表面活性剂在气液界面层性质的DFT理论研究

The DFT Theoretical Study on Properties of Surfactant at Gas and Liquid Interface

在温度273.15 K、压力1.013×10^(5) Pa条件下,该文采用密度泛函理论计算方法,应用Gaussian 03程序B3LYP方法6-31G基组对十二烷基二甲基氧化胺及十二烷基磺酸钠的水合物结构(水分子数n=1~3)进行了全优化计算,从分子水平上研究了在气液界面层中表面活性剂分子与水之间的相互相用,并对界面的形成、稳定性和影响因素进行了分析.分析结果表明:表面活性剂与水分子以氢键形成了稳定的水合物,在水合物中发生明显的电荷从表面活性剂分子向水分子的迁移现象,水合过程体系的吉布斯自由能降低,是一个自发的过程.通过计算水合物的电荷分布规律,对气液界面层表面活性剂分子间相互作用及排布方式进行了理论研究.研究结果表明:表面活性剂疏水基团与亲水基团连接部分带有与亲水基同种电荷,而远离亲水基的一端带有部分负电荷;气液界面层表面活性剂可以通过氢键及静电作用力形成稳定有序的排布.对十二烷基二甲基氧化胺及十二烷基磺酸钠复配协同增效作用进行了理论解释,表面活性剂水合物分子间除了氢键作用外,还存在较强的正负电荷静电作用力,从而提高了其界面稳定性.

Hydrations of dimethyldodecylamine-N-oxide and sodium dodecyl sulfonate are fully optimized calculation at 298 K and 1.013×10^(5) Pa with Gaussian 03 program.Calculations are carried out at the B3LYP/6-31G level using density functional theory.Interaction between surfactant and water molecules(number of water molecules n=1~3)is studied.And the formation,stability and influencing factors of the interface are also analyzed.The results clearly show that Hydrogen-bonded complexes of surfactant are stabile and a significant negative charge transfers from surfactant to water.Hydration of surfactant is spontaneous process.Gibbs energies of surfactant hydrate is reduced.On the basis of this DFT calculation,the charges distribution of hydration are also studied.And theoretical study on interaction and arrangement of surfactant at gas and liquid interface has been carried out.The results show that the hydrophobic part near to hydrophilic groups have like charges as the hydrophilic group,while the end of hydrophobic group far from the hydrophilic group has a partial negative charge.Surfactants can form a stable and ordered arrangement through hydrogen bonding and electrostatic forces in the gas and liquid interface layer.Furthermore,there is a strong positive and negative electrostatic force between the molecules of dodecyl dimethylamine oxide and sodium dodecyl sulfonate hydrate,which has a synergistic effect and improves interface stability.