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,
It's simple to understand the synthesis. Hydrothermal method is a chemical reaction in water in a sealed pressure vessel, which is in fact a type of reaction at both high temperature and pressure.
Different types of methods can be used for the preparation of Magnetic Nanoparticles, their advantages and disadvantages and applications of the materials in various fields are given in the presentation
This presentation contains a basic introduction to quantum dots,their discovery, properties, applications,advantages,limitations and future prospects.It also contains a brief overview of experimental work carried out and results obtained during my summer term project.
know more about nanomaterials and its apllication in future as well as current situation, and what wil we reserch on basis of nanomaterials and carbon structure and its aplication in such futuriastic manner.
Novel effects can occur in materials when structures are formed with sizes comparable to any one of many possible length scales, such as the de Broglie wavelength of electrons, or the optical wavelengths of high energy photons. In these cases quantum mechanical effects can dominate material properties. One example is quantum confinement where the electronic properties of solids are altered with great reductions in particle size. The optical properties of nanoparticles, e.g. fluorescence, also become a function of the particle diameter. This effect does not come into play by going from macrosocopic to micrometer dimensions, but becomes pronounced when the nanometer scale is reached.
Synthesis of Cobalt ferrite by Solid Reaction Methodsank_sanjay
Cobalt ferrite nano-crystalline powder was synthesized from the powder mixture of cobalt carbonate and iron oxide by mixed oxide ceramic method. The effects of temperature of calcination as well as molar ratio of CoCO3/Fe2O3 on the phase structure, morphology and magnetic properties of the products were studied using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and vibrating sample magnetometer (VSM) techniques, respectively. The samples calcined at 800 and 900˚C consisted of cobalt ferrite, iron oxide and cobalt oxide. In the sample calcined at 1000˚C, the reaction was completed and single phase CoFe2O4 with a mean crystallite and particle sizes of 49 and 300 nm, respectively was obtained.
It's simple to understand the synthesis. Hydrothermal method is a chemical reaction in water in a sealed pressure vessel, which is in fact a type of reaction at both high temperature and pressure.
Different types of methods can be used for the preparation of Magnetic Nanoparticles, their advantages and disadvantages and applications of the materials in various fields are given in the presentation
This presentation contains a basic introduction to quantum dots,their discovery, properties, applications,advantages,limitations and future prospects.It also contains a brief overview of experimental work carried out and results obtained during my summer term project.
know more about nanomaterials and its apllication in future as well as current situation, and what wil we reserch on basis of nanomaterials and carbon structure and its aplication in such futuriastic manner.
Novel effects can occur in materials when structures are formed with sizes comparable to any one of many possible length scales, such as the de Broglie wavelength of electrons, or the optical wavelengths of high energy photons. In these cases quantum mechanical effects can dominate material properties. One example is quantum confinement where the electronic properties of solids are altered with great reductions in particle size. The optical properties of nanoparticles, e.g. fluorescence, also become a function of the particle diameter. This effect does not come into play by going from macrosocopic to micrometer dimensions, but becomes pronounced when the nanometer scale is reached.
Synthesis of Cobalt ferrite by Solid Reaction Methodsank_sanjay
Cobalt ferrite nano-crystalline powder was synthesized from the powder mixture of cobalt carbonate and iron oxide by mixed oxide ceramic method. The effects of temperature of calcination as well as molar ratio of CoCO3/Fe2O3 on the phase structure, morphology and magnetic properties of the products were studied using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and vibrating sample magnetometer (VSM) techniques, respectively. The samples calcined at 800 and 900˚C consisted of cobalt ferrite, iron oxide and cobalt oxide. In the sample calcined at 1000˚C, the reaction was completed and single phase CoFe2O4 with a mean crystallite and particle sizes of 49 and 300 nm, respectively was obtained.
Physical and mechanical properties of composite brick from cement mortar, fly...eSAT Journals
Abstract Responding to the need of minimizing the extraction of natural resources like sand and lime, this study attempted to use industrial wastes such as fly ash and rubber crumbs as substitute materials in making composite brick. A composite brick was produced by varying the rubber crumbs composition, as sand substitute in the mixture, from 1030 wt.% relative to total aggregate weight. Fly ash, 20 wt.% relative to cement and fly ash weight, was used as binder substitute. After 28 days of curing, composite brick was tested in terms of compressive strength, density and water absorption capacity. Compressive test showed that the brick can only be used in less impacted area considering that it does not meet the minimum standard to be considered as substitute to the commercially available brick. A decreasing trend of its compressive strength is observed as the amount of rubber crumbs increases from 10 to 30% of the total aggregate weight. The addition of light rubber crumbs and fly ash desirably decrease the density of the composite brick when compared to those commercially sold in the market. Water absorption test revealed that the produced composite brick is more efficient in minimizing water absorption. This study demonstrated that composite brick can be made using industrial wastes as substitute for aggregate and binder, with huge implication in brick concrete making. Keywords: Composite brick, rubber crumbs, fly ash, and concrete brick
Gareth investigates the current state of play regarding lumen maintenance testing of outdoor lighting. This paper presents an analysis of the current street lighting test methods and discusses some possible alternatives to the current procedures.
