Physical Properties Of Polymers Research Articles

Effect of Mixing Parameter on Electrical Conductivity of Carbon Black/Graphite/Epoxy Nanocomposite Using Taguchi Method

Polymer composite has attracted many researchers from various field of application due to its unique features and properties including light weight, low cost, ease to process and shaping and corrosion resistant [1-3]. Fillers is typically added to enhance the chemical and physical properties of polymers [4, 5]. One of the properties is the electrical conductivity. Carbon based filler such as graphite (G), carbon black (CB), carbon fibers (CF) and carbon nanotubes (CNT) has been extensively used to improve electrical properties of polymer composite [6-8]. Electrical properties of the composite can be explained from percolation theory which means electrical percolation in mixtures of electrically conducting and non-conducting materials [9]. The concentration of conducting phase must above the critical value called percolation threshold, in order for the material become electrically conductive [10].

Accurate New Method for Molecular Orientation Quantification Using Polarized Raman Spectroscopy

The physical properties of polymers are strongly affected by their molecular orientation. In this paper, we demonstrate for the first time a new and improved Raman spectroscopy method to characterize this key parameter. In recent years, Raman spectroscopy has emerged as an indispensable tool for this purpose, but its widespread use is still largely restricted by the experimental complexity and the limitations imposed by the standard quantification procedure, referred in this article as the depol constant (DC) method. We have very recently proposed and established theoretically a simplified quantification approach that is based on the most probable orientation distribution (MPD method). Herein, we demonstrate its experimental validity and its wide applicability by studying a series of samples from three highly dissimilar polymers (HDPE, PET, and PS), and covering the full possible orientation range. We show that the new MPD method overcomes the experimental and theoretical difficulties faced with the curre...

Influences of properties and heating characteristics on the thermal decomposition of polymer/carbon nanotube nanocomposites

A comprehensive transport model (conductive, convective and radiative heat transfer, convective mass transport) is applied to simulate the thermal decomposition of thermoplastic polymer/carbon nanotube nanocomposites and corresponding neat polymers (poly(methylmethacrylatye), polypropylene, polystyrene). The flame retardant effectiveness of nanocomposites is confirmed and good quantitative agreement with measurements is shown. The effects of flame retardance are enhanced by increasing the intensity of the radiative heat flux and/or the sample thickness. Moreover, extensive parametric and sensitivity analyses, carried out by varying kinetic constants and polymer physical properties, indicate that activation energy, density, reaction heat and thermal conductivity exert the most significant role. Finally a crucial aspect in relation to the differences in the initial degradation behavior of neat polymers versus nanocomposites is played by the in-depth radiation absorption coefficient.

Direct observation and mutual diffusion of cyclic polymers

A cyclic polymer is one of the ideal model polymers with which to investigate the effects of chain topology on the physical properties of polymers. In this review, I summarize my recent work demonstrating that the chain structure of cyclic polymers can be directly observed by atomic force microscopy (AFM) and that the mutual diffusion of cyclic polymers is faster than that of corresponding linear ones. For direct evidence of the cyclic structure, isolated molecules of cyclic poly(sodium styrenesulfonate), which was derived from cyclic polystyrene, were observed by AFM. The mutual diffusion of cyclic polystyrene/cyclic deuterated polystyrene was investigated as a function of temperature and molecular weight by dynamic secondary ion mass spectroscopy. For the molecular weight of 113k, the mutual diffusion coefficient of cyclic polystyrene, DC, was approximately twofold larger than that of the corresponding linear polymer, DL, at all temperatures. Under an iso-free volume condition, the DC value was larger than the DL value for all the molecular weights. These results clearly show that the chain topology strongly affects the molecular motion of the whole chain. Isolated molecules of cyclic polymers were directly observed by atomic force microscopy. Interdiffusion of cyclic polystyrene/cyclic deuterated polystyrene bilayer films were investigated as functions of temperature and molecular weight by dynamic secondary ion mass spectroscopy.

