GROWING PROCESS OF SCATTERING DENSITY FLUCTUATION OF A MEDIUM DISTANCE IN THE HYDROGEL OF POLY(VINYL ALCOHOL) UNDER STRETCHING

The small-angle X-ray scattering technique using synchrotron radiation was employed to study the conformational change of the hydrogel of poly(vinyl alcohol) (PVA) under stretching. In the stretching process the PVA molecule in the gel mostly retains a folded structure as a structural domain characterized by a fractally rough interface which slightly changes. Simultaneously, the stretching not only induces the long-range orientation of the domains in the gel but also enhances a scattering density fluctuation with the medium distance of about 20 angstrom, accompanying the short-range ordering known to be microcrystallization. Alternatively, in the case of the PVA hydrogel the stretching gradually induces the rearrangement of the polymer chains around cross-linking points in the domain, which exhibits the scattering density fluctuation with about a 20-angstrom length scale, resulting in the microcrystallization over the gel to show the diffraction peak of crystallites in the high q region.