Effect of Surfactants in Aqueous Solutions on Oil-Resisting Performance of Membrane Surfaces with Charges by Atomic Force Microscopy

Abstract

The state of the surface of oil droplet can be changed obviously by adding a small amount of surfactant in water. The oil-resisting performance of membranes for water/oil separation has a significant influence on filtration efficiency and life span. The atomic force microscope (AFM) is commonly utilized to explore interface interaction. In this paper, the probe modified by an oil (hexadecane) droplet was used as a force sensor to detect adhesion forces between oil and the charged membranes in fluid. Under low concentration of cationic surfactant in water, the adhesion between oil and the nanofiltration (NF) membrane with negative charges was intensified, increasing from 91.04 nN in pure water to 152.33 nN. On the contrary, the low concentration of anionic surfactant resulted in lower adhesion, which decreased from 5.10 nN in pure water to 3.13 nN in this situation. The measured force behavior agreed well with experimental observation from contact angle measurement. However, the high percentage of ionic active agent caused lower interaction in the above two cases. Moreover, the effect of the nonionic active agent on the adhesion between oil and two kinds of charged membranes was also discussed. Results show that the interaction would be weakened with the aid of the nonionic active agent in water, regardless of the positive or negative charges on the membrane surface. 摘要: 通过在水中加入少量的表面活性剂,可以明显改变油滴表面的状态.油水分离膜的抗油性对过滤实验中的 分离效率和薄膜使用寿命有着重要的影响.原子力显微镜(AFM) 常用于探索界面的相互作用.本文用一个被油滴 (正十六;比)修饰的探针作为力传感器,检测油滴和表面带电荷薄膜在液相环境下两者之间的黎附力.在含有低浓 度的阳离子表面活性剂的溶液中,油滴和纳滤膜(膜表面带负电荷)之间的私附性增强,从在纯水中的 91.04 nN 增加到152.33 nN. 与此相反,低浓度的阴离子表面活性剂导致较低的和附性,从在纯水中的5.10 nN 减小到3.13 nN. 且测得的受力行为与接触角测量的实验观测值较吻合.然而,在上述两者情况下,离子型活性剂的高比例会引 发较低的相互作用.此外,本文也讨论了非离子活性剂对油滴和两种表面带电荷薄膜之间的称附性的影响.结果表 明,在含有非离子型活性剂的溶液中,无论膜表面上所带电荷为正或为负,两者间的相互作用都将被削弱.中图分类号: TB383 文献标志码:A 文章编号: 1672-6030(2018)01-0009-07 Keywords: oil-resisting performance, probe modification, surfactant, adhesion force, 关键词: 抗油性, 探针修饰, 表面活性剂, 站附力