Incorporating Biodopants into PEDOT Conducting Polymers: Impact of Biodopant on polymer properties and biocompatibility

ABSTRACTPoly(3,4-ethylenedioxythiophene) (PEDOT) was polymerized with the biological dopants dextran sulphate and chondroitin sulphate. Polymer physical and mechanical properties were investigated using quartz crystal microgravimetry with dissipation monitoring and atomic force microscopy, revealing polymer shear modulus and interfacial roughness to be significantly altered as a function of the dopant species. The adsorption of fibronectin, an important extracellular protein that is critical for a range of cellular functions and processes, was investigated using QCM-D, revealing protein adsorption to be increased on the DS doped PEDOT film relative to the CS doped film. PEDOT films have traditionally been doped with synthetic counterions such as polystyrene sulphonate (PSS), however the incorporation of biological molecules as the counterion, which has been shown to improve polymer biofunctionality, has received far less attention. In particular, there has been little detailed study on the impact of incorporating polyelectrolyte biomolecules into the PEDOT polymer matrix on fundamental polymer properties which are critical for biomedical applications. This investigation provides a detailed characterization of the interfacial and mechanical properties of biologically doped PEDOT films, as well as the efficacy of the composite films to bind and retain extracellular proteins of the type that are critical to the biocompatibility of the polymeric material.

Titanium-biphenoxide catalysts for ethylene polymerization

Titanium (IV) complexes containing sterically bulky ligands such as 2, 2′- methylenebis (4-methyl-6-tert butyl phenol) (MBTP) were synthesized by stoichiometric reaction between Ti(IV)alkoxide or halide and the biphenol. These catalyst precursors formulated as [Ti(O^O)RR′] were characterized by physicochemical and spectroscopic methods. The newly prepared Titanium biphenoxides were found to be active in polymerization of ethylene at high temperatures and pressures in combination with ethylaluminum sesquichloride (Et3Al2Cl3) as co-catalyst. The linear polyethylene obtained by this route exhibit low-molecular weights, are highly crystalline and display narrow polydispersities. The physical properties of polymers thus obtained closely resemble specialty PE waxes that are industrially important for surface coating, ink formulations and mar resistance applications.

An experimental–numerical study of moisture absorption in an epoxy

It is well known that moisture absorption impairs the mechanical and physical properties of polymers. Conventionally, the material’s hygric strains are described as the product of a constant coefficient of moisture expansion (CME) and moisture concentration. This hypothesis, however, has not been thoroughly examined experimentally. In this paper, the hygro-mechanical response of a DGBA based epoxy is reported as a function of moisture uptake. Cylindrical specimens are made of epoxy with an axially located optical fiber that contains a 23mm Bragg grating sensor (FBG). Strain data from the sensor and from a micrometer are combined with experimental absorption curves to determine the resin’s CME. The data indicate that diffusion and CME depend on moisture. Analysis of the experiments is carried out by numerical simulations of heat transfer, moisture diffusion and elastic stress analysis of the single fiber composite. The simulated results correlate well with the experimental data.

Predictive model for segmented poly(urea)

Segmented poly(urea) has been shown to be of significant benefit in protecting vehicles from blast and impact and there have been several experimental studies to determine the mechanisms by which this protective function might occur. One suggested route is by mechanical activation of the glass transition. In order to enable design of protective structures using this material a constitutive model and equation of state are needed for numerical simulation hydrocodes. Determination of such a predictive model may also help elucidate the beneficial mechanisms that occur in polyurea during high rate loading. The tool deployed to do this has been Group Interaction Modelling (GIM) – a mean field technique that has been shown to predict the mechanical and physical properties of polymers from their structure alone. The structure of polyurea has been used to characterise the parameters in the GIM scheme without recourse to experimental data and the equation of state and constitutive model predicts response over a wide range of temperatures and strain rates. The shock Hugoniot has been predicted and validated against existing data. Mechanical response in tensile tests has also been predicted and validated.

