The document discusses polymer brushes and methods for their synthesis. It provides an overview of polymer brushes, including their general features and how their properties depend on grafting density. It also describes various types of polymer brushes and common methods for synthesizing them, including grafting onto, grafting from, and grafting through approaches. Finally, it discusses uses of responsive polymer brushes and their potential applications in areas like drug delivery and microfluidic devices.
Miscibility and Thermodynamics of Polymer BlendsAbhinand Krishna
Presentation includes classification of polymer blends based on miscibility, phase diagram of polymer blends and thermodynamics polymer blends which includes Gibbs energy theory and Flory-Huggins Theory
Viton is a fluoroelastomer introduced in 1957 for use in the aerospace industry. It has excellent thermal stability and chemical resistance, being usable between -30°C to 280°C. Viton exists as co, ter, and tetra polymers and is commercially available as granular powder or dispersions. It has many applications due to its heat resistance, strength, and resistance to chemicals, hydrocarbons, weathering and oxidation. Research has shown Viton can act as a thermally stable binder and be used to coat magnesium particles to increase their oxidation resistance.
This document discusses the properties of polymers. It begins by introducing the topics that will be covered, including physical, thermal, electrical, mechanical, thermo-mechanical, and chemical properties of polymers. It then provides details on various physical properties such as molecular weight and density. Thermal properties like glass transition temperature and melting point are explained. Factors that influence properties like mechanical strength and electrical conductivity of polymers are also described. The document aims to explain the different types of properties exhibited by polymers and factors that impact these properties.
Polymer behaviour in solution & effect of molecular weight in polymerSyed Minhazur Rahman
Polymer chains of varying molecular weights exhibit different behaviors in solution. Higher molecular weight polymers swell more before dissolving and produce highly viscous solutions even at low concentrations. Their long, entangled chains confer properties like high strength, impact resistance, and chemical resistance. Lower molecular weight polymers dissolve immediately and yield low viscosity solutions. Their short chains act as plasticizers and impart softness, flexibility, and increased molecular mobility. A polymer's molecular weight determines the length of its chains and significantly impacts its solution behavior and material properties.
Dr. Harshali G. Wankhade discusses different types of copolymers including graft copolymers, block copolymers, and random copolymers. Graft copolymers have a backbone with branches of different polymer chains. Block copolymers have repeating blocks of different polymer units. Random copolymers have monomers distributed randomly. The document also describes methods for synthesizing these copolymers and characterization techniques like NMR, IR, XRD, DSC, TGA, and UV-Visible spectroscopy.
Environmental stress cracking resistanceSivaprakash S
This document discusses environmental stress cracking resistance (ESCR) testing of thermoplastic polymers. ESCR is one of the most common causes of unexpected brittle failure in plastics. The rate of ESCR depends on factors like a polymer's chemical makeup, molecular weight, and residual stress as well as the liquid's chemistry, temperature, and strain rate. The document describes an ESCR testing machine and procedure where samples are clamped and submerged in a detergent solution at elevated temperature for 30 minutes before being examined for surface cracks. The test determines a material's resistance to environmental stresses.
Immiscible blends are materials made from two polymers that do not fully mix and instead separate into distinct phases. While immiscible blends are usually weaker than pure polymers, they can be engineered to improve properties. The minor polymer phase can enhance the strength or toughness of the major polymer phase by dispersing as spheres, rods or in a co-continuous morphology. Adding a block copolymer or graft copolymer compatibilizer helps bond the phases together, allowing for more efficient transfer of stress between them. This makes immiscible blends stronger and higher performing.
Polymer Rheology(Properties study of polymer)Haseeb Ahmad
This document discusses fundamentals of polymer rheology. It defines rheology as the study of flow of matter, primarily liquids but also soft solids. Rheology is important for characterizing polymers and understanding how polymer structure affects processing behavior. The document describes different types of fluids and their viscosity properties. It also discusses various rheological measurement techniques like rotational rheometers, capillary rheometers and melt flow indexers.
Miscibility and Thermodynamics of Polymer BlendsAbhinand Krishna
Presentation includes classification of polymer blends based on miscibility, phase diagram of polymer blends and thermodynamics polymer blends which includes Gibbs energy theory and Flory-Huggins Theory
Viton is a fluoroelastomer introduced in 1957 for use in the aerospace industry. It has excellent thermal stability and chemical resistance, being usable between -30°C to 280°C. Viton exists as co, ter, and tetra polymers and is commercially available as granular powder or dispersions. It has many applications due to its heat resistance, strength, and resistance to chemicals, hydrocarbons, weathering and oxidation. Research has shown Viton can act as a thermally stable binder and be used to coat magnesium particles to increase their oxidation resistance.
This document discusses the properties of polymers. It begins by introducing the topics that will be covered, including physical, thermal, electrical, mechanical, thermo-mechanical, and chemical properties of polymers. It then provides details on various physical properties such as molecular weight and density. Thermal properties like glass transition temperature and melting point are explained. Factors that influence properties like mechanical strength and electrical conductivity of polymers are also described. The document aims to explain the different types of properties exhibited by polymers and factors that impact these properties.
Polymer behaviour in solution & effect of molecular weight in polymerSyed Minhazur Rahman
Polymer chains of varying molecular weights exhibit different behaviors in solution. Higher molecular weight polymers swell more before dissolving and produce highly viscous solutions even at low concentrations. Their long, entangled chains confer properties like high strength, impact resistance, and chemical resistance. Lower molecular weight polymers dissolve immediately and yield low viscosity solutions. Their short chains act as plasticizers and impart softness, flexibility, and increased molecular mobility. A polymer's molecular weight determines the length of its chains and significantly impacts its solution behavior and material properties.
Dr. Harshali G. Wankhade discusses different types of copolymers including graft copolymers, block copolymers, and random copolymers. Graft copolymers have a backbone with branches of different polymer chains. Block copolymers have repeating blocks of different polymer units. Random copolymers have monomers distributed randomly. The document also describes methods for synthesizing these copolymers and characterization techniques like NMR, IR, XRD, DSC, TGA, and UV-Visible spectroscopy.
Environmental stress cracking resistanceSivaprakash S
This document discusses environmental stress cracking resistance (ESCR) testing of thermoplastic polymers. ESCR is one of the most common causes of unexpected brittle failure in plastics. The rate of ESCR depends on factors like a polymer's chemical makeup, molecular weight, and residual stress as well as the liquid's chemistry, temperature, and strain rate. The document describes an ESCR testing machine and procedure where samples are clamped and submerged in a detergent solution at elevated temperature for 30 minutes before being examined for surface cracks. The test determines a material's resistance to environmental stresses.
Immiscible blends are materials made from two polymers that do not fully mix and instead separate into distinct phases. While immiscible blends are usually weaker than pure polymers, they can be engineered to improve properties. The minor polymer phase can enhance the strength or toughness of the major polymer phase by dispersing as spheres, rods or in a co-continuous morphology. Adding a block copolymer or graft copolymer compatibilizer helps bond the phases together, allowing for more efficient transfer of stress between them. This makes immiscible blends stronger and higher performing.
