Polymer Dynamics

3C spin-lattice relaxation times Tic of the a-methyl groups of amorphous poly(methyl methacrylate) samples with different tacticities have been measured over a wide range of temperatures by cross-polarization/dipolar decoupling 13C NMR spectroscopy. The Tic minimum has been clearly observed fo each sample, but the temperature dependences of the Tic values, especially the temperature at which Tic reaches the minimum, greatly depend on the tacticities of the samples. Such characteristic temperature dependences of the Tic's have been analyzed in terms of the multiple-correlation-time models where the three-fold rotation of the a-methyl group and the rapid fluctuation of the rotation axis are assumed to describe the motion of the C-H internuclear vector.

The American Physical Society Chain-Scale Polymer Dynamics Through Homogeneously Confining Nanoparticles ERIC BAILEY, HUIKUAN CHAO, ROBERT A. RIGGLE-MAN, KAREN I. WINEY, Univ of Pennsylvania -The addition of nanoparticles (NPs) to a polymer matrix can significantly enhance polymer mechanical and functional properties. Recent tracer diffusion experiments in nanocomposites show that polymer diffusion is significantly reduced relative to the bulk. In fact, a master curve was developed by plotting diffusion coefficients normalized by that of the bulk polymer against the confinement parameter, ID/2Rg, where ID is the interparticle distance and Rg is the tracer size. To further study the role of confinement, coarsegrained MD simulations are used to systematically study the independent effect of ID and Rg on chain-scale dynamics. A uniquely constructed simulation box with a monolayer of hexagonally packed NPs creates regions of homogeneously confined polymer and pristine bulk polymer. This reveals the magnitude and length scale of NP-induced perturbations for several values of ID/2Rg. Displacement distributions show significant asymmetries in polymer motion near NPs and localized diffusion coefficients show more than a 25% reduction in diffusion coefficient. Surprisingly, chain dynamics are perturbed several times Rg from the NP region. These MD simulations are then compared to calculations on a minimal model in the same simulation environment.

The American Physical Society Chain-Scale Polymer Dynamics Through Homogeneously Confining Nanoparticles ERIC BAILEY, HUIKUAN CHAO, ROBERT A. RIGGLE-MAN, KAREN I. WINEY, Univ of Pennsylvania -The addition of nanoparticles (NPs) to a polymer matrix can significantly enhance polymer mechanical and functional properties. Recent tracer diffusion experiments in nanocomposites show that polymer diffusion is significantly reduced relative to the bulk. In fact, a master curve was developed by plotting diffusion coefficients normalized by that of the bulk polymer against the confinement parameter, ID/2Rg, where ID is the interparticle distance and Rg is the tracer size. To further study the role of confinement, coarsegrained MD simulations are used to systematically study the independent effect of ID and Rg on chain-scale dynamics. A uniquely constructed simulation box with a monolayer of hexagonally packed NPs creates regions of homogeneously confined polymer and pristine bulk polymer. This reveals the magnitude and length scale of NP-induced perturbations for several values of ID/2Rg. Displacement distributions show significant asymmetries in polymer motion near NPs and localized diffusion coefficients show more than a 25% reduction in diffusion coefficient. Surprisingly, chain dynamics are perturbed several times Rg from the NP region. These MD simulations are then compared to calculations on a minimal model in the same simulation environment.

We study the effect of dehydration on the structure and mechanical properties of anisotropic lamellar hydrogels, consisting of alternative stacking of several thousands of nanoscale rigid bilayers from amphiphilic poly(dodecyl glyceryl itaconate) (PDGI) and submicroscale soft hydrogel layers from hydrophilic polyacrylamide (PAAm) networks. We found that the layered microstructure is well preserved with dehydration, and a ductile-brittle transition occurs at the critical water content. This transition is related to the rubbery-glassy transition of the PAAm layers, which occurs at 58 wt % water content and is much higher than 26 wt % of bulk PAAm hydrogels. Such specific behavior of the lamellar hydrogels indicates that the dynamics of the submicroscale PAAm hydrated layer intercalated between the rigid bilayers are very different from its bulk state.

We study the effect of dehydration on the structure and mechanical properties of anisotropic lamellar hydrogels, consisting of alternative stacking of several thousands of nanoscale rigid bilayers from amphiphilic poly(dodecyl glyceryl itaconate) (PDGI) and submicroscale soft hydrogel layers from hydrophilic polyacrylamide (PAAm) networks. We found that the layered microstructure is well preserved with dehydration, and a ductile-brittle transition occurs at the critical water content. This transition is related to the rubbery-glassy transition of the PAAm layers, which occurs at 58 wt % water content and is much higher than 26 wt % of bulk PAAm hydrogels. Such specific behavior of the lamellar hydrogels indicates that the dynamics of the submicroscale PAAm hydrated layer intercalated between the rigid bilayers are very different from its bulk state.

