Significance of glass transition temperature to polymer latex stabilisation by nonionic surfactants |
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Authors: | Z. Haq L. Thompson |
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Affiliation: | 1. Unilever Research Laboratory, Port Sunlight, Merseyside
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Abstract: | Equilibrium colloid stability measurements with nonionic surfactant (C12E8) stabilised polybutyl methacrylate (PBMA) latex dispersions indicate a sudden temperature induced destabilisation coinciding with the glass transition temperature,Tg, of the polymer. In control experiments with polystyrene latex particles of similar size, for whichTg was not approached, the flocculation temperature was significantly higher. The effect is interpreted in terms of a reduced adsorbed layer thickness aboveTg caused by mixing of part of the surfactant molecule with the polymer. This interpretation is supported by DSC, elastic modulus and mechanical damping measurements on films made from dispersions of the same latex containing commercial nonionic surfactants. These measurements indicate a shift inTg in the presence of surfactant consistent with partial penetration of the polymer surface by the surfactant. In addition, C12E8 adsorption measurements show increased adsorption (or absorption) onto PBMA aboveTg which is irreversible on both dilution and temperature reduction. |
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