Polymer Rheology(Properties study of polymer)Haseeb Ahmad
This document discusses fundamentals of polymer rheology. It defines rheology as the study of flow of matter, primarily liquids but also soft solids. Rheology is important for characterizing polymers and understanding how polymer structure affects processing behavior. The document describes different types of fluids and their viscosity properties. It also discusses various rheological measurement techniques like rotational rheometers, capillary rheometers and melt flow indexers.
This document discusses thermoplastic elastomers (TPEs). TPEs have both thermoplastic and elastomeric properties. They can be melt-processed like thermoplastics but are flexible and elastic like vulcanized rubbers. The most common TPE is a styrene-butadiene block copolymer, which has rigid polystyrene end blocks and soft polybutadiene mid blocks. This structure allows it to behave like a rubber at low temperatures but melt and flow like a thermoplastic at higher temperatures. Common applications of TPEs include automotive parts, medical devices, shoes, and cables due to advantages like recyclability and simpler processing compared to thermoset rubbers
This document provides an overview of polymers, including their classification, characterization techniques, and examples. It begins with an introduction to polymers, noting they are macromolecules composed of repeating structural units or monomers linked together. The document then discusses various polymer classifications including source, structure, and interaction with water. Several characterization techniques are outlined, such as tensile strength testing, X-ray diffraction, infrared spectroscopy, and differential scanning calorimetry. Specific techniques like atomic force microscopy and X-ray photoelectron spectroscopy are also summarized. The document concludes with examples of characterization applications.
This document summarizes key information about polypropylene (PP), a linear polymer composed of isopropane repeating units. PP is prepared using Ziegler catalysts under nitrogen atmosphere and its molecular weight can be controlled with hydrogen. Commercially, PP is usually 90-95% isotactic. Isotactic PP has properties like chemical resistance, stability in boiling water, and good electrical properties. It has applications in automotive parts, packaging, and electrical/electronics due to its workability and resistance to chemicals and heat. The document discusses the structure, properties, processing, additives and applications of PP.
This document discusses the history and chemistry of vulcanization and curing systems for rubber. Some key points include:
- Charles Goodyear discovered in 1839 that heating rubber with sulfur produced an elastic product that did not become sticky or brittle at high/low temperatures, launching the vulcanization process.
- Sulfur has remained the most important vulcanizing agent, though other chemicals have also been examined. Accelerators were later developed to speed up the vulcanization reaction.
- Efficient vulcanization systems using sulfur donors and accelerators produce vulcanizates with mainly mono- and disulfide crosslinks rather than unstable polysulfide crosslinks and pendant groups. This improves aging
Polypropylene is a linear hydrocarbon polymer made from the monomer propylene. It was first produced commercially in 1954 using catalysts developed for polyethylene. Polypropylene has applications in areas like automotive components, films, fibers, and foams due to its properties like being semi-rigid, tough, chemically resistant and heat resistant. It is produced via chain-growth polymerization of propene using gas-phase, bulk, or slurry polymerization processes.
This document discusses polyurethane, its history, properties, applications in biomedical engineering, and advantages and disadvantages for medical use. Polyurethane was discovered in 1937 and is formed from reacting a polyol with a diisocyanate. It has since been used in applications like aircraft insulation, prosthetics, catheters, and artificial hearts due to its biocompatibility and mechanical properties like tensile strength. However, long term use can lead to degradation issues. Overall, polyurethane is a versatile material that is widely researched for medical devices due to its tunable surface properties.
This document summarizes a seminar presentation on polymers used in the medical field. It discusses various bioplastics like PCL and PLA, as well as polymers used in medical devices and implants such as PEEK, which is used in spinal fusion devices. It also covers applications of polymers in general surgery as suture materials and surgical meshes, as well as uses in opthalmology like contact lenses and intraocular lenses. The document provides details on the properties and medical uses of these various polymers.
The document discusses tyre cord reinforcement and the properties required. It describes how textile fabrics are reinforced in rubber composites to impart strength, durability and dimensional stability. It discusses the requirements for reinforcing materials used in tyre carcasses and belts. The document outlines different tyre cord constructions and their properties. It provides details on hysteresis loops, cord size comparison, tyre structure components, and functions of tyre cords.
Plasticizers are chemicals added to polymers to improve flexibility and processing. They work by spacing out polymer molecules, allowing easier movement. Most plasticizers are organic esters added to PVC to make it flexible. Phthalates are the most widely used type, accounting for over 90% of plasticizers. Common phthalate plasticizers include DOP, DEHP, DINP and DIDP. Selection depends on the required properties and application. Health concerns have led to a search for safer alternatives to phthalates.
Determining molecular weights of polymers is important because it controls properties like solubility, elasticity, and mechanics. Polymers do not have uniform molecular weights but a distribution of different sizes. Molecular weight can be determined through various physical and chemical methods like end group analysis, light scattering, viscosity measurements, and gel permeation chromatography. These methods provide information about the number average molecular weight and distribution across molecules in a sample.
Polymer properties and characterisationArchana Nair
This document discusses various techniques used to characterize polymers. It begins with an introduction to polymers and their properties. It then describes several techniques including molecular weight determination using methods like light scattering and gel permeation chromatography. It also discusses vibrational spectroscopy using infrared and Raman spectroscopy. Other techniques covered include nuclear magnetic resonance spectroscopy, microscopy, thermal analysis, x-ray diffraction, and mechanical and rheological analyses. The document provides information on analyzing various properties of polymers including molecular structure, crystallinity, glass transition temperature, and viscoelastic behavior.
Main topic of the presentation is 'Conversion of Rubber'. You can easily found;
How conversion process are realized?
What type of process are used?
Application areas of conversion rubber.
If you have any questions, contact me. I would be happy to help.
If you like it, please would you like it and comment.
Nylon 6 is a semicrystalline thermoplastic polymer synthesized from caprolactam via ring-opening polymerization. It has high tensile strength, elasticity, and resistance to abrasion and chemicals. Common applications include fibers, ropes, bristles, gears, bearings, surgical sutures, and more. Nylon degrades slowly and is used for banners, flags, clothing like jackets, and other outdoor materials due to its durability against UV light and weathering.
This document discusses the fundamentals of rheology and how rheological tests can help with polymer processing and development. It describes different types of rheometers including capillary, rotational, and extensional rheometers. Capillary rheology provides information about how materials behave when melted and correlates flow parameters to mechanical properties. Capillary rheology can determine optimal processing parameters and investigate issues. The document also discusses how rheological properties relate to molecular weight and processing techniques like extrusion, injection molding, and blow molding that can be simulated using a capillary rheometer.
Process of Nanoindentation and use of finite element modellingD.R. Kartikayan
This document provides an overview of nanoindentation testing for measuring material properties. It discusses why nanoindentation is used, the requirements and procedure for nanoindentation testing, and how to analyze the load-displacement curves obtained from testing. Factors that can affect nanoindentation results are also covered, as well as how finite element modeling can be used to better interpret nanoindentation data and account for these influencing factors.
