含酰胺键Gemini表面活性剂在氨基酸溶液中的胶束热力学及聚集行为

Aggregation Properties and Thermodynamics of Micellization of Gemini Surfactant with Amido Bond in an Amino Acid Solution

采用两步法合成含酰胺键Gemini表面活性剂Gemini-14,其结构通过磁共振氢谱、红外光谱和元素分析进行鉴定。采用电导法研究该表面活性剂分别在水、L-丙氨酸、L-丝氨酸和L-脯氨酸溶液中的胶束形成热力学和聚集行为。结果表明,温度相同时,加入的氨基酸极性越大,表面活性剂的临界胶束浓度(cmc)值越高,Gemini-14越不易形成胶束;体系相同时,胶束形成的吉布斯自由能(ΔGm)和焓变(ΔHm)均为负值,而ΔSm为正值,为自发放热过程;在同一体系中,293.15～308.15K范围内,ΔGm和cmc的值随着温度升高而升高,而ΔHm和ΔSm随着温度升高而降低;胶束形成过程中存在焓-熵补偿现象。

A novel cationic Gemini surfactant with amide bond(Gemini-14)was synthesized through a simple two-step reactions,and its chemical structure was confirmed by 1H NMR,infrared radiation(IR)and element analysis.The aggregation behavior and thermodynamics of micellization for the Gemini surfactant in pure water,L-alanine,L-serine and L-proline aqueous solutions were measured by conductivity measurements.The results exhibit that the cmc of Gemini-14 increases with an increasing of the polarity for amino acid in the systems at the same temperature,and the process of micellization becomes less favorable.In the same investigated system,both the Gibbs free energy(ΔGm)and enthalpy(ΔHm)for micellization are negative,butΔSmis positive,which indicates that the micellization process is spontaneous and exothermic.At a given temperature(293.15-308.15K)and in the same system,ΔGmand cmc increase with the increasing temperature,whereasΔHmandΔSmdecrease.The enthalpy-entropy compensation for micellization are has been observed in all the studied mixed solvents.