Highly ordered hexagonal arrays of latex spheres on highly ordered pyrolytic graphite (HOPG) have been prepared from a Langmuir-Blodgett-like (LB-like) technique using both polymers and surfactants as spreading agents. The role of spreading agent concentration in forming a well-ordered, stable monolayer at the air-liquid interface was studied by means of atomic force microscopy, scanning electron microscopy, optical microscopy, and surface tension measurements for three different systems: a nonionic surfactant, octylphenoxy poly(ethyleneoxy)ethanol (Igepal CO 630); an anionic surfactant, sodium dodecyl sulfate; and a low-molecular-weight, water-soluble polymer, polyacrylamide. For both the anionic surfactant and the water soluble polymer, a correlation was found between a unique feature in surface tension measurements of the latex-spreading agent mixture and the concentrations at which hexagonal arrays of latex spheres form on the surface of HOPG. For the nonionic surfactant, no ordered structures were found on HOPG for any surfactant concentration, consistent with no appearance of the unique feature in surface tension measurements. These results show that a tensiometer can be used to determine the conditions under which well-ordered latex films have the possibility of forming on a substrate using the LB-like technique; however, other factors, such as pulling speed and surface chemistry, play a role as well.
A novel method for the formation of nanometer-scale polymer structures via template assisted admicellar polymerization (TAAP) is described. Admicellar polymerization uses a surfactant layer adsorbed on a surface to localize monomer to the surface prior to polymerization of the monomer. Nanostructures are formed by restricting adsorption to the uncovered sites of an already-templated surface, in this case to the interstitial sites between adsorbed latex spheres. Unlike most other process that form polymer nanostructures, polymer dimensions can be significantly smaller than the interstitial size because of sphere-surfactant interactions. Protein adsorption in the interstitial sites of colloidal arrays was also studied for three different proteins, and the results were compared with those obtained via admicellar polymerization.
Template assisted admicellar polymerization (TAAP) utilizes a surfactant layer adsorbed on a surface to localize a monomer to the surface prior to polymerization of the monomer. Nanostructures are formed by restricting adsorption to the uncovered sites of an already-templated surface, in this case, to the interstitial sites between adsorbed latex spheres. This work studies the factors affecting the synthesis of polymeric nanostructures from TAAP for three different monomers, aniline, pyrrole, and methyl methacrylate, and three different surfaces, highly ordered pyrolytic graphite (HOPG), gold, and SiO2. Among the parameters discussed are the effects of monomer and surfactant concentration, surfactant chain length, polymerization time and temperature, and solution ionic strength. Control of the aforementioned parameters allows some control over the nanostructure morphology. Polymer nanopillars, nanorings, honeycombs, and "honeytubes" have been synthesized. Important conclusions regarding the conditions favoring admicellar polymerization relative to polymerization in solution are drawn from the experimental results as well. Sample characterization includes scanning electron microscopy (SEM), Raman spectroscopy, and alternating current (ac) impedance measurements.
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