Dynamics of Amphiphilic Surfactants Confined in Montmorillonite Slits with Different Cation Exchange Capacities

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• 作者：Georgios Polizos ; Richard A. Vaia ; Hilmar Koerner ; Evangelos Manias
• 刊名：Journal of Physical Chemistry B
• 出版年：2013
• 出版时间：October 31, 2013
• 年：2013
• 卷：117
• 期：43
• 页码：13667-13678
• 全文大小：513K
• 年卷期：v.117,no.43(October 31, 2013)
• ISSN：1520-5207

文摘

Alkylammonium surfactants were nanoscopically confined between montmorillonite layers of varied negative surface charge, i.e., of varied cation exchange capacities. Dielectric relaxation spectroscopy was employed to probe the interfacial dynamics, arising from the mobility of the cations on the silicate surfaces, as a function of the confining walls鈥?surface charge. Standard methods to dry the organo-silicates were employed; however, water was still detected physisorbed in the galleries; the dynamics of these water molecules were also detected and were found to be coupled with the dynamics of the ammoniums at high temperatures. A transition in the mobility of the cations, approximately at 75 掳C (which is in good agreement with the conformational changes of the alkyl groups, reported in the literature), is observed, and a model is proposed on the basis of the dynamics of the confined water. Entropic contributions arising from variation in the surface charge density are also discussed in detail. The existence of water in the interlayer鈥攊n spite of drying the nanofillers in accordance to industrial practices鈥攁nd the interrelated surfactant/water dynamics bring forward important implications for the design and processing of polymer-based nanocomposites based on these fillers.