Unsaturated polyester resin is prepared from diethylene glycol and maleic anhydride and can be cross-linked with styrene. It is used as a matrix material for fiber reinforced composites. The document discusses the preparation of unsaturated polyester resin and its composites with nano silica, glass fibers, and bagasse fibers. It is found that adding these fillers improves the mechanical, electrical and thermal properties of the composites compared to neat resin. Nano silica composites in particular exhibit better electrical properties than micro silica or neat resin composites.
The objective of this presentation is to give an overview of rubber compounding. We will briefly focus on:
Elastomer System
Filler System
Protection system
Process Aids
Cure System
This document provides an overview of melt flow testing based on ISO 1133 and ASTM D1238 standards. Melt flow testing measures the mass or volume of melted polymer that flows through a die in 10 minutes at a specified temperature. It is commonly used for quality control of thermoplastics to verify materials, check quality, compare new materials, and predict polymer processing behavior. Key factors that can influence melt flow results include temperature accuracy and stability, sample preparation and moisture content, compaction method, density value used, manual test operations, die and piston maintenance, and cleaning procedures.
This document provides information about electrospinning, including:
1. Electrospinning uses electric fields to draw very fine polymer fibers from liquid solutions or melts, producing fibers with diameters as small as a few nanometers.
2. The process involves applying a high voltage to a liquid which forms a Taylor cone and ejects a charged jet of liquid that is stretched and thinned into fibers, which are deposited on a collector.
3. Electrospinning can be used to produce nanofibers from various polymers for applications like tissue engineering and filtration.
Michelle L. Coote et al., Polymer, 44, (2003), 7689 - 7700.Duncan Gordon
This document summarizes several theoretical models for describing the kinetics of interfacial grafting reactions between immiscible polymers containing reactive end groups. It discusses models by Kramer, O'Shaugnessy, and others. The models consider factors like diffusion control vs reaction control, grafting density, molecular weight, concentration of reactive groups, and the formation of brush-like grafted layers. Neutron reflectometry is identified as an experimental technique suitable for investigating these interfacial grafting reactions by quantitatively analyzing the excess polymer layer at the interface.
This chapter discusses molecular motions in complex media containing fluid-solid interfaces, such as porous media and colloidal particles. It aims to classify the key mechanisms determining molecular dynamics in these systems, including adsorption/desorption kinetics, translational and rotational diffusion, and liquid-vapor coexistence phenomena. The chapter distinguishes between effects due to fluid-wall interactions and geometric confinement in mesoporous spaces. It surveys fundamental definitions for characterizing pore spaces and fluid phases, and categories of restricted geometry effects on translational and rotational diffusion.
This document discusses thermoplastic elastomers (TPEs). TPEs have both thermoplastic and elastomeric properties. They can be melt-processed like thermoplastics but are flexible and elastic like vulcanized rubbers. The most common TPE is a styrene-butadiene block copolymer, which has rigid polystyrene end blocks and soft polybutadiene mid blocks. This structure allows it to behave like a rubber at low temperatures but melt and flow like a thermoplastic at higher temperatures. Common applications of TPEs include automotive parts, medical devices, shoes, and cables due to advantages like recyclability and simpler processing compared to thermoset rubbers
This document provides an overview of polymers, including their classification, characterization techniques, and examples. It begins with an introduction to polymers, noting they are macromolecules composed of repeating structural units or monomers linked together. The document then discusses various polymer classifications including source, structure, and interaction with water. Several characterization techniques are outlined, such as tensile strength testing, X-ray diffraction, infrared spectroscopy, and differential scanning calorimetry. Specific techniques like atomic force microscopy and X-ray photoelectron spectroscopy are also summarized. The document concludes with examples of characterization applications.
This document summarizes key information about polypropylene (PP), a linear polymer composed of isopropane repeating units. PP is prepared using Ziegler catalysts under nitrogen atmosphere and its molecular weight can be controlled with hydrogen. Commercially, PP is usually 90-95% isotactic. Isotactic PP has properties like chemical resistance, stability in boiling water, and good electrical properties. It has applications in automotive parts, packaging, and electrical/electronics due to its workability and resistance to chemicals and heat. The document discusses the structure, properties, processing, additives and applications of PP.
This document discusses the history and chemistry of vulcanization and curing systems for rubber. Some key points include:
- Charles Goodyear discovered in 1839 that heating rubber with sulfur produced an elastic product that did not become sticky or brittle at high/low temperatures, launching the vulcanization process.
- Sulfur has remained the most important vulcanizing agent, though other chemicals have also been examined. Accelerators were later developed to speed up the vulcanization reaction.
- Efficient vulcanization systems using sulfur donors and accelerators produce vulcanizates with mainly mono- and disulfide crosslinks rather than unstable polysulfide crosslinks and pendant groups. This improves aging
Polypropylene is a linear hydrocarbon polymer made from the monomer propylene. It was first produced commercially in 1954 using catalysts developed for polyethylene. Polypropylene has applications in areas like automotive components, films, fibers, and foams due to its properties like being semi-rigid, tough, chemically resistant and heat resistant. It is produced via chain-growth polymerization of propene using gas-phase, bulk, or slurry polymerization processes.
This document discusses polyurethane, its history, properties, applications in biomedical engineering, and advantages and disadvantages for medical use. Polyurethane was discovered in 1937 and is formed from reacting a polyol with a diisocyanate. It has since been used in applications like aircraft insulation, prosthetics, catheters, and artificial hearts due to its biocompatibility and mechanical properties like tensile strength. However, long term use can lead to degradation issues. Overall, polyurethane is a versatile material that is widely researched for medical devices due to its tunable surface properties.
This document summarizes a seminar presentation on polymers used in the medical field. It discusses various bioplastics like PCL and PLA, as well as polymers used in medical devices and implants such as PEEK, which is used in spinal fusion devices. It also covers applications of polymers in general surgery as suture materials and surgical meshes, as well as uses in opthalmology like contact lenses and intraocular lenses. The document provides details on the properties and medical uses of these various polymers.
The document discusses tyre cord reinforcement and the properties required. It describes how textile fabrics are reinforced in rubber composites to impart strength, durability and dimensional stability. It discusses the requirements for reinforcing materials used in tyre carcasses and belts. The document outlines different tyre cord constructions and their properties. It provides details on hysteresis loops, cord size comparison, tyre structure components, and functions of tyre cords.
Plasticizers are chemicals added to polymers to improve flexibility and processing. They work by spacing out polymer molecules, allowing easier movement. Most plasticizers are organic esters added to PVC to make it flexible. Phthalates are the most widely used type, accounting for over 90% of plasticizers. Common phthalate plasticizers include DOP, DEHP, DINP and DIDP. Selection depends on the required properties and application. Health concerns have led to a search for safer alternatives to phthalates.
Determining molecular weights of polymers is important because it controls properties like solubility, elasticity, and mechanics. Polymers do not have uniform molecular weights but a distribution of different sizes. Molecular weight can be determined through various physical and chemical methods like end group analysis, light scattering, viscosity measurements, and gel permeation chromatography. These methods provide information about the number average molecular weight and distribution across molecules in a sample.
