C. Nakamoto et al., Preparation pressure dependence of structure inhomogeneities and dynamic fluctuations in poly(N-isopropylacrylamide) gels, MACROMOLEC, 34(4), 2001, pp. 911-917
The structure inhomogeneities and dynamic fluctuations in poly(N-isopropyla
crylamide) (PNIPA) gels have been investigated by dynamic light scattering
as a function of gel-preparation pressure, P-prep. The ensemble average lig
ht scattered intensity ((I)(E)), a measure of structure inhomogeneities, wa
s found to be an increasing function of P-prep and diverged at P-prep = 168
MPa. This indicates that PNIPA gels undergo phase separation by increasing
P-prep. The corresponding PNIPA solution was transparent and had no P-prep
dependence. It is concluded that the structure of gels depends not only on
the pressure at observation P-obs but also on P-prep and the inhomogeneiti
es increase with P-prep. On the other hand, the dynamic fluctuations were i
ndependent of P-prep. This shows that cross-linking plays a major role in f
ormation of built-in structure inhomogeneities.