In this paper, the theoretical predictions of mechanical properties of functionally graded and uniform distributions Epoxy/clay nanocomposites are presented. The specimens were prepared for uniformly distribution of nanoclay with different nano particles weight percent (pure, 3 wt%, 5 wt% and 7 wt%) and functionally graded distribution. The distribution of nanoparticles has been investigated by Field Emission Scanning Electron Microscopy (FESEM). For uniformly distribution of nanoclay, it is shown that there is no sign of the agglomerates found via FESEM imaging which can address well the distribution of nanoclay particles in epoxy. In addition, for functionally graded distributions, it is found that dispersion of nanoclays vary smoothly and continuously from one surface to the other one. The mechanical properties have been determined by simple extension tests. The results of extension tests show that elastic modulus begins to increase up to 5 wt% of nanoclay and then decreases. So, for functionally graded distribution, the elastic modulus is generally larger than the corresponding values for uniform distribution of nanoclay. The theoretical predictions of Young's modulus for functionally graded and uniform distributions nanocomposites are calculated using a genetic algorithm procedure. The formulation for Young modulus includes the effect of nanoparticles weight fractions and it is modified for functionally graded distribution. To investigate the accuracy of the present theoretical predictions, a comparison is carried out with the experimental results. It is found that the results obtained from the theoretical predictions of genetic algorithm procedure are in good agreement with the experimental ones.

In this paper, the theoretical predictions of mechanical properties of functionally graded and uniform distributions Epoxy/clay nanocomposites are presented. The specimens were prepared for uniformly distribution of nanoclay with different nano particles weight percent (pure, 3 wt%, 5 wt% and 7 wt%) and functionally graded distribution. The distribution of nanoparticles has been investigated by Field Emission Scanning Electron Microscopy (FESEM). For uniformly distribution of nanoclay, it is shown that there is no sign of the agglomerates found via FESEM imaging which can address well the distribution of nanoclay particles in epoxy. In addition, for functionally graded distributions, it is found that dispersion of nanoclays vary smoothly and continuously from one surface to the other one. The mechanical properties have been determined by simple extension tests. The results of extension tests show that elastic modulus begins to increase up to 5 wt% of nanoclay and then decreases. So,...

Polymer dynamics in the melt state cover a wide range in time and frequency, for both molecular weights below and above the entanglement length. Nuclear Magnetic Resonance (NMR) offers a number of techniques that cover a broad section of this frequency range, with frequency dependent (i.e., magnetic field dependent) relaxometry providing the widest window. Combining fast field cycling techniques with frequency-temperature superposition has recently improved the understanding of polymer melt dynamics from the local to global range. At the same time, a detailed theoretical approach that separates intra-and intermolecular contributions to relaxation times has been developed. These methods are shown to improve the description of segmental dynamics in polymers, being related to time-dependent diffusion coefficients, and to distinguish between these two different relaxation contributions for a number of model compounds. The findings represent the foundation for a more thorough understanding of polymers under external restrictions and bear potential to provide a conceptually new access to biopolymer dynamics and interactions.

Submitted for the MAR13 Meeting of The American Physical Society The Role of Excluded Volume on the Reduction of Polymer Diffusion into Nanocomposites JEFF METH, DuPont Co, SANGAH GAM, RUS-SELL COMPOSTO, KAREN WINEY, University of Pennsylvania-An analytic model for the reduction of polymer chain diffusion in nanocomposites attributable to excluded volume effects is presented. The nanocomposite is modeled as an ensemble of cylinders through which the polymer chain diffuses. The distribution of cylinder diameters in the ensemble is predicted from statistical mechanical theories based on the packing of spheres. The reduction in polymer diffusion is accounted for by the truncation of the partition function for a random walk in a cylinder. For low loadings of spherical particles in nanocomposites, we show that this theory results in a master curve for the reduced diffusion coefficient. The theory, with no adjustable parameters, is in agreement with recent data for tracer diffusion measurements in polymer nanocomposites at low loading.

IONIC LIQUIDS AS ADDITIVES FOR POLYMER NANOCOMPOSITES R. K. DONATO, H. S. SCHREKKER, L. MATĚJKA Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovský Sq. 2, 162 06 Prague 6, Czech Republic and Laboratory of Technological Processes and Catalysis, Institute of Chemistry, Universidade Federal do Rio Grande do Sul, Av. Bento Gonçalves 9500, Porto Alegre, RS, Brazil

The melt flow dynamics of acrylonitrile-butadiene-styrene (ABS) and polypropylene (PP) in a variable thickness microimpression was assessed by monitoring cavity temperature and pressure as relevant process parameters. A micromoulding block with a variable thickness cavity was designed, manufactured and instrumented with pressure and temperature sensors, acting as monitoring devices as well as flow position markers during filling. A full factorial design of experiment (DOE) was carried to optimize the filling of the microimpression. This study with ABS and PP suggests that mould temperature is the more important parameter for the entire micromoulding thickness range under analysis. Nevertheless, the influence of the melt temperature and the injection speed were found to depend on the micromoulding thickness and the polymer type.