Thermo-optic Coefficient of Polyisobutylene Ultrathin Films Measured with Integrated Photonic Devices

The optical properties of polymeric materials, such as transmission loss and the thermo-optic coefficient, determine their utility in numerous applications, ranging from nanotechnology to the automotive and aerospace industries. However, because of the wide variation in the physical properties of polymers, many are unsuited for characterization using conventional techniques; consequently, their optical properties are unknown. One such polymer is polyisobutylene, which is viscous at room temperature and therefore is not compatible with conventional transmission loss and the thermo-optic coefficient characterization techniques because they rely on contact measurements. To overcome this, we have developed an integrated, microscale optical sensor that relies on an evanescent wave to study the material's optical behavior. Using this device, we successfully determined the refractive index, the transmission loss, and the thermo-optic coefficient of ultrathin films of polyisobutylene. The films are deposited on the sensor's silica surface using either spin coating or surface-initiated cationic polymerization, demonstrating the flexibility of this approach.

EPR study of radical annihilation kinetics of γ-ray-irradiated acrylic (PMMA) at elevated temperatures

High-energy irradiations of polymers may cause bond cleavage or crosslinking and change the structures and physical properties of the polymers, which may offer various applications. Despite wide investigation, relationship between the kinetics and mechanism of annihilation after irradiations and the structure and some physical properties of irradiated polymers is still poorly established. We have been exploring such possible relationship and report herein investigation of the kinetics of radical annihilation of γ-ray irradiated acrylic, i.e., poly(methylmethacrylate) or PMMA, at elevated temperatures with EPR spectroscopy. The EPR spectra consist of three components, a quintet Ra, a quartet Rb, and a broad singlet Rc. Ra and Rb follow second-order annihilation kinetics, while the decay of the radical Rc is comprised of at least two parallel kinetic processes, a slow second-order pathway and a fast pathway which can be equally well fitted to first- or second-order kinetics. The kinetics is analogous to that for the radical decays in irradiated 2-hydroxyethyl methacrylate copolymer. On the basis of the large hyperfine coupling constant of 2.3 mT, Ra may be assigned to a radical adjacent to two groups of protons, such as a doublet of quartet with similar coupling constants due to an anti-methylene proton and a methyl group; the Rb signal, possibly a methyl radical; and the broad singlet Rc, a magnetically coupled combination species. Alternative assignments of the radicals have also been suggested. The rate constant increases with increasing dose for each radical at a given temperature, possibly due to increase in radical concentrations at higher doses. The rate constants satisfy the Arrhenius equation, suggesting a single mechanistic pathway for the annihilation process in the temperature range; wherein the activation energy decreases with increasing dose for all radicals, possibly due to higher concentrations of free radicals in close proximity produced at higher doses.

New Catalysts for Next Generations of Plastics

Plastics, which are basically polymer materials, are now an integral part of our daily lives: packaging, transport, textile, Hi-technology… Total Petrochemicals produces and develops useful lightweight and durable plastics that play a key role in the sustainable development of our world, making our lives easier, cleaner, safer and more enjoyable. These products include polyethylene, polypropylene, polystyrene but also since recently polylactic acid, a biopolymer based on a renewable raw material. Plastics are produced by polymerizing monomer units (ethylene in the case of polyethylene) under certain temperature and pressure conditions and most of the time in the presence of a catalyst. Catalysts, and more particularly organometallic species, are the cornerstones of the production of these polymers. Since 1980, the polyolefin field has undergone a revolution with the development of single-site catalysts referred to as metallocenes. The metallocene catalyst technology helps produce polyolefins, which boast improved chemical and physical properties and are less heavy and less bulky than those traditionally produced. Total Research Center-Qatar (TRC-Q) researchers, jointly with Total Petrochemicals Research and Development teams, prospect and develop new catalysts to design and manufacture innovative high-level performance plastics. The objective is to optimize the catalysts synthesis for industrial scale application and to produce such catalysts in high yields in the most efficient way. There is a direct relation between the catalyst structure and the polymer chemical and physical properties. The relation is investigated by changing the size and type of the catalyst substituents; metallic centers … (steric, electronic and symmetrical modifications of the catalysts); and studying the impact of such changes on the polymer microstructure. A set of products has been selected to explain this relation and bring to light new advances in polyolefins and biopolymers catalysis.

