Preparation of silica-on-titania patterns with a wettability contrast

Simple and Scalable Chemical Surface Patterning via Direct Deposition from Immobilized Plasma Filaments in a Dielectric Barrier Discharge

In this work, immobilization of the often unwanted filaments in dielectric barrier discharges (DBD) is achieved and used for one-step deposition of patterned coatings. By texturing one of the dielectric surfaces, a discharge containing stationary plasma filaments is ignited in a mix of argon and propargyl methacrylate (PMA) in a reactor operating at atmospheric pressure. From PMA, hydrophobic and hydrophilic chemical and topographical contrasts at sub-millimeter scale are obtained on silicon and glass substrates. Chemical and physical characterizations of the samples are performed by micrometer-scale X-ray photoelectron spectroscopy and infrared imaging and by water contact angle and profilometry, respectively. From the latter and additional information from high-speed imaging of the plasma phase and electrical measurements, it is suggested that filaments, denser in energetic species, lead to higher deposition rate with higher fragmentation of the precursor, while surface discharges igniting outwards the filaments are leading to smoother and slower deposition. This work opens a new route for a one-step large-area chemical and morphological patterning of surfaces at sub-millimeter scales. Moreover, the possibility to separately deposit coatings from filaments and the surrounding plasma phase can be helpful to better understand the processes occurring during plasma polymerization in filamentary DBD.

Self-assembly patterning of ultrafine zirconia nanocrystal films fabricated on chemically patterned templates

Ultra-thin zirconia (ZrO₂) nanocrystal films were fabricated by using a controlled dip-coating process. ZrO₂ nanocrystals possess a cubic crystalline phase and large surface-to-volume area. The film composite with only several layers of nanocrystals were obtained by controlling the withdrawal speed and mass concentration of the colloidal solution. The optical properties of ZrO₂ nanocrystal films were accessed by UV-vis spectroscopy, which indicated the dense and uniform structure of the nanocrystal films. The high reflection index suggested that the films could be used in the reflection coating industry. Furthermore, a micro-pattern of self-assembled monolayers of silane molecular was used as a chemical mold for selective deposition of ZrO₂ nanocrystals. As a result, a self-assembly patterning of ZrO₂ nanocrystals with a neat edge was fabricated on silicon substrate. The low-cost fabricating method is compatible with conventional very-large-scale integration processes and can be extended to other kinds of nanocrystals.

Surface-modification of poly(dimethylsiloxane) membrane with self-assembled monolayers for alcohol permselective pervaporation

The use of self-assembled monolayers (SAMs) has recently been recognized as an effective way to tailor the surface properties of films used in various applications. However, application of SAMs in the preparation of separation membranes remains unexplored. In the present study, surface-modified poly(dimethylsiloxane) (PDMS) membranes were prepared using SAMs to fabricate a membrane for use in pervaporation separation of ethanol/water mixtures. A cross-linked PDMS/polysulfone (PSf) composite membrane was transformed by introducing hydroxyl functionalities on the PDMS surface through a UV/ozone conversion process. (Tridecafluoroctyl)triethoxysilane was allowed to be adsorbed on the resulting Si-OH substrate to increase the hydrophobicity of the membrane. Results from Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectrometry, atomic force microscopy, and contact angle analyses suggest that the fluoroalkylsilane monolayer was successfully formed on the modified PDMS/PSf membrane treated by 60 min UV/ozone exposure. The newly SAM-modified membrane exhibited a separation factor of 13.1 and a permeate flux of 412.9 g/(m(2) h), which are higher than those obtained from PDMS membranes.

Bioinspired steel surfaces with extreme wettability contrast

The exterior structures of natural organisms have continuously evolved by controlling wettability, such as the Namib Desert beetle, whose back has hydrophilic/hydrophobic contrast for water harvesting by mist condensation in dry desert environments, and some plant leaves that have hierarchical micro/nanostructures to collect or repel liquid water. In this work, we have provided a method for wettability contrast on alloy steels by both nano-flake or needle patterns and tuning of the surface energy. Steels were provided with hierarchical micro/nanostructures of Fe oxides by fluorination and by a subsequent catalytic reaction of fluorine ions on the steel surfaces in water. A hydrophobic material was deposited on the structured surfaces, rendering superhydrophobicity. Plasma oxidization induces the formation of superhydrophilic surfaces on selective regions surrounded by superhydrophobic surfaces. We show that wettability contrast surfaces align liquid water within patterned hydrophilic regions during the condensation process. Furthermore, this method could have a greater potential to align other liquids or living cells.