A lab-synthesized graphene oxide (GO) is utilized as a dispersing agent for nanoclay (NC) in epoxy-phenolic. Various weight ratios of GO/NC as composite particles are prepared. They are used at 1 wt% concentration. Analytical techniques, i.e. X-ray diffraction and thermo-gravimetric analysis are used. The results show the composite particles have obtained greater d-spacing. They certify that GO has been able to cover up the clay lamellae like a surfactant. Mechanical performance is evaluated by both dynamic and static mechanical measurements as well as fracture morphology assessment. The outcomes show the composite particles have been able to simultaneously increase the mechanical strength and fracture energy. Some composite particle-containing samples show an increase of 23.5% in storage modulus, 36.3% in Young modulus and 51% in fracture energy. The fracture patterns likewise show much more scattered paths, an evidence for the enhanced state of dispersion of the composite particles.

A lab-synthesized graphene oxide (GO) is utilized as a dispersing agent for nanoclay (NC) in epoxy-phenolic. Various weight ratios of GO/NC as composite particles are prepared. They are used at 1 wt% concentration. Analytical techniques, i.e. X-ray diffraction and thermo-gravimetric analysis are used. The results show the composite particles have obtained greater d-spacing. They certify that GO has been able to cover up the clay lamellae like a surfactant. Mechanical performance is evaluated by both dynamic and static mechanical measurements as well as fracture morphology assessment. The outcomes show the composite particles have been able to simultaneously increase the mechanical strength and fracture energy. Some composite particle-containing samples show an increase of 23.5% in storage modulus, 36.3% in Young modulus and 51% in fracture energy. The fracture patterns likewise show much more scattered paths, an evidence for the enhanced state of dispersion of the composite particles.

The entropic effects of anchored polymers on biomembranes are studied using simulations of a meshless membrane model combined with anchored linear polymer chains. The bending rigidity and spontaneous curvature are investigated for anchored ideal and excluded-volume polymer chains. Our results are in good agreement with the previous theoretical predictions. It is found that the polymer reduces the line tension of membrane edges, as well as the interfacial line tension between membrane domains, leading to microdomain formation. Instead of the mixing of two phases as observed in typical binary fluids, densely anchored polymers stabilize small domains. A mean field theory is proposed for the edge line tension reduced by anchored ideal chains, which reproduces our simulation results well.

We investigated the polymer backbone dynamics of entangled and cross-linked polymer melts using dielectric spectroscopy (DS) and rheology. The entangled and cross-linked melts were prepared by end-linking linear and three armed poly(oxypropylene), respectively. Because of dipole inversion at the junctions DS is sensitive only to end-to-end distance fluctuations of the polymer sections between entanglements or cross-links. DS shows that the dynamics between covalent crosslinks and entanglements are identical. The dipole relaxation is strongly modified by end-linking.

We investigated the polymer backbone dynamics of entangled and cross-linked polymer melts using dielectric spectroscopy (DS) and rheology. The entangled and cross-linked melts were prepared by end-linking linear and three armed poly(oxypropylene), respectively. Because of dipole inversion at the junctions DS is sensitive only to end-to-end distance fluctuations of the polymer sections between entanglements or cross-links. DS shows that the dynamics between covalent crosslinks and entanglements are identical. The dipole relaxation is strongly modified by end-linking.

In this work we present a dielectric relaxation study of Acrilyc/Polyurethane polymers synthesized via miniemulsion photo-polymerization. Three different samples, both parts of the synthesized hybrid latex (SOL and GEL fractions) and a full acrylic sample as reference have been considered. Besides dielectric experiments using broadband Dielectric Spectroscopy (BDS) technique, complementary Differential Scanning Calorimetry measurements have been performed. The thermodynamic characterization outcomes evidence very similar characteristics of the glass transition phenomena among the investigated samples without any signature of melting/crystallization. However BDS experiments show three well resolved dielectric relaxation processes above Tg, two of them evidence marked differences among the samples. A detail study allows us to provide a molecular origin for these three dielectric relaxation processes in connection with the sample characteristics. In particular, our results show that the characterization of these hybrid Acrylic/PU by BDS can provide access to some of the structural features that would ultimately influence the adhesives properties.