Talk by Dr Gareth John, Photometric and Optical Testing Services
With the introduction of multi-touch and gesture support coming in Qt, application developers now have the possibility of introducing new types of input and interaction to their applications. We will examine the various types of devices that one can expect to encounter in the multi-touch and gesture "world". This presentation will also introduce and explain the new API, walk through some example code, and show some demos of some of the possibilities we foresee with this technology.
Presentation by Jens Bache-Wiig held during Qt Developer Days 2009.
http://qt.nokia.com/developer/learning/elearning
In order to properly predict the performance of an LED lighting system and to accurately compare results to competing LED and conventional lighting systems, lighting engineers and designers must be particularly careful to use appropriate LED Maintenance Factors.
Calculations to predict performance lighting installation are fundamental to the practice of lighting design and lighting engineering. These calculations allow lighting engineers and designers to predict lighting performance and whether the design meets and complies with the correct specification and performance recommendations.
Talk by Darryl Bullock MSc BEng (Hons) BA CEng MILP MIET, National Project Manager of Light and Energy Design
There has been a lot of press recently concerning the effect of LED street lights on both humans and the surrounding
environment...
Talk by Kelly Smith, Global Lighting Applications Engineer, Thorn Lighting Ltd
Nano Scale Surface Characterization of Poly Ethyleneterephthalate Silicon Rub...ijtsrd
Atomic force microscopy has been used to investigated the surface properties of different materials, in this paper it is used to measure the surface roughness and surface adhesive force of three different membrane samples Poly ethyleneterephthalate PET , Silicon Rubber SR and PET SRcopolymers. This analytical method allows images representing the topography and adhesive force Phase image of the surface to be captured simultaneously at a molecular nanometer resolution. The distribution of hydrophilic polar groups and the surface roughness on the investigated surfaces ofthese membrane samples influences the subsequent processing of polymeric membrane manufacture as well as their performance. From the results a clear distinction was observed between the three samples in both images the topography surface roughness images and adhesive force images. Promising result were obtained for the PET SRcopolymer samples to be a good candidate in membrane separation applications. This study may also help to explain the differences in membrane performances and efficiency during applications in the separation process. Dr. Abduelmaged Abduallah | Dr. Kamal M. Sassi | Dr. Mustafa T. Yagub "Nano-Scale Surface Characterization of Poly (Ethyleneterephthalate) - Silicon Rubber Copolymers using Atomic Force Microscopy" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-5 | Issue-4 , June 2021, URL: https://www.ijtsrd.compapers/ijtsrd43688.pdf Paper URL: https://www.ijtsrd.comengineering/chemical-engineering/43688/nanoscale-surface-characterization-of-poly--ethyleneterephthalate--silicon-rubber-copolymers-using-atomic-force-microscopy/dr-abduelmaged-abduallah
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
International Journal of Engineering Research and DevelopmentIJERD Editor
Electrical, Electronics and Computer Engineering,
Information Engineering and Technology,
Mechanical, Industrial and Manufacturing Engineering,
Automation and Mechatronics Engineering,
Material and Chemical Engineering,
Civil and Architecture Engineering,
Biotechnology and Bio Engineering,
Environmental Engineering,
Petroleum and Mining Engineering,
Marine and Agriculture engineering,
Aerospace Engineering.
Viscoelastic response of polymeric solids in sliding contactspadmanabhankrishnan4
Abstract: The viscoelastic response of polymeric solids to sliding contact conditions
is observed and analyzed with respect to the sliding speed, material composition,
and geometry. It was discovered that polymeric solids produced their own distinct
viscoelastic signatures that cause resonance at certain sliding speeds which can be
explained with resonance conditions for electromagnetic waves. The observed viscolelastic phenomenon is characterized with respect to the relaxation and recovery
times for rigid polymeric solids. It is confirmatory as a demonstration of proof of
existence of viscoelasticity and self-organization in these materials under sliding contact conditions. Viscoelastic observations are also made on the aged specimens in
sliding contact.
