Surface tensions of viscous molten polymers were measured with the modified Wilhelmy method. Small diameter fibers were used as vertical surface tension probes giving rise to rapid equilibration of the wetting meniscus. Noise due to thermal convection currents was suppressed by the use of a baffle tube to protect the electro-balance which allowed us to extend our studies to temperatures exceeding 400°C. The precision of the surface tension measurement at T<350°C for n≤10,000 Poise is better than 0.5%. Discussion is made of the rate of meniscus equilibration as a function fiber diameter. The surface tensions of polystyrene(PS), polydimethylsiloxane(PDMS), poly(ethylene glycol)(PEG), poly(propylene glycol)(PPG), and polyethylene(PE) were determined as a function of MW and temperature in order to compare with theoretical predictions. The Cahn-Hilliard interfacial gradient theory is used in conjunction with equation of state models using pressure-volume-temperature data as the input. Good agreement with experiment is found using one adjustable parameter which is independent of MW, for both polar and non-polar polymers.

This work shows that, in studies on porous disordered organic material such as cross-linked resin of poly(4- vinylpyridine, one has to consider a possible interfacial adsorption of solvents. We propose the nuclear relaxation associated with ESR of y-ray induced radicals as an efficient method to estimate the extent of solvent penetration into the interface of the polymer network. This method is however limited to the case where free radicals resulting from solvent-substrate interactions can be selectively generated at interfaces.

We have developed a Monte-Carlo computer simulation to study associating polymer interactions. In our model we treat the associations as geometrical constraints. Each polymer chain contains two‘stickers’. The chains are treated as lattice selfavoiding random walks. Each sticker is constrained to be adjacent to one other sticker, but the stickers are free to exchange partners. This freedom to exchange results in an attraction between the chains, as anticipated by Cates and Witten.1 We find that in equilibrium the mutual excluded volume of two such chains passes from repulsive to attractive when the ratio of the sticker distance to the chain length is approximately 0.8. These results are independent of the chain length: they should apply to real polymers subject to these topological constraints in any good solvent at sufficiently high molecular weight.

The internal associations of comb-shaped associative thickeners are modeled by Gaussian statistics to predict the probability of chain collapse and that for various types of internal associations. In addition to the idealization of the polymer backbone to a random walk, the hydrophobic groups at the ends of each tooth of the comb are treated as point“stickers.” The model considers all the ways by which stickers can form clusters of two or more teeth. The number of teeth per chain is not limited by the model, but rather by computation facilities. It is predicted that even with weak pairwise sticker interactions (2kT) adding short teeth to a long backbone drastically increases the probability of some internal associations, though the probability of complete chain collapse decreases significantly as teeth are added, due to the effect of backbone entropy.

A unique, molecular architecture was developed based on a hydrocarbon soluble backbone with a liquid crystalline side group. Lightly sulfonated polystyrene (SPS) ionomer was complexed with poly(y-benzyl-L-glutamate) (PBLG), an amine terminated synthetic polypeptide, by solution blending in either THF or chloroform. Complexation first occurred by proton transfer from the pendent acid to the amine terminal group. A secondary interaction involved hydrogen-bonding between the sulfonic acid and the carbonyl group on the PBLG chain. This material will have the potential as a molecular composite and unusual solution behavior was observed when the interaction occurred.

We examine the role of molecular architecture on the phase diagram of the PS/PVME (poly[styrenel /poly[vinyl methyl ether]) blend, a mixture which in previous studies with linear chains exhibited a lower critical solution temperature, (LCST) i.e. it phase separated on heating. In this investigation, two blends with components exceeding the critical molecular weight for entanglement were compared: one consisting of linear PS and PVME and a second with cyclic PS and linear PVME. Cloud point experiments over a broad composition range reveal that the blend containing cyclic PS undergoes phase separation at temperatures 7-8 °C higher than the analogous linear blend. In other words, the mixture of cycles and linear chains is more thermodynamically stable than the mixture of two linear chains.

