Solvent dynamics, local friction, and the viscoelastic properties of polymer solutions

Abstract

Classical assumptions concerning the contribution of the solvent to the v-stic properties of polymer solutions are shown to be invalid. The presence of polymer affects the mean solvent rotational mobility, in some cases even enhancing it relative to the neat solvent case. The resulting changes in local friction modify both the polymer relaxation times and thesolvent contribution to the solution properties. The effect is quantified through an intrinsic "effective solvent viscosity", [qJ, which can be positive or negative. To a first approximation, [qe] appears as an additive correction to the measured intrinsic viscosity, [ q ] ; this correction can be substantial, particularly for polymers of low ,molecular weight. Furthermore, Ille] largely accounts for the anomalous high-frequency limiting viscosity, designated [q'-], even in those cases where [q'-] is negative. These results remain to be incorporated successfully into a kinetic theory framework; however, a phenomenological interpretation is offered. The central, unresolved issue is to predict how the local dynamics of molecules in a mixture are modified relative to the unmixed state; the same issue arises in the dynamics of polymer biends. Introductioa

Apparent relaxation‐time spectrum cutoff in dilute polymer solutions: An effect of solvent dynamics

“…27 Single relaxation-time behavior for the solvating environment in this frequency range is consistent with previous electric birefringence studies. 31 The solid curves have been obtained by subtracting this contribution from the experimental data for the solution, in much the same way that one used to subtract the frequency independent SЈ ϱ to obtain the polymer global motion contribution to the solution properties. However, in this work we have subtracted from S* a complex quantity S* e ϩ (S* P ) L instead of a real number (SЈ ϱ ).…”

“…It is well known that the presence of polymer chains in solution modifies the solvent dynamics and that the extent and sign of this modification depend on the polymer/solvent system. 26,28,31,32,51 In the case of finite concentration solutions, although PI causes the relaxation time of Aroclor to shift to shorter times (higher frequencies), the effect of PS is of the opposite sign and larger in magnitude, shifting the frequency dependence of Aroclor to lower frequencies. At the same time, the relaxation times for the global motion polymer contribution to the PS/Aroclor solution properties shift even further, thus enhancing the high-frequency plateau ( s / N becomes larger).…”

“…This last effect is attributed to modification of the solvent dynamics in the vicinity of a polymer chain. 28,31 Similarly, modifications of the solvent dynamics are observed in OFB measurements of the mechanooptic coefficient, where the frequency-independent high-frequency plateau in SЈ, denoted SЈ ϱ , usually differs from the pure solvent value, S s . Although one set of measurements in a polyisoprene (PI) solution in Aroclor hinted at some frequency dependence in the Ј ϱ region, 32 no other previous measurements attained a high enough effective frequency to see any detectable solvent viscoelasticity.…”

“…The Rouse-Zimm bead-spring model (BSM) 24,25 is remarkably successful in predicting the contributions from the global motions of the polymer to these experimentally measured properties, provided that the actual solvent contribution to the solution properties is considered. 10,11,22,23 In many systems the solvent contribution differs substantially from the pure solvent viscosity and birefringence, 26,28,31 especially at lower temperatures. For both experiments, the measured response of a solution is taken as the sum of polymer and solvating environment contributions (the subscripts p and e denote polymer and environmental contributions, respectively).…”

Size exclusion chromatography with multiple detectors: Solution properties of linear chains of varying flexibility in tetrahydrofuran

“…The data are shown in Tables 111-VIII. Rg values smaller than about 12 nm are not reported due to the lack of precision in the measurement for molecules below this size. In Table VIII polymers where the data cover only the high molecular weight range (PIB and PODMA), the results can be adequately described by a straight line.…”