New Technique for Measuring and Controlling the Permeability of Polymeric Mem...Editor IJCATR
Membranes have wide uses in industry and medicine applications. Polymer membranes are important materials because of their high chemical resistance, but they are of weak mechanical resistance against high pressures. Therefore, it was essential to modify a permeability measuring technique free from high pressure application. The current work represented a modification for the permeability measuring technique of membranes, where ionic salt was added with known concentration to water as common solvent and the electrolyte current was measured behind the membrane. The electrolysis current was correlated to the flow rate of water across a polyvinyl alcohol (PVA) membrane. Some other problems were raised such that polarization on electrodes and changes in electrolyte contents during the long time of the slow process. Pulsed potential on electrodes resolved these problems and other associated problems like rush in current and the double layer capacitance effect. An empirical equation was suggested to evaluate the permeability of polymer membranes by this modified method. Easy and accurate measurement of permeability helped authors to change the permeability of PVA membranes by adding copper nano particles in membrane to reduce its permeability, and adding silicone dioxide micro particles to the PVA membranes to increase its permeability. Authors suggested a mechanism for these permeability changes. Scanning electron microscope images for the filled PVA membranes supported the suggested mechanism.
New Technique for Measuring and Controlling the Permeability of Polymeric Mem...Editor IJCATR
Membranes have wide uses in industry and medicine applications. Polymer membranes are important materials
because of their high chemical resistance, but they are of weak mechanical resistance against high pressures. Therefore, it was
essential to modify a permeability measuring technique free from high pressure application. The current work represented a
modification for the permeability measuring technique of membranes, where ionic salt was added with known concentration
to water as common solvent and the electrolyte current was measured behind the membrane. The electrolysis current was
correlated to the flow rate of water across a polyvinyl alcohol (PVA) membrane. Some other problems were raised such that
polarization on electrodes and changes in electrolyte contents during the long time of the slow process. Pulsed potential on
electrodes resolved these problems and other associated problems like rush in current and the double layer capacitance effect.
An empirical equation was suggested to evaluate the permeability of polymer membranes by this modified method. Easy and
accurate measurement of permeability helped authors to change the permeability of PVA membranes by adding copper nano
particles in membrane to reduce its permeability, and adding silicone dioxide micro particles to the PVA membranes to
increase its permeability. Authors suggested a mechanism for these permeability changes. Scanning electron microscope
images for the filled PVA membranes supported the suggested mechanism
Gaskets in joints play an important role in the sealing performance of bolted flange joints, and their behavior is
complex due to nonlinear material properties combined with permanent deformation. The variation of contact stresses due to
the pressure of the flange and the material properties of the gasket play important roles in achieving a leak proof joint. In this
paper, a three-dimensional finite element analysis (FEA) of bolted flange joints has been carried out by taking experimentally
obtained loading and unloading characteristics of the gaskets for various thicknesses and loads. Analysis shows that the
distribution of contact stress has a more dominant effect on sealing performance than the limit on flange rotation specified by
ASME.
Similar to MECHANICAL & THERMAL PROPERTIES OF NANO COMPOSITES (20)
EFFECT OF FLAME RETARDANT ADDITIVES IN FLAME RETARDANT GRADE OF ABSArjun K Gopi
In this study the effect of flame retardants in flame retardant grade of abs is compared with natural ABS grade. ABS is a flammable material. It is easily burn with high flammability value. ABS materials without flame retardant are easily burned with a luminous yellow flame, smoking strongly and continue to burn after removal of the ignition source. So for some particular applications we are incorporating flame retardants into ABS. But the addition of flame retardants may leads to variation in properties. For that I have done several physical, thermal, and rheological tests to investigate the properties of the respective ABS grades. The results obtained was very interesting
The Internet is amazing, but overwhelming. This list of sites covers a wide array of interests, and each site listed can give you the information that you need without having to spend your valuable time searching and searching. Here are some of the most useful websites on the internet that you may not know about. These web sites, well most of them, solve at least one problem really well and they all have simple web addresses (URLs) that you can memorize.
Original Post http://www.attittudeblogger.in/2016/12/list-of-100-very-useful-websites.html
Richard's entangled aventures in wonderlandRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
A brief information about the SCOP protein database used in bioinformatics.
The Structural Classification of Proteins (SCOP) database is a comprehensive and authoritative resource for the structural and evolutionary relationships of proteins. It provides a detailed and curated classification of protein structures, grouping them into families, superfamilies, and folds based on their structural and sequence similarities.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Nutraceutical market, scope and growth: Herbal drug technologyLokesh Patil
As consumer awareness of health and wellness rises, the nutraceutical market—which includes goods like functional meals, drinks, and dietary supplements that provide health advantages beyond basic nutrition—is growing significantly. As healthcare expenses rise, the population ages, and people want natural and preventative health solutions more and more, this industry is increasing quickly. Further driving market expansion are product formulation innovations and the use of cutting-edge technology for customized nutrition. With its worldwide reach, the nutraceutical industry is expected to keep growing and provide significant chances for research and investment in a number of categories, including vitamins, minerals, probiotics, and herbal supplements.
