气相二氧化硅/季铵Gemini表面活性剂稳定的泡沫体系

以zeta电位法研究了季铵Gemini表面活性剂亚甲基-α, ω-双(十二烷基二甲基溴化铵) (12-s-12, s=2, 6)在水溶液中修饰气相二氧化硅(F-SiO₂)粒子。这些粒子随表面活性剂浓度C增加经历了表面从原先的亲水到疏水再重新亲水的改变，其中疏水粒子可以自发吸附在气泡液膜中，从而很好地稳定泡沫。重新亲水的粒子脱附出液膜，仅留下表面活性剂稳定气泡。强的液膜弹性对应于稳定的泡沫。联接链长度影响了Gemini在F-SiO₂粒子表面的吸附，因而也影响了液膜的弹性和对泡沫的稳定。超短s=2联接链的12-2-12由于反离子解离不完全而带有较少的正电荷，在粒子表面的初始吸附弱于12-6-12，但因此减少了吸附分子头基间的静电排斥，可以形成更致密的吸附层。由于12-2-12本身比12-6-12具有更强的界面吸附能力，F-SiO₂粒子和12-2-12的协同作用可以更好地稳定泡沫体系。

Foams Stabilized by Fumed Silica Particles with a Quaternary Ammonium Gemini Surfactant

Fumed silica (F-SiO₂) particles were hydrophobized in situ in aqueous solutions of alkanediyl-α, ω-bis(dodecyldimethylammoniumbromide) (12-s-12, s=2, 6) gemini surfactants. This process was assessed using zeta potential measurements. The particles were found to transit from their original hydrophilic nature to hydrophobic and then back to hydrophilic with increases in the surfactant concentration (C). The hydrophobic particles could spontaneously adsorb at the air/water interface, resulting in significant stabilization of aqueous foams. The re-hydrophilic particles desorbed from the interface, leaving only surfactant molecules to stabilize the foam. The strong interfacial elasticity of the surface films was reflected in the highly stable foams. The length of the surfactant spacer also affected the adsorption of the gemini surfactant on the F-SiO₂ particles, and therefore had an effect on the elasticity of the adsorbed film and the stability of the foam. The 12-2-12 surfactant, having a relatively short spacer, carried less positive charges because of the incomplete dissociation of its counter ions, resulting in less initial adsorption on the F-SiO₂ particles compared with the 12-6-12, but eventually formed a denser monomeric layer because of decreased repulsion between the adsorbed molecules. The 12-2-12 exhibited stronger adsorption at the air/water interface; therefore, the synergistic action of the F-SiO₂ particles together with the 12-2-12 produced better foam stabilization compared with the 12-6-12.