Mahawar Pankaj, Praveena M, Bhuyan Shreyanil, Pillai Dipin S, Chandran Sivasurender
Soft and Biological Matter Laboratory, Department of Physics, Indian Institute of Technology Kanpur, Kanpur 208016, India.
Department of Chemical Engineering, Indian Institute of Technology Kanpur, Kanpur 208016, India.
ACS Polym Au. 2024 May 13;4(4):302-310. doi: 10.1021/acspolymersau.4c00018. eCollection 2024 Aug 14.
Pattern formation during solution evaporation is common in several industrial settings and involves a complex interplay of multiple processes, including wetting/dewetting, diffusion, and rheological characteristics of the solution. Monitoring the emergence of patterns during evaporation under controlled conditions may allow deconvolution of different processes and, in turn, improve our understanding of this common yet complex phenomenon. Here, we probe the importance of initial conditions, defined by the solution concentration , on the pattern formation in evaporating polymer solutions on the air-water interface. Intriguingly, the initial decrease in the lateral length scale (ξ), characterizing the patterns, takes an upturn at higher concentrations, revealing reentrant behavior. We employ a gradient dynamics model consisting of coupled evolution equations for the film height and the polymer fraction in the solution. Our simulations capture two different length scales revealing the reasons underlying the re-entrant behavior of ξ( ). While the long-range destabilizing interactions between suspension and water result in the dewetting of thin film solutions, the phase separation between the polymer and solvent occurs at shorter length scales. Our results demonstrate the importance of initial concentration on pattern formation and, thereby, on the resultant properties of thin polymer films.
溶液蒸发过程中的图案形成在多个工业场景中很常见，涉及多个过程的复杂相互作用，包括溶液的润湿/去湿、扩散和流变特性。在受控条件下监测蒸发过程中图案的出现，可能有助于对不同过程进行反卷积分析，进而增进我们对这种常见但复杂现象的理解。在此，我们探究由溶液浓度定义的初始条件对空气-水界面上蒸发聚合物溶液中图案形成的重要性。有趣的是，表征图案的横向长度尺度（ξ）最初的减小在较高浓度时出现回升，呈现出折返行为。我们采用了一个梯度动力学模型，该模型由薄膜高度和溶液中聚合物分数的耦合演化方程组成。我们的模拟捕捉到了两个不同的长度尺度，揭示了ξ（ ）折返行为背后的原因。虽然悬浮液与水之间的长程不稳定相互作用导致薄膜溶液去湿，但聚合物与溶剂之间的相分离发生在较短的长度尺度上。我们的结果证明了初始浓度对图案形成的重要性，进而对所得聚合物薄膜的性能也很重要。
