Conducting polymer-gold co-patterned surfaces via nanosphere lithography.

HYPOTHESIS: Co-patterned arrays comprised of conjugated polymers and nanostructured gold is an important matrix for sensing and stimuli-responsive plasmonic applications. Nanosphere lithography (NSL) is an easy-to-use patterning technique and viable method to fabricate inverse honeycomb structures with electrochemically deposited conjugated polymers. The cross-sectional height of the conducting polymer pattern can be tuned such that the macropores of the honeycomb structure expose electrochemically accessible areas for further gold deposition. Using time-dependent electrochemical reduction, Au(3+) is reduced to Au(0) and selectively deposit on the macropores thus forming a co-patterned surface. EXPERIMENTS: The Langmuir-Blodgett-like deposition was used to assemble polystyrene spheres on a conductive substrate. Then the carbazole-based monomer was electropolymerized within the interstices of the colloidal template, which was subsequently dissolved. A potentiostatic technique was used to deposit Au in the macropores. FINDINGS: Fabrication of the polycarbazole-Au co-patterned surface was characterized by atomic force microscopy (AFM), electrochemical quartz crystal microbalance (EC-QCM), and X-ray photoelectron spectroscopy (XPS). Surface plasmon resonance spectroscopy (SPS) data supported backfilling behavior and quantified the complex refractive index of the array. UV-Vis absorption spectroscopy shows overlapping polycarbazole and gold LSPR peaks useful for plasmonic sensing applications. The colloidal templating approach reported in this study was further used in the fabrication of highly ordered Au nanodisks.

High interfacial activity of polymers "grafted through" functionalized iron oxide nanoparticle clusters.

The mechanism by which polymers, when grafted to inorganic nanoparticles, lower the interfacial tension at the oil-water interface is not well understood, despite the great interest in particle stabilized emulsions and foams. A simple and highly versatile free radical "grafting through" technique was used to bond high organic fractions (by weight) of poly(oligo(ethylene oxide) monomethyl ether methacrylate) onto iron oxide clusters, without the need for catalysts. In the resulting ∼1 µm hybrid particles, the inorganic cores and grafting architecture contribute to the high local concentration of grafted polymer chains to the dodecane/water interface to produce low interfacial tensions of only 0.003 w/v % (polymer and particle core). This "critical particle concentration" (CPC) for these hybrid inorganic/polymer amphiphilic particles to lower the interfacial tension by 36 mN/m was over 30-fold lower than the critical micelle concentration of the free polymer (without inorganic cores) to produce nearly the same interfacial tension. The low CPC is favored by the high adsorption energy (∼10(6) kBT) for the large ∼1 µm hybrid particles, the high local polymer concentration on the particles surfaces, and the ability of the deformable hybrid nanocluster cores as well as the polymer chains to conform to the interface. The nanocluster cores also increased the entanglement of the polymer chains in bulk DI water or synthetic seawater, producing a viscosity up to 35,000 cP at 0.01 s(-1), in contrast with only 600 cP for the free polymer. As a consequence of these interfacial and rheological properties, the hybrid particles stabilized oil-in-water emulsions at concentrations as low as 0.01 w/v %, with average drop sizes down to 30 µm. In contrast, the bulk viscosity was low for the free polymer, and it did not stabilize the emulsions. The ability to influence the interfacial activity and rheology of polymers upon grafting them to inorganic particles, including clusters, may be expected to be broadly applicable to stabilization of emulsions and foams.

Iron Oxide Nanoparticles Grafted with Sulfonated and Zwitterionic Polymers: High Stability and Low Adsorption in Extreme Aqueous Environments.

A facile "grafting through" approach was developed to tether tunable quantities of poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) as well as zwitterionic poly([3-(methacryloylamino)propyl]dimethyl(3-sulfopropyl)ammonium hydroxide) (PMPDSA) homopolymer onto iron oxide (IO) nanoparticles (NPs). In this case, homopolymers may be grafted, unlike "grafting to" approaches that often require copolymers containing anchor groups. The polymer coating provided steric stabilization of the NP dispersions at high salinities and elevated temperature (90 °C) and almost completely prevented adsorption of the NPs on silica microparticles and crushed Berea sandstone. The adsorption of PAMPS IO NPs decreased with the polymer loading, whereby the magnitude of the particle-surface electrosteric repulsion increased. The zwitterionic PMPDSA IO NPs displayed 1 order of magnitude less adsorption onto crushed Berea sandstone relative to the anionic PAMPS IO NPs. The ability to design homopolymer coatings on nanoparticle surfaces by the "grafting through" technique is of broad interest for designing stable dispersions and modulating the interactions between nanoparticles and solid surfaces.

Colloidally templated two-dimensional conducting polymer arrays and SAMs: binary composition patterning and chemistry.

A facile approach and strategy toward binary-composition, two-dimensional (2D) patterned surfaces of conducting polymer periodic arrays, together with thiol self-assembled monolayers (SAMs) is described. The method involved a Langmuir-Blodgett (LB)-like deposition of latex microsphere particles, electropolymerization via cyclic voltammetric (CV) techniques, and self-assembly of an amphiphile. The LB-like technique enabled the monolayer deposition of different sizes of polystyrene (PS) particles in hexagonal packing arrangement on planar substrates. Combining the LB-like method with CV electropolymerization is advantageous because it provides deposition control of a polymer interconnected network, controlled composition ratio of polymer and SAMs, and control of 2D size and spacing of the spherical void pattern. Electrochemical-quartz crystal microbalance (EC-QCM) in situ monitoring of the film deposition quantified a constant and linear growth rate, with varying viscoelastic behavior of the conducting polymer adsorption on planar and PS-templated substrates. The dual-patterned surface provided a good imaging contrast as observed by atomic force microscopy (AFM). Complementary analyses such as X-ray photoelectron spectroscopy (XPS), attenuated total internal reflection infrared (ATR IR) spectroscopy, ultraviolet-visible (UV-vis) spectroscopy, and static contact angle measurements were used to characterize the formation of the patterned surface. The versatility of the method enables the potential for making various types of quantitative binary compositions and patterned surfaces using different combinations of conducting polymer or functional SAMs, which can be extended in the future to polymer brushes and layer-by-layer assembly of various materials.