| Micro/nano-scale patterned materials, owing to their unique physical andchemical properties, have been attached great importance and have attracted greatattention for a wide range of applications in several scientific and technological fields,such as microreactors, optical and photonic devices, imformation store devices, andbiological or chemical sensors. The abilities of constructing micro/nano-scalepatterned structure have become the key factors to fabricate new-concept micro/nanodevices and materials. Facing these demond, a great many of conventional orunconventional micromanufacture techniques for the fabrication of micro/nanostructures have been developed rapidly. As one special micro/nano patterned materials,asymmetric microstructured materials have been shown to impart unique anisotropyin their physical and chemical properties, and these properties are of wide interest forapplications including energy conversion, microelectronics, chemical and biologicalsensing, and bioengineering. To date, because of the problem existing in thefabrication of asymmetric microstructured materials, researches in this field are still inits original stage. Currently, most of the asymmetric microstructured materials werefabricated using conventional top-down fabrication techniques, however, thesetechniques are rather costly and time-consuming, this fact greatly restricts the furtherdevelopment and application of the asymmetric microstructured materials.Additionally, based on the bottom-up strategy, it is still very difficult to organizeasymmetric building blocks into ordered arrangment over large areas. Therefore, thedevelopment of facile, lowcost, and effective strategies for controllable fabrication ofasymmetric microstructures is urgently expected in potential applications of anisotropic optical or magnetic devices and chemical or biological sensors.In chapter2, we demonstrate a facile modified micromolding method to fabricatemorphology-controlled elliptical hemisphere arrays (EHAs) by using stretchedpoly(dimethylsiloxane)(PDMS) nanowell arrays as mold. The PDMS nanowell arrayswere fabricated via casting PDMS prepolymer onto two-dimensionalnon-close-packed colloidal sphere arrays. By varying the stretching direction,stretching force, size of the colloidal spheres used and other experimental conditionsin the fabrication process, we can control the shape, aspect ratio and size of theresulting microstructures. Moreover, our method does not involve any costlymicromanufacture technique and can be applied to a great many of materials, such asoil soluble polymer (e.g. polystyrene), water soluble polymer (e.g. poly(vinylpyrrolidone)), cross-link polymer (e.g. photopolymerizable resin) and a variety ofcomposites (e.g. polymer/nanoparticle composite). Anisotropic wetting property ofthese EHAs was demonstrated. Potential application of the EHAs is to provide amodel for fundamental research of anisotropic surfaces and a template or mask for thefabrication of anisotropic surface patterns for potential applications ofshape-dependent optical and magnetic devices.In chapter3, we demonstrated a facile etching method to fabricate siliconelliptical pillar arrays using polystyrene elliptical hemisphere arrays as mask. Theelliptical masks were fabricated via the micromolding method reported in chapter2.By varying the experimental conditions in the fabrication process, the morphology ofthe resulting microstructures can be controlled exactly. Due to the asymmetricmorphology of the elliptical pillar arrays, the as-prepared arrays show uniqueanisotropic surface reflection and anisotropic wetting property. In order to furtherincrease the asymmetry of the Si pillar arrays, the elliptical pillars were turned into“Janus†ones through oblique evaporation deposition of Au and selective chemicalmodification. Owing to the further increased asymmetry, the “Janus†Si-EPA showsmore peculiar anisotropic properties. Further more, based on “Janus†Si-EPAs withunique anisotropic wetting property, we fabricated a one-way-valve for microfluidic system through introducing the “Janus†Si-EPAs into a PDMS microfluidic channel.The valve ability of the “Janus†array was proved by studying the moving behavior ofwater in the T-shaped microchannel. Through investigating the moving behaviorunder different flow rate and liquid pressure, it was found that the “Janus†Si-EPAsmay serve similar as the normally closed elastomeric membrane valve in themicrofluidic system without any other external control parts. Additionally, someinfluence factors of the valve ability are also studied. Finally, the gas-liquid seperationin microfluidic channel is realised based on the as-prepared one-way-valve. Webelieve that the one-way-valve would show potential applications in the futuremicrofluidic chips.In chapter4, a thermo-responsive surface based on PNIPAM/MHA “Janus†Sipillar array was fabricated through combining SI-ATRP, oblique evaperation andselective modification. The as-prepared thermo-responsive “Janus†arrays switchedbetween anisotropic wetting and isotropic wetting when the temperature is above orbelow the LCST of PNIPAM molecule. Moreover, through combining a T-shapedPDMS channel with the “Janus†array and investigating the flowing behavior ofaqueous solution in the microfluidic channel at different temperatures, we found thatthe as-prepared thermo-responsive “Janus†arrays showed great abilities to manipulatethe liquid flowing in the microfluidic system and served as a smart thermo-valve inthe microfluidic channel. Additionally, through introducing infrared lamp to adjust thetemperature of the fluidic system, a further proof-of-concept light-controlled valve ofmicrofluidic system was also established. We believe that our thermo-responsive“Janus†Si-EPAs would show potential applications in the future microfluidic chips.Additionally, it is also expected to fabricate other peculiar microfluidic devices,especially other stimuli-responsive switches, based on the “Janus†Si pillar arraysthrough modifying the surface of the “Janus†Si pillar arrays with otherstimuli-responsive materials.In chapter5, we demonstrate a facile modified colloidal lithography (CL) methodfor the fabrication of morphology-controlled elliptical nanoring arrays (ERAs), which combines template-guided dewetting of polymer film and oxygen reactive ion etching.The elliptical templates were fabricated via a modified micromolding method usingcolloidal nanosphere arrays as the original templates, which were used to guide thedewetting of the polymer film to form ERAs. The height, aspect ratio and size of theresulting arrays could be controlled exactly. Moreover, through etching the underlyingfunctional materials or mixing functional materials into the polymer film, ellipticalring arrays of diferent functional materials could also be fabricated, such as goldERAs, silicon ERAs, ferromagnetic Fe–Ni composite ERAs, Fe3O4ERAs andfluorescent ERAs. A potential application of the as-prepared functional ERAs is toprovide a model for the fundamental research of anisotropic properties of theasymmetric patterned surface arrays and the fabrication of anisotropic surface patternbased devices for potential applications of shape-dependent optical and magneticdevices. |
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