Department of Chemistry, Faculty of Science , Kyushu University , 744 Motooka Nishi-ku, Fukuoka 819-0395 , Japan.
Department of Chemistry , Durham University , Stockton Road , Durham DH1 3LE , U.K.
Langmuir. 2018 May 29;34(21):6205-6209. doi: 10.1021/acs.langmuir.8b01088. Epub 2018 May 15.
Penetration of alkane molecules into the adsorbed film of a cationic surfactant gives rise to a surface freezing transition at the alkane-water interface upon cooling. In this paper, we show that surface freezing of hexadecyltrimethylammonium chloride (CTAC) at the tetradecane-water interface stabilizes oil-in-water (OW) emulsions. For concentrations of CTAC near the critical micelle concentration, an OW emulsion coalesced readily above the surface freezing transition whereas the OW emulsion was stable in the surface frozen state. There was a discontinuous change in the stability of the OW emulsion at a temperature very close to the surface phase transition temperature as determined by interfacial tensiometry and ellipsometry on a planar oil-water interface. The mechanical elasticity of the surface frozen layer opposes film drainage and density fluctuations that could lead to rupture and is the most likely cause of the enhanced emulsion stability.
烷烃分子进入阳离子表面活性剂吸附膜会导致冷却时在烷烃-水界面发生表面冷冻转变。本文表明，十六烷基三甲基氯化铵（CTAC）在十四烷-水界面的表面冷冻稳定了油包水（OW）乳液。在接近临界胶束浓度的 CTAC 浓度下，OW 乳液在表面冷冻转变之上很容易聚结，而在表面冷冻状态下 OW 乳液是稳定的。在通过界面张力仪和椭圆偏振仪在平面油水界面上测定的表面相转变温度附近的一个温度下，OW 乳液的稳定性发生了不连续变化。表面冷冻层的机械弹性阻碍了可能导致破裂的薄膜排水和密度波动，这是增强乳液稳定性的最可能原因。
