Wang Ziheng, Servio Phillip, Rey Alejandro D
Department of Chemical Engineering, McGill University, 3610 University St., Montréal, QC H3A 0C5, Canada.
Nanomaterials (Basel). 2022 May 4;12(9):1555. doi: 10.3390/nano12091555.
Surface wrinkling is closely linked to a significant number of surface functionalities such as wetting, structural colour, tribology, frictions, biological growth and more. Given its ubiquity in nature's surfaces and that most material formation processes are driven by self-assembly and self-organization and many are formed by fibrous composites or analogues of liquid crystals, in this work, we extend our previous theory and modeling work on in silico biomimicking nanowrinkling using chiral liquid crystal surface physics by including higher-order anisotropic surface tension nonlinearities. The modeling is based on a compact liquid crystal shape equation containing anisotropic capillary pressures, whose solution predicts a superposition of uniaxial, equibiaxial and biaxial egg carton surfaces with amplitudes dictated by material anchoring energy parameters and by the symmetry of the liquid crystal orientation field. The numerical solutions are validated by analytical solutions. The blending and interaction of egg carton surfaces create surface reliefs whose amplitudes depend on the highest nonlinearity and whose morphology depends on the anchoring coefficient ratio. Targeting specific wrinkling patterns is realized by selecting trajectories on an appropriate parametric space. Finally, given its importance in surface functionalities and applications, the geometric statistics of the patterns up to the fourth order are characterized and connected to the parametric anchoring energy space. We show how to minimize and/or maximize skewness and kurtosis by specific changes in the surface energy anisotropy. Taken together, this paper presents a theory and simulation platform for the design of nano-wrinkled surfaces with targeted surface roughness metrics generated by internal capillary pressures, of interest in the development of biomimetic multifunctional surfaces.
表面起皱与大量表面功能密切相关，如润湿性、结构色、摩擦学、摩擦力、生物生长等等。鉴于其在自然表面中普遍存在，且大多数材料形成过程由自组装和自组织驱动，许多是由纤维复合材料或液晶类似物形成，在这项工作中，我们扩展了之前关于使用手性液晶表面物理进行计算机模拟生物仿生纳米起皱的理论和建模工作，纳入了高阶各向异性表面张力非线性。该建模基于一个包含各向异性毛细管压力的紧凑液晶形状方程，其解预测了单轴、等双轴和双轴蛋盒表面的叠加，其振幅由材料锚定能量参数和液晶取向场的对称性决定。数值解通过解析解进行了验证。蛋盒表面的混合和相互作用产生了表面起伏，其振幅取决于最高非线性，其形态取决于锚定系数比。通过在适当的参数空间上选择轨迹来实现针对特定起皱模式。最后，鉴于其在表面功能和应用中的重要性，对直至四阶的图案几何统计进行了表征，并与参数锚定能量空间相关联。我们展示了如何通过表面能各向异性的特定变化来最小化和/或最大化偏度和峰度。综上所述，本文提出了一个理论和模拟平台，用于设计具有由内部毛细管压力产生的目标表面粗糙度指标的纳米起皱表面，这在仿生多功能表面的开发中具有重要意义。
