title: Periodic parallel array of nanopillars and nanoholes resulting from colloidal stripes patterned by geometrically confined evaporative self-assembly for unique anisotropic wetting.
abstract: In this paper we present an economical process to create anisotropic microtextures based on periodic parallel stripes of monolayer silica nanoparticles (NPs) patterned by geometrically confined evaporative self-assembly (GCESA). In the GCESA process, a straight meniscus of a colloidal dispersion is initially formed in an opened enclosure, which is composed of two parallel plates bounded by a U-shaped spacer sidewall on three sides with an evaporating outlet on the fourth side. Lateral evaporation of the colloidal dispersion leads to periodic "stick-slip" receding of the meniscus (evaporative front), as triggered by the "coffee-ring" effect, promoting the assembly of silica NPs into periodic parallel stripes. The morphology of stripes can be well controlled by tailoring process variables such as substrate wettability, NP concentration, temperature, and gap height, etc. Furthermore, arrayed patterns of nanopillars or nanoholes are generated on a silicon wafer using the as-prepared colloidal stripes as an etching mask or template. Such arrayed patterns can reveal unique anisotropic wetting properties, which have a large contact angle hysteresis viewing from both the parallel and perpendicular directions in addition to a large wetting anisotropy.
authors.affiliation: Micro- and Nanotechnology Research Center, State Key Laboratory for Manufacturing Systems Engineering, Xi'an Jiaotong University , Xi'an, Shaanxi 710049, China.
authors.forename: Xiangmeng
authors.initials: X
authors.lastname: Li
authors.forename: Chunhui
authors.initials: C
authors.lastname: Wang
authors.forename: Jinyou
authors.initials: J
authors.lastname: Shao
authors.forename: Yucheng
authors.initials: Y
authors.lastname: Ding
authors.forename: Hongmiao
authors.initials: H
authors.lastname: Tian
authors.forename: Xiangming
authors.initials: X
authors.lastname: Li
authors.forename: Li
authors.initials: L
authors.lastname: Wang
keywords: anisotropic wetting; geometrically confined evaporative self-assembly; nanohole array; nanopillar array; silica nanoparticles; stripe patterns