系列离子液体型Gemini咪唑表面活性剂在水溶液中的分子动力学模拟

利用分子动力学模拟方法研究了系列离子液体型Gemini咪唑表面活性剂在水溶液中的表面活性和胶束化能力.模拟结果表明,压力张量法得到的表面张力模拟值偏小,需乘以修正系数矫正;分子动力学模拟得到的临界胶束浓度变化规律与实验相符,可以定性比较不同结构的离子液体型Gemini咪唑分子间的胶束化能力;温度的升高会加剧分子的热运动,不利于离子液体型Gemini咪唑表面活性剂在水溶液中形成胶束;此外,研究还发现联接基不同的离子液体型Gemini咪唑表面活性剂可能遵循不同的胶束化机理.S≤6时,单个分子自组装成胶球后发生聚合形成大胶团.随着咪唑上长烷烃链碳数的增加,Cn-4-Cnim]胶束化能力提高;而随着联接链长度增加,C10-S-C10im]胶束化能力降低;当S>6时,分子联接基弯曲并伸入其它分子烷烃链内部以减小头基分离力,从而形成稳定的胶束或胶团.随着联接基团亚甲基数的增加,头基斥力减小,附加疏水相互作用增强,C10-S-C10im]胶束化能力提高.

Molecular Dynamics Simulation of Ionic Liquid-type Gemini Imidazolium Surfactants in Aqueous Solutions

The surface activity and the ability of micellization of ionic liquid-type Gemini imidazolium surfactants in aqueous solution were investigated by the molecular dynamics simulation.The simulation re-sults indicate that the surface tension calculated from pressure tensor is lower and need to be corrected by multiplying the modified coefficient.The critical micelle concentration calculated by molecular dynamics simulation is consistent with experimental values,and can be used to discriminate the capacity of micelliza-tion of ionic liquid-type Gemini imidazolium surfactants.As the temperature rises,the micellization of ionic liquid-type Gemini imidazolium surfactants becomes more difficult with the aggravation of molecular movement.In addition,we found that ionic liquid-type Gemini imidazolium surfactants with different spacer lengths should follow the various mechanism of micellization.At S≤6,the self-assembly ball of single molecule begin to form the larger micelle.As the carbon atoms of the alkyl chains on the imidazole increase,the formation ability of the micelles of Cn-4-Cnim] is enhanced.But the formation ability of the micelles of C10-S-C10im] decrease with the longer spacer.However,at S>6,one molecule inserts the crooked spacer into the interspace between the alkyl chains of the other molecule which leads to the formation of the larger micelles.Therefore,the micelle formation ability of C10-S-C10im] enhances because the repulsion forces decrease and the hydrophobic interactions become stronger with the spacer lengths increasing.