The present rheological study reveals for the first time that entangled polymer solutions made of linear polystyrene or poly(methyl methacrylate) can exhibit strain hardening due to non-Gaussian stretching during startup shear at sufficiently high rates and temperatures well above their overall glass transition temperatures: T g,solute > T exp > T g,solution. The solutions made of high-T g polymers only show partial yielding in the sense that both shear and normal stresses grow monotonically in time until a point of rupture, signified by an emergent cusp in the stress vs strain curve and macroscopic breakup along a shear plane. The shear softening-to-hardening transition, which occurs as a function of the applied shear rate, happens at lower equivalent rate with decreasing temperature, violating the time−temperature superposition principle.

end groups in polymers are a molecular tool to reversibly connect and disconnect chains to combine properties of both short polymer and large supramolecular structures. The topology of the latter and in turn the respective properties can be tuned by the choice of the functional group. This is shown in a series of polydimethyl siloxanes (PDMS) of different molecular weight (MW) which are terminated by amino and carboxylic (-COOH) groups, respectively. Differential scanning calorimetry and dielectric spectroscopy measurements reveal that segmental dynamics are identical for the chains with two different end groups. In contrast, rheology unravels a mechanical reinforcement for PDMS-COOH and a rise in viscosity by 2 decades. This is accompanied by a 2nd Tg and a corresponding dielectric relaxation process which indicates phase separation of the end groups in clusters forming a physically crosslinked network. As a consequence, the viscoelastic properties can be tuned from common short polymer chains at high temperatures to highly entangled or even crosslinked systems at T close and below the 2nd Tg. This suggests a promising route to combine easy processibility of low MW polymers with the desired mechanical performance of high MW polymers or even crosslinked networks.

We present the internal structure and dynamics of novel coordination polymers based on two metal-containing moieties Ru-X (X: Ag, Au, Co), bridged through the phosphine PTA (3,5,7-triaza-phosphaadamantane). X-ray scattering gives the heterometallic polymer organization. Quasi-elastic neutron scattering measurements over a broad temperature range show a transition from vibrational Debye-Waller behavior to a more dynamically active state, but with rather localized motions, coinciding with the loss of structural water at around room temperature. Light scattering reveals that the polymers self-associate to form stable micro-particles in aqueous solution with a thermally driven volume transition. This is described by the Flory theory for polymers in solution, in which the polymer solvency is calculated as a function of the temperature. Polymer self-organization is further studied by small-angle neutron scattering and electron microscopy. A polymer parallel-plane model with gaps controlled by the environmental temperature is proposed.

Starting from experimental macro-rheological data, we develop a fitting protocol that succeeded in the separation of the overlapping relaxation phenomena in the dissipative regime for a set of intrinsic healing polymers healing most effectively near their glass transition temperature T g. To allow for a proper deconvolution, the rheological master curves are converted to a relaxation spectrum (H(t)) and this is fitted using an optimized mechanical model, e.g. the Maxwell-Weichert model. The deconvolution of overlapping segmental mobility and reversible interactions is successfully demonstrated for a set of polyimide and polyamide polymers containing none, one and two reversible dynamic features near-T g. Through the fitting parameters, the relaxation timescale of each feature and their apparent process enthalpies are obtained. The quantitative data obtained using the fitting protocol are then compared to macroscopic healing results. As a result, a clear correspondence between the energy stored by the system to accomplish reversible (e.g. H-bonds, p-p) and chain interdiffusion relaxation transitions and the healing efficiency of such polymers are obtained. The implementation of this protocol allows for a clearer identification of the relevant mechanisms in self-healing polymers and paves the way for the development of more efficiently healable polymeric systems.

The translocation of molecules across cellular membranes or through synthetic nanopores is strongly affected by thermal fluctuations. In this work we study how the dynamics of a polymer in a noisy environment changes when the translocation process is driven by an oscillating electric field. An improved version of the Rouse model for a flexible polymer has been adopted to mimic the molecular dynamics, by taking into account the harmonic interactions between adjacent monomers and the excluded-volume effect by introducing a Lennard-Jones potential between all beads. A bending recoil torque has also been included in our model. The polymer dynamics is simulated in a two-dimensional domain by numerically solving the Langevin equations of motion. Thermal fluctuations are taken into account by introducing a Gaussian uncorrelated noise. The mean first translocation time of the polymer centre of inertia shows a minimum as a function of the frequency of the oscillating forcing field. This finding represents the first evidence of the resonant activation behaviour in the dynamics of polymer translocation.

Composites made of epoxy-based systems are popular in many engineering applications because of their enhanced mechanical performance, fatigue properties, and other physical and thermal properties, but their low fracture toughness can limit their usefulness in high-performance structural applications. This study aims to enhance the fracture properties of epoxy-based composites by adding cost-effective ball-milled graphitic nanoparticles. Herein, dry ball

