液滴在仿"鸡皮疙瘩"表面的摩擦力动态调控

目的 利用机械拉伸和松弛在仿"鸡皮疙瘩"表面实现不同粗糙度的动态调控,并且利用毛细管投影传感技术(MPCP)定量表征液滴在仿"鸡皮疙瘩"表面的摩擦力,揭示液滴在固体表面的详细运动特征.方法 模仿人体鸡皮疙瘩现象,制备了混有聚苯乙烯(PS)小球的聚二甲基硅氧烷(PDMS)仿生表面,利用机械拉伸和松弛,动态调控表面微结构,实现了对表面微观结构不同粗糙度的可逆调控.同时,利用毛细管投影传感技术,定量表征了液滴在平面和条纹结构表面的摩擦力,详细讨论了两种表面在不同拉伸状态下的拉伸量与拉伸方向、液滴体积和移动速度对液固界面摩擦力的影响规律.结果 随着样品延伸率的增大,PDMS表面突出的PS小球数量更多、高度更大,使表面粗糙度增大,从而减小了摩擦力.但在拉伸方向(DS)和垂直方向(DV)的摩擦力大小不同,表现出各向异性.随着液滴尺寸增大,DS和DV两个方向的摩擦力也增大.在测试范围内,液滴的移动速度对液固界面摩擦力的影响可以忽略不计.结论 利用PS小球/PDMS混合物制备的模仿人体"鸡皮疙瘩"现象的仿生表面,由于模量差异,在外力拉伸下,PS小球突出表面,导致表面粗糙度增大,模仿了人体的"鸡皮疙瘩"应激反应.移除拉力,"鸡皮疙瘩"消失,实现了表面粗糙度的可逆调控.用毛细管投影传感技术定量表征固体表面的摩擦力,揭示了滚动角测试所无法揭示的液固界面作用规律.

The Dynamic Regulation of Friction Force of a Water Droplet on Goose Bumps-inspired Surfaces

In this paper, mechanical stretching and relaxation are used to realize the dynamic control of the roughness of goose bumps-inspired surfaces, and capillary projection sensing technology (MPCP) is used to quantitatively characterize the friction force of droplets on simulated goose bumps, revealing the detailed motion characteristics of droplets on solid surfaces. The surface of polydimethylsiloxane (PDMS) mixed with polystyrene (PS) beads is prepared to imitate the goose bumps of human body. Due to the difference of modulus, PS beads protrude from the surface under external tension, which leads to the increase of surface roughness and mimics the stress response of goose bumps in human body. When the tension is removed, "goose bumps" disappear. The reversible adjustment of the roughness of surface microstructure is thus realized. At the same time, capillary projection sensing technology is used to quantitatively characterize the friction force of liquid droplets on planar and striped surfaces, and the effects of stretching amount, stretching direction, droplet volume and moving speed on the friction force of liquid-solid interface are discussed in detail. With the increase of stvetching, the number and height of PS beads protruding from PDMS surface increases, which increases the surface roughness and reduces the friction force. However, the frictional forces in the stretching direction (DS) and the vertical direction (DV) are different, showing anisotropy. With the increase of droplet size, the frictions in DS and DV directions increase. In the test range, the influence of droplet moving speed on the friction force of liquid-solid interface can be neglected. The friction force of solid surface is quantitatively characterized by capillary projection sensing technology, which reveals the function law of liquid-solid interface that could not be revealed by rolling angle test.