Kargupta Kajari, Sharma Ashutosh
Department of Chemical Engineering, Indian Institute of Technology, Kanpur, 208016, India.
J Colloid Interface Sci. 2002 Jan 1;245(1):99-115. doi: 10.1006/jcis.2001.7860.
Spontaneous formation of locally ordered patterns during dewetting of thin films on homogeneous and heterogeneous substrates is investigated based on the 3-D nonlinear equation of motion. Physicochemical heterogeneities engender the rapid formation of the primary holes that serve as "seeds" for the formation of locally ordered structures. The secondary multiring structure surrounding the primary hole evolves by one of the following two different pathways depending on the film thickness vis-à-vis the location of the minimum in the spinodal curve: (A) Thick films evolve by the formation of secondary satellite holes that originate from a ring-like depression behind the rim of the primary hole. The process of ordering is repeated until the true spinodal holes appear on the remaining substrate. (B) Ordering in a relatively thin film occurs by the formation of droplets caused by the disintegration of the elevated rim that surrounds the primary hole. The radial distance between the successive ordered layers is close to the spinodal length scale, lambda(m). Droplets within the same layer are separated by a distance slightly greater than lambda(m), whereas holes within the same layer are separated by a distance slightly less than lambda(m). The number density of holes or droplets in the ordered pattern is of the same order as the predictions of the spinodal theory. The number of ordered layers and the size of the locally ordered domain depend significantly on the relative magnitudes of the time scales for the following events: (1) formation of the primary hole, (2) growth of holes (inverse of hole-growth velocity), (3) formation of a secondary feature (hole or droplet) adjacent to the primary hole, (4) true spinodal rupture far from the primary hole. The morphology of an ordered structure can therefore be tailored by modulation of the film thickness and the short- and long-range intermolecular interactions (substrate surface properties), since these affect the time scales 1 to 4 in different ways.
基于三维非线性运动方程，研究了均匀和非均匀基底上薄膜去湿过程中局部有序图案的自发形成。物理化学不均匀性导致初级孔洞迅速形成，这些孔洞成为局部有序结构形成的“种子”。围绕初级孔洞的二级多环结构通过以下两种不同途径之一演化，这取决于薄膜厚度与旋节线曲线最小值位置的相对关系：(A) 厚膜通过形成二级卫星孔洞演化，这些卫星孔洞起源于初级孔洞边缘后方的环状凹陷。有序化过程不断重复，直到真正的旋节孔洞出现在剩余基底上。(B) 相对较薄的薄膜中的有序化是由围绕初级孔洞的凸起边缘解体形成液滴而产生的。连续有序层之间的径向距离接近旋节长度尺度λ(m)。同一层内的液滴之间的距离略大于λ(m)，而同一层内的孔洞之间的距离略小于λ(m)。有序图案中孔洞或液滴的数密度与旋节理论的预测值处于同一量级。有序层数和局部有序域的大小显著取决于以下事件时间尺度的相对大小：(1) 初级孔洞的形成，(2) 孔洞的生长（孔洞生长速度的倒数），(3) 与初级孔洞相邻的二级特征（孔洞或液滴）的形成，(4) 远离初级孔洞的真正旋节破裂。因此，有序结构的形态可以通过调节薄膜厚度以及短程和长程分子间相互作用（基底表面性质）来定制，因为这些因素以不同方式影响时间尺度1至4。
