疏水基支链化对甜菜碱表面扩张流变性质的影响

利用悬挂滴方法研究了同分异构的直链(C_(16)PB)和支链(C_(16)GPB)十六烷基羟丙基羧酸甜菜碱的表面扩张流变性质,考察了时间、表面压、工作频率及体相浓度对扩张模量和相角的影响.研究发现,羟丙基甜菜碱分子在溶液表面上吸附时,整个亲水基团倾向于平铺在表面上,造成较高的表面扩张模量,表面膜性质由亲水基团取向变化等膜内过程控制.甜菜碱分子疏水烷基的支链化造成分子间相互作用增强,不仅能增大模量,而且在高浓度条件下出现动态模量的最大值现象,说明表面膜的强度与分子排布密切相关,并非单纯由表面分子浓度决定.

Effect of Branched Hydrophobic Group on the Surface Dilational Rheology of Betaine Surfactants

The surface dilational rheological properties ofisomeric compounds, straight chain(C16PB) and branched chain(C16GPB) hexadecyl hydroxypropyl carboxybetaines were investigated by drop shape analysis.The influences of ageing time, surface pressure, dilational frequency and bulk concentration on surface dilational modulus and phase angle were expounded.It is found that the whole hydrophilic part of betaine molecule inclines to flat on the surface when betaine adsorbs, which will lead to higher dilational modulus.The nature of adsorption film is determined by in-surface processes, such as the variation of orientation of hydrophilic group.The branched hydrophobic alkyl chains of betaine molecules improve the intermolecular interactions, not only results in higher moduli, but causes a maximum in dynamic modulus at high betaine concentration.This result indicates that the strength of surface film is strongly related to molecular arrangement, not simply determined by the surface molecule concentration.