Phase behavior and kinetics of phase separation of a nonionic microemulsion of C12E5/water/1-chlorotetradecane upon a temperature quench.
Phase behavior and kinetics of phase separation of a nonionic microemulsion of C12E5/water/1-chlorotetradecane upon a temperature quench.
复制标题
C12E5/水/1-氯十四烷非离子微乳液在温度骤冷时的相行为和相分离动力学。
DOI：
--
复制
发表时间：
2009
影响因子：
3.3
通讯作者：
J. S. Pedersen
中科院分区：
文献类型：
--
作者：
G. Roshan Deen;C. L. Oliveira;J. S. Pedersen
研究了由十二烷基五乙二醇醚（C12 E5）、水和1-氯十四烷组成的三元非离子微乳液模型体系的相行为和相分离动力学。随着温度的升高，微乳液表现出以下富相行为：水包油相（L1+O）、液滴微乳液相（L1）、层状液晶相（L比例）和海绵状（液体）相（L3）。具有0.81的固定表面活性剂与油体积分数比（Phis/Phio）和0.087的液滴体积分数的微乳液通过从L1区域（24 ℃）到不稳定区域L1+O（13 ℃）的温度淬火而从平衡扰动，其中过量油相与微乳液液滴处于平衡。在不稳定区域的相分离的过程中，其次是时间分辨小角X射线散射（TR-SAXS）和时间分辨浊度法。由于TR-SAXS方法可以获得大范围的散射矢量（q=0.004-0.22 A（-1）），因此可以同时研究油滴的生长和由于相分离而导致的微乳液滴的收缩。采用先进的多分散椭球硬球模型，对实验曲线进行了定量分析。微乳液液滴被建模为多分散核壳椭球粒子，使用分子约束，和油滴被建模为多分散球体。由拟合参数得到了油滴的旋转半径、微乳液中油的体积分数和多分散性。在实验的160 min内，微乳液液滴的表面活性剂头部和尾部之间的中性面处的体积当量半径从76 A减小到51 A，而油滴的半径增加到217 A。在温度淬火约48分钟后，系统达到稳定状态，并通过奥斯特瓦尔德熟化以0.51的油在油相中的恒定分数继续粗化，其中Roil比例的幂律依赖性，变量t1/3。通过时间分辨浊度法确定的油滴的大小与TR-SAXS的大小一致，突出了该方法在绝对尺度上确定水包油微乳液的大小的有用性。
The phase behavior and phase separation kinetics of a model ternary nonionic microemulsion system composed of pentaethylene glycol dodecyl ether (C12E5), water, and 1-chlorotetradecane were studied. With increasing temperature, the microemulsion exhibits the following rich phase behavior: oil-in-water phase (L1+O), droplet microemulsion phase (L1), lamellar liquid crystalline phase (Lproportional), and sponge-like (liquid) phase (L3). The microemulsion with a fixed surfactant-to-oil volume fraction ratio (Phis/Phio) of 0.81 and droplet volume fraction of 0.087 was perturbed from equilibrium by a temperature quench from the L1 region (24 degrees C) to an unstable region L1+O (13 degrees C), where the excess oil phase is in equilibrium with the microemulsion droplets. The process of phase separation in the unstable region was followed by time-resolved small-angle X-ray scattering (TR-SAXS) and time-resolved turbidity methods. Due to the large range of scattering vector (q=0.004-0.22 A(-1)) that is possible to access with the TR-SAXS method, the growth of the oil droplets and shrinking of the microemulsion droplets as a result of phase separation could be studied simultaneously. By using an advanced polydisperse ellipsoidal hard-sphere model, the experimental curves have been quantitatively analyzed. The microemulsion droplets were modeled as polydisperse core-shell ellipsoidal particles, using molecular constraints, and the oil droplets are modeled as polydisperse spheres. The radius of gyration (Rg) of the growing oil droplets, volume fraction of oil in the microemulsion droplets, and polydispersity were obtained from the fit parameters. The volume equivalent radius at the neutral plane between the surfactant head and tail of the microemulsion droplet decreased from 76 to 51 A, while the radius of oil drop increased to 217 A within the 160 min of the experiment. After about 48 min from the temperature quench, the system reaches a steady state and continues to coarsen at a constant fraction of the oil of 0.51 in the oil phase by Ostwald ripening with the power law dependence of Roil proportional, variant t1/3. The size of the oil droplets determined by the time-resolved turbidity method is in good agreement with that of the TR-SAXS, highlighting the usefulness of the method in the size determination of oil-in-water microemulsions on an absolute scale.