Polymer Conformation near the Critical Point of a Binary Mixture

Abstract

Conformation of a flexible linear polymer (polyacrylic acid, PAA) in a binary mixture ( $\mathrm{water}+2$,6-lutidine, LW) near the critical point of LW is studied using dynamic light scattering (DLS) by which the diffusivities of the polymer molecules and the critical composition fluctuation of the LW are measured. The DLS measurements, supplemented by viscosity data, show that the PAA molecule in LW shrinks when approaching the critical point of LW. At temperature $T$ close to the critical temperature ${T}_{c}$ when the correlation length $\ensuremath{\xi}$ of LW is comparable to the intermolecular distance of PAA, we find that $\ensuremath{\xi}\ensuremath{\propto}(1\ensuremath{-}T/{T}_{c}{)}^{\ensuremath{-}\ensuremath{\nu}}$ with $\ensuremath{\nu}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.44\ifmmode\pm\else\textpm\fi{}0.03$ which is smaller than $\ensuremath{\nu}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.60$ of pure LW.