Introduction:
RNA interference (RNAi) or Post-Transcriptional Gene Silencing (PTGS) is an important biological process for modulating eukaryotic gene expression.
It is highly conserved process of posttranscriptional gene silencing by which double stranded RNA (dsRNA) causes sequence-specific degradation of mRNA sequences.
dsRNA-induced gene silencing (RNAi) is reported in a wide range of eukaryotes ranging from worms, insects, mammals and plants.
This process mediates resistance to both endogenous parasitic and exogenous pathogenic nucleic acids, and regulates the expression of protein-coding genes.
What are small ncRNAs?
micro RNA (miRNA)
short interfering RNA (siRNA)
Properties of small non-coding RNA:
Involved in silencing mRNA transcripts.
Called “small” because they are usually only about 21-24 nucleotides long.
Synthesized by first cutting up longer precursor sequences (like the 61nt one that Lee discovered).
Silence an mRNA by base pairing with some sequence on the mRNA.
Discovery of siRNA?
The first small RNA:
In 1993 Rosalind Lee (Victor Ambros lab) was studying a non- coding gene in C. elegans, lin-4, that was involved in silencing of another gene, lin-14, at the appropriate time in the
development of the worm C. elegans.
Two small transcripts of lin-4 (22nt and 61nt) were found to be complementary to a sequence in the 3' UTR of lin-14.
Because lin-4 encoded no protein, she deduced that it must be these transcripts that are causing the silencing by RNA-RNA interactions.
Types of RNAi ( non coding RNA)
MiRNA
Length (23-25 nt)
Trans acting
Binds with target MRNA in mismatch
Translation inhibition
Si RNA
Length 21 nt.
Cis acting
Bind with target Mrna in perfect complementary sequence
Piwi-RNA
Length ; 25 to 36 nt.
Expressed in Germ Cells
Regulates trnasposomes activity
MECHANISM OF RNAI:
First the double-stranded RNA teams up with a protein complex named Dicer, which cuts the long RNA into short pieces.
Then another protein complex called RISC (RNA-induced silencing complex) discards one of the two RNA strands.
The RISC-docked, single-stranded RNA then pairs with the homologous mRNA and destroys it.
THE RISC COMPLEX:
RISC is large(>500kD) RNA multi- protein Binding complex which triggers MRNA degradation in response to MRNA
Unwinding of double stranded Si RNA by ATP independent Helicase
Active component of RISC is Ago proteins( ENDONUCLEASE) which cleave target MRNA.
DICER: endonuclease (RNase Family III)
Argonaute: Central Component of the RNA-Induced Silencing Complex (RISC)
One strand of the dsRNA produced by Dicer is retained in the RISC complex in association with Argonaute
ARGONAUTE PROTEIN :
1.PAZ(PIWI/Argonaute/ Zwille)- Recognition of target MRNA
2.PIWI (p-element induced wimpy Testis)- breaks Phosphodiester bond of mRNA.)RNAse H activity.
MiRNA:
The Double-stranded RNAs are naturally produced in eukaryotic cells during development, and they have a key role in regulating gene expression .
Richard's aventures in two entangled wonderlandsRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
The increased availability of biomedical data, particularly in the public domain, offers the opportunity to better understand human health and to develop effective therapeutics for a wide range of unmet medical needs. However, data scientists remain stymied by the fact that data remain hard to find and to productively reuse because data and their metadata i) are wholly inaccessible, ii) are in non-standard or incompatible representations, iii) do not conform to community standards, and iv) have unclear or highly restricted terms and conditions that preclude legitimate reuse. These limitations require a rethink on data can be made machine and AI-ready - the key motivation behind the FAIR Guiding Principles. Concurrently, while recent efforts have explored the use of deep learning to fuse disparate data into predictive models for a wide range of biomedical applications, these models often fail even when the correct answer is already known, and fail to explain individual predictions in terms that data scientists can appreciate. These limitations suggest that new methods to produce practical artificial intelligence are still needed.
In this talk, I will discuss our work in (1) building an integrative knowledge infrastructure to prepare FAIR and "AI-ready" data and services along with (2) neurosymbolic AI methods to improve the quality of predictions and to generate plausible explanations. Attention is given to standards, platforms, and methods to wrangle knowledge into simple, but effective semantic and latent representations, and to make these available into standards-compliant and discoverable interfaces that can be used in model building, validation, and explanation. Our work, and those of others in the field, creates a baseline for building trustworthy and easy to deploy AI models in biomedicine.
