Summary: Electrospinning of polymer blends offers the potential to prepare functional nanofibers for use in a variety of applications. This work focused on control of the internal morphology of nanofibers prepared by electrospinning polymer blends to obtain core‐sheath structures. Polybutadiene/polystyrene, poly(methylmethacrylate)/polystyrene, polybutadiene/poly(methylmethacrylate), polybutadiene/polycarbonate, polyaniline/polycarbonate, and poly(methylmethacrylate)/polycarbonate blends were electrospun from polymer solutions. It was found that the formation of core‐sheath structures depends on both thermodynamic and kinetic factors. Incompatibility and large solubility parameter difference of the two polymers is helpful for good phase separation, but not sufficient for the formation of core‐sheath structures. Kinetic factors, however, play a much more important role in the development of the nanofiber morphology. During the electrospinning process, the rapid solvent evaporation requires systems with high molecular mobility for the formation of core‐sheath structures. It was found that polymer blends with lower molecular weight tend to form core‐sheath structures rather than co‐continuous structures, as a result of their higher molecular mobility. Rheological factors also affect the internal phase morphology of nanofibers. It was observed the composition with higher viscosity was always located at the center and the composition with lower viscosity located outside.TEM image of electrospun polybutadiene/polycarbonate nanofibers at 25/75 wt.‐% ratio after staining by osmium tetroxide. The dark regions are polybutadiene and the light region is polycarbonate.magnified imageTEM image of electrospun polybutadiene/polycarbonate nanofibers at 25/75 wt.‐% ratio after staining by osmium tetroxide. The dark regions are polybutadiene and the light region is polycarbonate.

Summary: Core‐sheath nanofibers with conductive polyaniline as the core and an insulating polymer as the sheath were prepared by electrospinning of blends of polyaniline with either polystyrene or polycarbonate. These unique core‐sheath structures offer potential in a number of applications including nanoelectronics. When polyaniline was blended with poly(methyl methacrylate) and poly(ethylene oxide), only isolated domains of polyaniline in beadlike structures were formed. The phase morphology of electrospun fibers is thought to be dependent on the high‐surface tension of the solution and the molecular weight of the polymers. Incompatibility of the polymers and low molecular weight of compositions played a key role in the formation of core‐sheath structures, as opposed to co‐continuous morphologies.TEM image of electrospun polyaniline/polystyrene nanofiber after staining by OsO4. The dark regions are polyaniline.magnified imageTEM image of electrospun polyaniline/polystyrene nanofiber after staining by OsO4. The dark regions are polyaniline.

Gold nanoparticles protected with thiophene-terminated alkanethiols having different alkane chain lengths have been synthesized, and vapor-sensing properties of their spin-coated films have been investigated. Transmission electron microscopy and measurement of the sulfur and gold peak areas of the films by X-ray photoelectron spectroscopy indicate gold core diameters in the 3−5-nm range. Exposure of the films to chloroform, toluene, hexane, and ethanol vapors results in significant and selective increases in electrical resistance, with the response to the vapors having the following order:  toluene > chloroform > hexane ≫ ethanol. The magnitude of the maximum resistance change correlates well with solubility properties of the protected gold nanoparticles, as determined by optical absorbance spectroscopy and the energy of the gold plasmon. The detection sensitivity of the films increases with increasing alkanethiol chain length. These data are consistent with a sensing mechanism in which organic vapors cause swelling of the nanoparticle film, resulting in increased distance between the gold cores. In the case of ethanol, a decrease in resistance occurs at high vapor concentration, presumably due to an increase in the dielectric constant of the medium between the cores.

