HIERARCHICAL STRUCTURE OF POLY(VINYL ALCOHOL) GELS

The structure of poly(vinyl alcohol) (PVA) gels formed in mixtures of dimethyl sulfoxide (DMSO) and water was studied using several scatteri ng techniques such as wide-angle neutron scattering (WANS), small-angl e neutron scattering (SANS), ultra-small angle neutron scattering (U-S ANS), and light scattering (LS), covering a very wide Q range from 10( -4) to 10 Angstrom(-1). The WANS measurements have revealed that the c ross-linking points of the gels are crystallites, and the spatial dist ribution has been evaluated by SANS measurements. The SANS results hav e also shown that the structure observed in a low Q range below 10(-2) Angstrom(-1) is dominated by a liquid-liquid phase separation. The ea rly stage of the phase separation has been studied in more detail usin g a time-resolved LS technique, while the late stage has been investig ated by a U-SANS technique because the LS technique cannot be applied to opaque samples. On the basis of the results, we have proposed a sch ematic model for the structure of PVA gels.