分子模拟研究醇醚类表面活性剂耐盐机理

采用分子动力学模拟方法研究十二烷基羧酸钠(sodium dichloroisocyanurate, SDC)与十二烷基醇聚氧乙烯醚羧酸盐(dodecyl alcohol polyoxyethylene ether carboxylate, C₁₂E₃C)在水溶液和盐溶液中的聚集行为,并分析其与钠离子、钙离子之间的相互作用,从分子水平上解释两种表面活性剂的耐盐机理。结果表明在盐溶液中,钙离子与两种表面活性剂形成盐桥结构,降低了表面活性剂的静电作用,使得胶束结合更为紧密;钙离子进入表面活性剂的极性头,改变极性头周围的水化结构。通过分析极性头与离子之间的均力势,发现阳离子与C₁₂E₃C结合所需跨越的能垒高于SDC,在宏观上表现出醇醚羧酸类表面活性剂的耐盐性要高于烷基类羧酸盐。

Salt-tolerant mechanism of alcohol ether carboxylate investigated by molecular dynamics simulation

The aggregation behavior in solution of the surfactants, sodium dichloroisocyanurate(SDC)and dodecyl alcohol polyoxyethylene ether carboxylate(C₁₂E₃C)were investigated by unit-atoms molecular dynamic simulation. Interactions between the surfactants and Na⁺, Ca²⁺ were analyzed, and the salt-tolerant mechanism of srufacants on molecular level were explained. Salt-bridging structure, which reduced the electrostatic interaction of the surfactant micelles, thus led to the closer combination of the micelle, between Ca²⁺ and nearest neighbor headgroup pair in salt solution was observed. Ca²⁺ changed the structure of hydration layers around the headgroup of surfactant. The potential of mean force(PMF)showed that the energy barriers between the headgroup and Ca²⁺ and Na⁺ in the C₁₂E₃C system were higher than those in the SDC system, which indicated that SDC binds the ions more easily than C₁₂E₃C, and the ions have strong influences on SDC system.