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>Investigation of the phase diagram and critical fluctuations of the system polyvenylmethylether anddhyphen;polystyrene with neutron small angle scattering
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Investigation of the phase diagram and critical fluctuations of the system polyvenylmethylether anddhyphen;polystyrene with neutron small angle scattering
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机译：Investigation of the phase diagram and critical fluctuations of the system polyvenylmethylether anddhyphen;polystyrene with neutron small angle scattering
The system PVME/dhyphen;PS has been investigated by neutron small angle scattering. By extrapolating the critical scattering, the spinodal was determined and used to calculate the Floryndash;Huggins parameter khgr;(fgr;,T) in the frame of mean field theory. Separating the Gibbs potential of mixing Dgr;Gin a Floryndash;Huggins term khgr;(fgr;,T) and a configurational term for the entropy Dgr;S, it turns out that khgr; is independent of the molecular weight, and of the weight distribution, i.e., it is a local or lsquo;lsquo;segmentalrsquo;rsquo; quantity. The critical scattering was carefully investigated at the critical concentration. At temperaturesTcminus;T2.4thinsp;K(Tc=141.9thinsp;deg;C), a mean field behavior of the susceptibilityS(Q=0) was clearly observed, with a critical exponent ggr;=1. However, in a region ofTcminus;2.4thinsp;Kle;TTc, a crossover occurs to a critical exponent ggr;bartil;1.26; it resembles the Ising behavior which is well established for normal liquid mixtures. The functionS(Q) also describes the characteristic segmental length sgr;. Both sgr; and the range parameter of khgr;,r0, are independent of molecular weight and weight distribution within experimental errors. The binodal, i.e., the line between the homogeneous and the twohyphen;phase region was identified by a change of critical scattering caused by the precipitated domains. The spinodal approaches the binodal nearTcin a characteristic way as predicted for polydisperse systems.
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