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Shear Induced Demixing and Rheological Behavior of Aqueous Solutions of Poly( N ‐isopropylacrylamide)
Author(s) -
Badiger Manohar V.,
Wolf Bernhard A.
Publication year - 2003
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.200390026
Subject(s) - rheology , aqueous solution , lower critical solution temperature , shear rate , poly(n isopropylacrylamide) , polymer , shear (geology) , cloud point , thermodynamics , transmittance , materials science , phase (matter) , chemistry , polymer chemistry , composite material , organic chemistry , copolymer , optoelectronics , physics
The interrelation between the phase separation behavior and the rheological performance of aqueous solutions of high molecular weight ( M w = 1 600 kg/mol) poly( N ‐isopropylacrylamide) was investigated. The system demixes upon heating and the cloud point temperature, T cp decreases steadily with rising polymer concentration up to 10 wt.‐%. The application of shear supports phase separation and reduces T cp markedly. This observation is interpreted in terms of destruction of intersegmental clusters formed in the quiescent state owing to favorable interactions. Intrinsic viscosities and Huggins coefficients as well as the viscosities, η at higher polymer concentrations are closely connected with the thermodynamic conditions. [ η ] decreases by almost two orders of magnitude upon heating, whereas the corresponding increase of k H is less pronounced. The η values (constant shear rate) of the moderately concentrated solutions as function of T pass a maximum at the corresponding phase separation temperatures. The existence of clusters also manifests in terms of stress overshoot and of particularities observed with solutions that are sheared for the first time.Transmittance (ratio of intensities of the transmitted light and the incidence light) of a 2.0 wt.‐% PNIPAm solution in water as a function of temperature at different shear rates indicated. Heating rate is 0.22 °C/min.