Shyam Sudip, Gaikwad Harshad Sanjay, Ghalib Ahmed Syed Abu, Chakraborty Bibek, Mondal Pranab Kumar
Microfluidcs and Microscale Transport Processes Laboratory, Department of Mechanical Engineering, Indian Institute of Technology Guwahati, Guwahati, Assam 781039, India.
Department of Mechanical Engineering, Tezpur University, Napaam, Tezpur, Assam 781048, India.
Langmuir. 2021 Jan 12;37(1):63-75. doi: 10.1021/acs.langmuir.0c02354. Epub 2020 Dec 23.
We study the spreading dynamics of a sphere-shaped elastic non-Newtonian liquid drop on a spherical substrate in the capillary-driven regime. We use the simplified Phan-Thien-Tanner model to represent the rheology of the elastic non-Newtonian drop. We consider the drop to be a crater on a flat substrate to calculate the viscous dissipation near the contact line. Following the approach compatible with the capillary-viscous force balance, we establish the evolution equation for describing the temporal evolution of the contact line during spreading. We show that the contact line velocity obtained from the theoretical calculation matches well with our experimental observations. Also, as confirmed by the present experimental observations, our analysis deems efficient to capture the phenomenon during the late stage of spreading for which the effect of line tension becomes dominant. An increment in the viscoelastic parameter of the fluid increases the viscous dissipation effect at the contact line. It is seen that the higher dissipation effect leads to an enhancement in the wetting time of the drop on the spherical substrate. Also, we have shown that the elastic nature of the fluid leads to an increment in the dynamic contact angle at any temporal instant as compared to its Newtonian counterpart. Finally, we unveil that the phenomenon of the increasing contact angle results in the time required for the complete wetting of drop, which becomes higher with increasing viscoelasticity of the fluid. This article will fill a gap still affecting the existing literature because of the unavailability of experimental investigations of the spreading of the elastic non-Newtonian drop on a spherical substrate.
我们研究了在毛细驱动状态下，球形弹性非牛顿液滴在球形基底上的铺展动力学。我们使用简化的范 - 田 - 坦纳模型来描述弹性非牛顿液滴的流变学特性。为了计算接触线附近的粘性耗散，我们将液滴视为平基底上的一个凹坑。遵循与毛细 - 粘性力平衡相兼容的方法，我们建立了用于描述铺展过程中接触线时间演化的演化方程。我们表明，理论计算得到的接触线速度与我们的实验观测结果吻合良好。此外，正如当前实验观测所证实的，我们的分析认为能够有效地捕捉铺展后期线张力效应占主导的现象。流体粘弹性参数的增加会增大接触线处的粘性耗散效应。可以看出，更高的耗散效应会导致液滴在球形基底上的润湿时间增加。而且，我们已经表明，与牛顿流体相比，流体的弹性性质会导致在任何时刻动态接触角增大。最后，我们揭示了接触角增大的现象导致液滴完全润湿所需的时间增加，且随着流体粘弹性的增加而变长。由于缺乏弹性非牛顿液滴在球形基底上铺展的实验研究，本文将填补现有文献中仍然存在的一个空白。
