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The dynamics of aqueous crosslinked poly( N ‐isopropyl‐acrylamide) microgel particles under good solvency conditions
Author(s) -
Zhu Peng Wei,
Napper Donald H.
Publication year - 1999
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/(sici)1521-3935(19990401)200:4<783::aid-macp783>3.0.co;2-j
Subject(s) - aqueous solution , dynamic light scattering , relaxation (psychology) , polymer chemistry , lower critical solution temperature , chemistry , activation energy , atmospheric temperature range , exponential decay , exponent , thermodynamics , materials science , analytical chemistry (journal) , polymer , nanoparticle , nanotechnology , copolymer , chromatography , organic chemistry , psychology , social psychology , linguistics , physics , philosophy , nuclear physics
From a dynamic light scattering study of the concentration and temperature dependencies of weakly crosslinked poly( N ‐isopropylacrylamide) (PNIPAM) microgel particles in aqueous solutions it was found that the decay of the time correlation function is markedly slowed down with increasing microgel concentration and with decreasing temperature. The microgel particles exhibit an exponential decay in very dilute solutions or at higher temperatures; this changes to a stretched exponential at higher concentrations or at lower temperatures. The observed slowing down occurrs over a relatively narrow concentration range, which has not been observed in some corresponding systems consisting of hard spheres. The time correlation function data were analyzed with the aid of a coupling model. The relaxation time that was calculated from this model increases with increasing concentration by a power law ( τ ∝ c 2.6 ) in higher concentration or with decreasing temperature, the result that is physically in accord with the change in the value of the stretched exponent. A wave vector dependence of the relaxation time was observed. The results have been interpreted as arising from the formation of neighboring cages of the microgel particles. Over the concentration range studied, the apparent activation energy of the relaxation processes operating in the cage structures was found initially to increase with increasing microgel concentration and then to approach a plateau value.