Electric-field-induced structure in polymer solutions near the critical point

Denis Wirtz, Klaus Berend, Gerald G. Fuller

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Abstract

In the vicinity of the coexistence curve, binary solutions exhibit large concentration fluctuations. Such fluctuations can be anisotropically distorted through the application of an electric field, which induces both electric birefringence and enhanced forward light scattering as the system approaches the coexistence curve. Using time-dependent small-angle light scattering (SALS) and form dichroism measurements on semidilute polystyrene/cyclohexane systems (molecular weight range 400 000-1 800 000), two new phenomena have been observed: electric scattering dichroism in the one-phase region and electric-field-induced remixing in the two-phase region. A mean-field theory that predicts the evolution of the scattering patterns in the presence of an electric field above the coexistence curve has been developed. In particular, it is predicted that, in the plane perpendicular to the propagation of the incident light, circular scattering patterns become elliptical patterns having the minor axis along the direction of the applied field. As a consequence, scattering dichroism is shown to be induced in the vicinity of the critical point. Moreover, the same phenomenological model predicts that the presence of an electric field lowers the coexistence curve and results in electric-field-induced remixing of binary mixtures at a temperature below the quiescent coexistence curve. The influence of temperature, molecular weight, and concentration of the polymer in solution as well as the influence of the electric field strength on SALS patterns and induced scattering dichroism measurements is studied. The experimental observations are in fairly good agreement with the trends predicted by a phenomenologically-based, mean-field theory.

Original languageEnglish (US)
Pages (from-to)7234-7246
Number of pages13
JournalMacromolecules
Volume25
Issue number26
Publication statusPublished - 1992
Externally publishedYes

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ASJC Scopus subject areas

  • Materials Chemistry

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