Polymer properties and characterisationArchana Nair
This document discusses various techniques used to characterize polymers. It begins with an introduction to polymers and their properties. It then describes several techniques including molecular weight determination using methods like light scattering and gel permeation chromatography. It also discusses vibrational spectroscopy using infrared and Raman spectroscopy. Other techniques covered include nuclear magnetic resonance spectroscopy, microscopy, thermal analysis, x-ray diffraction, and mechanical and rheological analyses. The document provides information on analyzing various properties of polymers including molecular structure, crystallinity, glass transition temperature, and viscoelastic behavior.
Main topic of the presentation is 'Conversion of Rubber'. You can easily found;
How conversion process are realized?
What type of process are used?
Application areas of conversion rubber.
If you have any questions, contact me. I would be happy to help.
If you like it, please would you like it and comment.
Nylon 6 is a semicrystalline thermoplastic polymer synthesized from caprolactam via ring-opening polymerization. It has high tensile strength, elasticity, and resistance to abrasion and chemicals. Common applications include fibers, ropes, bristles, gears, bearings, surgical sutures, and more. Nylon degrades slowly and is used for banners, flags, clothing like jackets, and other outdoor materials due to its durability against UV light and weathering.
This document discusses the fundamentals of rheology and how rheological tests can help with polymer processing and development. It describes different types of rheometers including capillary, rotational, and extensional rheometers. Capillary rheology provides information about how materials behave when melted and correlates flow parameters to mechanical properties. Capillary rheology can determine optimal processing parameters and investigate issues. The document also discusses how rheological properties relate to molecular weight and processing techniques like extrusion, injection molding, and blow molding that can be simulated using a capillary rheometer.
Process of Nanoindentation and use of finite element modellingD.R. Kartikayan
This document provides an overview of nanoindentation testing for measuring material properties. It discusses why nanoindentation is used, the requirements and procedure for nanoindentation testing, and how to analyze the load-displacement curves obtained from testing. Factors that can affect nanoindentation results are also covered, as well as how finite element modeling can be used to better interpret nanoindentation data and account for these influencing factors.
Unsaturated polyester resin is prepared from diethylene glycol and maleic anhydride and can be cross-linked with styrene. It is used as a matrix material for fiber reinforced composites. The document discusses the preparation of unsaturated polyester resin and its composites with nano silica, glass fibers, and bagasse fibers. It is found that adding these fillers improves the mechanical, electrical and thermal properties of the composites compared to neat resin. Nano silica composites in particular exhibit better electrical properties than micro silica or neat resin composites.
The objective of this presentation is to give an overview of rubber compounding. We will briefly focus on:
Elastomer System
Filler System
Protection system
Process Aids
Cure System
This document provides an overview of melt flow testing based on ISO 1133 and ASTM D1238 standards. Melt flow testing measures the mass or volume of melted polymer that flows through a die in 10 minutes at a specified temperature. It is commonly used for quality control of thermoplastics to verify materials, check quality, compare new materials, and predict polymer processing behavior. Key factors that can influence melt flow results include temperature accuracy and stability, sample preparation and moisture content, compaction method, density value used, manual test operations, die and piston maintenance, and cleaning procedures.
This document provides information about electrospinning, including:
1. Electrospinning uses electric fields to draw very fine polymer fibers from liquid solutions or melts, producing fibers with diameters as small as a few nanometers.
2. The process involves applying a high voltage to a liquid which forms a Taylor cone and ejects a charged jet of liquid that is stretched and thinned into fibers, which are deposited on a collector.
3. Electrospinning can be used to produce nanofibers from various polymers for applications like tissue engineering and filtration.
Michelle L. Coote et al., Polymer, 44, (2003), 7689 - 7700.Duncan Gordon
This document summarizes several theoretical models for describing the kinetics of interfacial grafting reactions between immiscible polymers containing reactive end groups. It discusses models by Kramer, O'Shaugnessy, and others. The models consider factors like diffusion control vs reaction control, grafting density, molecular weight, concentration of reactive groups, and the formation of brush-like grafted layers. Neutron reflectometry is identified as an experimental technique suitable for investigating these interfacial grafting reactions by quantitatively analyzing the excess polymer layer at the interface.
This chapter discusses molecular motions in complex media containing fluid-solid interfaces, such as porous media and colloidal particles. It aims to classify the key mechanisms determining molecular dynamics in these systems, including adsorption/desorption kinetics, translational and rotational diffusion, and liquid-vapor coexistence phenomena. The chapter distinguishes between effects due to fluid-wall interactions and geometric confinement in mesoporous spaces. It surveys fundamental definitions for characterizing pore spaces and fluid phases, and categories of restricted geometry effects on translational and rotational diffusion.
This document is a summer internship report submitted by Prafull Kumar Sharma studying the depletion attraction between branched polymers using computer simulations. The report introduces the concepts of polymers, depletion attraction between colloids, dendrimer structure, and the bond fluctuation method used in the simulations. The goal is to understand depletion attraction between dendrimers with and without solvent using umbrella sampling to calculate free energy. Simulation results and their discussion are presented in section 3.
Adhesion is linked with surface forces like capillary pressure and is thus detrimental at the
nanoscale where body forces are negligible. It can lead to instant failure during fabrication and
operation but it can also lead to overtime failure because of induced friction and wear. However,
when it is possible, coating a device with hydrophobic materials reduces drastically that mechanism.
Understanding how adhesion works is crucial to design new systems and to enable new
technologies. Two models (JKR and DMT) are studied in this paper and model adhesion in different
cases. Photolithography and particularly the release step must be carefully designed to prevent
contamination and stiction. Materials must be chosen and designed wisely to prevent adhesion
failure during operation but lubricants can be used to reduce its impact as well as the impact of
friction and wear.
how do the different architectures of a polymer affect their propertie.docxcliftonl1
how do the different architectures of a polymer affect their properties?
Solution
Polymers are affected by molecular weight and crystallinity.
Linear polymers - single chains, flexible , van der Waals between molecules.
Branched polymers - side branches , packing is less efficient, lower density,less crystalline than linear.
Branching also affects chain entanglement, the ability of chains to slide past one another, in turn affecting the bulk physical properties. Long chain branches may increase polymer strength, toughness, and the glass transition temperature (T g ) due to an increase in the number of entanglements per chain.
From an adsorption point-of-view, the bottle-brush homopolymers have the ability to attach to the surface through both side chain and backbone segments. If adsorption occurs through the attachment of the side chains on the surface, then the polymer attains a flat conformation at the interface since the gain in adsorption energy increases with the number of contact points between the side chain segments and the surface
Dendrimers are a special case of branched polymer where every monomer unit is also a branch point. This tends to reduce intermolecular chain entanglement and crystallization. A related architecture, the dendritic polymer, are not perfectly branched but share similar properties to dendrimers due to their high degree of branching.
.
This document discusses computer simulations of the structure and thermodynamics of colloidal solutions interacting through Yukawa or Lu-Marlow potentials. It presents:
1) A new attractive potential proposed by Lu and Marlow that takes into account particle size and is proportional to the inverse sixth power of distance for large separations.
2) Use of this potential and a repulsive electrostatic potential in a variational method to calculate theoretical structure factors, finding good agreement with experimental data.
3) Choice of hard spheres as a reference system and use of the Gibbs-Bogoliubov inequality to obtain an upper bound for the free energy of the colloidal system.
