SAXS, SANS AND PHOTOELASTICITY OF POLY(N,N-DIETHYLACRYLAMIDE) NETWORKS .1. STRUCTURE CHANGES AFTER TEMPERATURE JUMPS

The development of microphase separation after temperature jumps in po ly(N,N-diethylacrylamide) hydrogels was studied by means of small-angl e neutron (SANS) and X-ray (SAXS) scattering. The curves of excess SAN S and SAXS for temperature jumps from 25 to 30-degrees-C were differen t in character from those for jumps from 30 to 35-degrees-C. After the temperature jump from 25 to 30-degrees-C two polymer phases with diff erent water content are formed (excess scattering intensity I(ex) appr oximately q-2, where q is the length of the scattering vector); howeve r, after the jump from 30 to 35-degrees-C the dilute phase is formed b y water droplets (pronounced two-phase structure, I(ex) approximately q-4). Photoelastic measurements on the equilibrium swollen samples ind icate that correlations exist between side groups at temperatures grea ter than or equal to 33-degrees-C. The association of side groups lead s to microsyneresis and to the differences observed in scattering beha viour.