Stabilization of Surfactant-Free Emulsion and its Application for Novel Reaction Field

采用动态光散射（DLS）和冷冻断裂电子显微镜（FFEM）研究了无表面活性剂条件下油/水乳液中烃类液滴（06-016：正己烷、环己烷、正辛烷、正癸烷、正十二烷、正十四烷和正十六烷）的生长过程。DLS结果表明，随着烃链长度的增加，液滴尺寸的增长速度减小。例如，正己烷液滴在1小时内从亚微米级生长到微米级，而几十纳米大小的正十六烷液滴在24小时内保持分散性。根据Lifshitz-Slyozov-Wagner理论和Smoluchowski方程确定其生长过程为聚结和分子扩散（Ostwald成熟）。此外，利用FFEM对其生长机理进行了详细的研究。通过FFEM对正己烷和环己烷液滴的直接成像，我们可以观察到非常细小的油滴（直径约为10 nm），而DLS无法检测到这些油滴，这表明正己烷和环己烷等较短的碳氢化合物在制备后很短的时间内通过分子扩散和聚结过程生长出了细小的油滴。

Growth processes of hydrocarbon droplets (06-016: n-hexane, cyclohexane, n-octane, n-decane, n-dodecane, n-tetradecane, and n-hexadecane) in oil/water emulsions under surf actant-free conditions were examined by dynamic light scattering (DLS) and freeze-fracture electron microscopy (FFEM). DLS results showed that the growth rate of droplet size decreased with, increase in hydrocarbon chain length. For example, n-hexane droplets grew within 1 h from submicrometer to micrometer droplets, while n-hexadecane droplets with sizes of several tens of nanometers kept their dispersibility for 24 h. The growth processes were determined as coalescence and molecular diffusion (Ostwald ripening) in terms of the Lifshitz-Slyozov-Wagner theory and the Smoluchowski equation. Furthermore, FFEM was used to examine the growth mechanism in detail. Direct imaging of n-hexane and cyclohexane droplets by FFEM allowed us to observe very fine oil droplets (ca.10 nm in diameter) though DLS could not detect these droplets, suggesting that fine droplets of shorter hydrocarbons such as n-hexane and cyclohexane grow via both molecular diffusion and coalescence processes in a very short time after preparation.