Lecture: Dynamics of Polymer Solutions and Melts Nikolai Priezjev
Lecture notes on Structure and Properties of Engineering Polymers
Course Objectives:
The main objective is to introduce polymers as an engineering material and emphasize the basic concepts of their nature, production and properties. Polymers are introduced at three levels; namely, the molecular level, the micro level, and macro-level. Through knowledge of all three levels, student can understand and predict the properties of various polymers and their performance in different products. The course also aims at introducing the students to the principles of polymer processing techniques and considerations of design using engineering polymers.
Osmotic pressure and light scattering methods are used to determine the number-average and weight-average molecular weights of polymers in solution. Polymers can be characterized as amorphous, semicrystalline, or crystalline depending on their chain structure and interactions. Thermoplastics exhibit glass transitions and/or melting points while thermosets only exhibit glass transitions.
The document discusses the molecular requirements and properties that give materials rubber-like elasticity. Rubber elasticity arises from the entropy change that occurs when stretched. Rubber molecules are long chains that are cross-linked, allowing them to reversibly unfold and recover their random coil configuration, driven by entropy. The elasticity can be modeled using statistical mechanics calculations of molecular configurations. Key factors include the polymer's molecular weight, cross-linking, and mobility above the glass transition temperature.
2003 self-organization processes in impurity subsystem of solid solutionsДарья Орлова
This document presents new experimental results on critical phenomena in solid solutions at low impurity concentrations. It was observed that the X-ray diffraction linewidth decreases anomalously, while the lattice thermal conductivity and heat capacity increase in the impurity concentration range below 1.0 atomic percent in some ternary solid solutions based on IV-VI semiconducting compounds. These experimental results are analyzed using percolation theory and the theory of second-order phase transitions. It is suggested that self-organization processes of impurity atoms accompany the percolation phenomena. The results provide further evidence that critical phenomena occur universally when transitioning from an impurity discontinuum to an impurity continuum in solid solutions.
Gel permeation chromatography (GPC) is a type of size exclusion chromatography used to analyze polymers. In GPC, polymer samples are separated based on molecular size as they pass through a column containing porous beads. Larger polymer molecules elute from the column first as they are excluded from the pores, while smaller molecules penetrate deeper and elute later. This allows the whole molecular mass distribution of a polymer sample to be measured. Calibration with polymer standards of known molecular weights is required to determine molecular weights of analyzed polymers. GPC provides information on molecular weight averages and dispersity.
MECHANICAL & THERMAL PROPERTIES OF NANO COMPOSITESArjun K Gopi
This document discusses the mechanical and thermal properties of polymer nanocomposites. It explains that polymer nanocomposites consist of a polymer matrix reinforced with nanoparticles, which have high surface area. This results in enhanced bonding between the polymer and nanoparticles. As a result, polymer nanocomposites often demonstrate improved mechanical properties over micro-composites, such as increased elastic modulus. A key factor influencing the mechanical properties is the interphase layer that forms between the polymer matrix and nanoparticles. The properties of this interphase region, which can differ from the bulk materials, largely determine how stress is transferred between phases. Several experimental techniques for characterizing the structure and properties of polymer nanocomposites are described, including tensile testing,
The document summarizes a summer training report on the characterization of 8 mole% yttria stabilized zirconia obtained from different sources. The objectives were to characterize and compare YSZ powders from ISRO, IRE and TOSOH, and to optimize sintering conditions to achieve high density pellets suitable for use as a solid oxide fuel cell electrolyte. Characterization techniques included tap density measurement, BET surface area analysis, X-ray diffraction for phase analysis, particle size distribution analysis, and density measurement of sintered pellets.
1) Researchers used dissipative particle dynamics simulations to model the regeneration of a composite polymer gel with embedded nanorods after severing. Initially, nanorods localized at the interface escaped into the regrowing gel layer.
2) To strengthen the interface, researchers introduced an additional cross-linker that formed covalent bonds between the original and regrown gel layers. With 5% additional cross-linker, a uniform interface was achieved without altering the gel density.
3) Higher concentrations of additional cross-linker above 5% led to intra-gel cross-linking within the original layer, causing inhomogeneous density. The optimal concentration of 5% additional cross-linker regenerated a composite gel that resembled the original.
Research on Contact Characteristics between Bump End Effector and WaferIJRES Journal
In the IC industry, commonly used methods are wafer clamping friction transmission type and vacuum suction. Combining science and theological contact theory,the contact friction transmission characteristics when using the bump and transmission actuator wafer, the wafer and the end actuators. Starting from the material properties of the wafer by ANSYS simulation analysis in contact with the wafer bump deformation due to its own gravity, and verify that it meets the requirements of small deformation wafer transfer. Compute and solve the friction contact with the wafer bump bristles between.
A contact angle goniometer measures the contact angle of a liquid on a solid surface and can
obtain surface energy of a solid. This instrument is used in all the major industries; especially
where research is done in coming up with newer materials. Low values of contact angle indicate
greater wettability and higher values mean that the solid doesn’t attract the liquid as much. This
instrument already exists but with my design it costs over ten times less, which will make it more
accessible to school labs and small-scale industries.
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Webinar Recording: https://www.panagenda.com/webinars/hcl-notes-und-domino-lizenzkostenreduzierung-in-der-welt-von-dlau/
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Wir erklären Ihnen, wie Sie häufige Konfigurationsprobleme lösen können, die dazu führen können, dass mehr Benutzer gezählt werden als nötig, und wie Sie überflüssige oder ungenutzte Konten identifizieren und entfernen können, um Geld zu sparen. Es gibt auch einige Ansätze, die zu unnötigen Ausgaben führen können, z. B. wenn ein Personendokument anstelle eines Mail-Ins für geteilte Mailboxen verwendet wird. Wir zeigen Ihnen solche Fälle und deren Lösungen. Und natürlich erklären wir Ihnen das neue Lizenzmodell.
Nehmen Sie an diesem Webinar teil, bei dem HCL-Ambassador Marc Thomas und Gastredner Franz Walder Ihnen diese neue Welt näherbringen. Es vermittelt Ihnen die Tools und das Know-how, um den Überblick zu bewahren. Sie werden in der Lage sein, Ihre Kosten durch eine optimierte Domino-Konfiguration zu reduzieren und auch in Zukunft gering zu halten.
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- Wie funktionieren CCB- und CCX-Lizenzen wirklich?
- Verstehen des DLAU-Tools und wie man es am besten nutzt
- Tipps für häufige Problembereiche, wie z. B. Team-Postfächer, Funktions-/Testbenutzer usw.
- Praxisbeispiele und Best Practices zum sofortigen Umsetzen
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Full-RAG: A modern architecture for hyper-personalization
Polymer Brushes
1. In recent years, the synthesis of polymer brushes has received significant attention. In
this presentation we talked about several different aspects of polymer brushes and
synthetic strategies for the generation of polymer brushes . Finally, example is
provided that highlight some recent developments aimed at strategies for the
functionalization of surfaces with polymer brushes, at ways of realizing smart
surfaces with switchable properties.
