Netsu Sokutei, 35 (4), p. 192, (2008)



Synergism in Cationic Surfactant Mixtures and Counterion Mixing in Adsorbed Films and Micelles Studied by Surface Tension Measurement

表面張力測定の結果をもとにして,(1) 疎水基の鎖長の差を親水基の水和直径と同程度に調整すると,同族列の陽イオン性界面活性剤混合系でも,スタッガード構造形成によって疎水基間相互作用が増大し,混合吸着膜,ならびに混合ミセルにおいて協同効果が発現できること,(2) 更に,片方の界面活性剤の対イオンを交換することで,対イオンの混合エントロピーによって,陰イオン性界面活性剤?非イオン性界面活性剤混合系よりも顕著な協同効果を期待できることが熱力学的に示された。共通イオンが存在しない界面活性剤混合系では原理的に熱力学からは求めることができない界面活性剤イオンと対イオンの界面活性剤集合体中での組成を,(1),(2) の研究で得られた吸着,ならびにミセル形成の剰余ギブスエネルギーを利用して近似的に計算する手法を議論した。
The surface tension measurements revealed that an appropriate coincidence in the difference in the hydrocarbon chain lengths between two surfactants with the hydrated hydrophilic group diameter caused the synergetic adsorption and micelle formation in the aqueous solutions of the mixture of hexadecyltrimethylamonium bromide (HTAB) - dodecyltrimethylammonium bromide (DTAB). This is explained by the theory of the staggered structure formation driven by the strong dispersion interaction between the alkyl chains of different surfactants. Furthermore, it was found that the synergism was considerably strengthened in the mixed system without common ions; hexadecyltrimethylammonium chloride (HTAC) - dodecyltrimethyammonium bromide (DTAB) system by the preferential adsorption of bromide ions over chloride ions onto the adsorbed film and micelle. A useful analytical procedure was developed to evaluate the composition of individual ions in the adsorbed film and micelle and applied to the HTAC-DTAB system.