Bio
Dr. Michel Dumontier is the Distinguished Professor of Data Science at Maastricht University, founder and executive director of the Institute of Data Science, and co-founder of the FAIR (Findable, Accessible, Interoperable and Reusable) data principles. His research explores socio-technological approaches for responsible discovery science, which includes collaborative multi-modal knowledge graphs, privacy-preserving distributed data mining, and AI methods for drug discovery and personalized medicine. His work is supported through the Dutch National Research Agenda, the Netherlands Organisation for Scientific Research, Horizon Europe, the European Open Science Cloud, the US National Institutes of Health, and a Marie-Curie Innovative Training Network. He is the editor-in-chief for the journal Data Science and is internationally recognized for his contributions in bioinformatics, biomedical informatics, and semantic technologies including ontologies and linked data.
2. A polymer composite is a combination of a polymer
matrix and a strong reinforcing phase, or filler.
A polymer nanocomposite is a polymer matrix with a
reinforcing phase consisting of particles with one
dimension in the nano-sized regime.
A general conclusion has been drawn that
nanocomposites show much improved mechanical
properties over their micro-sized similar systems.3,
Because of their small size, nanoparticles have a high
surface to volume ratio and provide high energy
surfaces.
3. An expected result of embedding nanoparticles into a
polymer matrix is enhanced bonding between the polymer
matrix and filler, resulting from the nanoparticles’ high
interfacial energy.
Polymer composite theory predicts that improved bonding
between polymer and matrix leads to improved
mechanical properties.
Some experimental data has shown that reduced particle
size improves mechanical properties, specifically elastic
modulus.
4. Although studies have focused on many different matrix-
filler systems, a common feature of all polymer
composites is the existence of a phase border between
the matrix and filler and the formation of an interphase
layer between them.
The properties of the interphase can differ dramatically
from the bulk and influence the mechanical properties of
the composite.
5. Consider, Alumina (Al2O3) nanoparticles and magnetite
(Fe3O4) nanoparticles were each dispersed in polystyrene
(PS) and poly(methyl methacrylate) (PMMA) matrices.
Mechanical characterization can be done by using tensile
testing, dynamic mechanical testing (DMA), and
nanoindentation.
Particle size and distribution were characterized using
scanning electron microscopy (SEM) and transmission
electron microscopy (TEM).
Interphase bonding, density, and thickness were
confirmed using Fourier transform infrared spectroscopy
(FT-IR) and thermal gravimetric analysis (TGA)
6. To achieve the optimal mechanical properties have
focused on maximizing the interaction between the
polymer matrix and the filler.
Despite the huge variety of polymer composite systems, a
common thread among all the systems is the existence of
a phase border between the matrix and filler and the
formation of an interphase layer between them.
7.
8. The interphase layer extends well beyond the adsorption
layer of the matrix chains bound to the filler surface.
The structure of the interphase is different than either
the filler or matrix phases, and it varies depending on the
distance from the bound surface.
The interphase is important to the mechanical properties
of the composite because its distinct properties control
the load transfer between matrix and filler.
The concept of interphase is not unique to nano
composites, but due to the large surface area of nano
particles, the interphase can easily dominate the
properties of nanocomposites.
9. The inter phase has a characteristic structure consisting
of flexible polymer chains, typically in sequences of
adsorbed segments (trains), loops, and tails.
10. If all areas of the surface are capable of adsorption, the
polymer chain is sufficiently flexible, and segments are
readily adsorbed, the loops will be short and the
macromolecule will form a flat (ie dense) layer close to
the surfaceadas shon fig2(a).
If the chain segments have weak interaction with the
surface, or the chain is rigid, the loops and tails extend
farther into the matrix and form a region of lower
density, as as shown in Figure 2(b).1
11.
12. Many studies have identified the interphase as an
important factor in the mechanical properties of
composites.
They explained an increase in modulus, yield, and tensile
strength in composite systems by defining the properties
of the interphase region.
According to their theory, if a polymer adhered to a filler
particle surface where modulus is high, there would be an
area of high density, and thus, high modulus next to the
particle.
13. While there has been a great amount of experimental
work that has taken place in the area of polymer
nanocomposites, a consensus has not yet been reached on
how nano-sized inclusions affect mechanical properties.
Several studies have shown that reduced size improves
mechanical properties, specifically elastic modulus.
14. The improved modulus increases with volume fraction,
the yield stress and tensile strength decrease with
increased volume fraction, while the ultimate strain does
not change with volume fraction.
16. The yield stress increased with increasing filler
concentration and increased slightly as the size of the
particles decreased .