Field-cycling NMR relaxometry is a well-established technique for probing molecular dynamics in a frequency range from typically a few kHz up to several tens of MHz. For the interpretation of relaxometry data, it is quite often assumed that the spin-lattice relaxation process is of an intra-molecular nature so that rotational fluctuations dominate. However, dipolar interactions as the main type of couplings between protons and other dipolar species without quadrupole moments can imply appreciable inter-molecular contributions. These fluctuate due to translational displacements and to a lesser degree also by rotational reorientations in the short-range limit. The analysis of the inter-molecular proton spin-lattice relaxation rate thus permits one to evaluate self-diffusion variables such as the diffusion coefficient or the mean square displacement on a time scale from nanoseconds to several hundreds of microseconds. Numerous applications to solvents, plastic liquids and polymers will be reviewed. The technique is of particular interest for polymer dynamics since intermolecular spin-lattice relaxation diffusometry bridges the time scales of quasi-elastic neutron scattering and field-gradient NMR diffusometry. This is just the range where model-specific intra-coil mechanisms are assumed to occur. They are expected to reveal themselves by characteristic power laws for the time-dependence of the mean-square segment displacement. These can be favorably tested on this basis. Results reported in the literature will be compared with theoretical predictions. On the other hand, there is a second way for translational diffusion phenomena to affect the spin-lattice relaxation dispersion. If rotational diffusion of molecules is restricted, translational diffusion properties can be deduced even from molecular reorientation dynamics detected by intra-molecular spin-lattice relaxation. This sort of scenario will be relevant for adsorbates on surfaces or polymer segments under entanglement and chain connectivity constraints. Under such conditions, reorientations will be correlated with translational displacements leading to the so-called RMTD relaxation process (reorientation mediated by translational displacements). Applications to porous glasses, protein solutions, lipid bilayers, and clays will be discussed. Finally, we will address the intriguing fact that the various time limits of the segment mean-square displacement of polymers in some cases perfectly reproduce predictions of the tube/reptation model whereas the reorientation dynamics suggests strongly deviating power laws.

The Mori-Zwanzig projection operator technique was employed to derive the effective Hamiltonian for spin-segment coupling. The fluctuations of this operator are responsible for spin-lattice relaxation in polymer chains. In detail, dipolar interaction of spins is rigorously analyzed by components representing fluctuations of the Kuhn segment end-to-end vectors and local fluctuations on a length scale shorter than the root mean square Kuhn segment length. The former correspond to the usual coarse-grain picture of polymer chain mode theories. It is shown that these non-local chain modes dominate proton spin-lattice relaxation dispersion of flexible polymers at frequencies up to about 10 8 Hz. A corresponding evaluation of experimental data for polybutadiene melts is presented.

Carbon-13 spin-lattice relaxation rates were determined for 1,3,5-triphenylbenzene in CDC13 over a temperature range of WC, and the results interpreted in terms of the molecular dynamics. Dynamic models appropriate to the problem, including the effects of anisotropic motion and internal jumping between two or four states, were derived and the results evaluated comparatively for several different models. Similarities in the activation energies based on temperature-dependent measurements for all carbons suggests that either fortuitously similar barriers characterize both overall and internal motion, or that all relaxation rates depend primarily on a single type of motion, with the individual T, differences reflecting geometric factors. The latter interpretation leads to a rapid internal jump motion with a range of-6O", as would be predicted on the basis of theoretical conformational energy calculations. Application of a four-state jump model in which the jump rates are assumed to depend on the 0 and 90" theoretically determined rotational barriers allow an estimation of the rates of internal motion consistent with the relaxation data. The physical basis for complex terms which occur in the bistable (and tristable) jump models is discussed.

The translocation of molecules across cellular membranes or through synthetic nanopores is strongly affected by thermal fluctuations. In this work we study how the dynamics of a polymer in a noisy environment changes when the translocation process is driven by an oscillating electric field. An improved version of the Rouse model for a flexible polymer has been adopted to mimic the molecular dynamics, by taking into account the harmonic interactions between adjacent monomers and the excluded-volume effect by introducing a Lennard-Jones potential between all beads. A bending recoil torque has also been included in our model. The polymer dynamics is simulated in a two-dimensional domain by numerically solving the Langevin equations of motion. Thermal fluctuations are taken into account by introducing a Gaussian uncorrelated noise. The mean first translocation time of the polymer centre of inertia shows a minimum as a function of the frequency of the oscillating forcing field. This finding represents the first evidence of the resonant activation behaviour in the dynamics of polymer translocation.

The study of the noise induced effects on the dynamics of a chain molecule crossing a potential barrier, in the presence of a metastable state, is presented. A two-dimensional stochastic version of the Rouse model for a flexible polymer has been adopted to mimic the molecular dynamics and to take into account the interactions between adjacent monomers. We obtain a nonmonotonic behavior of the mean first passage time and its standard deviation, of the polymer center of inertia, with the noise intensity. These findings reveal a noise induced effect on the mean crossing time. The role of the polymer length is also investigated.

Composites based on an epoxy resin, diglycidyl ether of bisphenol A and SiO 2 nanoparticles, unmodified and surface-modified with a coupling agent 3-glycidyloxypropyltrimethoxysilane, were prepared. Successful modification of the nanoparticles was confirmed by infrared spectroscopy and combined differential scanning calorimetry and thermogravimetric analysis (DSC-TG). Composite materials were prepared by adding 0.5-5 phr (parts per hundred parts of resin) of modified and unmodified nanoparticles into the epoxy resin which was then cured with a poly(oxypropylene) diamine. Curing was followed by DSC, and cured materials were characterised by tensile and hardness testing. Morphology of fractured surfaces after tensile testing was investigated by scanning electron microscopy (SEM). Thermal stability of cured materials was studied by TG and their glass transition temperature determined by DSC. The presence of the filler was found not to influence the curing mechanism of the epoxy resin nor the degradation mechanism of the crosslinked epoxy-amine matrix. Glass transition exhibits a small shift to higher temperatures in composites, which also exhibit increased char formation-at lower filler content for the composite with unmodified nanoparticles and at higher for the one with modified nanoparticles. All composites show improved mechanical properties in comparison with the neat epoxy. For the unmodified particles, strength and modulus are particularly improved at lower nanofiller content due to their better dispersion, as observed by SEM. The modified nanoparticles contributed to a significant increase in elongation at break, increasing the toughness of the cured resin while retaining its strength and without having an adverse influence on the modulus.