The LCST nature of the system facilitates examining chain mobility by considering the phase separation kinetics. Time-resolved light scattering studies of blends near their critical compositions tracked the spinodal decomposition following a rapid temperature jump from the one-phase to the two-phase region. An analysis of the scattering intensity growth ultimately led to mutual diffusion coefficients whose temperature dependence confirmed the observed cloud points. An approximation of the second derivative of the free energy function based on SANS studies of the linear PS/PVME blend allowed us to estimate mutual mobilities. The values determined for the cycle-containing blend were considerably lower than those for the blend of linear chains at these molecular weights.

The variation of the radius of gyration RG and the hydrodynamic size RH are followed as the ionic strength of the medium is monitored for a flexible polyelectrolyte compound in solutions. In addition, a comparison between the thermodynamical and hydrodynamical interaction parameters is given for the present system.

In order to improve our ability to simulate the complex behavior of polymers, we introduce dynamical models in the class of Cellular Automata (CA). Space partitioning methods enable us to overcome fundamental obstacles to large scale simulation of connected chains with excluded volume by parallel processing computers. A highly efficient, two-space algorithm is devised and tested on both Cellular Automata Machines (CAMs) and serial computers. Preliminary results on the static and dynamic properties of polymers in two dimensions are reported.

We discuss the threshold fracture energy, GO, of networks over a wide range of cross-link density. C, for networks with an average number of main chain steps, ςc, that compare favorably with the entanglement spacing, ςc, follow the 1/2 power law, Go - ς1/2. Two views of molecular fracture, one a chain-breaking mechanism and the other a suction process, produce the 1/2 power law. For lightly cross-linked networks (ςc ≫ ςe), Go appears to decrease with increasing ςc. Trapped entanglements limit the extensibility and fracture energy of these networks. Consideration of rupture of trapped entangled chains gives Go -ςc-1/2; this form agrees reasonably well with data at high ςc.

We discuss both theory and simulation of fracture of ideal and almost ideal crystals at finite temperature. We propose that a solid under stress is in a metastable state, and that the onset of fracture may be characterized as the nucleation of the (stable) broken phase from the (metastable) intact phase. The role of atomic-scale defects is also discussed.

The Brillouin light scattering technique is used for the investigation of structural relaxations in glass-forming liquids at high temperatures. From the analysis of the line shapes of Rayleigh and Brillouin peaks, the friction coefficients, which are associated with the atomic scale mechanisms of the structural relaxations in these systems, are determined. Results for a series of K2O-SiO2 compositions, which were chosen as model substances, are reported. As a function of temperature, maxima in the Brillouin line widths were observed, which reflect resonant conditions of molecular scale structural motions, where the relaxation time is of the order of the reciprocal Brillouin frequency shift. Due to thermal activation of the component mobilities, different relaxation mechanisms couple at different temperatures. Typically, at least one strongly absorbing regime is observed in between the glass transition and the equilibrium melting temperatures. The prominence of this regime decreases with increasing silica concentration. The friction coefficients approach the hydrodynamic viscosity in the high temperature limit, when the relaxation times become short in comparison with the time scale of the Brillouin shift.

We develop exact integral equations satisfied by the spin-spin correlation functions of a realistic spin glass model. This is done by considering the magnetic particles in a spin glass to be bound states of hard sphere ‘atoms’ and classical ‘spins’, the former of which are quenched in position, while the latter are allowed to equilibrate. We develop the replica Ornstein-Zernike (ROZ) equations, which are satisfied by the correlation functions of such a partly quenched mixture. We prove that two widely used OZ closures, the Percus-Yevick approximation and mean-spherical approximation are indifferent to quenched disorder, i.e., they give tihe same results for quenched and for fully annealed systems. We extend the ROZ equations to apply to the spin glass by using the proper interaction-site formalism. Preliminary numerical results are discussed.

The influence of a solid-liquid interface on the relaxation of a point dipole embedded in the liquid side is discussed. The dielectric friction of a dipole as a function of its distance from a boundary is calculated. The calculations are carried out assuming a nonlocal dielectric function of the liquid, characterized by a typical correlation length which may depend on temperature. The corrections to the relaxation of a dipole due to the presence of a boundary are shown to be small. Larger corrections can be introduced by postulating structural changes in the nature of the liquid near the boundary.

We show that the presence of a bump, in the profile of spreading films driven by forces such as surface tension gradients, can be explained by a simple analysis of the steady-state velocity, without taking into account contact line effects.