1
3. Polymer brushes
A polymer brush consists of end-tethered (grafted, anchored) polymer chains
stretched away from the substrate so that in the given solvent the brush height (h) is
larger as compared to the end-to-end distance (<r2>1/2) of the same non-grafted
chains dissolved in the same solvent. In polymer brushes the distance between
grafting points (d) is smaller than the chain end-to-end distance. Polymer brushes can
be introduced as thin films of end-grafted polymer molecules when the following
conditions are satisfied: h> <r2>1/2, d < <r2>1/2. Outside these conditions the grafted
layers are in the “mushroom regime” (see next slide).
3
4. Polymer Brushes: General Features
When polymer molecules are tethered (grafted) to a surface, two basic cases must be
distinguished depending on the graft density of the attached chains.
1. If the distance between two anchoring sites is larger than the size of the surface-
attached polymers, the segments of the individual chains do not “feel” each other
and behave more or less like single chains “nailed” down onto the surface by one
end. Depending on the strength of interaction of the polymer segments with the
surface, again two cases must be distinguished. If the interaction between the
polymer and the surface is weak (or even repulsive), the chains form a typical random
coil that is linked to the surface through a “stem” of varying size. For such a situation,
the term “mushroom” conformation has been coined (Slide). However, if the
segments of the surface attached chains adsorb strongly to the underlying surface,
the polymer molecules obtain a flat, “pancake”-like conformation (Slide)
2. A completely different picture is obtained if the chains are attached to the surface
at such short distances between the anchor points that the polymer molecules
overlap. In this case, the segments of the chains try to avoid each other as much as
possible and minimize segment–segment interactions by stretching away from the
surface (slide). This chain stretching, however, reduces the number of possible
polymer conformations, which is equivalent to a reduction in the entropy of the
chains.
4
5. This loss of entropy gives rise to a retracting force trying to keep the chains coiled, as
occurs in a stretched piece of rubber. Thus, a new equilibrium at a higher energy level
is obtained in which the chains are stretched perpendicular to the surface.
The structure of a surface-immobilized polymer can be evaluated by the inverse value
of the distance between grafting points (D). As the size of grafted polymer chains
approaches the distance between grafting points, the grafted chains overlap. This
point is a transition point between a single grafted chain (mushroom) regime and
brush regime. A commonly used literature parameter for quantitative
characterization of this transition is the reduced tethered density
where Rg is radius of gyration of a tethered chain at specific experimental conditions
of solvent and temperature. The definition of grafting density (σ) is determined by
Where h is the brush thickness; ρ, bulk density of the brush composition; and NA,
Avogadro’s number. It is generally recognized that three regimes occur in brush
formation: (1) the ‘‘mushroom’’ or weakly interacting regime (∑ < 1), (2) the
crossover regime (∑ ~ 1), and (3) the highly stretched regime (∑ >1). However, in real
systems, the transition between single grafted chains and a polymer brush is less
sharp because of the statistical characteristic of grafting and polydispersity of the
tethered chains
5
6. The term “responsive behavior” is rather a term which reflects applications, and
consequently, there is no universal definition of responsiveness. For many applications
we suppose to obtain a steep and well noticeable change (switching) of the given
property, thus, transitions from the state which can be characterized by some property to
the state with the contra property. Responsiveness of polymer brushes to external stimuli
refers to changes of polymer molecule conformations. The size of polymer chains is
sensitive to its environment. In Θ solvents (attraction and repulsion are compensated)
isolated polymer chains of the degree of polymerization N possess ideal coil
conformation when <r2>1/2 ~ N1/2. The size of the isolated chain is a function of solvent
quality (that may be expressed in terms of the χ-Flory-Huggins interaction parameter or
Θ temperature).
In good solvents and at high polymer concentrations the excluded volume effect (Chains
cannot take the position of other chains) modifies chain conformations substantially. In
semi-diluted polymer solutions the chain size decreases with the 1/8th power of the
polymer volume fraction in a good solvent. In theta solvents the polymer chain size is
concentration independent. In poor solvents bulk polymer solutions undergo a phase
separation into two phases: almost pure solvent and concentrated polymer solution of
overlapping Gaussian coils. Both the scaling exponent and the prefactor are sensitive to
solvent quality. Constraints due to the end grafting of the polymer chains introduce a
specific character of the response which is somewhat different from the response of
isolated chains in solution or melt. In the crowded grafted layers (polymer brushes) the
chains stretch out of the grafting surface until the excluded volume effect is compensated
by elastic energy (stretching entropy) of polymer coils. Polymer brushes expand in good
solvents and collapse in poor solvents. The change of characteristic size between good
and poor solvents is much larger for polymer brushes as compared to the polymer chain
in solution.
6
7. Mechanism of Responsiveness
The general idea behind the theoretical description of polymer brushes is that the
free energy F of the chains is obtained from a balance between the interaction energy
between the statistical segments Fint and energy difference between stretched and
unstretched polymer chains Fel (elastic free energy) caused by the entropy loss of the
chains:
F = Fint + Fel
The most important parameters, which are of interest for a description of brush
systems, are the segment density profile (ϕ(z)) of the surface-attached chains and/or
the brush height h as a function of the graft density σ, the molecular weight (/degree
of polymerization) of the surface-attached chains, and the solvent quality of the
contacting medium (Fig.1).
(Fig.1)Two hundred chains of a polymer brush (chain length
N = 100) under good solvent conditions.
7
8. The first description of such a brush system has been attempted by Alexander for
monodisperse chains consisting of N segments, which are attached to a flat, non-
adsorbing surface with an average distance of the anchor points d much smaller than
the radius of gyration of the same unperturbed chains not in contact with the surface
(Fig.2).
(Fig.2).Schematic illustration of the Alexander model for the
theoretic description of polymer brushes. The chain
segments with the “blobs” (indicated by the circles) behave
as random (“Gaussian”) coils. (d represents the average
distance between anchor points.)
If both the interaction energy resulting from binary monomer– monomer interactions
and the elastic energy of a Gaussian chain are calculated and minimized in respect to
the brush height h, the following equation is obtained for brushes in a good solvent:
In a poor solvent – that is, close to Θ conditions – the exponent describing the
influence of the grafting density is slightly different and is obtained.
It should be noted, that in both cases the brush height scales linearly with the degree
of polymerization/molecular weight of the polymer molecules, which is a much
stronger dependency than that of the size of a polymer coil in solution on the
molecular weight, where the radius of gyration Rg, scales with Rg ~ N0.59 for a
polymer in a good solvent and Rg ~ N0.50 for solutions close to Θ conditions.
In addition to these somewhat straightforward calculations, more complicated
situations have also been tackled where the polymer chains have a distinct
polydispersity, which exhibit a significant curvature also on the molecular scale, and
to brushes which carry charges along the polymer chain. In particular, the latter case
can become very complicated if the polymer chains interact specifically with ions in
the surrounding medium, as under these circumstances the situation can no longer
be described by simple mean field approaches, but specific complex formation and
(local) changes in the solubility of the polymer play a key role in describing the
swelling behavior of such brushes.
