Nano-scale structure and dynamics of poly(vinyl alcohol) gels

Takahashi, Nobuaki; Kanaya, Toshiji*; Nishida, Koji*; Seto, Hideki*; Nagao, Michihiro*; Takeda, Takayoshi*

We have extensively studied nano-scale structure and dynamics of three types of poly(vinyl alcohol) (PVA) gels by using small-angle neutron scattering (SANS) and neutron spin-echo (NSE) techniques; two physical gels and one chemical gel. The first one was a PVA gel in a mixture of deuterated dimethyl sulfoxide (DMSO-d6) and D2O with volume fraction of DMSO-d6 being 0.6, in which cross-links were made of crystallites. On the basis of NSE results, SANS intensity was divided into static and dynamic fluctuations to find that the former contribution was dominant in the present wave vector (Q) range. The latter, dynamic fluctuations were analyzed in terms of fluctuations of cross-links in the quasi-equilibrium position. The second gel was PVA in aqueous borax solution. The intermediate scattering functions of the gel as well as the sol were well described by Zimm mode and gel mode in Q regions of above and below a critical wave vector (Qc). The last one was the chemically cross-linked PVA gel. The intermediate scattering function was also described by Zimm mode in a short-time region, suggesting that it behaves like polymer solution. However, in a long-time region, the data points deviated from Zimm-scaled master curve, suggesting that it was restricted by the cross-links made of covalent bonds.