Effects of Bulk Colloidal Stability on Adsorption Layers of Poly(diallyldimethylammonium Chloride)/Sodium Dodecyl Sulfate at the Air鈥揥ater Interface Studied by Neutron Reflectometry

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• 作者：Richard A. Campbell ; Marianna Yanez Arteta ; Anna Angus-Smyth ; Tommy Nylander ; Imre Varga
• 刊名：Journal of Physical Chemistry B
• 出版年：2011
• 出版时间：December 29, 2011
• 年：2011
• 卷：115
• 期：51
• 页码：15202-15213
• 全文大小：1058K
• 年卷期：v.115,no.51(December 29, 2011)
• ISSN：1520-5207

文摘

We show for the oppositely charged system poly(diallyldimethylammonium chloride)/sodium dodecyl sulfate that the cliff edge peak in its surface tension isotherm results from the comprehensive precipitation of bulk complexes into sediment, leaving a supernatant that is virtually transparent and a depleted adsorption layer at the air/water interface. The aggregation and settling processes take about 3 days to reach completion and occur at bulk compositions around charge neutrality of the complexes which lack long-term colloidal stability. We demonstrate excellent quantitative agreement between the measured surface tension values and a peak calculated from the surface excess of surfactant in the precipitation region measured by neutron reflectometry, using the approximation that there is no polymer left in the liquid phase. The nonequilibrium nature of the system is emphasized by the production of very different interfacial properties from equivalent aged samples that are handled differently. We go on to outline our perspective on the 鈥渢rue equilibrium鈥?state of this intriguing system and conclude with a comment on its practical relevance given that the interfacial properties can be so readily influenced by the handling of kinetically trapped bulk aggregates.