writer：Wang Liao; Yongjun Zhang*; Ying Guan; X.X. Zhu*
keywords：PNIPAM microgel, gelation, kinetics
source：期刊
specific source：Macromolecular Chemistry and Physics
Issue time：2011年
In the absence of added salt, thermosensitive poly(N-isopropylacrylamide) (PNIPAM) microgel dispersions are colloidally stable even at temperature well above their volume phase transition temperature (VPTT). However at high ionic strength they gel upon heating. The kinetics of the heat-induced gelation is investigated at various polymer concentrations, temperatures, and NaCl concentrations using small-deformation oscillatory rheological measurements. In situ gelation is achieved by isothermal heating. Gelation times are determined as the point where the storage and loss moduli, G'' and G'''', crossover. The effects of two dominating factors, polymer concentration, and temperature, on gelation time are investigated. At constant NaCl concentration, the gelation time decreases with increasing polymer concentration. The critical gelation  concentration  is determined  to  be  ca  0.4 wt.-%.  At  constant  polymer  and  NaCl concentration, the gelation time decreases with increasing  temperature.  At  each  NaCl  concentration,  the  critical gelation temperature is slightly  higher than  the corresponding VPTT. The gelation  kinetics  of  PNIPAM  microgel  dispersion can be well-described by the Tobitani–Ross-Murphy model.