Deposition of cationic polymer micelles on planar and patterned silicon dioxide surfaces.

摘要

The deposition of PS-PVPH+ polymer micelles from a pH 1 aqueous solution onto Si wafers has been studied using a simple dip-coating technique. It has been found that the rate of evaporation of the solvent and the rate of withdrawal have a considerable influence on the density and ordering of the adsorbed micelles. The highest density and degree of ordering (as judged by the 2D pair correlation function) is achieved when solvent evaporation dominates the deposition process, but a fairly homogeneous distribution of polymer micelles can be achieved over a distance of at least 3–4 mm by controlling the solvent evaporation rate and the rate of substrate withdrawal. We did not observe any significant effect of added KCl (up to 0.1 M) during the deposition process or soaking in 1 M KCl after deposition. The attachment of these micelles is quite robust as they cannot be washed off in pH 1 water (with or without KCl) without significant mechanical assistance. However we did find that the micelles are rather easily caused to dewet and partially aggregate under the influence of 65°C water vapor.; The concept of graphoepitaxy is applied to the deposition of cationic polymer micelles from the solution phase onto a Si/SiO₂ surface with 100 nm deep ion-etched trenches of variable widths. It has been found that the micelle density is substantially higher and the ordering of the micelles is improved for micelles that adsorb in the 100 nm depressions in the width range of ca. 500 to 5000 nm. We ascribe these effects to capillary forces that pull the aqueous solution into the canyons where the micelles can be trapped. While the ordering of the micelles can be substantial, they do not form a perfect hexagonal crystal. If the surface is chemically modified by a Au coating or a layer of sodium poly(styrene sulfonate)) the micelle surface-interaction is strengthened and the degree of ordering is diminished. These results demonstrate that a combination of graphoepitaxy and processing conditions (speed of substrate withdrawal, pH, evaporation of solvent) can be used to make fairly ordered polymer micelle arrays over a space of (at least) several mm.