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Gelation Kinetics of Thermosensitive PNIPAM Microgel Dispersions
Author(s) -
Liao Wang,
Zhang Yongjun,
Guan Ying,
Zhu X. X.
Publication year - 2011
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/macp.201100137
Subject(s) - rheology , kinetics , polymer , polymer chemistry , ionic strength , chemical engineering , dispersion (optics) , materials science , cloud point , isothermal process , chemistry , thermodynamics , aqueous solution , composite material , physics , quantum mechanics , engineering , optics
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.