The relative permittivity and dielectric strength have been determined for a bisphenol A polycarbonate (BPA-PC), in which a cyanoethyl group has been substituted for one of the geminal dimethyl groups. The new material (CN-PC) has a glass transition temperature that is 19 K higher than that for BPA-PC. In addition, the dielectric strength of CN-PC, 405 V/μm, is somewhat smaller than that for BPA-PC, 620 V/μm. The relative permittivity was determined from 10 to 10 5 Hz over a wide temperature range and at pressures up to 0.25 GPa. While the real part of the relative permittivity at 10 3 Hz and room temperature for BPA-PC is about 3, that for CN-PC is found to be greater than 4. Correspondingly, the γ relaxation region in CN-PC is very strong. For the γ relaxation, a strong increase in peak height as temperature increases and a strong decrease in peak height as pressure increases are observed. A relaxation is found at temperatures higher than the γ relaxation. This process is labeled as the β relaxation because it appears to be related to the β relaxation in BPA-PC in that the strength and position depend on the history of the material. The effects of pressure on the γ relaxation for both CN-PC and BPA-PC are quite large and similar to those previously seen for the γ relaxation in a fluorinated tetraaryl bisphenol A polycarbonate (DiF p-TABPA-PC). In fact, the activation volume is found to be approximately the same for all three BPA-PC-based materials despite wide variations in both peak position and peak height. Finally, computer studies of the model compounds, 4,4′-diphenylpentanenitrile and diphenyl carbonate, were carried out. Both provide insight into the nature of the γ relaxation with the latter yielding an activation volume in approximate agreement with the experimental values.

A dilute-solution spin-lattice relaxation time study was performed on a bisphenol polycarbonate related to the PlOlycarbonate of bisphenol A except the two methyl, isopropylidene unit is replaced by a cyclohexyl 3 group. C spin-lattice relaxation times were measured at three Larmor frequencies: 50.3, 75.4, 125.7 MHz. The motion of cyclohexyl ring is seen to be isotropic on the spin-lattice relaxation time scale even though cyclohexyl rings undergo slow conformational change. Cyclohexyl ring relaxation is caused by segmental motion and was well interpreted in terms of the Hall-Helfand correlation function. The apparent activation energies for cooperative and individual bond transitions were 17 and 22 kJ mol-l, while the corresponding Arrhenius prefactors were 15 x 10 13 and 5 x 10 13 s. This cyclohexyl polycarbonate differs from many other polycarbonates in that the two phenylene groups are inequivalent, one being axial and the other equatorial relative to the cyclohexyl ring. This difference could be clearly seen in the low temperature 13C spectrum at a Larmor frequency of 125.7 MHz. In addition to segmental motion, it was found the equatorial phenyl ring underwent anisotropic internal rotation which could be described by the Woessner model, while the axial phenyl ring underwent restricted rotational diffusion which could be described by the Gronski model. Since full anisotropic rotation was observed in bisphenol A polycarbonate and restricted anisotropic rotational diffusion was observed in norbornyl polycarbonate, a clear picture of the effects of substitution in the isopropylidene units on local dynamics is developing.

Field-cycling NMR relaxometry is a well-established technique for probing molecular dynamics in a frequency range from typically a few kHz up to several tens of MHz. For the interpretation of relaxometry data, it is quite often assumed that the spin-lattice relaxation process is of an intra-molecular nature so that rotational fluctuations dominate. However, dipolar interactions as the main type of couplings between protons and other dipolar species without quadrupole moments can imply appreciable inter-molecular contributions. These fluctuate due to translational displacements and to a lesser degree also by rotational reorientations in the short-range limit. The analysis of the inter-molecular proton spin-lattice relaxation rate thus permits one to evaluate self-diffusion variables such as the diffusion coefficient or the mean square displacement on a time scale from nanoseconds to several hundreds of microseconds. Numerous applications to solvents, plastic liquids and polymers will be reviewed. The technique is of particular interest for polymer dynamics since intermolecular spin-lattice relaxation diffusometry bridges the time scales of quasi-elastic neutron scattering and field-gradient NMR diffusometry. This is just the range where model-specific intra-coil mechanisms are assumed to occur. They are expected to reveal themselves by characteristic power laws for the time-dependence of the mean-square segment displacement. These can be favorably tested on this basis. Results reported in the literature will be compared with theoretical predictions. On the other hand, there is a second way for translational diffusion phenomena to affect the spin-lattice relaxation dispersion. If rotational diffusion of molecules is restricted, translational diffusion properties can be deduced even from molecular reorientation dynamics detected by intra-molecular spin-lattice relaxation. This sort of scenario will be relevant for adsorbates on surfaces or polymer segments under entanglement and chain connectivity constraints. Under such conditions, reorientations will be correlated with translational displacements leading to the so-called RMTD relaxation process (reorientation mediated by translational displacements). Applications to porous glasses, protein solutions, lipid bilayers, and clays will be discussed. Finally, we will address the intriguing fact that the various time limits of the segment mean-square displacement of polymers in some cases perfectly reproduce predictions of the tube/reptation model whereas the reorientation dynamics suggests strongly deviating power laws.

