Lim Sangwook, Horiuchi Hiroki, Nikolov Alex D, Wasan Darsh
Department of Chemical and Biological Engineering, Illinois Institute of Technology, Chicago, Illinois 60616, United States.
Langmuir. 2015 Jun 2;31(21):5827-35. doi: 10.1021/acs.langmuir.5b00799. Epub 2015 May 21.
We report the results of our studies on the changes in the contact angle and interfacial tension using a nanofluid composed of silica nanoparticles dispersed in water on three different solid substrates: gold (partially hydrophobic), glass (hydrophilic), and a silicon wafer (hydrophilic). We used both the goniometric method and drop-shape analysis to make the measurements. On the basis of the results of the drop-shape analysis using the Laplace equation, we evaluated the contributions of the interfacial tension change to the equilibrium contact angle and the presence of nanoparticles near the solid substrate, thereby elucidating the change in the wettability of the solid substrate. We found that the nanoparticles decrease the contact angle of the substrate with the increase in the nanoparticle concentration. To rationalize our experimental observations on the decrease in the contact angle of the solid substrate in the presence of nanoparticles, we calculated the surface volume fraction of the nanoparticles in the layer near the solid substrate using the particle layering model (based on the nanoparticles' excluded volume effect). We found that the volume fraction of the nanoparticles in the layer close to the substrate increased with an increase in the nanoparticle volume fraction in the bulk and correlated qualitatively with the change in the substrate wettability. The extent of the wettability alteration depends on the volume fraction of the nanoparticles, their size, and the type of substrate. We found a strong correlation between the change in the substrate wettability and the nanoparticle volume fraction in the layer closer to the substrate surface.
我们报告了关于接触角和界面张力变化的研究结果。该研究使用了一种由分散在水中的二氧化硅纳米颗粒组成的纳米流体，作用于三种不同的固体基材：金（部分疏水）、玻璃（亲水）和硅片（亲水）。我们使用测角法和液滴形状分析法进行测量。基于使用拉普拉斯方程的液滴形状分析结果，我们评估了界面张力变化对平衡接触角的贡献以及固体基材附近纳米颗粒的存在情况，从而阐明了固体基材润湿性的变化。我们发现，随着纳米颗粒浓度的增加，纳米颗粒会减小基材的接触角。为了合理解释我们在存在纳米颗粒时固体基材接触角减小的实验观察结果，我们使用颗粒分层模型（基于纳米颗粒的排除体积效应）计算了固体基材附近层中纳米颗粒的表面体积分数。我们发现，靠近基材的层中纳米颗粒的体积分数随着本体中纳米颗粒体积分数的增加而增加，并且与基材润湿性的变化定性相关。润湿性改变的程度取决于纳米颗粒的体积分数、它们的尺寸以及基材的类型。我们发现基材润湿性的变化与更靠近基材表面的层中纳米颗粒的体积分数之间存在很强的相关性。
