Gelation Process of Poly(vinyl alcohol) As Studied by Small-Angle Neutron and Light Scattering

Abstract

The authors report small-angle neutron scattering (SANS) and light scattering (LS) studies on poly(vinyl alcohol) (PVA) gels formed in a mixture of deuterated dimethyl sulfoxide (DMSO-d{sub 6}) and heavy water at 23 C. It was reported in a previous paper that the SANS intensity I(Q) of the PVA gels is well described by the Ornstein-Zernike (OZ) formula I(0)/(1 + {zeta}{sup 2}Q{sup 2}) and Porod`s law Q{sup {minus}4} for 0.01 {angstrom}{sup {minus}1} < Q < 0.035 {angstrom}{sup {minus}1} and 0.05 {angstrom}{sup {minus}1} < Q < 0.1 {angstrom}{sup {minus}1}, respectively. In this work, the authors extended the Q range down to 3 {times} 10{sup {minus}3} {angstrom}{sup {minus}1} and found that I(Q) turns up for Q < 8 {times} 10{sup {minus}3} {angstrom}{sup {minus}1} to deviate from the OZ formula. This upturn has been assigned to structure due to phase separation based on the results of SANS and LS measurements. In order to investigate the gelation process, time-resolved SANS measurements were carried out on the PVA solutions after quenching to 23 C from 100 C. It was found that the correlation length {zeta} evaluated by the OZ formula in a Q range of 0.01--0.035 {angstrom}{sup {minus}1} is dominated by concentration fluctuations in the earlymore » stage of the gelation before crystallization (t < 200 min) while, after the crystallization initiates, the average correlation distance between the nearest-neighboring crystallites becomes a dominant factor in {zeta}. Distance distribution function P(r) which is defined by inverse Fourier transformation of the scattering intensity was calculated to see the size and the distribution of the crystallites.« less