Structure of Polymer Gels Controlled by Phase Separation

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We have studied structure of poly (vinyl alchol) (PVA) gels and its formation process after quenching from homogeneous solutions at a high temperature (100ﾟC) using time resolved light and small angel neutron scattering techniques.In the light scattering measurements at 23ﾟC,it was clearly observed that the scattering intensity profile shows a broad peak at Q (length of scattering vector) =5*10^<-4> *^<-1>. The peak position is independent of time while intensity increases exponentially with time, suggesting that spinodal decomposition-like phase separation occurs in the PVA gels at 23ﾟC.On the other hand, no peak is observed in the scattering profile after quenching to -40ﾟC from a high temperature (100ﾟC). This means that in the PVA gels formed at low temperatures, phase separation dose not occurs and the gels are rather homogeneous.On the basis of the small angle neutron scattering measurements, we elucidated structure of the network of the gels and its formation process. It was found that the cross-linking points are crystallite with radius of about 70* and the average distance between crystallites is about 200*.From both the light and neutron scattering experiments, we concluded that the final structure of the PVA gels are determined by competition between the rate of crystallite formation and the rate of the phase separation. By controlling the two rates, it would be possible to control the structure of PVA gel.