Segmental Dynamics in Miscible Polymer Blends:  Modeling the Combined Effects of Chain Connectivity and Concentration Fluctuations

Abstract

The dynamic heterogeneity of the segmental dynamics in miscible polymer blends has been alternatively interpreted in terms of either chain connectivity effects or thermal concentration fluctuations. Taking into account that both phenomena seem to be relevant, in this work we propose a minimal model which combines these two effects. This model basically assumes the self-concentration approach recently proposed by Lodge and McLeish [Macromolecules 2000, 33, 5278] and introduces a distribution of the effective concentration around a given segment mainly due to the effect of thermal concentration fluctuations. The proposed model has been checked in two blend systems, PVME/PS and PoCLS/PS700. Each of these systems allows to selectively observe by dielectric spectroscopy either the low-or highglass transition temperature component of the blend, respectively. The model provides a good quantitative description of the dielectric segmental relaxation in both cases with only one free parameter: the variance of the distribution of the effective concentration. This parameter results to be hardly dependent on temperature, at least in the two blends investigated.

The Role of Density and Temperature in the Dynamics of Polymer Blends

“…Its limitations have led to modifications entailing additional parameters. 54 As seen in Figure 2, eq 2 overestimates T g for the blends by e10%. Also included in the figure are DSC results 55 for a PPO/PS blend of comparable molecular weights.…”

Relationship between the α‐ and β‐relaxation processes in amorphous polymers: Insight from atomistic molecular dynamics simulations of 1,4‐polybutadiene melts and blends

“…These models attempt to explain the dynamical response of miscible polymer blends and the perplexing behavior of the lower T g component by considering heterogeneity in the composition of the local environment of polymer segments and local structure (e.g., density fluctuations, chain connectivity, etc.). While it has been shown that parameters of these models can be fitted to quantitatively reproduce composition and temperature dependence of segmental relaxation times for variety of miscible polymer blends, 31,32,36,37 there are number of blends in which these models are able to predict only qualitative trends observed in experiments 32,34 or fail completely, 36,38 indicating that some physics of segmental relaxation in polymers blends might be missing in those models.…”

Multiple glass transitions and local composition effects on polymer solvent mixtures

“…In a recent work, Leroy et al have treated the variance as a fitting parameter in accounting for the spectral width of dielectric relaxation data in polymer blends. 12 However, Salaniwal et al 9 have addressed this problem by estimating variances in local composition using the random phase approximation (RPA) applied to the contents of a finite spherical volume. This yields an integral expression involving the RPA structure factor that must be evaluated numerically.…”