Drying methods affecting the particle sizes, phase transition, deswelling/reswelling processes and morphology of poly(N-isopropylacrylamide) microgel beads

The influence of drying methods on the micromeritics, phase transition, deswelling/reswelling process and surface topography of poly (N-isopropyl-acrylamide) (PNIPAAM) microgel beads was investigated. Three different drying methods (quick-freezing, slow-freezing and oven-drying) were applied to prepare the dried PNIPAAM microgel beads. Undried PNIPAAM microgel beads were used as control. The results indicate that although different drying methods significantly influenced the particle size distribution, deswelling/reswelling volume, surface topography and morphology of PNIPAAM microgel beads, it did not seem to affect the lower critical solution temperature (LCST) of 32 degrees C-34 degrees C and molecular interaction in PNIPAAM microgel beads. According to ATR/FT-IR/DSC microscopic study, above the LCST, the free form of non-hydrogen bonded C=O band and intra-molecular hydrogen bonding played a dominant role in the molecular structure of PNIPAAM microgel beads, which was contrary to our previous study in which the non-hydrogen bonding contributed less to the molecular structure of PNIPAAM aqueous solution without a cross-linking agent. (C) 1999 Elsevier Science Ltd. All rights reserved.