Effect of Junction Length in Poly(vinyl alcohol) Physical Gel on Mechanical Strength

Young's modulus measurements and junction length estimates have been performed on poly (vinyl alcohol) (PVA) sample in mixtures of dimethyl sulfoxide (DMSO) and water with various mixing ratios to investigate the relationship between gel structure and mechanical strength. The interaction parameter between PVA and DMSO/water mixed solvent was also estimated from swelling experiments. The junction length zeta in number of vinyl alcohol units was estimated with the aid of the Tanaka and Stockmayer theory (TS theory), which is based upon the conjecture that junction points of a gel are aggregates comprised of zeta units in length and S sequences in cross section. The Young's modulus value of PVA gel increased with an increase in the DMSO volume fraction up to about 60 vol% and the further increased fractions led to a decrease in Young's modulus. Both chi(12) and zeta were also dependent on the DMSO volume fraction, similar to Young's modulus. These results indicate that gelation of PVA in a poorer solvent provided the longer junction lengths, resulting in the PVA gel formation with high mechanical strength.