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

用动态光散射(DLS)和冷冻断口电子显微镜(FFE)研究了油水乳状液中正己烷、环己烷、正辛烷、正十二烷、正十四烷和正十六烷等6种碳氢化合物液滴在无表面活性剂条件下的生长过程。DLS结果表明，随着碳氢链长的增加，液滴尺寸的增长速度减小。例如，正己烷液滴从亚微米到微米液滴在1h内生长，而尺寸为几十纳米的正十六烷液滴在24 h内保持其分散性，根据Lifshitz-Slyosov-Wagner理论和Smoluchowski方程，生长过程被确定为合并和分子扩散(Ostwald成熟)。并用有限元方法对其生长机制进行了详细的分析。通过有限元分析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的油滴(直径约10 nm)，尽管DLS无法检测到这些液滴，这表明正己烷和环己烷等较短碳氢化合物的细滴在制备后很短的时间内通过分子扩散和合并过程生长。

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.