Patchy and multiregion janus particles with tunable optical properties.

Multiregion and patchy optically active Janus particles were synthesized via a hierarchical self-assembly process. Gold nanoparticles were assembled on the top surfaces of nano- and submicrometer silica particles, which were selectively protected on their bottom surfaces by covalent attachment to a copolymer film. The morphologies of the gold particle layer, and the resulting optical properties of the Janus particles, were tuned by changing the surface energy between the silica and gold particles, followed by annealing.

Bacterial plaque retention on oral hard materials: effect of surface roughness, surface composition, and physisorbed polycarboxylate.

Bacterial adhesion to oral hard materials is dependent on various factors, for example, surface roughness and surface composition. In this study, bacteria retention on three oral hard substrates, hydroxyapatite (HAP), enamel, and polished enamel (p-enamel) were investigated. The surface morphology and roughness of the three substrates were measured by scanning probe microscopy. HAP had the roughest surface, followed by enamel and polished enamel. For each individual substrate type, the roughness was shown to increase with scan size up to 50 microm x 50 microm. For HAP and enamel, roughness decreased considerably after formation of a pellicle, while addition of polymer coating to the pellicle layer reduced roughness much less in comparison. Bacterial surface coverage was measured at 30 min, 3 h, and 24 h on both native and surface-modified substrates, which were coated with two different polycarboxylate-based polymers, Gantrez S97 and Carbopol 940. As a result, the polymer coated surfaces had reduced bacteria coverage compared with the native surfaces over all time points and substrates measured. The reduction is the combined effect of electrostatic repulsion and sequestering of Ca(2+) ions at the surface, which plays a key role in the initial adhesion of bacteria to enamel surfaces in models of plaque formation.

Tunable wetting of nanoparticle-decorated polymer films.

In this paper, amine-modified silica nanoparticles (NPs) with diameters (d) from 15 to 230 nm are covalently linked to poly(styrene-random-acrylic acid) (P(S-ran-AA)) films, and wettability is studied as a function of diameter and NP surface coverage. During attachment, films swell and exhibit long and short scale roughness, consisting of a ridged, honeycomb structure, approximately 1 mum wide and 45-50 nm deep, which encircles nanoscale features 10-15 nm high and approximately 50 nm apart. A maximum NP coverage of approximately 70% was achieved for d less than or nearly equal to the nanoscale roughness induced by surface swelling. For d several times greater than this nanoscale roughness, the maximum coverage was limited by interparticle repulsion and reached only approximately 30%. For NPs with diameters of 15-106 nm, the water contact angle increased from 75 degrees to 120 degrees as NP coverage increased from 0 to 70%. At low and high NP coverage, the Wenzel and Cassie models, respectively, accurately describe the data. However, at intermediate NP coverage, neither model is satisfactory. An increase in surface roughness alone cannot account for this discrepancy. Atomic force microscopy (AFM) studies show that the NPs partially embed into the swollen P(S-ran-AA) surface, suggesting that the amine-coated NPs are wet by the copolymer, exposing low surface energy styrene. These studies demonstrate that control over surface properties of coatings, such as wetting, can be achieved by selecting NP sizes that complement film roughness.