MEH-PPV films cast from chloroform and tolu- the CODEX measurements suggests that the overall tor- 543
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520 ene at 293 K. The average rotation angles were obtained sional motions are similar in all cases. If we associate the 544
521 by simulating the experimental curves based on principal amplitude of these torsional motions with the conforma- 545
522 values and orientation of the chemical shift tensor. For tional disorder along the polymer backbone, we might con- 546
523 that, the chemical shift anisotropy principal values were clude that the motional induced conformational disorder is 547
524 measured using a standard Herszfeld and Berger analysis. similar for both studied films. However, it should be 548
525 [37] The orientation of the chemical shift principal axis pointed out that the average rotation angle obtained by 549
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526 systems of phenyl rings para-carbons is similar in different CODEX cannot be associated with a particular segment in 550
527 systems. Thus, we assumed the same orientation of p-xy- the polymer backbone, but reflects the average behavior 551
528 lene, i.e., the principal value r33 (z-axis) is 1° tilted from of all backbone segments, including those poorly conju- 552
529 the normal to the phenylene ring plane and the x-axis, cor- gated that do not contribute to the photoluminescence. Be- 553
530 responding to r11 is 1° away from the 1–4 axis, as shown in sides that, because the motional amplitude is rather small, 554
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531 Fig. 5b. Because the molecular motions in polymers do not proton-driven spin-diffusion [38] may have a non-negligi- 555
532 involve single but distributed rotation angles, the simula- ble contribution to the CODEX exchange intensity, which 556
533 tions were performed considering Gaussian shaped distri- masks the possible differences that may exist among the 557
534 butions of reorientation angles centered at 0° and with torsional motion of the samples. 558
535 full-width at half-maximum (FWHM), hwi, that represents
536 the average reorientation angle. 4. Conclusions 559
537 It can be observed in Fig. 8 that, within the experimen-
538 tal uncertainty, all curves can be fitted using the same dis- This work provided new results of distinct aspects of 560
539 tribution of reorientation angles with hwi $10°. This means the dynamics and supramolecular organization in MEH- 561
540 that no significant differences among the overall motional PPV films cast from two different solvents. The NMR exper- 562
541 amplitudes of the backbone phenylene rings could be ob- iments were particularly useful for describing general and 563
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a direct evidence of the presence of interchains dissocia- 589
tion and increased disorder of the phenyl rings. Consider- 590
ing that the increase of conformational disorder may 591
quench some interchain processes that contributes to the 592
luminescence, the results confirms our previously pro- 593
posed model (dissociation of the interchain species during 594
the MEH-PPV relaxation processes) based on PL and NMR 595
results [13]. More specifically, the intensity increase ob- 596
served at 200 K is associated with in appearing of motional 597
ring torsions due to the onset of the side-chain motions 598
and the stronger intensification at 300 K to the increasing 599
of these motions due to the onset of the glass transition. 600
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In both relaxation processes the blue shift is attributed to 601
the increase of the motional induced conformational 602
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disorder. 603
Acknowledgements 604
Authors thank FAPESP, CNPq, CAPES and MCT/PADCT/ 605
IMMP for the financial support and fellowships. TDZA 606
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and RFC thank FAEPEX/Unicamp for financial support and 607
fellowships. ERdA thanks Prof. Kay Saalwachter for provid- 608
ing the spin dynamics simulation program and for helpful 609
discussions. WAXS data were collected under proposals 610
D11A-SAXS1 #4247 and #4293 of the Brazilian Synchro- 611
tron Light Laboratory (LNLS). 612
D
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