Plasma-Synthesized Silver Nanoparticles on Electrospun Chitosan Nanofiber Surfaces for Antibacterial Applications.

Chitosan nanofibers have been electrospun with poly(ethylene oxide) and silver nitrate, as a coelectrospinning polymer and silver nanoparticle precursor, respectively. The average diameter of the as-spun chitosan nanofibers with up to 2 wt % silver nitrate loading was approximately 130 nm, and there was no evidence of bead formation or polymer agglomeration. Argon plasma was then applied for surface etching and synthesis of silver nanoparticles via precursor decomposition. Plasma surface bombardment induced nanoparticle formation primarily on the chitosan nanofiber surfaces, and the moderate surface plasma etching further encouraged maximum exposure of silver nanoparticles. UV-vis spectra showed the surface plasmon resonance signature of silver nanoparticles. The surface-immobilized nanoparticles were visualized by TEM and were found to have average particle diameters as small as 1.5 nm. Surface analysis by infrared spectroscopy and X-ray photoelectron spectroscopy confirmed the interactions between the silver nanoparticles and chitosan molecules, as well as the effect of plasma treatment on the nanofiber surfaces. Finally, a bacteria inhibition study revealed that the antibacterial activity of the electrospun chitosan nanofibers correspondingly increased with the plasma-synthesized silver nanoparticles.

Conducting silver networks based on electrospun poly(methyl methacrylate) and silver trifluoroacetate.

Silver networks with high transmittance and low resistance were prepared on transparent substrates via a polymer-assisted electrospinning technique and post treatments. Nonaqueous media containing poly(methyl methacrylate) (PMMA) and silver trifluoroacetate (STA) were formulated and electrospun as polymer/metal-precursor nanofibers with as-spun fiber diameters ranging from 640 to 3000 nm. Nanofibers randomly deposited on transparent substrates formed a plane scaffold, which served as the raw material for the conducting silver network. Post-thermal treatment at a moderate temperature of 100 °C reduced the STA precursors to silver nanoparticles (Ag NPs). Further heat treatment at elevated temperatures thermally decomposed the organic polymer and triggered sintering of the Ag NPs into a connected one-dimensional (1D) domain. Silver fibers with diameters ranging between 800 and 4500 nm formed continuous conducting networks on the substrate surface. The sheet resistances of these conducting silver networks revealed strong correlations with the original STA/PMMA ratios and with the silver network morphologies after the polymers were removed. The material fabrication was carefully investigated, and the surface plasmon resonances (SPRs), fiber morphologies, and electrical and optical properties of the products were examined. The optimized conducting silver networks exhibited sheet resistances as low as 15 Ω/sq and diffusive optical transparencies of approximately 54%.

Assembly and manipulation of Fe(3)O(4)/coumarin bifunctionalized submicrometer Janus particles.

Magnetic and fluorescent bifunctionalized Janus particles were fabricated via sequential particle embedding and surface modifications. The two hemispherical surfaces of a 500 nm silica particle were separately functionalized with Fe3O4 nanoparticles and coumarin dye molecules. The Fe3O4 hemisphere exhibited magnetically driven particle orientation and alignment, whereas the coumarin hemisphere served as an anisotropic emission indicator. The photoluminescence of these orientated and solidified Janus particles revealed anisotropic emission contrast as high as 40% between the magnet-aspect and the dye-aspect excitations. The dynamic anisotropic emission of the bifunctionalized Janus suspension under magnetic manipulation also revealed a nonsynchronized bulk correlation time that was much slower than that of an individual 500 nm particle. Under a static magnetic field, the suspended Janus particles assembled into a grape-like bunch, with random particle orientation. Unlike their microscale counterparts, the submicrometer magnetic Janus particles were less sensitive to gravity and more vulnerable to particle-particle interactions.

Energetic-assisted scanning thermal lithography for patterning silver nanoparticles in polymer films.

Energetic-assisted scanning thermal lithography (SThL) was demonstrated with the addition of benzoyl peroxide (BPO) for patterning silver nanoparticles. SThL samples were prepared by spin-coating poly(methyl methacrylate) (PMMA) thin films preloaded with BPO and silver nitrate precursors. Localized thermal analysis via probe heating demonstrated that the BPO decomposition in the polymer film took place at the temperature of 80 °C. Above this temperature, the thermal probe initiated the decomposition of the peroxide, which resulted in the in situ discharge of exothermal energy to compensate the joule shortage and the rapid cooling in the SThL thin film samples. The additional joule energy thermally enhanced the synthesis of silver nanoparticles, which were patterned and embedded in the PMMA thin film. Surface plasmon resonance scattering of these silver nanoparticles was observed by dark-field optical microscopy, whereas the nanoparticle distribution was examined by transmission electron microscopy. Variations in the scanning probe temperatures and peroxide concentrations were carefully investigated to optimize the thermal lithography efficiency upon the addition of energetics.

