Zhang Wannian, Zhang Ming-Yuan, Wang Kai, Sun Ruixia, Zhao Shanlin, Zhang Zhiqiang, He Yu-Peng, Yu Fang
Key Laboratory for Functional Material, Educational Department of Liaoning Province, School of Chemical Engineering, University of Science and Technology Liaoning Anshan 114051 P. R. China
State Key Laboratory of Fine Chemicals, Ningbo Institute of Dalian University of Technology No. 26 Yucai Road, Jiangbei District Ningbo 315016 P. R. China
RSC Adv. 2021 Aug 20;11(45):28286-28294. doi: 10.1039/d1ra04669a. eCollection 2021 Aug 16.
Understanding the effect of surfactant structure on their ability to modify interfacial properties is of great scientific and industrial interest. In this work, we have synthesized four amide based ionic surfactants under acidic or basic conditions, including CTHA·HCl, CTEA·HCl, CTHANa and CTEANa. Experiments have proved that the anionic surfactant with polyethylene oxide groups (CTEANa) had the lowest surface tension on the water/-decane interface. Molecular dynamics simulations have been applied to investigate the structural effect on the adsorption behavior of four different surfactants. The surface tension, interface thickness, interface formation energy, density profiles, order parameters, radial distribution function on the water/-decane interfaces were calculated and compared. During the equilibrium states, we found that the interface configuration of two cationic surfactants are almost linear while the two anionic surfactants are changed to bending shapes due to the different positions of the hydrophilic head groups. Further DFT study and wavefunction analysis of surfactants have shown that CTEANa can form stronger vdW interactions with -decane molecules due to a more neutral electrostatic potential distribution. Meanwhile, the introduction of polyethylene oxide groups has offered more H-bonding sites and resulted in more concentrated H-bonding interactions with water molecules. The difference of weak interactions may contribute to the conformational change and finally affect the interface properties of these ionic surfactants.
了解表面活性剂结构对其改变界面性质能力的影响具有重大的科学和工业意义。在这项工作中，我们在酸性或碱性条件下合成了四种酰胺基离子表面活性剂，包括CTHA·HCl、CTEA·HCl、CTHANa和CTEANa。实验证明，带有聚环氧乙烷基团的阴离子表面活性剂（CTEANa）在水/癸烷界面上具有最低的表面张力。分子动力学模拟已被用于研究四种不同表面活性剂的结构对吸附行为的影响。计算并比较了水/癸烷界面上的表面张力、界面厚度、界面形成能、密度分布、序参量、径向分布函数。在平衡状态下，我们发现两种阳离子表面活性剂的界面构型几乎是线性的，而两种阴离子表面活性剂由于亲水头基位置的不同而变为弯曲形状。进一步的DFT研究和表面活性剂的波函数分析表明，由于更中性的静电势分布，CTEANa可以与癸烷分子形成更强的范德华相互作用。同时，聚环氧乙烷基团的引入提供了更多的氢键位点，并导致与水分子形成更集中的氢键相互作用。弱相互作用的差异可能导致构象变化，最终影响这些离子表面活性剂的界面性质。