Low molecular wieght 1,2-polybutadiene (Aldrich) tacticity was determined by 13CNMR (100.6 MHz). It was found that the olefinic methylene carbon has the highest splitting and a combination of pentad and heptad sequences was determined which is in agreement with the theoretical calculations. For the first time aliphatic methine carbon assignment of 1,2-polybutadiene was performed. Furthermore, olefinic methine carbon assignment was also performed and the results were compared with the theoretical calculations. For all carbons Bernoullian and first-order Markov-chain propagation statistics were used to fit the experimental data and a good agreement was obtained indicating an atactic polymer (Pm= 0.467). It was shown that the most probable reaction before gelation which happens by heating the polymer under vacuum at 250°C, is crosslinking accompanied with methyl group formation. The decrease in double bond intensity of the pendant group together with constant cis and trans double bond ...

The physical properties and processing behavior of polymers are related to the broad range of length and times scales over which dynamical processes occur. The theory has undergone significant evolution over the last decades due to the introduction of new methods and concepts that have extended the frontier from dilute solutions, in which polymers move independently, to concentrated solutions, where many macromolecules entangle.
The aim of this chapter is to review briefly the background of polymer dynamics in solution and to provide the recent achievements in this field. A good understanding of polymer dynamics in solution and the possibility to predict their behavior under flow in different media may help out to a large extent to the synthesis of high-performance polymers, with tailored properties.

The PVC/TiO 2 nanocomposite samples were structurally characterized by scanning electron microscope that ascertains its polymer nanocomposite nature. The dynamic mechanical response, i.e., storage moduli and phase transition temperature accompanied by temperature have been studied through Dynamic Mechanical Analyzer (Tritec 2000 DMA). The intrinsic viscosity and phase transition activation energy is resolute in using these data. The results reveal that TiO 2 nanoparticle dispersion in PVC causes prominent enhancement in observed properties. However, the enhancement depends on proportion of nanoparticles.

Particulate polymer composites comprise of polymer as matrix and variety of micro or nano fillers. The main objective behind inclusion of filler material in polymer matrix is to improve the various properties as well as make the composite economically viable. In the present work, graphite (size less than 75 μm) is taken as micro filler for preparation of epoxy composites. Experimental study has been carried out to study the effect of addition of fly ash at different weight percentage i.e 3wt%, 6wt%, 9wt% and 12wt% on the mechanical properties of epoxy composites. Mechanical properties such as Impact strength, Flexural strength, Flexural modulus and Fracture toughness are studied as per ASTM standards. Specimens are prepared using open mould casting. The results showsthe enhancement in Impact strength, fracture toughness, Flexural strength and Flexural modulus is by 100% and 50.96%, 73.5% and 19% at 12wt% of graphite in epoxy composites as compared to pure Epoxy. KEYWORDSGraphite, Ep...

Nousétudions expérimentalement la dynamique de pelageà vitesse imposée d'un rouleau de ruban adhésif, et en particulier son régime dit de stick-slip qui consiste en des oscillationsà haute fréquence entre des phases lentes et rapides du pelage. Grâceà l'analyse d'images de caméra rapide, nous mesurons les caractéristiques de l'instabilité (durée et amplitude) pendant ces phases lentes et rapides lors du régime de pelage stationnaire. Nous montrons que leurs dépendances avec la vitesse de pelage et la longueur de bande pelée sont radicalement différentes de celles présentées dans desétudes antérieures.

Nitrogen-Doped Graphene Aerogel (N-GA) nanomaterials can significantly improve the functional efficiency of polymer composites due to its three-dimensional structure and suitable physical properties. The preparation process affects the performance improvement. In this study, the effect of preparation method and the mechanisms affecting the strength behavior of Nitrogen-doped Graphene Aerogel/Epoxy (N-GA/E) nanocomposites was investigated. For this purpose, nanoparticles of Graphene Oxide (GO) were produced using Hummers’ method; then, the N-GA was synthesized using the hydrothermal method and the freeze-drying process. The characterization experiments were used in order to confirm the structure and quality of the synthesized nanomaterials. Then, specimens of nanocomposite were prepared by adding weight percentages of 0.05, 0.1, 0.2, 0.5, 1, and 2 from the synthesized N-GA to the epoxy resin. In other preparation processes, N-GA/E nanocomposite specimens were produced using auxiliary...