Santosh K. Gupta: Professor extraordinaire and inspiration to several generations

Santosh K. Gupta: Professor extraordinaire and inspiration to several generations

Polymer Molecular Weight Analysis by 1H NMR Spectroscopy

The measurement and analysis of molecular weight and molecular weight distribution remain matters of fundamental importance for the characterization and physical properties of polymers. Gel permeation chromatography (GPC) is the most routinely used method for the molecular weight determination of polymers whereas matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) is a fast-emerging absolute, and therefore accurate, technique. Although NMR spectroscopy is one of the most powerful tools available for polymer microstructure characterization, among others, its utility in the molecular weight analysis of polymers is somewhat underappreciated. It is a reliable and more readily available teaching tool in comparison to other known techniques, such as GPC and MALDI-TOF MS, for the molecular weight determination of polymers. Demonstrated herein are the simplicity, reproducibility, and convenience of 1H NMR spectroscopy in the analysis of polymer number-average molecular weig...

Short review on the crystallization behavior of PET/clay nanocomposites

In recent years, the area of polymer nanocomposites based on organically modified clay has attracted much interest in academia and industry because of their peculiar and fascinating properties. Nanomaterials are presently considered to be high potential filler material, with high aspect ratio and extremely large surface area. They improve mechanical and physical properties of polymers. Lighter, thinner, stronger and cheaper structures are the goals of materials science and engineering applications nowadays. Appropriate addition of nanoparticles to a polymer matrix can enhance its performance by simply focussing on the nature and properties of the nanoscale filler. So, the properties of polymer nanocomposites depend greatly on the chemistry of polymer matrix, nature of nanofillers and the way in which they are prepared. Various analysis techniques were used to characterize the dispersion and the properties of the nanocomposites, using XRD, TGA, SEM, DSC, TEM, DMTA, etc. Several polymers such as polypropylene, polyamide 6, polyethylene, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polylactic acid (PLA), etc., have been tested as matrices. This paper emphasises on the overview of the crystallization properties of PET/clay nanocomposites by different authors. It has been reported that nanoparticles of clay dispersed in PET polymer matrix act as nucleating agent. In this way, they enhance the crystallization rates of PET/clay nanocomposites. Key words: Nanocomposites, polyethylene terephthalate (PET), clay, crystallization.

Structure of Ultralong Polyaniline Nanofibers Using Initiators

Detailed morphological and structural characterization of high-aspect-ratio polyaniline nanofibers obtained using a small amount of p-aminodiphenylamine (dimer) or p-phenylenediamine (diamine monomer) as an initiator into a rapidly mixed reaction is presented. Structural characteristics have been investigated by FT-IR, UV−vis−NIR, solid-state 13C NMR, and 15N NMR, while the morphology was examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Nanofibers obtained with the addition of an initiator appear longer and less entangled than those obtained without any initiators. TEM analysis revealed a distinct morphological difference between the nanofibers synthesized with different additives. The p-aminodiphenylamine-initiated polyaniline possesses an electrical conductivity of 3.0 S cm−1, while the p-phenylenediamine-initiated counterpart has a conductivity of 1.7 S cm−1. FT-IR, 1H−13C cross-polarization (CP), 15N direct polarization (DP), and UV−vis−NIR spectroscopy confirm that a regular polyaniline structure prevails in both nanofibers. Therefore, various initiators only result in a slight difference in the final polymer molecular structure and physical properties, but such minor divergence dictates the subsequent chain assembly and affects the supramolecular morphology significantly.

Effects of gamma irradiation on poly(ethylene isophthalate)

Radiation methods are largely used for polymerisation and polymer modification, since irradiation induces transformations in the structure of materials which can be exploited to improve their performance. On the other hand, combined action of ionising radiation and oxygen may lead to degradation of the polymer, with worsening of properties such as mechanical strength or electrical insulation resistance. Therefore, the change of the chemical and physical properties of polymers under irradiation is a dynamic topic of research. In this work there are discussed data on the physical features of a polyester, poly(ethylene isophthalate) (PEI), subjected to gamma irradiation up to 1 MGy. PEI is a semicrystalline polymer with a structure similar to polyethylene terephthalate. Viscosity and differential scanning calorimetry measurements were carried out which allowed the monitoring of changes in the structure in terms of variations in the molecular weight, as well as of the percentage crystallinity depending on the dose. Furthermore, positron annihilation lifetime spectroscopy supplied information on the free volume present in the amorphous phase of the irradiated polymer.

