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    Effect of surfactant concentration on the responsiveness of a thermoresponsive copolymer/surfactant mixture with potential application on "Smart" foams formulations

    Year: 2018

    Journal: J. Colloid Interface Sci., Volume 512, FEB 15, page 455–465

    Authors: Soledad Lencina, M. M.; Fernandez Miconi, Eugenio; Fernandez Leyes, Marcos D.; Dominguez, Claudia; Cuenca, Ezequiel; Ritacco, Hernan A.

    Organizations: Universidad Nacional del Sur [PGI-UNS 24/F067]; Agencia Nacional de Promocion Cientifica y Tecnologica (ANPCyT) [2070, 0787]; Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET) [11220130100668CO]; CONICET

    Keywords: Polyelectrolyte-surfactants; Foams; Responsive foams; Surface tension; Surface rheology

    Hypothesis: Previous efforts to formulate smart foams composed of mixtures of PNIPAAm, a thermore-sponsive uncharged polymer, and surfactants have failed because the surfactant displaces the PNIPAAm from the liquid-air interface, removing the thermal responsiveness. We hypothesized that thermoresponsive foams could be formulated with such a mixture if a charged surfactant were used in order to anchor an oppositely charged brush-type polyelectrolyte, for which PNIPAAm could be incorporated as side chains, to the interface. Experiments: A brush-type negatively charged co-polyelectrolyte (Cop-L) with PNIPAAm as side chains was synthetized. Its mixtures with DTAB, a cationic surfactant, in aqueous solution were characterized by dynamic light scattering, surface tension and surface compression viscoelasticity measurements, as a function of both surfactant concentration and temperature. The foam stability and its responsiveness to temperature changes were studied with a homemade apparatus. Findings: The Cop-L/DTAB mixtures were capable of producing thermoresponsive foams but only in a very narrow surfactant concentration (CO range, 0.3 < c(s) < 1.6 mM. The responsiveness is due to a modification of the interfacial compression elasticity induced by conformational changes of the Polyeletrolyt/surfactant aggregates at the interface. This is possible only for c(s) < 1.6 because higher surfactant concentrations induce the polymer collapse at all temperatures, eliminating the thermal responsiveness. (C) 2017 Elsevier Inc. All rights reserved.
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