支链化甜菜碱和阳离子表面活性剂在聚甲基丙烯酸甲酯表面的吸附及其润湿性质

利用座滴法研究了两性离子表面活性剂支链十六烷基(聚氧乙烯)_n醚羟丙基羧酸甜菜碱(n = 0, 3)和阳离子表面活性剂支链十六烷基(聚氧乙烯)_n醚羟丙基季铵盐溶液在聚甲基丙烯酸甲酯(PMMA)表面上的润湿性质,考察了表面活性剂类型、结构及浓度对接触角的影响趋势。研究发现,表面活性剂浓度低于临界胶束浓度(cmc)时,分子通过氢键以平躺的方式吸附到PMMA界面,亲水基团靠近固体界面, PMMA表面被轻微疏水化;表面张力和粘附张力同时降低,导致此阶段接触角随浓度变化不大。浓度高于cmc时,表面活性剂通过疏水作用吸附,亲水基团在外, PMMA表面被明显亲水改性,接触角随浓度升高显著降低。由于具有相同的支链烷基,表面活性剂类型变化和聚氧乙烯基团的引入对接触角影响不大。

Adsorption and Wettability of Branched Betaine and Cationic Surfactants on a Poly(methyl methacrylate) Surface

The wetting properties of the poly(methyl methacrylate) (PMMA) surface by aqueous solutions of the branched zwitterionic surfactants, hexadecanol glycidyl ether glycine betaine and hexadecanol polyoxyethylene(3) glycidyl ether glycine betaine, and branched cationic surfactants, hexadecanol glycidyl ether ammonium chloride and hexadecanol polyoxyethylene (3) glycidyl ether ammonium chloride, were investigated using sessile drop analysis. The influence of the surfactant type, structure, and concentration on contact angle was explored. The results indicate that the PMMA surface was slightly hydrophobically modified with the bulk concentration of surfactant before reaching the critical micelle concentration (cmc) because the adsorbed surfactant molecules are parallel to the substrate surface through hydrogen bonding and the hydrophilic groups are close to the surface. At this stage, the contact angle stays almost constant because of the simultaneous decrease in the surface tension and adhesional tension. However, at concentrations higher than the cmc, the surfactant molecules can adsorb on the PMMA surface through the hydrophobic interactions and the hydrophilic groups toward the bulk phase of solution. This leads to the increase in the hydrophilic character of the PMMA surface. The contact angle decreases dramatically with the increase in bulk surfactant concentration. The variation in the surfactant type and the introduction of ethylene oxide units has little effect on the contact angle because the alkyl chain in these four surfactant molecules is branched in the same way.