Structure of Polymer Gels Controlled by Phase Separation

利用时间分辨光和小角中子散射技术研究了聚乙烯醇（PVA）凝胶在高温（100℃）下淬火后的结构和形成过程。在23 C的光散射测量中，可以清楚地观察到散射强度曲线在Q（散射矢量长度）=5*10^<-4> *^<-1>处呈现出一个宽峰。峰的位置与时间无关，而强度随时间呈指数增长，表明在23℃时PVA凝胶发生了类似于spinodal分解的相分离。另一方面，从高温（100ºC）淬火到-40ºC时，在散射曲线上没有观察到峰。这意味着在低温下形成的PVA凝胶中，不会发生相分离，凝胶相当均匀。在小角中子散射测量的基础上，我们阐明了凝胶网络的结构及其形成过程。交联点为半径约70*的结晶，晶间平均距离约200*。从光散射和中子散射实验中，我们得出结论，PVA凝胶的最终结构是由晶体形成速率和相分离速率之间的竞争决定的。通过控制这两个速率，可以控制聚乙烯醇凝胶的结构。

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.