季铵盐型双子表面活性剂与十八醇的混合单分子膜

研究了双子表面活性剂12-2-16和12-2-12分别与十八醇(C18H37OH)在空气-水界面上混合单分子膜的π-A等温线. 在相分离表面压以下, 比较了不同表面压下和不同混合比单分子膜的混合表面过剩自由能ΔGMexo, 分析了双子表面活性剂与脂肪醇在空气-水界面上混合膜中的相容性. 结果表明, 12-2-16与C18H37OH在所有混合摩尔比下随着表面压增高, 自由能增大. 12-2-12与C18H37OH混合膜体系的相容性取决于两者的混合比, ΔGMexo随所加入C18H37OH摩尔分数的增加逐渐增大, 从异种分子间净的吸引作用转变到相互排斥作用体系, 转变点为C18H37OH加入量的摩尔分数0.65. 当混合为热力学自发过程时, 增大表面压将有利于混合; 而对相互排斥体系, 增加表面压将使体系内异种分子之间的相互排斥作用更大.

Mixed Monolayers of Quaternary Ammonium Gemini Surfactants with Octadecyl Alcohol

π-A isotherms were studied for mixed monolayers formed from each of two cationic gemini surfactants(dissymmetrical gemini surfactant 12-2-16 and symmetrical gemini surfactant 12-2-12) with octadecyl alcohol(C18H37OH) on air-water interface. The mixed surface excess free energy, ΔGMexo, was analyzed for each mixed monolayer with various mixed molar ratios at different surface pressures under the point of phase separation, to analyze the compatibility of each of the gimini surfactants and the fatty alcohol in the monolayer. The results show that ΔGMexo changes with the nature of the mixed molecules, mixed molar ratio, and surface pressure. Mixed monolayers of 12-2-16 and C18H37OH were considered as incompatible because ΔGMexo>0 in all mixed molar ratios. While for a system where 12-2-12 is mixed with C18H37OH, the compatibility of the mixed monolayer lies mostly on the mixed molar ratio. The values of ΔGMexo augment with increasing the C18H37OH molar ratio, changing from a net attractive interaction to a net repulsive interaction between 12-2-12 and C18H37OH with a critical point of C18H37OH molar ratio 0.65 added in the mixed system. When the mixing system is thermodynamically favored, increasing surface pressure will promote the mixing; In contrast, increasing surface pressure for a repulsive mixed system will be more thermodynamically unfavorable.