层状液晶凝胶对微泡沫的稳定作用

Stabilizing Effect of Lamellar Liquid Crystal Gels on Microfoams

以非离子表面活性剂单硬脂酸甘油酯(GMS)制备出稳定的微泡沫.采用偏光显微镜、冷冻断裂蚀刻透射电子显微镜(FF-TEM)、差示扫描量热仪(DSC)和流变仪对其表面活性剂溶液相态、泡沫体系的微观结构、相变行为和流变性进行研究以探索微泡沫的稳定机理.实验结果表明,表面活性剂分子吸附在气泡界面,发生晶化形成有序、紧密排列的层状液晶凝胶相液膜,该液膜具有较强的刚性,能抵抗由Laplace附加压力驱使的气泡溶解和聚并行为.微泡沫可稳定10个月,无明显的相分离和气泡破裂现象.其稳定作用机理是通过影响泡沫排液过程,增强Gibbs-Marangoni效应,从而提高了气泡液膜强度,减缓了气相扩散速率.

Highly stable microbubble dispersions with mean bubble diameter of less than 100 um were prepared simply by nonionic surfactant of glyceryl monostearate （GMS）. The microstructure, phase transition and rheological properties on these colloidal systems were studied using optical microscopy, freeze fracture transmission electron microscopy（ FF-TEM）, differential scanning calorimetry（DSC） and a controlled stress rheo- meter in an attempt to explore its stabilization mechanisms. The experimental results reveal that the GMS molecules are adsorbed at the air/water interface, which results in the self-aggregate of lamellar liquid crystal gel phase. The rigid lamellar could arrest the Laplace-pressure-driven dissolution due to the ordered and tightly stacking of GMS molecules. The interfacial crystallization as well as the formation of a three-dimensional network of GMS in the continuous phase determines the stability against coalescence behavior of the microbubbles. The stable microbubbles could sustain for more than 10 months without occurrence of phase separation and collapse. It is concluded that the stability of the microfoams prepared solely by GMS surfactant is attributed to the presence of lamellar liquid crystalline gels covered at the gas/liquid interface. The role of liquid crystal gel in stabilizing microfoams can be related to its effect on several mechanisms including hydrodynamic drainage, mechanical strength of the liquid film and the diffusion rate of entrapped gas.