Ultimate strain decreased greatly, however, as
concentration increased and particle size decreased .
The debonding process was examined to explain the
differences in the mechanical properties between the
particle sizes as shown in Figure 4.
The study suggests that the 12 nm particles tend to
gather into aggregates and a multiple debonding process
results from debonding around each individual particle.
17. The aggregates, therefore, act like large soft particles
during the deformation process.
The 50 nm particles are well distributed, however, and
would preferentially undergo a single debonding process .
The debonding theory was also used to explain why the
volume of the polymer nanocomposites increased, with
the greatest increase occurring in systems with the
smallest particles.
19. Consider four system poly(methyl methacrylate) (PMMA,
pure/reference), PMMA-Fe3O4, PMMA-Al2O3, polystyrene
(PS, pure/reference), PS-Fe3O4, and PS-Al2O3.
20. Tensile testing was performed to determine elastic
modulus, ultimate stress, and ultimate strain for all six
systems .
In tensile testing, a “dog-bone” shaped sample is placed
in the grips of movable and stationary fixtures in a screw
driven device.
which pulls the sample until it breaks and measures
applied load versus elongation of the sample.
21.
22. The testing process requires specific grips, load cell, and
extensometer for each material and sample type.
The load cell is a finely calibrated transducer that
provides a precise measurement of the load applied.
The extensometer is calibrated to measure the smallest
elongations.
Output from the device is recorded in a text file including
load and elongation data.
Mechanical properties are determined from a stress vs.
strain plot of the load and elongation data.
23. Using pure polymer references for comparison that
undergo the same processing as the nanocomposites
enhances the reliability of the data .
Tensile testing data was plotted in stress versus strain
curves, examples of which are shown in Figure .
Elastic modulus is defined as the slope of the linear
portion of the stress/strain curve.
The linear portion of the curves for most systems was
determined to be between 5 MPa and 15 MPa stress.
24.
25.
26. DMA determines elastic modulus, loss modulus, and
damping coefficient as a function of temperature,
frequency, or time.
Samples in DMA, depending on the equipment, can be quite
small, in the range of 40 mm X 5 mm X 1 mm.
The sample is clamped into movable and stationary fixtures
and then enclosed in a thermal chamber, as shown in
Figure.
28. Equipment available for this study required small
rectangular samples approximately 25 mm long, 5-10 mm
wide, and 0.100-2 mm thick.
To meet this requirement, thin film samples on glass
slides were created .
This technique, however, enough mixture was poured to
cover the entire slide.
Because the slides were approximately 25 mm wide this
approach allowed cutting multiple samples from the same
slide .
29. Samples were cut from the slides using a low speed
diamond wheel saw.
Each sample was labeled with a marker, and width and
depth were measured and recorded at two places on each
sample .
30. In DMA, the glass transition temperature, Tg, of a sample
can be accurately determined from the elastic and loss
modulus response to temperature and stress.
The data near the higher temperature end of each test
was considered invalid, the initial elastic modulus near
room temperature was considered accurate.
Dynamic testing results were processed by the computer
software and provided as a plot of storage (elastic)
modulus, loss modulus, and tan δ versus temperature.
31. DMA was performed to determine the bulk mechanical
properties of polymer nanocomposites.
Dynamic testing results were processed by the computer
software and provided as a plot of storage (elastic)
modulus, loss modulus, and tan δ versus temperature.
The goal of using modulus results was for direct
comparison between the nanocomposites and the pure
polymer reference systems, the room temperature
modulus was the primary result evaluated .
32. Figure shows sample output from a DMA test of the PS-
Al2O3 system for a test that ran nearly to completion .
The peak of the red tan δ curve provides the glass
transition temperature of the nanocomposite .
Because so few tests ran to the point of reaching a
maximum in tan δ, the current study will not report glass
transition temperatures from DMA.
33. DMA dynamic test results for PS-Al2O3 nanocomposite system that ran
nearly to completion, giving a maximum tan δ, or glass transition
temperature
34. DMA dynamic test results for PS-Fe3O4 nanocomposite system in which
sample buckled prior to reaching its glass transition temperature.
35. DMA results for the nanocomposite systems show a
consistent trend of decreased elastic modulus over the
pure polymer reference systems .
36. Loss modulus is the capacity of a material to dissipate
energy when placed when stressed.
Theoretically, the addition of filler to a polymer matrix
should increase the loss modulus.
As the polymer segments bond to the surface, the loops
and chains that extend toward the bulk matrix are
expected to support a mechanical interlocking with the
bulk chains.
This interaction can be effective in transmitting stress
between the matrix and the filler.20,
37. As shown in Figure 22, loss modulus of the PMMA-based
nanocomposites is lower than that of the pure material .