8
9. This slide presents the density profiles vs. distance from the grafting surface at
different β-stretching parameter values (1/β = d = <r2>1/2 /h). As the grafting density
increases from the mushroom regime (β < 1) to the strong stretching limit (β = 100)
the profile changes dramatically. The impenetrable grafting surface causes a decrease
of the polymer density close to the grafting surface when the grafting density
maximum is located in some distance from the grafting surface. This distance
increases as the grafting density decreases. The grafting density profile is much more
sensitive to the brush characteristic at moderate grafting densities as compared to a
very high stretching regime.
9
10. Types of polymer brushes
There are many different criteria to classify polymer brushes but based on the
constitution we have following types of polymer brushes:
Homopolymer brushes
Polyelectrolyte brushes
Block copolymer brushes
Molecular brushes
Reversible Self assembled brush
10
11. Typically there are three main methods for synthesising polymer brushes:
•Grafting onto (grafting to)
•Grafting from
•Grafting through
Amonge these three, the first two one are more important ,so some of the advantage
and disadvantages have been mentioned above.
11
12. In Grafting onto method a polymer chain which has a functional group at the end
diffuses through the surface, on the surface there are other functional groups , which
can react and therefore chain will graft to the surface.
It has to be metioned that due to the stereochemical hinderence , density of grafting
in this method is not high.
12
13. In Grafting from method a proper initiater is attach to the surface first, and then
surface will encounter with the monomer at approprate condition for polymerization
in side the reactor. At the polymerization media chains will grow on the surface,
while they have been grafted to it from the begining.
13
15. The uniformed polymer chain growth, which leads to low polydispersity, stems from
the transition metal based catalyst. This catalyst provides an equilibrium between
active, and therefore propagating, polymer and an inactive form of the polymer;
known as the dormant form. Since the dormant state of the polymer is vastly
preferred in this equilibrium, side reactions are suppressed.
This equilibrium in turn lowers the concentration of propagating radicals, therefore
suppressing unintentional termination and controlling molecular weights.
There are five important variable components of Atom Transfer Radical
Polymerizations. They are the monomer, initiator, catalyst, solvent and temperature.
The following section breaks down the contributions of each component to the
overall polymerization.
Monomer
Monomers that are typically used in ATRP are molecules with substituents that can
stabilize the propagating radicals; for example, styrenes, (meth)acrylates,
(meth)acrylamides, and acrylonitrile. ATRP are successful at leading to polymers of
high number average molecular weight and a narrow polydispersity index when the
concentration of the propagating radical balances the rate of radical termination. Yet,
the propagating rate is unique to each individual monomer. Therefore, it is important
that the other components of the polymerization (initiator, catalysts, ligands and
solvents) are optimized in order for the concentration of the dormant species to be
greater than the concentration of the propagating radical and yet not too great to
slow down or halt the reaction.
15
16. Initiator
The number of growing polymer chains is determined by the initiator. The faster the
initiation, the fewer terminations and transfers, the more consistent the number of
propagating chains leading to narrow molecular weight distributions. Organic halides
that are similar in the organic framework as the propagating radical are often chosen
as initiators.[Alkyl halides such as alkyl bromides are more reactive than alkyl
chlorides and both have good molecular weight control.
Catalyst
The catalyst is the most important component of ATRP because it determines the
equilibrium constant between the active and dormant species. This equilibrium
determines the polymerization rate and an equilibrium constant too small may inhibit
or slow the polymerization while an equilibrium constant too large leads to a high
distribution of chain lengths.
There are several requirements for the metal catalyst:
there needs to be two accessible oxidation states that are separated by one electron
the metal center needs to have a reasonable affinity for halogens
the coordination sphere of the metal needs to be expandable when its oxidized so to
be able to accommodate the halogen
a strong ligand complexation.
The most studied catalysts are those that polymerizations involving copper, which has
shown the most versatility, showing successful polymerizations regardless of the
monomer.
Solvent
Toluene,1,4-dioxane
Temperature
16
17. ATRP has been conducted from a range of surfaces since the concept was first
disclosed, Because of their appearance these materials have been called polymer
brushes. The two most common types of polymer brushes are illustrated above and
have been formed by both "grafting from" and "grafting to" inorganic particles and
flat surfaces. The synthesis of organic/inorganic hybrid materials is an area of growing
interest as the useful properties of disparate components can be combined into a
single material.
Spherical particles:
Organic/inorganic hybrid nanoparticles containing an inorganic core and tethered
glassy or rubbery homopolymers or copolymers have been prepared by the ATRP of
styrene and (meth)acrylates from colloidal initiators.
Flat Surfaces:
Modification of surfaces with thin polymeric films allows one to tailor surface
properties such as wetability, biocompatibility, biocidal activity, adhesion, adsorption,
corrosion resistance and friction. Polymers with reactive groups or segments can be
prepared for "grafting onto" surfaces or functional groups can be attached to the
surface for a more efficient "grafting from" approach. The properties of surfaces are
addressed elsewhere on this site in this section we primarily address "grafting from"
surface tethered initiators. It is also possible to prepare block copolymers where one
or more segments of the block copolymer had been prepared by a non-CRP
procedure. The only requirement is to ensure the terminal functional groups present
on the initial functional polymer can be converted into radically transferable atom(s)
for the second controlled ATRP step
17
19. Diffrent products with diffrent morphology, for diffrent sufesticated applycations can
be produced by ATRP.
Many researching groups are working in this area, therefore just for making an
impression aboat visatility of ATRP the following slides have made.
In each photo the mode of grafts are diffrent.
19
22. The major objective for the application of responsive polymer brushes is to regulate,
adjust, and switch interaction forces between the brush and its environment constituted
of liquid, vapor, solid, another brush, particles, etc. The simplest formulation of the
Responsive Polymer Brushes problem is switching between attraction and repulsion. For
example, the polymer brush like layer stabilizes colloidal dispersion, however, upon
change of its environment the colloid coagulates because the repulsive forces of the
brush have been “switched off.” This simple effect has numerous important applications
in various technologies and it is not fully explored and engineered yet. The same simple
problem is important if the friction coefficient, adhesion, or wetting could be rapidly
changed to switch off and on capillary flow, cell adhesion, protein adsorption, cell
growth, membrane permeability, and drug release.
One of the targets is the application of the responsive brushes for smart devices such as
drug delivery devices, microfludic analytical devices, and sensors. Smart drug delivery
devices are seen as a drug loaded capsule coated with a brush-like shell. Expansion and
shrinking of responsive polymer brushes can be used to fabricate mechanical actuators.
The effect of switching of wetting behavior of the mixed weak PEL brushes upon a
change of pH was recently explored for the fabrication of “smart” microfluidic devices.
The passage of liquids through the microfluidic channels was regulated by responsiveness
of the mixed brushes of different compositions. Reversible changes of mixed brush
morphologies in solvents of different thermodynamic quality were used for the motion of
nanoparticles deposited on the brush surface. The simplest device which explores
polymer brush responsiveness is a sensor working on the principle of the brush
expansion–collapse transitions upon changes in its environment. Currently, research is
focused on how the interactions with polymer brushes may be precisely tuned and
monitored in a controlled environment.
