Coupling model analysis of polymer dynamics in solution: Probe diffusion and viscosity

Abstract

Articles you may be interested inProbing solvent dynamics in concentrated polymer films with a highfrequency shear mode quartz resonatorThe coupling model of Ngai et al. ͓K. L. Ngai, Disorder Effects in Relaxation Processes, edited by R. Richert and A. Blumen ͑Springer-Verlag, Berlin, 1994͔͒ is applied to treat polymer dynamics in solution. Important dynamic quantities considered here include the zero-shear viscosity and the light-scattering spectrum ͑field correlation function͒ g (1) (t) of optical probes suspended in solution. The coupling model describes systems in terms of two times, a basic relaxation time 0 and a crossover time t c , and a coupling exponent n. Use of scaling arguments allows us to extract values for n from the concentration dependence of and, by three separate paths, from the concentration, time, and scattering vector dependencies of g (1) (t). Values of n from these four distinct physical approaches are shown to be mutually consistent, especially in the higher-concentration, large-probe-particle regime in which the scaling arguments are most likely to be valid. The behavior of n above the solutionlike-meltlike viscosity transition, and the effect of probe size on n, are briefly discussed.

Relaxational mode structure for optical probe diffusion in high molecular weight hydroxypropylcellulose

“…36 -38 First, stretched-exponential functions of (t) describe well g (1) (t) of many polymer systems. 11,15,17,39 -41 In terms of our notation, ␤ ϭ 1 Ϫ n. Second, it was shown by Ngai and Phillies 21 that the phenomenological concentration dependence of ␤ 11,15,17,40,42 is often consistent with coupling model predictions for 1 Ϫ n. Third, the coupling model predicts 21 that the relaxation time depends on q as ϵ…”

“…If all four ␤ agree with each other, then the model is selfconsistent. Phillies and Ngai 21 were able to demonstrate the success of the model for probe diffusion 17 in 300 kDa HPC solutions. They demonstrated that ␤ c , ␤ q , and ␤ t from g (1) (t), and ␤ from (c) agree with each other.…”

“…21 The coupling model has been successfully applied to a variety of complex physical systems. 32 Even though the coupling model for real complex systems has no theoretical derivation from the first principles yet, from simulating simple systems with idealized Hamiltonians there are several encouraging theoretical results [33][34][35] that directly support basic elements of the coupling model.…”

“…Here we discuss properties of the spectral parameters that reveal the physical nature of the relaxational mode structure. In our analysis of the physical nature of modes, we also attempted to apply the coupling/scaling model 21 analysis to our system. 22 The following sections introduce experimental methods, give the important results of ref.…”

Guides to solving the glass transition problem

“…This crossover property is found also in other many-body relaxation systems besides glass-formers [7,[56][57][58][59][60][61][62], and hence it is a general property. The magnitude of t c depends on the intermolecular potential V (r ).…”