Department of Chemical Engineering, Illinois Institute of Technology, Chicago, IL 60616, United States.
J Colloid Interface Sci. 2019 Dec 1;557:591-597. doi: 10.1016/j.jcis.2019.09.057. Epub 2019 Sep 18.
The film meniscus is a capillary system that is part of everyday observed phenomena, such as in foams, emulsions, liquid suspensions of nanoparticles (nanofluids), and liquid-wetting solids. The capillarity of a microscopic free foam lamella with a meniscus is important for a fundamental understanding of the role of the surface forces vs. thickness and stability of dispersed systems. The film-meniscus transition region, known as the Gibbs-Plateau border, and macroscopic contact angle, defined by the extrapolated meniscus Laplace surfaces, are the characteristics of capillary systems that reveal how the surface forces contribute to the stability of the dispersed systems. The foam nanofilm formed from a nanofluid due to nanoparticle self-layering under the film surface confinement thins in a multiple regular stepwise manner (not like soap films) above the CMC. The equilibrium thickness of the nanofilm is governed by the film area rather than the capillary pressure, as was reported for common and Newtonian films. Our video clip shows that the nanofilm thins layer by layer as the film area decreases. Our observation reveals that the nanofilm with a small film area remains at the equilibrium thickness with several layers. An iterative method is proposed to locate the film meniscus contact line. The film-meniscus profile of the transition region is examined using the reflected light interferometry and by applying the two radii of curvature. The micro- and macroscopic contact angles between nanofilm and meniscuses are calculated. The foam nanofilm's structural free energy is calculated vs. the number of layers. The knowledge gained from this research will help to improve the understanding of the dispersion stability of foams, emulsions, and liquid suspensions of nanoparticles.
半月板膜是一种毛细系统，是日常观察到的现象的一部分，如泡沫、乳液、纳米粒子的液体悬浮液（纳米流体）和液体润湿固体。具有半月板的微观自由泡沫薄片的毛细现象对于理解表面力与分散系统的厚度和稳定性的关系至关重要。半月板膜过渡区，称为 Gibbs-Plateau 边界，以及由扩展的半月板 Laplace 表面定义的宏观接触角，是毛细系统的特征，它们揭示了表面力如何有助于分散系统的稳定性。由于纳米粒子在膜表面限制下的自分层，纳米流体形成的泡沫纳米膜在 CMC 以上以多次规则的分步方式（不像肥皂膜）变薄。纳米膜的平衡厚度由膜面积而不是毛细压力控制，这与常见的牛顿膜不同。我们的视频片段显示，随着膜面积的减小，纳米膜逐层变薄。我们的观察结果表明，具有小膜面积的纳米膜在几层时仍保持在平衡厚度。提出了一种迭代方法来定位膜半月板接触线。通过反射光干涉法和应用两个曲率半径来检查过渡区的膜半月板轮廓。计算纳米膜和半月板之间的微观和宏观接触角。计算了泡沫纳米膜的结构自由能与层数的关系。从这项研究中获得的知识将有助于提高对泡沫、乳液和纳米粒子液体悬浮液的分散稳定性的理解。