Although the PS-based systems results are extremely
close, the loss modulus does decrease slightly with the
addition of nanoparticles.
38. Nanoindentation was used as another approach to gather
comparative elastic modulus and hardness data for the six
systems .
The basic concept of indentation testing involves touching
a material whose mechanical properties are of interest
with a material whose properties are known .
Nanoindentation is a specialized indentation test in which
the penetration distance is measured in nanometers .
39. One of the key factors in analyzing indentation data is the
contact area between the indenter and specimen.
In typical indentation testing the area of contact is simply
calculated from measurements of the residual impression
left on the specimen.
Instead, the depth of penetration into the specimen
surface is measured and combined with the known
geometry of the indenter to calculate the contact area
The load displacement data gathered during the
indentation process, shown in Figure, provides the means
to calculate modulus and hardness.
40. A typical indentation force-displacement curve. Pmax and hmax are
the maximum load and displacement, respectively. S* is the slope of
the tangent to the maximum load on the unloading curve.44
41. The maximum indenter depth achieved for a particular
load and the slope of the unloading curve measured at
the tangent to the data point at maximum load is used to
calculate hardness and modulus .
Note that nanoindentation provides both load and unload
elastic modulus and hardness data for each test, but the
unload data is most representative of the material
properties.
42.
43. Scanning electron microscopy (SEM) was used to
determine particle size and distribution and to examine
fracture surfaces.
The SEM consists of an electron gun producing a source of
electrons at an energy range of 1-40keV.
Electron lenses reduce the diameter of the electron beam
and place a small focused beam on the specimen
44. The electron beam interacts with the near-surface region
of the specimen to a depth of about 1μm and generates
signals used to form an image.
The smaller the beam size, the better the resolution of
the image.
The SEM used for this study is capable of differentiating
particle detail as small as 1 nm depending on elemental
contrast and other parameters.
45. SEM is run under a vacuum to minimize beam interactions
with gas molecules which would retard resolution .
Non-conductive specimens, such as most polymers, often
suffer from variations in surface potential which introduce
astigmatism, instabilities, and false x-ray signals.
Charging, a condition during which charge accumulates on
the surface of a non-conducting specimen causing excessive
brightness, often occurs making it difficult to obtain quality
images.
46. SEM images of PMMA-Fe3O4, (a) low magnification view of particle
dispersion
48. SEM images were taken of the dogbone fracture surfaces
of all four polymer nanocomposite systems.
The fracture surfaces were sputter coated with gold
atoms prior to imaging to avoid charging, but that did not
negatively affect the image quality.
The above figures shows images showing the dispersion of
particles .
Generally, the particles were not consistently dispersed .
Flocculants of varying sizes, some very large, were found
at the fracture sites.
49. First figure provides a low magnification (7,000 X) view of
the PMMA-Fe3O4 fracture surface.
Many particles of varying sizes are visible, appearing as
small bright dots, fairly well dispersed across the image.
second Figure however, shows a different area of the
sample at the same magnification, and very few particles
are present most of which have flocculated into two
larger clusters.
The total particle size measured in SEM images includes
both the diameter of metal oxide cluster and the
thickness of the polymer layer bound to the surface of the
cluster.
50. By calculating the diameter of metal oxide clusters based
on reference data and assumed geometry, one can solve
for L eff, which is a key component of this
characterization approach.
Note that even the distinct particles within the
flocculants were measured individually because they
appeared to also be capped with a polymer layer
51. Sample SEM images of the dogbone fracture sites for (a) PS-Fe3O4, (b)
PMMA-Al2O3, (c) PMMA-Fe3O4, and (d) PS-Al2O3. Images were used to
measure particle diameter.
52. Thermal gravimetric analysis (TGA) was used to
determine the changes in polymer decomposition
temperatures between samples and to help determine the
thickness of the polymer layer surrounding the
nanoparticles.
53. TGA continuously measures the weight of a sample as a
function of temperature and time.
The sample is placed in a pan held in a microbalance .
The pan and sample are heated in a controlled manner
and weight is measured throughout the heating cycle.
Changes in weight at specific temperatures correspond
to reaction or changes in the sample such as
decomposition.
The weight loss experienced during the decomposition
experiment corresponds to the amount of polymer that
was attached to the particles in the sample.
54. TGA decomposition data was obtained from capped
particles to determine the weight fraction of the polymer
layer adsorbed on the metal oxide particles .
In the figure the polymer layer comprised 9.1% of the
PMMA-Al2O3 particles and 15.1% of the PMMA-Fe3O4
particles.
Based only on this data, one might conclude that the
Fe3O4 surfaces are more reactive with PMMA since more
chains anchored to the surface .
