Direct Photopatterning Research Articles

Colloidal assemblies on patterned silane layers.

The site-selective assembly of colloidal polymer particles onto laterally patterned silane layers was studied as a model system for the object assembly process at mesoscale dimensions. The structured silane monolayers on silicon oxide substrates were fabricated by a combination of liquid- and gas-phase deposition of different trialkoxysilanes with a photolithographic patterning technique. By using this method various types of surface functionalizations such as regions with amino functions next to areas of the bare silica surface or positively charged regions of a quaternary ammonium silane surrounded by a hydrophobic octadecylsilane film could be obtained. Furthermore, a triethoxysilane with a photoprotected amino group was synthesized, which allowed direct photopatterning after monolayer preparation, leading to free NH(2) groups at the irradiated regions. The different silane monolayer patterns were used to study the surface assembly behavior of carboxylated methacrylate particles by optical and scanning electron microscopy. In dependence of the assembly conditions (different surface functionalizations, pH, and drying conditions), a selective preference of the particles for a specific surface type versus others was found. Site-specific colloid adsorption could be observed also on the photosensitive silane layers after local deprotection with light. From the photosensitive silane and positively charged ammonium silane, molecularly mixed monolayers were prepared, which allowed particle adsorption and photoactivation within the same monolayer as shown by fluorescence labeling.

Novel synthesis route to conductive antimony-doped tin dioxide and micro-fabrication method

A novel method for the fabrication of directly photopatternable pure and antimony-doped organo tin polymers via free-radical polymerization is presented. With all synthesized materials, 3 μm feature sizes can be photopatterned by using a mercury I-line UV-lamp. Photopolymerized organo tin films are crystallized by thermal annealing to obtain conductive pure or antimony-doped tin dioxide thin films. The results indicate that the direct photopatterning process increases the conductivity of fabricated films with all Sb-doping concentrations in comparison with the films fabricated without direct photopatterning. The smallest obtained resistivity for the single layer structure was 0.08 Ω cm.

Functional hydrogel structures for autonomous flow control inside microfluidic channels

Hydrogels have been developed to respond to a wide variety of stimuli, but their use in macroscopic systems has been hindered by slow response times (diffusion being the rate-limiting factor governing the swelling process). However, there are many natural examples of chemically driven actuation that rely on short diffusion paths to produce a rapid response. It is therefore expected that scaling down hydrogel objects to the micrometre scale should greatly improve response times. At these scales, stimuli-responsive hydrogels could enhance the capabilities of microfluidic systems by allowing self-regulated flow control. Here we report the fabrication of active hydrogel components inside microchannels via direct photopatterning of a liquid phase. Our approach greatly simplifies system construction and assembly as the functional components are fabricated in situ, and the stimuli-responsive hydrogel components perform both sensing and actuation functions. We demonstrate significantly improved response times (less than 10 seconds) in hydrogel valves capable of autonomous control of local flow.