Highly ordered arrays of periodic nanostructures [1] show interesting characteristics for applications in photonics, [2] electronics, [3] optoelectronics, [4] sensing, [5] biochips, [6] and catalysis. [7] The array properties are determined by the choice of material and can be tuned further by varying the geometry, chemical composition, periodicity, and the size of the nanostructures. [4,8] Such controlled and elaborate arrays are commonly fabricated by X-ray or electron-beam lithography. However, there are limitations to patterning over large areas using these lithographical techniques due to long processing times, which result in higher costs. Relatively simple and costeffective nanopatterning processes have been developed to address these inherent limitations, including interference lithography, [9] nanosphere lithography, [10] and soft lithography. [11] In order to pattern metals or metal oxides, however, the non-conventional methods still require multistep processing as does conventional photoresist lithography. In this paper, we demonstrate a novel but simple methodology for the fabrication of periodic structures comprising metal oxides at the sub-100 nm scale using polymeric templates, colloids, and common laboratory equipment. Thus, this nanopatterning technique does not require high-vacuum deposition, etching, or photoresists, which are common in other processes. The patterns produced with this method were periodic and composed of 1D or 2D arrays of nanostructures over large areas. Fabrication of these metal oxide nanostructures required only a few hours once the nanometer-sized colloid of the metal oxide and polymeric templates were available. The structural resolution of the resulting pattern was determined by the amount of colloidal deposition onto the grooves (or grating) of the templates used. Although this process utilized microstructured templates, it is possible to fabricate features of metal oxide at the 100 nm scale. The geometry and periodicity of the structure can be well defined and controlled through selection from a wide variety of polymeric templates fabricated by numerous techniques. This unique strategy to achieve controlled nanopatterning can utilize a wide variety of inorganic colloids and/or intricate templates (or masks) available from various established lithographic methods. Microstructured polymeric templates have been prepared using a single-step holographic patterning process by exposing films of azobenzene-functionalized polymers (AFPs) on substrates to an argon-ion laser (488 nm) interference pattern. [12] The interference pattern produced photoinduced mass transfer in the polymer film giving rise to a surface-relief structure without additional processing.[13] Such surface modulation leads to 1D or 2D periodic arrays of surface-relief-grating (SRG) structures on the polymeric films. A variety of holographic surface structures can be designed and fabricated with good control over the modulation and periodicity of the patterns. In this work, SRG structures from thin films of ...

Ordered multilayer nanocomposites have been prepared by electrostatic layer-by-layer assembly between exfoliated aluminosilicate nanoplatelets and substituted ionic polyacetylenes. Aluminosilicate saponite particles were exfoliated by means of extensive shaking and sonication of their water suspension. Atomic force microscopy and transmission electron microscopy data suggest that the exfoliated platelets have the shape of ultrathin disks with an average width of 170 ± 30 nm. Conjugated ionic polyacetylene poly(N-octadodecyl-2-ethynylpyridinium bromide) (PEPy-C18) was synthesized by spontaneous polymerization of 2-ethynylpyridine quaternized with 1-bromooctadecane. Linear build-up of multilayer nanocomposites between the exfoliated saponite particles and substituted ionic polyacetylenes was monitored by UV−vis absorption spectroscopy. AFM surface topography of the resulting films indicates that the saponite platelets cover the entire surface of the underlying layers. TEM cross-sectional images of such films show that the saponite platelets are aligned parallel to the film surface to form ordered layers. Polarized UV−vis absorption spectroscopy suggests that the polyacetylene chains are oriented parallel to the surface of the saponite layers.

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Biomimetic synthesis of ceramic materials is increasing in popularity because it offers many advantages. In this work, aluminum silicate nanoparticles were obtained on a self-assembled organic multilayer at near room temperature (30 < or = T < or = 50 degrees C) and at atmospheric pressure. Morphological and microanalytical characterization was carried out by means of transmission electron microscopy and subsequent image analysis. The roles of some process parameters such as template type, reactant concentration, [Al]:[Si] molar ratio, number of initiation steps (IS) of mineralization, and reaction time (rt) were assessed by comparing images, diffraction patterns, and EDX spectra. Generally, the Si-rich phase exhibited higher crystallinity, whereas the Al-rich phase was mostly amorphous. Crystal structure resulted with rt > or = 4 days for template-grown materials. Images of materials obtained at T = 50 degrees C, rt = 3 days, and 1 < or = IS < or = 4 were further analyzed by "spectrum enhancement," an algorithm based on the Fourier transform. Morphological indicators were extracted from suitably processed power spectral densities, a correlation matrix was formed, and multivariate statistics was carried out. Visual differences in nanoaggregate morphology were quantitatively translated. Materials were ranked by the spatial uniformity of nanoparticle distribution: the most uniform aggregates were those grown on templates by IS > or = 2. Univariate statistics validated the conclusion: the particles of those same materials had a narrower size distribution and sharper edges. This last property has been ascribed to crystalline structure, independently demonstrated by diffraction patterns.