One important consideration, however, is that more
tightly bound chains can shield the surface from other
chains likely resulting in fewer but more tightly bound
chains.
55. Therefore, this higher weight fraction of
bound chains on Fe3O4 is likely due to weaker
bonding of a higher number of chains with
the surface.
56.
57. Differential scanning calorimetry has been
widely applied in the investigation of
numerous phenomena occurring during the
thermal heating of organoclays and
polymer/clay nanocomposites ornanotubes,
involving glass transition (Tg), melting,
crystallization and curing.
58. Referring to clay nanocomposites, DSC technique is able
to highlight appreciable enhancements in Tg brought
about by the presence of nanosized montmorillonite in
many polymers.
This effect wa typically ascribed to the confinement of
intercalated polymers within the silicate galleries that
prevents the segmental motions of the polymer chains. In
the case of polyurethane (PU)—urea nanocomposites,the
changes in the glass transition temperature were also
interpreted as a result of effective links between
polymeric chains and the silicate surface.
59. It was pointed out that these anchored polymer chains
could form an interphase region, where the segment
relaxation was slower than in the bulk.
Nanocomposite adhesives obtained using a
montmorillonite, modified with organiccations (OMMT), in
a polyurethane matrix were recently synthesized and
characterized byMaterials .
A mix of exfoliated and intercalated layers was obtained,
as ascertained by the measurements of structural and
macroscopic properties of the nanocomposites.
60. A significant increase of Tg of the nanocomposites as
function of OMMT content was also observed by
calorimetric analysis, confirming the mentioned
limitations to chain segment mobility induced by OMMT.
Differential scanning calorimetry was also used by Greco
et al. [49] to study the thermal characteristics of the
species produced during the ring opening polymerization
of cyclic butylene-terephthalate (CBT).
The effects of the addition of small amounts of sodium
and organo-modified montmorillonite on a tin-catalyzed
polymerization were analyzed. It was found that the
addition of the nanofiller significantly affected the
polymerization of CBT, shifting the onset of the
polymerization reactions to higher temperatures.
61. This is evident by comparing DSC curves of
theCBT01(unfilled) and CBT13MMT (filled with OMMT)
systems heated up to different temperatures in an first
heating scan.
62. DSC curves of the CBT01 (unfilled) and CBT13MMT (filled with
OMMT) systems.
63. The first interphase characterization approach calculates
the density of the interphase by investigating the bonding
mechanism in the PMMA-based systems using FT-IR.
The chemistry behind the interaction of PMMA and
aluminum oxide surfaces is well established.
The aluminum oxide nanoparticle surface molecules
react with atmospheric water vapor creating
oxyhydroxide surface groups:
64. •This hydration reaction has been proven to occur with several metal oxides, including
Al, Cr, Co, and Cu.
•The presence of the OH group on the nanoparticle surface facilitates hydrolysis of the
PMMA ester group to produce either a COOH acid group or its conjugate COO- base
group, according to the following reaction.
65. The COO- group directly interacts with the positively
charged Al atoms to generate a bond between the
polymer segment and the aluminum oxide nanoparticle
surface.
FT-IR was performed on the PMMA-capped Fe3O4 and Al2O3
nanoparticles to confirm the interaction of the PMMA
segments with the nanoparticles.
The goal was to confirm that bonding occurs as described
above, and to translate that bonding into interphase
structure .
FT-IR spectra for the two PMMA systems were examined
for particular bands .
66.
67.
68. Figure 31Figure 31(a) indicates the lower absorbance of
the 2950 peak for PMMA adsorbed on both Al2O3 and Fe3O4
particles.
The lower absorbance indicates the first step in reaction,
the detachment of the methyl group.
The lower absorbance of the 1730 peak as compared to
the PMMA/chlorobenzene spectra in Figure 31(b) indicates
that some C=O bonds in the ester groups are no longer
isolated, that is, they have been hydrolyzed to form the
carboxylic acid (COOH) and carboxylic base (COO-)
groups, the second and third steps of reaction.
69. Tannenbaum, R., Zubris, M. David, K., Jacob,
K., Jasiuk, I., Dan, N., Characterization of
Metal-Polymer Interfaces in Nanocomposites and
the Implications to Mechanical Properties,
Georgia Institute of Technology. p. 1-20.
Lipatov, Y.S., Polymer Reinforcement. 1995:
ChemTec Publishing. 385.
Su, S., Jiang, D.D., Wilkie, C.A., Methacrylate
Modified Clays and Their Polystyrene and
Poly(methyl methacrylate) Nanocomposites.
Poly. Adv. Technol., 2004. 15: p. 225-231.