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We studied a system formed by a mixture of a thermoresponsive negativelycharged graft copolymer (Alg-g-PNIPAAm) with a brush-type structure, and anoppositely charged surfactant (DTAB), in bulk and at the air-solutioninterface. We performed experiments of surface tension, electrophoreticmobility, dynamic and static light scattering and atomic force microscopy inorder to characterize the complexes formed as a function of DTAB concentrationand temperature. We found that these polymer-surfactant complexes are able torespond by changing their sizes, both in bulk and at the air-solutioninterface, when T is increased above the coil-globule transition temperature(LSCT) of the copolymer. However, the thermoresponse was found to be dependenton surfactant concentration, cs: for cs < 2.8 mM, the size of the aggregatesdecreases as T increases but, for cs >= 2.8 mM, the opposite behavior takesplace, i.e. the size increases with T. At the interface, the intensity of theeffect produced on the surface tension by increasing T above LCST diminishescontinuously as cs increases, reducing the ability of the interfacial complexto respond to temperature changes. We studied the stability of aqueous foamsformulated with these mixtures as a function of T and cs. We found that thestability of the foam can be modulated by changing T, but we observed that thiseffect is dependent on the surfactant concentration range. We found acorrelation between changes in the aggregates sizes, the surface tensionbehavior and the responsiveness of foam stability to changes of temperature.

journal of colloid and interface science

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