Editorial

SIMS, as a non-destructive surface analysis technique for polymeric materials, started about 30 years ago; which happened co-instantaneously with the foundation of the journal Surface and Interface Analysis (SIA). Over the 30-year developments, SIMS has become one of the most important surface analysis techniques for polymeric materials owing to the combination of its unique capabilities: high molecular specificity, high surface sensitivity and sub-micrometer imaging resolution. In recent years, many advances have been made in the SIMS analysis of organic material surfaces such as molecular dynamics simulations, instrumental developments (e.g. cluster ion beams), data interpretation (e.g. multivariate analysis) and new methodology (metal-assisted SIMS). These advances have not only improved the SIMS capabilities for polymer analysis but also opened up new application perspectives. For example, it is now possible for some polymers to perform molecular depth profiles and construct 3D molecular images. Consequently, it seems timely and appropriate to gather research articles on the recent advancements of SIMS analysis on polymers into this special issue of SIA. The papers in this special issue are organized as follows. The volume starts with a concise and informative review by Delcorte et al. on their recent studies on the use of atomic and polyatomic ions in SIMS analysis of organic materials. The review covers both the theoretical study using molecular dynamics simulation and the experimental SIMS work and presents a nice overview on the progress on several areas such as molecular depth profiling, metal-assisted SIMS, molecular SIMS imaging. The strength and weakness of polyatomic versus atomic ion sources in these areas has also been critically assessed. The subsequent paper by Piwowar and Vickerman systematically studies the effects of molecular weights on the ToF SIMS spectra of poly(methyl methacrylate) (PMMA) when Au+ and C60+ are used as primary ions respectively. Their results have clearly shown that the C60+ ion source produces much higher secondary ion yields than Au+ ion source and the ion yield enhancements are consistent across the entire investigated molecular weight range. Three papers in this special issue are focused on the depth profiling of polymers. The paper by Mahoney presents a thorough investigation of the effect of polymer stereochemistry on depth profiling. Three stereo-specific PMMA samples (isotactic, atactic and syndiotactic) were depth profiled using SF5+ polyatomic ion source at different temperatures and the damage characteristics of these samples were compared. The results clearly showed that a polymer's physical properties also play an important role in molecular depth profiling. The paper by Houssiau and Mine provides a detailed investigation on the feasibility of molecular depth profiling of PMMA, polycarbonate (PC) and polystyrene (PS) using low energy (250 eV) Cs+ and Xe+ ions. All the three polymers can be successfully profiled using Cs+ but not all by Xe+. These results allowed the authors to point out the special beneficial effects of low energy Cs+ in polymer depth profiling, namely the negative ion signal enhancement and the inhibition of cross-linking reactions due to Cs reactivity. Finally, the paper by Lee et al. presents a nice application of ToF SIMS depth profiling using Cs+ and C60++ to a polystyrene-poly(n-propyl methacrylate) diblock copolymer system. Their results clearly showed that the microstructure changes of the copolymer due to annealing temperatures and times are reflected in the SIMS profiles. The last three papers in this special issue provide real applications of SIMS in combination with XPS to different polymeric materials. Baytekin et al. showed how the combination of ToF SIMS and XPS can be used to provide full surface chemistry and wettability of micro-fluidic devices and to monitor the effectiveness of their processing. On the other hand, Shimizu et al. have used ToF SIMS and XPS to study the interfacial interaction between polymeric methylene diphenyl diisocyanate (PMDI) and aluminum. Their results clearly showed that the reaction of PMDI with water can be quantitatively followed by ToF SIMS and XPS and a covalent bonding between PMDI and aluminum was unambiguously proven from ToF SIMS results. Finally, the paper by Lau et al. demonstrated that the surface composition changes of liquid crystalline polymers as a result of molecular ordering can be easily monitored using ToF SIMS combined with principal component analysis.

