Abstract: Highly stable microbubble dispersions with mean bubble diameter of less than 100 μm 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 rheometer 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.

Key words: Microfoam, Stability, Lamellar liquid crystal, α-Gel, Coagel