One-Step Preparation of Regular Micropearl Arrays for Two-Direction Controllable Anisotropic Wetting

Abstract

In this paper, one simple method to control two-direction anisotropic wetting by regular micropearl arrays was demonstrated. Various micropearl arrays with large area were rapidly fabricated by a kind of improved laser interference lithography. Specially, we found that the parallel contact angle (CA) theta(2) decreased from 93 degrees to 67 degrees as the intensity ratio of four laser beams increased from 2:1 to 30:1, while the perpendicular CA theta(1) determined by the thickness of the resin remained constant. This was interpreted as the decrease of height variations Delta h from 1100 to 200 nm along the parallel direction caused by the increase of the intensity ratio. According to this rule, both theta(1) and theta(2) could be simultaneously controlled by adjusting the height variation Delta h and the resin thickness. Moreover, by combining appropriate design and low surface energy modification, a natural anisotropic rice leaf exhibiting CAs of 146 degrees +/- 2 degrees/153 degrees +/- 3 degrees could be mimicked by our anisotropic biosurface with the CAs 145 degrees +/- 1 degrees/150 degrees +/- 2 degrees. We believe that these controlled anisotropic biosurfaces will be helpful for designing smart, fluid-controllable interfaces that may be applied in novel microfluidic devices, evaporation-driven micro/nanostructures, and liquid microdroplet directional transfer.

Engineering of Micro‐ and Nanostructured Surfaces with Anisotropic Geometries and Properties

“…For example, controllable anisotropic wetting behavior has been demonstrated on a surface generated by 2 pairs of laser beams by varying intensity ratio between the pairs. [ 40 ] Multiple exposures can also be employed as shown in Figure 4 d. In the case of multi-beam IL, the resultant geometry is governed by the beam arrangement, relative phase differences of the beams, the polarization, the change in the relative phase differences, and the fl uence of the beams. [ 41 , 42 ] Other techniques that use multiple-grating masks [ 43 ] and Diffraction Element Assisted Lithography (DEAL) [ 39 ] can also generate 2D anisotropic surface features, but instead these utilize diffraction phenomena of a single light source.…”

“…(c) "Micropearl" pattern made using 2 pairs of laser beams arranged at right angles. Reproduced with permission, [ 40 ] copyright 2010 ACS. (d) 3D FCC lattice in patterned with double exposure, where the second exposure was phase shifted using two quarter wave plates.…”

Laser interference fabrication of large-area functional periodic structure surface

“…Inspired by the antireflective structure of moth eyes, structural antireflection through manufactured subwavelength structures was proposed by tuning the refractive index from step to gradual (shown in (iii) of Fig. 7(a)) [44][45][46]. Subwavelength periodic nanopillars were fabricated at bottom-emitting OLED windows by soft imprinting of periodic structures, which were fabricated by four-beam interference (shown in (i) and (ii) of Fig.…”

Mechanical stretch for tunable wetting from topological PDMS film

“…Various topographical patterned surfaces to govern anisotropic wetting behavior have been obtained by many micro-and nanofabrication techniques. [19][20][21][22][23] Dynamic tuning of anisotropic wetting on surfaces or switching between isotropic and anisotropic wetting should provide useful methods for liquid handling, droplet transfer, ow valves, and cell alignment. As a typical correlative investigation Chung et al fabricated anisotropic micro-wrinkled surfaces with sinusoidal proles by using ultraviolet-ozone treated PDMS elastomer, on which mechanical compression controlled the anisotropic wetting of droplets.…”