Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
J Chem Phys. 2009 Sep 7;131(9):094508. doi: 10.1063/1.3212002.
We consider the condensation transition of microemulsion droplets of oil which are dispersed in water in the presence of surfactant. Since a macroscopic oil phase is formed due to this transition, it is called "emulsification failure." Based on the free energy approach, we determine the transition lines between the spherical and the cylindrical droplet phases as well as the phase boundary lines of the emulsification failure. The phase diagrams are calculated by changing the physical properties of the surfactant monolayer such as the saddle-splay modulus and the spontaneous curvature. For a negative saddle-splay modulus, the spherical droplet phase coexists with the excess oil phase. In some cases, a re-entrant transition (sphere-->cylinder-->sphere) is expected to take place. For a positive saddle-splay modulus, the system undergoes a direct transition from the cylindrical droplet phase to the macroscopically phase separated state. The sphere-to-cylinder transition line approaches the emulsification failure boundary as the saddle-splay modulus becomes larger.
我们研究了在表面活性剂存在下分散在水中的油微乳液滴的冷凝相变。由于这种转变会形成宏观油相，因此它被称为“乳化失败”。基于自由能方法，我们确定了球形和圆柱形液滴相之间的转变线以及乳化失败的相界线。通过改变表面活性剂单层的物理性质，如鞍形弯曲弹性模量和自发曲率，计算了相图。对于负的鞍形弯曲弹性模量，球形液滴相与过量油相共存。在某些情况下，预计会发生再入转变（球体->圆柱->球体）。对于正的鞍形弯曲弹性模量，系统会从圆柱形液滴相直接转变为宏观相分离状态。随着鞍形弯曲弹性模量的增大，球体到圆柱的转变线趋近于乳化失败边界。