Determination of Chemical Homogeneity of Fire Retardant Polymeric Nanocomposite Materials by Near-Infrared Multispectral Imaging Microscopy

Polymer nanocomposites containing layered double hydroxide (LDH) additives offer great potential for improving polymer physical properties. Of particular interest is the possibility of improving the fire retardancy and thermal stability of polymers using low loadings of this emerging class of nano-additives. Understanding the relationship between the quality of additive dispersion in the polymer matrix (i.e., chemical homogeneity) and selected flammability properties is a key question for optimizing LDHs for use in fire retardant formulations. We have demonstrated, for the first time, that the near infrared multispectral imaging (NIR-MSI) microscope can be successfully used to characterize the chemical homogeneity of a model system containing a magnesium aluminum hydroxide LDH modified with interlayer undecenoate anions mixed with poly(ethylene). The NIR-MSI is suited for this task because it can simultaneously record spectral and spatial information of a sample with high sensitivity (single pixel resolution) and high spatial resolution (∼0.9 μm/pixel). At 20% added, LDH was found to distributed inhomogeneously in a poly(ethylene) nanocomposite sample on the micron scale.

Polymer-Nanoparticle Composites: From Synthesis to Modern Applications

The addition of inorganic spherical nanoparticles to polymers allows the modification of the polymers physical properties as well as the implementation of new features in the polymer matrix. This review article covers considerations on special features of inorganic nanoparticles, the most important synthesis methods for ceramic nanoparticles and nanocomposites, nanoparticle surface modification, and composite formation, including drawbacks. Classical nanocomposite properties, as thermomechanical, dielectric, conductive, magnetic, as well as optical properties, will be summarized. Finally, typical existing and potential applications will be shown with the focus on new and innovative applications, like in energy storage systems.

Pseudofragmental descriptors based on combinations of atomic properties for prediction of physical properties of polymers in quantitative structure—property relationship studies

Among a great number of QSPR/QSAR approaches to the prediction of physical and chemical properties and biological activity of organic com� pounds, the methods using fragmental descriptors play a specific role [1, 2]. The values of the latter can be either the occurrence numbers or indicators of the presence of some fragments in the structures of chem� ical compounds. Advantages of these descriptors are their transparent meaning and the possibility of fast automatic generation on the basis of only the struc� tural formula. Fragmental descriptors can be calcu� lated without knowledge of the 3D structure or elec� tronic structure of molecules and, therefore, can be easily used for operating large databases. One of the disadvantages of fragmental descriptors is the problem of rare fragments that can be absent in the training set but can exist in the compounds for which the prediction is performed. Since the contribu� tions of rare fragments cannot be determined on the basis of the training set, considerable errors of predic� tion are expected for compounds containing such fragments. We suggest solving this problem by intro� ducing additional descriptors with the values being to an extent related to the contributions of fragments to the predicted property. For this purpose, we also sug� gest using special fragmental descriptors with the val� ues being calculated by combining the properties of the atoms that constitute these fragments. Such descriptors are referred to as pseudofragmental descriptors in order to distinguish them from “proper” descriptors assigned the values of the occurrence num� bers or indicators of the presence of certain fragments in the structures of chemical compounds. The atomic properties that are believed to influence the contribu� tions of fragmental descriptors to the predicted prop� erty, for example, the atomic weight, number of elec� trons, covalent radius, electronegativity, ionization potential, etc., can be used for predicting physical and chemical properties of organic molecules. It is also important for the used combinations of properties to have a clear physical meaning since this provides a bet� ter chance for the existence of correlation of their val� ues with fragmental contributions. If such a correla� tion exists, a small number of pseudofragmental descriptors enter into statistical models instead of numerous proper fragmental descriptors, including potentially rare, thus acting as a compressed generali� zation of the latter. This largely solves the problem of rare fragments if the pseudofragmental descriptors are constructed on the basis of frequently encountered fragments consisting of separate atoms or short chains of arbitrary atoms, which are present almost in all molecules.