Poly(NIPAM) microgel particle de-swelling: a light scattering and small-angle neutron scattering study

Small-angle neutron scattering (SANS) has been used to investigate structur al changes during the de-swelling of poly(N-isopropylacrylamide) [poly(NIPA M)] microgel particles induced by temperature variation and the addition of free polymer [poly(ethylene oxide)]. The extent of particle de-swelling wa s characterized by photon correlation spectroscopy (PCS). Thermally-induced de-swelling of poly(NIPAM)/deuterated water dispersions occurred on increa sing the temperature in the region of the lower critical solution temperatu re (LCST). The latter was found to be 34 degrees C, which is 2 degrees C hi gher than the value reported for poly(NIPAM) particles dispersed in water. The SANS data exhibit a Pored form (Q(-4)) of scattering in regard to the s ize of the colloidal particles. However, in the swollen state, the scatteri ng measured at temperatures less than the LCST, also has a contribution fro m poly(NIPAM) chains in a solution-like environment (Ornstein-Zernike scatt ering). The trends observed in the SANS data as a function of temperature w ere simulated using a model comprised of Pored and Ornstein-Zernike scatter ing terms. The SANS data confirm earlier PCS measurements showing that addi tion of free polymer induces particle de-swelling. The SANS data obtained u sing added free polymer are the first examples of their type to be reported . (C) 1999 Elsevier Science B.V. All rights reserved.