22
23. Reversible Cantilever actuation by PEL-Brushes
The bending of microcantilevers upon adsorption of polymers (DNA, proteins) or
small molecules has great potential for the development of highly sensitive sensors
and efficient nanoactuators. For microcantilevers to be useful as actuators, precise
positioning, reversibility, and large-scale bending are prerequisites. Conventional
modification by self-assembled monolayers (SAMs) usually generates small cantilever
deflections. By grafting polymers to the cantilever surface, a much wider range of
responses can be achieved due to conformational changes in the polymer backbones,
and recently, the bending of pH responsive copolymer brush-coated AFM cantilevers
was studied under different conditions. However, reversible and multi-stage actuation
of cantilevers remains a significant challenge. The use of polyelectrolytes and their
collapse in response to salt has recently emerged as a promising potential synthetic
equivalent of one of the most powerful biological motors: the spasmoneme spring.
23
24. Polyelectrolyte brushes
Polyelectrolytes are polymers whose repeating units bear an electrolyte group. These
groups will dissociate in aqueous solutions (water), making the polymers charged.
Polyelectrolyte properties are thus similar to both electrolytes (salts) and polymers
(high molecular weight compounds), and are sometimes called polysalts. PEL in
aqueous solutions attract great interest because of their relevance to many biological
systems. Interactions which involve charged macromolecules are strongly modified by
Coulomb forces. The charge density on a polymer chain in a polar solvent depends on
the chain constitution and degree of dissociation (f) of ionizable groups. If ionizable
groups are strong acids or bases (strong PE) f is equal to 1 and is not affected by the
environment. If ionizable groups are weak acids or bases (weak PEL) f depends on
local pH. For the latter case charges are mobile within the polymer chain.
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26. For the dense strong PEL brush (high f and grafting density) all counterions are
trapped inside the brush (Slide.b). The brush height is determined by the balance
between osmotic pressure of the trapped counter-ions and the stretching entropy of
the chains (so called osmotic brush regime). The contribution of the excluded volume
effect depends on the grafting density. At very high densities the excluded volume
effect may dominate while at moderate densities the electrostatic nature will have a
major contribution. The latter will be reflected in the prefactor in the scaling
relationship h ~ N. These brushes are insensitive to local pH. Added salt does not
affect the brush unless the ionic strength of the solution approaches the level of the
ionic strength inside the brush (Slide.d). In that case the prefactor is an inverse cubic
root function of the external salt concentration and the grafting density (so called
salted brush regime). Thus, in terms of responsive applications strong PEL are
interesting for design of responsiveness to humid and aqueous environments when
the high swelling of the brush in water or a humid atmosphere is resulted from strong
osmotic pressure of trapped counterions (Slide. a,b). Weak PEL brushes represent
one of the most interesting responsive behaviors. They demonstrate responsiveness
to changes in external pH and ionic strength. Weak PEL brushes carrying basic
functionalities expand upon a decrease of pH, while acidic PEL brushes expand upon
an increase of pH (Slide. c, d). At a high salt concentration weak PEL brushes shrink
due to the same mechanism as strong PEL brushes. However, it is noteworthy, that in
some range of pH values they shrink also at no salt added or at very small salt
concentrations, thus, expressing non-monotonous dependence of the brush height
vs. salt concentration. This behavior originates from the sensitivity of f for weak
PEL(s) to the local electric field.
26
27. Slide shows the experimental setup to measure the deflection of cantilever while
switching between different environments.
27
28. Behaviour of PMEP brush modified cantilever
The conformational changes of the brushes in response to salt solution or pH are
schematically shown in Scheme 1.
Scheme 1. Schematic of Reversible Swollen/Collapse of PMEP Brush
PMEP can be switched between three ionic states: fully protonated,
monoprotonated/ monobasic, and dipotassium salt/dibasic states, depending
depending on pH. Slide (above) displays the bending of brush-coated cantilevers
when varying the pH of the solution between 1 and 13. In region I, the brushes are
fully protonated, while in region III, they are fully deprotonated, and compressive
stress is generated in both strongly acidic (pH < 2) and basic (pH > 8) environments.
At pH < 2, the protonated brushes are no longer soluble and will collapse, generating
a compressive surface stress since the “footprint” of the polymers is too small to
accommodate the collapsing chain. This effect is consistent with previous reports that
polymer brushes generate a compressive surface stress upon polymer collapse.
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29. At pH > 8, the PMEP brushes are fully deprotonated, and the electrostatic repulsion
between charged polymer chains leads to the development of a large compressive
stress. The maximum deflection of the cantilevers, up to micrometer scale
(approximate 1300 nm), is found in this fully charged state. It should be noted that
the cantilever deflections are highly reversible, and that the brushes can be cycled
through a number of pH cycles. The magnitude and sensitivity of the response to salt
depend strongly on the length of the brushes, the grafting density, and the degree of
charging of the polymer. Generally there is no or very small deflection for low (<10%
initiator) grafting densities of brushes.
29
30. Slide shows the reversible bending and return to equilibrium position of the brush-
coated cantilever when switching between a 100 mM KCl solution and pure water,
respectively. The response of the cantilever to changes of solution is very fast (30 s).
The return to zero deflection upon addition of water is slow due to the slow diffusion
of excess salt away from the brush layer. The compressive stress is generated by the
brushes collapsing under the influence of the high salt environment; this situation is
similar to the compressive stress generated at low pH (see above). The control
experiments (black line) show that non-brush-modified cantilevers show no response
to changes in salt concentration.
30
31. Control over the actual position of cantilever can be achieved by exposing the brush-
coated cantilevers to different salt concentrations between 0 and 100 mM. By
gradually increasing or decreasing the salt concentration, the actuation can be
precisely manipulated in discrete multiple steps. By plotting the bending of the
cantilever versus the salt concentration (slide), or to the logarithm of the salt
concentration (inset), one can distinguish two distinct response regimes. At salt
concentrations below 1 mM, the response is small (remaining below 10% of
maximum bending amplitude), whereas at higher concentrations, a much larger
response is observed. Conversely, when lowering the salt concentration, we can see
an approximately linear dependence of log[salt] versus normalized bending
amplitude. Polyelectrolyte brush theory predicts that for annealed brushes at low salt
concentrations the brush heights (and therefore surface stress) first increase slightly
due to the exchange between external cations and associated protons. At higher
concentrations, charge screening (removal) is the dominant effect, leading to collapse
of the brushes and generation of much more significant compressive stress. It should
be noted that the chemical nature of the ions (valency, lipophilicity, etc.) also
influences the collapse process, opening up possibilities for selectivity.
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32. Conclusion
The field of responsive polymer brushes is a continuously expanding area of research.
The expansion is not very fast because of the complexity of the systems for the
fabrication as well as for investigations. Nevertheless, the continuous and successful
development of the field is predetermined by the fact that the polymer brushes are
the most effective structures to regulate complex interactions in synthetic colloidal
and natural living systems. The potential for the design of the interactions is very
high. Mimicking natural systems and designing new structures will accompany the
development of the field of polymer brushes. That will stimulate expansion of
theoretical and experimental investigations. We may also benefit from the
combination of polymer brushes and gels in complex responsive devices.
32