Simple Method for the Preparation of Colloidal Particle Monolayers at the Water/Alkane Interface

Abstract

Monolayers of monodisperse colloidal particles are formed by self-assembly. Such 2-D particle arrays are interesting objects for applications as lithographic masks, optical gratings, multilens arrays, antireflecting surface, synthetic membranes, data storage media, etc. Different techniques were proposed for the fabrication of such arrays. One approach uses monolayer film formation in a thin wetting film. In the simplest modification it consists of slow drying of the particle suspension prepared as a thin film on a solid or liquid substrate. 1-7 More sophisticated modifications require special apparatus. 8-10 Another approach relies on electrophoretic deposition of particles onto an electrode. 11 Both approaches have a drawback in the difficulty to control monolayer formation, because areas thicker than a monolayer can be formed. On the other hand, it is possible to build a monolayer on the liquid-air interface. Colloidal particles apparently can be trapped at the liquid surface as a result of the electrostatic and surface tension forces. 12-15 However, application of the Langmuir-Blodgett (LB) technique to colloidal particles led to sub-monolayers with a coverage not more than 80%. 16,17 Only recently Tredgold and coworkers 18 reported on the successful Langmuir-Schaefer transfer of monolayers of silica particles modified with 3-aminopropyl groups. However, the properties of these arrays were not reported in detail. Kondo et al. 19 were able to fabricate close packed 2-D arrays of silica particles transferred from benzene/air interface by a simple technique without using a LB trough. However, this requires an additional chemical step of silica particle modification by alkoxylation. Only particles modified with dodecyl chains (thus highly hydrophobic) formed ordered close packed monolayers. The authors 19 believe that the monolayer formation involves a two-stage process with particles laterally moving on the solid substrate to form finally close packed array. Recently Aveyard et al. 20 investigated the monolayer behavior of polystyrene (PS) particles at the water/octane interface and found a formation of highly ordered arrays of large 1.5 and 2.6 µm particles. The particles were highly repulsive in contrast to the behavior at the air/water interface. In this work no attempt to the transfer of particles onto a solid substrate was reported. Thus it seems that despite many years of studies of the behavior and aggregation of colloidal particles at the water/ air interface 12-23 there is still a lack of data on the transfer of the monolayer onto the solid substrates.The recent results 18,20 led us to a new very simple and fast method of the fabrication of close packed arrays of large latex and silica particles. Large particles have also the advantage to be easily imaged by optical microscopy. We used monodisperse 0.74 and 1.2 µm polystyrene (PS) particles (obtained according to ref 24 by an emulsifierfree, aqueous radical polymerization), 0.94 µm polystyrene-2-hydroxyethyl methacrylate (PS-HEMA) particles, 1.2 and 1...

Self‐Assembled Nanoparticles Based Fabrication of Gecko Foot‐Hair‐Inspired Polymer Nanofibers

“…[30] Figure 2a shows the scanning electron microscopy (SEM) image of the ordered structures of polystyrene particles, (356 ± 14) nm in diameter, on a silicon substrate. The particles were subsequently etched-back using an oxygen plasma etcher resulting in a mean particle diameter of (250 ± 10) nm and an inter-particle spacing of (100 ±10) nm, as illustrated in Figure 2b.…”

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