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Core−shell polystyrene−silica spheres with diameters of 800 nm and 1.9 μm were synthesized by soap-free emulsion and dispersion polymerization of the polystyrene core, respectively. The polystyrene spheres were used as templates for the synthesis of silica shells of tunable thickness employing the Stöber method [Graf et al. Langmuir2003, 19, 6693]. The polystyrene template was removed by thermal decomposition at 500 °C, resulting in smooth silica shells of well-defined thickness (15−70 nm). The elastic response of these hollow spheres was probed by atomic force microscopy (AFM). A point load was applied to the particle surface through a sharp AFM tip, and successively increased until the shell broke. In agreement with the predictions of shell theory, for small deformations the deformation increased linearly with applied force. The Youngʼs modulus (18 ± 6 GPa) was about 4 times smaller than that of fused silica [Adachi and Sakka J. Mater. Sci.1990, 25, 4732] but identical to that of bulk silica spheres (800 nm) synthesized by the Stöber method, indicating that it yields silica of lower density. The minimum force needed to irreversibly deform (buckle) the shell increased quadratically with shell thickness. [ABSTRACT FROM AUTHOR]

Bilayer nanostructured poly(3,4-ethylenedioxythiophene) (PEDOT) and polyaniline (PANI) conducting polymer composites have been successfully prepared by oxidative polymerization of the parent monomers, aniline (An) and 3,4-ethylenedioxythiophene (EDOT), in aqueous solutions of p-toluenesulfonic acid ( p-TSA). As the first step, PANI nanofibers were obtained in the p-TSA solution using ammonium persulfate (APS) as the oxidant. Subsequently, PEDOT was coated onto the PANI nanofibers by the oxidative polymerization of EDOT to form PEDOT/PANI bilayer nanofibers. The resulting nanostructured material was characterized by SEM and a range of spectroscopic methods, which confirmed that the surface layer of the synthesized materials had features typical of chemically synthesized PEDOT. The presence of the PEDOT layer increased the room temperature electrical conductivity of the PEDOT/PANI nanocomposites by 2 orders of magnitude in comparison with the parent PANI nanofibers. Moreover, PEDOT/PANI nanocomposites on a glassy carbon electrode showed stronger electrocatalytic activity for the oxidation of ascorbic acid than PANI nanofibers. [ABSTRACT FROM AUTHOR]

Self-assembled poly(o-methoxyaniline) (POMA) hollow nanospheres were prepared in a solution of poly(methyl vinyl ether-alt-maleic acid) (PMVEA) by oxidative polymerization using ammonium persulfate as the oxidant. The weight ratio of PMVEA to o-methoxyaniline in the solution had a significant effect on the morphology of the poly(o-methoxyaniline) nanospheres as determined by scanning electron microscopy. The diameter of the hollow nanospheres decreased from 440 to 210 nm with an increase in the PMVEA concentration from 1% to 5%. Freeze-fracture transmission electron microscopy results showed the presence of spherical micelles composed of PMVEA/ o-methoxyaniline prior to polymerization, which also decreased in size as more PMVEA was added to the solution, and can act as soft templates for the formation of the hollow POMA nanospheres. The POMA/PMVEA hollow nanospheres were characterized by means of Fourier transform infrared, UV-visible, x-ray photoelectron spectroscopy, elemental analysis and conductivity measurements. [ABSTRACT FROM AUTHOR]

In this work, we systematically investigated the morphologies of polymers prepared by chemical oxidation of aniline and methyl-, methoxy-, or ethoxy-substituted aniline under the same experimental conditions. No matter the presence or absence of 10-camphorsulfonic acid (CSA), the oxidation of aniline produces nanotubes, while the oxidation of most aniline derivatives produce hollow microspheres under the same experimental conditions. These results illustrate the oligomers with phenazine-like structures produced at the initial oxidation of aniline are crucial for the formation of PANI nanotubes. The formation mechanism of the hollow microspheres of PANI derivatives is discussed. The main factors to control the polymer morphology are stability of droplets of aniline and its derivatives formed in an aqueous solution and the rate of exothermal reaction. The fast exothermal reaction benefits the formation of uniform microspheres. We also suggest that the hole on the surface of microspheres forms at the initial oxidation stage and is maintained by the flux of water and water-soluble components in the course of polymerization. [ABSTRACT FROM AUTHOR]

Coaxially aligned polyaniline (PANI) nanofibers doped with 3-thiopheneacetic acid (TAA) were chemically synthesized by the interfacial polymerization of aniline in the presence of TAA, using iron (III) chloride hexahydrate (FeCl3·6H2O) as the oxidant. The morphology, crystallinity, room temperature conductivity, and coaxial alignment of the PANI-TAA nanofibers were highly dependent on the organic solvent used for the interfacial polymerization, the oxidant, and also the molar ratio of the aniline to TAA. Hexane, diethyl ether, dichloromethane, chloroform, and acetone were used as the organic solvents, and chloroform proved to be the best solvent for the formation of PANI-TAA nanofibers. The redox potential of the oxidant is the key to controlling the morphology and diameter of the PANI-TAA nanofibers. The use of FeCl3 as the oxidant leads to the formation of thin (~50 nm) PANI-TAA nanofibers, which increased in length, crystallinity, conductivity, and coaxial alignment as the molar ratio of TAA to aniline was increased from 0.1 : 1 to 1 : 1. By comparison, only granular PANI was obtained when ammonium persulfate (APS), which has a higher redox potential, was used as the oxidant. The doping function of TAA in the PANI-TAA nanofibers was confirmed by means of FTIR and UV-Visible spectroscopy. [ABSTRACT FROM AUTHOR]

Dual functional unimolecular micelles based on a pH-responsive amphiphilic star polymer β-CD-(PLA-b-PDMAEMA-b-PEtOxMA)21 have been developed for the co-delivery of imiquimod and plasmid DNA to dendritic cells. The star polymer with well-defined triblock arms was synthesized by combining activator regenerated by electron-transfer atom-transfer radical polymerization with ring-opening polymerization. Dissipative particle dynamics simulation showed that core-mesophere-shell-type unimolecular micelles could be formed. Imiquimod-loaded micelles had a drug loading of 1.6 wt % and a larger average size (28 nm) than blank micelles (19 nm). The release of imiquimod in vitro was accelerated at the mildly acidic endolysosomal pH (5.0) in comparison to physiologic pH (7.4). Compared with blank micelles, a higher N:P ratio was required for imiquimod-loaded micelles to fully condense DNA into micelleplexes averaging 200-400 nm in size. In comparison to blank micelleplexes, imiquimod-loaded micelleplexes of the same N:P ratio displayed similar or slightly higher efficiency of gene transfection in a mouse dendritic cell line (DC2.4) without cytotoxicity. These results suggest that such pH-responsive unimolecular micelles formed by the well-defined amphiphilic star polymer may serve as promising nano-scale carriers for combined delivery of hydrophobic immunostimulatory drugs (such as imiquimod) and plasmid DNA with potential application in gene-based immunotherapy. [ABSTRACT FROM AUTHOR]