C. M. Vrentas

Predictive methods for self-diffusion and mutual diffusion coefficients in polymer-solvent systems

Abstract Methods are presented for the prediction of solvent self-diffusion coefficients and mutual diffusion coefficients in polymer–solvent systems for the complete concentration range and over wide temperature ranges. Procedures are developed for both rubbery and glassy polymer–solvent systems.

Step strain deformations for viscoelastic fluids : experiment

Shear stress and normal stress relaxation data were collected for a range of shear strains for a polystyrene–dibutyl phthalate solution. Data from single‐step shear strain experiments were used to test time–strain factorability and to check on the applicability of the Lodge–Meissner rule. Significant departures from time–strain factorability were found, but the shear and normal stress data were in excellent agreement with the Lodge–Meissner prediction. Data from double‐step shear strain experiments were used to check the predictions of the K–BKZ and Doi–Edwards theories. It was found that these theories do not generally provide adequate descriptions of double‐step shear strain deformations.

Integral sorption in glassy polymers

A new theory is developed for integral sorption and desorption processes in glassy polymers. The theory can describe both case II diffusion and the classical case of Fickian diffusion. Predictions of the theory are compared with general experimental observations.

Dissolution of rubbery and glassy polymers

A mathematical model is formulated for solvent dissolution of rubbery and glassy polymers. An exact solution to the problem is derived for the constant diffusivity case, and a weighted residual solution is developed for the case of a concentration-dependent diffusion coefficient. The solution is used to calculate concentration profiles, dissolution curves, dissolution half-times, and pseudointerface positions at various times.

Prediction of mutual diffusion coefficients for polymer–solvent systems

A new equation is proposed for relating solvent self-diffusion coefficients and mutual diffusion coefficients for polymer-solvent systems. The formulation of the new equation avoids a friction-coefficient formalism, and hence the new equation does not require the thermodynamic properties of the polymer-solvent system. A comparison has been made of the predictions of the proposed equation with experimental data for the benzene-rubber system.

Slow bubble growth and dissolution in a viscoelastic fluid

A simple equation is derived for the time dependence of the bubble radius for the diffusion-induced slow growth or dissolution of a spherical gas bubble in a viscoelastic fluid of infinite extent. The constitutive equation for a first-order fluid and a surface–volume perturbation scheme are used to develop the solution, and the effect of viscosity level and elasticity on the bubble dynamics is considered.

Finite amplitude oscillations of viscoelastic fluids

Abstract Finite amplitude oscillatory shear experiments are used to study the mechanical behavior of viscoelastic materials. Four rheological relations are derived which can be used to determine both linear and nonlinear rheological properties of simple fluids from data obtained using large amplitude oscillatory experiments. Two consistency conditions are derived for a fluid which obeys the K-BKZ constitutive equation, and these relations are used in conjunction with data from a finite amplitude oscillatory experiment to check the validity of the K-BKZ equation.

Differential sorption in glassy polymers

Anomalous sorption curves have often been observed for differential sorption experiments in glassy polymers. A model is proposed to describe this non-Fickian behavior. This model is based on the presence of interfacial resistance caused by slow rate processes at the phase boundary. Predictions of the model are compared with general experimental observations.

Anticipation of anomalous effects in differential sorption experiments

The concept of a diffusion Deborah number is used to anticipate the presence of anomalous effects in differential sorption experiments. The method is illustrated using sorption data for five experiments involving polymer-solvent mixtures.

Integral sorption in rubbery polymers

Simple equations are derived that describe integral sorption and desorption experiments under conditions where moving boundary effects in polymer films and spheres can be large because of high solvent concentrations. General conclusions are formulated about the nature of sorption and desorption experiments for both rectangular and spherical geometries.