Generally, line widths are reduced by increasing the contact angle and by reducing the inlet/substrate velocity ratio. The conditions providing the minimum stable line width are bounded by a regime of capillary instability -we anticipate that this instability could be exploited to create periodic arrays of dots.The advantages of h4PL are that we can use computer-aided design to define any arbitrary 2-D pattern and that we can use any desired combination of surfactant and functional silane as ink to selectively define different functionalities at different locations. However ikiPL is a serial technique: In situations where it is desirable to create an entire pattern with the same functionality, it would be preferable to employ a parallel technique in which the deposition process occurred simultaneously in multiple locations. Schem~~( Figure 3) illustrates a rapid, parallel patterning procedure, dip-coating on patterned SAMS.This procedure uses micro-contact printing20 or electrochemical patteming2 1 of hydroxyl-and methyl-terminated SAMS to define hydrophilic and hydrophobic patterns on the substrate surfi~ce. ..,&., .-, ,., ., ...<. !.-.7 '?--..-., hydrophilic patterns in seconds. As described for A4PL, further evaporation accompanying the dip-coating operation induces self-assembly of silic~surfac~t mesophases.The patterned dip-coating procedure may be conducted with organic dyes or functional silanes (see Table 1). Scheme 2 illustrates patterned deposition of a propyl-amine derivatized cubic mesophase followed by a conjugation reaction with a pH-sensitive dye, 5,6-carboxyfluorescein, succinimidyl ester (5,6-FAM, SE). The uniform continuous porosity of the amine-derivatized and dye-conjugated films is confirmed by TEM and surface acoustic wave (SAW)-based nitrogen sorption isotherms22 of the corresponding films deposited on SAW substrates (Figure 4). The reduction in film porosity after dye conjugation reflects the volume occupied by the attached dye moieties. The patterned, functional array can be used to monitor the pH of fluids introduced at arbitrary locations and transported by capillary flow into the imaging cell. Figure 4a shows the fluorescence image of an array contacted with three different aqueous solutions prepared at pH 4.8, 7.7, and 12.0. Figure 4b shows the corresponding emission spectra and provides a comparison with solution data. In combination, the fluorescence image ( Fig. 4a) and plan-view and cross-sectional TEM micrographs (Figures 3 and 4c) of the dye-conjugated film demonstrate the uniformity of macro-and mesoscale features achievable by this evaporation-induced, de-wetting and self-assembly route. In comparison, films formed by nucleation and growth of thin film mesophases on patterned SANIS1 are observed to have nonhomogeneous, globular morphologies.Finally we can create patterned nanostructures by combining E]SA with a variety of aerosol processing schemes. For example, Figure 5 compares an optical micrograph of a macroscopic array of spots formed by inkjet printing LIPlo~1lon a sili...
Inorganic mesoporous thin-films are important for applications such as membranes, sensors, low-dielectricconstant insulators (so-called low κ dielectrics), and fluidic devices. Over the past five years, several research groups have demonstrated the efficacy of using evaporation accompanying conventional coating operations such as spin-and dip-coating as an efficient means of driving the self-assembly of homogeneous solutions into highly ordered, oriented, mesostructured films. Understanding such evaporation-induced self-assembly (EISA) processes is of interest for both fundamental and technological reasons. Here, we use spatially resolved 2D grazing incidence X-ray scattering in combination with optical interferometry during steady-state dipcoating of surfactant-templated silica thin-films to structurally and compositionally characterize the EISA process. We report the evolution of a hexagonal (p6 mm) thin-film mesophase from a homogeneous precursor solution and its further structural development during drying and calcination. Monte Carlo simulations of water/ethanol/surfactant bulk phase behavior are used to investigate the role of ethanol in the self-assembly process, and we propose a mechanism to explain the observed dilation in unit cell dimensions during solvent evaporation.
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