Wetting of nanogrooved polymer surfaces
Wetting of nanogrooved polymer surfaces
复制标题
DOI：
10.1021/la700558v
复制
发表时间：
2007-07-03
期刊：
影响因子：
3.9
通讯作者：
Pakkanen, Tapani A.
中科院分区：
文献类型：
--
作者：
Hirvi, Janne T.;Pakkanen, Tapani A.
采用分子动力学模拟方法研究了PE和PVC聚合物纳米沟槽表面的润湿性。分析了两种纳米水滴在不同尺度的一维周期性粗糙表面上的接触角、平衡状态和平衡形状。在最粗糙的PE表面上观察到复合固液接触，这在实际应用中是优选的，并且其中液滴停留在表面粗糙体的顶部上，而水填充在PVC表面上的类似但稍深的凹槽。当与平坦表面的接触角达到表观Wenzel和Cassie接触角相等的值时，发生从润湿到复合接触状态的过渡。凹槽PE表面上的液滴与复合接触表现出的接触角与Cassie方程一致，但在更光滑的表面与润湿接触的疏水性的增加小于预期的Wenzel方程。模拟值与理论值之间的差异随着表面沟槽尺寸的增加而减小。由于平坦PVC表面的疏水性较低，在凹槽PVC表面上观察到接触角仅略微增加或甚至略微减小。在这两种聚合物上，纳米液滴在复合接触中呈现球形。在PE表面上的润湿接触中仅观察到较小的各向异性，而在有凹槽的PVC表面上甚至观察到高度各向异性的形状。沿沟槽方向的接触角小于垂直于沟槽方向的接触角，且两者的差值随着水滴尺寸的增大而减小。
Molecular dynamics simulations were used to study the wetting of nanogrooved PE and PVC polymer surfaces. The contact angles, equilibrium states, and equilibrium shapes of two nanosized water droplets were analyzed on surfaces with 1D-arranged periodic roughness of various dimensions. The composite solid-liquid contact, which is preferred in practical applications and in which a droplet rests on top of the surface asperities, was observed on the roughest PE surfaces, whereas water filled the similar but slightly deeper grooves on PVC surfaces. The transition from the wetted to composite contact regime occurred when the contact angle with a flat surface reached the value at which the apparent Wenzel and Cassie contact angles are equal. Droplets on grooved PE surfaces with the composite contact exhibited contact angles in agreement with Cassie's equation, but the increase in hydrophobicity on smoother surfaces with the wetted contact was less than expected from Wenzel's equation. The difference between the simulated and theoretical values decreased as the dimensions of the surface grooves increased. Only a slight increase or even a slight decrease in the contact angles was observed on the grooved PVC surfaces, owing to the less hydrophobic nature of the flat PVC surface. On both polymers, the nanodroplet assumed a spherical shape in the composite contact. Only minor anisotropy was observed in the wetted contact on PE surfaces, whereas even a highly anisotropic shape was seen on the grooved PVC surfaces. The contact angle in the direction of the grooves was smaller than that in the perpendicular direction, and the difference between the two angles decreased with the increasing size of the water droplet.