Constructing metal-based structures on nanopatterned etched silicon

Silicon surfaces with nanoscale etched patterns were obtained using polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) block copolymer films as templates, followed by brief immersion in HF(aq). The resulting interfaces were comprised of pseudohexagonal arrays of pits on the silicon, whose shapes depended upon the chosen silicon orientation. The top unetched face of silicon remains capped by the native oxide, and the pit interiors are terminated by Si-H(x). Selective chemical functionalization via these two chemical handles was demonstrated to be a viable approach toward building nanostructured metal oxide and metal features within these silicon pits and on the top face. Using a series of interfacial chemical reactions, including oxidation (of Si-H(x)-terminated regions), hydrosilylation, and alkoxysilane-based chemistry on silicon oxide, the growth of metal-based structures can be spatially controlled. In the first approach, titania nanobowls were grown within the etch pits, and in the second, galvanic displacement was used to produce gold nanoparticles either within the etch pits, on the top silicon face, or both.

Surface patterning of bonded microfluidic channels

Microfluidic channels in which multiple chemical and biological processes can be integrated into a single chip have provided a suitable platform for high throughput screening, chemical synthesis, detection, and alike. These microchips generally exhibit a homogeneous surface chemistry, which limits their functionality. Localized surface modification of microchannels can be challenging due to the nonplanar geometries involved. However, chip bonding remains the main hurdle, with many methods involving thermal or plasma treatment that, in most cases, neutralizes the desired chemical functionality. Postbonding modification of microchannels is subject to many limitations, some of which have been recently overcome. Novel techniques include solution-based modification using laminar or capillary flow, while conventional techniques such as photolithography remain popular. Nonetheless, new methods, including localized microplasma treatment, are emerging as effective postbonding alternatives. This Review focuses on postbonding methods for surface patterning of microchannels.

Wetting studies of hydrophilic-hydrophobic TiO2@SiO2 nanopatterns prepared by photocatalytic decomposition

TiO(2)@SiO(2) nanopatterns were prepared with the evaporation-induced self-assembly (EISA) technique. The material consists of an ultrathin (approximately 2 nm) layer of titania with hexagonally ordered craters of roughly 30 nm in diameter, on a silica substrate. The open pore structure and high homogeneity of the pattern makes these materials ideal for detailed wetting studies. The nanopatterns were functionalized with a fluoroalkylsilane (FAS), which attached on both titania and silica, resulting in a hydrophobic surface. By irradiating the composite material with UV light for different lengths of time, the hydrophilic/hydrophobic contrast in the nanopattern could be tuned. This is a result of the very different photocatalytic properties of titania and silica. The area fraction covered with FAS, f(FAS), as a function of UV irradiation time was calculated from water contact angle measurements of the composite film and corresponding reference samples, by using existing wetting models for heterogeneous surfaces. The results were compared to area fractions derived from X-ray photoelectron spectroscopy (XPS). f(FAS)-values determined from static water contact angles gave the best agreement with XPS, while advancing and receding contact angles overestimated and underestimated the f(FAS)-values, respectively. The Cassie model gave a slightly better fit to the XPS data than the Israelachivili model.

Subsurface oxidation for micropatterning silicon (SOMS)

Here we present a straightforward patterning technique for silicon: subsurface oxidation for micropatterning silicon (SOMS). In this method, a stencil mask is placed above a silicon surface. Radio-frequency plasma oxidation of the substrate creates a pattern of thicker oxide in the exposed regions. Etching with HF or KOH produces very shallow or much higher aspect ratio features on silicon, respectively, where patterning is confirmed by atomic force microscopy, scanning electron microscopy, and optical microscopy. The oxidation process itself is studied under a variety of reaction conditions, including higher and lower oxygen pressures (2 and 0.5 Torr), a variety of powers (50-400 W), different times and as a function of reagent purity (99.5 or 99.994% oxygen). SOMS can be easily executed in any normal chemistry laboratory with a plasma generator. Because of its simplicity, it may have industrial viability.

Solid-Liquid Interactions and Functional Surface Wettability

The interaction between a liquid and a solid surface is the key to understanding wetting phenomena. A very large number of natural and industrial processes rely on the delicate manipulation of this interaction. Controlled wetting is of central importance in microfluidics, mineral flotation, high speed coating, electronic display technologies, oil recovery, lubrication, and plant protection. At the molecular level, one can alter the distribution and charge of surface groups on functional surfaces, vary the number of hydrogen bonds, change molecular configuration, perform chemical grafts, and so forth. External stimuli such as light, electric potential, and heat can lead to subtle control of wettability, which is based strictly on thermodynamics.