Adam-Gibbs based model to describe the single component dynamics in miscible polymer blends under hydrostatic pressure

Gustavo A Schwartz,Juan Colmenero,Ángel Alegría

doi:10.1063/1.2780157

Abstract

We present in this work a new model to describe the component segmental dynamics in miscible polymers blends as a function of pressure, temperature, and composition. The model is based on a combination of the Adam-Gibbs (AG) theory and the concept of the chain connectivity. In this paper we have extended our previous approach [D. Cangialosi et al. J. Chem. Phys. 123, 144908 (2005)] to include the effects of pressure in the component dynamics of miscible polymer blends. The resulting model has been tested on poly(vinyl methyl ether) (PVME)/polystyrene (PS) blends at different concentrations and in the temperature range where the system is in equilibrium. The results show an excellent agreement between the experimental and calculated relaxation times using only one fitting parameter. Once this parameter is known the model allows calculating the size of the relevant length scale where the segmental relaxation of the dielectrically active component takes place, i.e., the so called cooperative rearrangement region (CRR) in the AG framework. Thus the size of the CRR for PVME in the blends with PS has been determined as well as its dependence with pressure, temperature, and concentration.

Highlights

The dynamics of polymer blends has attracted the interest of many researchers during the last years because the peculiar features displayed by these systems
Among them one of the most interesting is the presence of two distinct time scales for the component segmental dynamics due to the heterogeneous dynamics at the length scale of the segmental relaxation
A different approach to describe the component segmental dynamics in miscible polymer blends has been proposed by us[8,9] starting from the theory of Adam and GibbsAG,[10] which relates the dynamic and thermodynamics behaviors of glass formers and has allowed us to describe the molecular dynamics closeand above Tg.[11,12]. In those works we provided a new approach to describe the component segmental dynamics of athermal miscible polymer blendsat atmospheric pressurecombining the concept of chain connectivity, expressed in terms of the selfconcentration, and the AG model

Summary

Introduction

The dynamics of polymer blends has attracted the interest of many researchers during the last years because the peculiar features displayed by these systems. Lodge and co-workers[3,6] have used the idea that in miscible polymer blends the local concentration of one component will, on average, be richer in that component compared to the bulk

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Results

Conclusion