We investigated the linear viscoelastic properties in the melt of a series of nearly monodisperse poly(nbutyl acrylate)(PnBA) chains center-functionalized with a bis-urea sticker group, able to self-associate by quadruple hydrogen bonding. All materials are viscoelastic liquids at 40°C and their Newtonian viscosity varies from 100 to 5000Pa.s. However we show clearly that the viscosity changes non monotonously going through a minimum for a molecular weight (M n) of 20 kg/mol and a sticker density of 1.1 wt%. We found two regimes: For M n < 20 kg/mol, the viscosity increases with decreasing M n , the linear viscoelastic properties change dramatically with temperature, forming a viscoelastic gel at 0°C and flowing at 40°C and the strength of the stickers association controls the size of molecular aggregates. However for M n > 20 kg/mol, the viscosity increases with M n , the rheology is controlled by the polymer dynamics and the stickers simply increase the terminal relaxation time relative to unfunctionalized PnBA of the same M n , as expected from sticky reptation theory. Despite clear evidence of sticker-sticker interactions by FTIR, none of the materials self-assemble at 20°C into structures with a long range order detectable by SAXS. Scheme 1: Structure of the studied PnBA. They were synthesized by ATRP according to Fonteneau et al 26 with molar masses ranging between 5 and 115kg/mol.

The PVC/TiO 2 nanocomposite samples were structurally characterized by scanning electron microscope that ascertains its polymer nanocomposite nature. The dynamic mechanical response, i.e., storage moduli and phase transition temperature accompanied by temperature have been studied through Dynamic Mechanical Analyzer (Tritec 2000 DMA). The intrinsic viscosity and phase transition activation energy is resolute in using these data. The results reveal that TiO 2 nanoparticle dispersion in PVC causes prominent enhancement in observed properties. However, the enhancement depends on proportion of nanoparticles.

Field-cycling NMR relaxometry is a well-established technique for probing molecular dynamics in a frequency range from typically a few kHz up to several tens of MHz. For the interpretation of relaxometry data, it is quite often assumed that the spin-lattice relaxation process is of an intra-molecular nature so that rotational fluctuations dominate. However, dipolar interactions as the main type of couplings between protons and other dipolar species without quadrupole moments can imply appreciable inter-molecular contributions. These fluctuate due to translational displacements and to a lesser degree also by rotational reorientations in the short-range limit. The analysis of the inter-molecular proton spin-lattice relaxation rate thus permits one to evaluate self-diffusion variables such as the diffusion coefficient or the mean square displacement on a time scale from nanoseconds to several hundreds of microseconds. Numerous applications to solvents, plastic liquids and polymers will be reviewed. The technique is of particular interest for polymer dynamics since intermolecular spin-lattice relaxation diffusometry bridges the time scales of quasi-elastic neutron scattering and field-gradient NMR diffusometry. This is just the range where model-specific intra-coil mechanisms are assumed to occur. They are expected to reveal themselves by characteristic power laws for the time-dependence of the mean-square segment displacement. These can be favorably tested on this basis. Results reported in the literature will be compared with theoretical predictions. On the other hand, there is a second way for translational diffusion phenomena to affect the spin-lattice relaxation dispersion. If rotational diffusion of molecules is restricted, translational diffusion properties can be deduced even from molecular reorientation dynamics detected by intra-molecular spin-lattice relaxation. This sort of scenario will be relevant for adsorbates on surfaces or polymer segments under entanglement and chain connectivity constraints. Under such conditions, reorientations will be correlated with translational displacements leading to the so-called RMTD relaxation process (reorientation mediated by translational displacements). Applications to porous glasses, protein solutions, lipid bilayers, and clays will be discussed. Finally, we will address the intriguing fact that the various time limits of the segment mean-square displacement of polymers in some cases perfectly reproduce predictions of the tube/reptation model whereas the reorientation dynamics suggests strongly deviating power laws.

Graphene is emerged as superior reinforcing filler for the polymer matrix due to its superior mechanical, electrical and ther-mal properties. But, the challenge is that graphene form aggregates in the polymer matrix due to the strong Vander Waals forces of attraction between the graphene nanosheets. In this regard, surfactant assisted dispersion strategy will be adopted to overcome the problem of aggregation in epoxy nanocomposites. This project will be carried out in two stages, first is to es-tablish the high concentration dispersion of graphene using the suitable surfactant, and second is to use this high concentra-tion dispersion of graphene for the preparation of epoxy nanocomposites. The graphene dispersion and its nanocomposites will be characterized using various characterization techniques such as UV-Vis-NIR spectroscopy, Flexural testing, Tensile testing, Scanning electron microscope (SEM) studies.