Fabrication and characterization of asymmetric Janus and ternary particles.

Asymmetric Janus and ternary silica particles with an average diameter of 450 nm were fabricated by sequentially arranged particle-embedding and surface-modification processes. Thermally induced embedding of particles into polymer-fiber substrates allowed for precise control of the degree of particle submergence and the subsequent chemical modification of the hemispherical exposed particle surfaces. In addition to Janus particles with the desired surface-functionality ratios of 1:2, 1:1, and 2:1, this unique fabrication approach was also used to produce complicated and well-defined heterogeneous materials, including bifunctionalized Janus and ternary particles. The bifunctionalized Janus particles were produced with two hemispherical surfaces alternately labeled with gold and iron oxide nanoparticles, which simultaneously enabled anisotropic surface-plasmon resonance and a magnetic response. Ternary particles were also constructed, yielding submicrometer spheres with functionalized equatorial belts. The surface distributions of functional components in these spherical materials were carefully examined for uniformities in particle embedding. Statistical analyses revealed that the functional components were distributed with a uniformity of over 80% for all of the asymmetric Janus and ternary particles.

Enhancement of light scattering and photoluminescence in electrospun polymer nanofibers.

Poly(methyl methacrylate) nanofibers with desired fiber diameters that ranged from 336 to 896 nm were electrospun as light scattering and propagation materials. The light scattering behavior of these samples as a function of the fiber diameter and fiber deposition thickness was examined by UV-vis spectrophotometry, which revealed the scattering bands in the absorption spectra. The scattering bands of these nanofibers were linearly proportional to the fiber diameter, which shows good agreement with a scattering model based on the Mie theory. The light scattering and prolonged light path lengths in the nanofiber scaffolds were monitored and quantified by the photoluminescence of a fluorescent dye, Coumarin 6, which was preloaded into the polymer nanofibers. The photoluminescence after proper normalization showed a second-order dependence on the dye loading per unit area, which is significantly different from the spin-coated thin-film samples following a first-order relationship. Nonlinear photoluminescence enhancements indicated prolonged light path lengths and multiple light absorptions within the fiber scaffolds as a result of light scattering. Even with relatively broad scattering band widths, the light scattering and photoluminescence of the electrospun nanofibers exhibited considerable wavelength selectivity, especially as the scattering bands overlapped with the excitation wavelengths of the fluorescence reagent.

Dependence of surface atomic arrangement of titanium dioxide on metallic nanowire nucleation by thermally assisted photoreduction.

Through studying the optical, electrical and photocatalytic properties of anatase TiO(2) films with different preferred orientations, (101) and (004), this study clarified the relationship between the formation of metallic nanowires by thermally assisted photoreduction process and surface atomic bonding conditions of TiO(2). Experimental results show that the (101) anatase films which yielded much more Ag nanowires than the (004) oriented films and exhibited more complex superficial atomic bonding, which could be demonstrated by the Gaussian bands in photoluminescence spectra. This might lead to higher carrier concentration and mobility, as well as longer life time for photo-exited electrons and consequently a greater photocatalytic activity for reducing metallic ions. The fact that the anatase (101) surface acted as the preferred nucleation sites for Ag nanowires was supported by high resolution transmission electron microscopy lattice image of a TiO(2) nanofiber where an Ag nanowire was grown.

Novel fabrication of Janus particles from the surfaces of electrospun polymer fibers.

A novel synthetic approach for the efficient fabrication of Janus silica particles was demonstrated by embedment of zero-dimensional colloids on one-dimensional polymer fiber surfaces, followed by the surface modification on the exposed silica hemispheres. Electrospinning of poly(methyl methacrylate) and poly(4-vinyl pyridine) blends produced polymer fibers with high specific surface area and desired surface hydrophilicities. Fiber compositions determined the colloid adsorption density and uniformity. The colloid embedding resulted from the polymer softening was manipulated by the isothermal heat treatment. Subsequent silianization completed the amino functionalities on hemispherical surfaces of embedded silica colloids. Janus particles with uniform asymmetric chemical features were further labeled with gold nanoparticles before their recovery from fiber substrates. Fabrication of Janus particles, including colloid adsorption, temperature-driven embedding, and hemispherical surface modification, were investigated and are discussed.