Adsorption Behavior of Perfluorinated Sulfonic Acid Ionomer on Highly Graphitized Carbon Nanofibers and Their Thermal Stabilities

A systematic adsorption study of perfluorinated sulfonic acid Nafion ionomer on ribbon-type highly graphitized carbon nanofibers (CNFs) was carried out using fluorine-19 nuclear magnetic resonance spectroscopy. On the basis of the values obtained for the equilibrium constant (<i>K</i>_eq, derived from Langmuir isotherm), the ionomer has varying affinities for CNFs (<i>K</i>_eqbetween 5 and 22) as compared to Vulcan (<i>K</i>_eq = 18), depending on surface treatments. However, the interactions are most likely governed by different adsorption mechanisms depending on hydrophilicity/hydrophobicity of the adsorbent carbon. The ionomer is probably adsorbed via the polar sulfonic group on hydrophilic Vulcan, whereas it is adsorbed primarily via hydrophobic −CF₂– backbone on the highly hydrophobic pristine CNFs. Ionomer adsorption behavior is gradually altered from apolar to polar group adsorption for the acid-modified CNFs of decreasing hydrophobicity. This is indicated by the initial decrease and then increase in the value of <i>K</i>_eqwith the increasing strength of the acid treatment. The corresponding carbon–ionomer composite also showed varying thermal stability depending on Nafion orientation. The specific maximum surface coverage (Γ_Smax) of the CNFs is 1 order of magnitude higher than that of Vulcan. The large discrepancy is due to the fact that the ionomers are inaccessible to the internal surface area of Vulcan with high microporosity

Polypeptide-Based Aerosol Nanoparticles: Self-Assembly and Control of Conformation by Solvent and Thermal Annealing

Nanoconfined self-assemblies within aerosol nanoparticles and control of the secondary structures are shown here upon ionically complexing poly­(l-lysine) (PLL) with dodecylbenzenesulfonic acid (DBSA) surfactant and using solvents chloroform, 1-propanol, or dimethylformamide. Different solvent volatilities and drying temperatures allowed tuning the kinetics of morphology formation. The supramolecular self-assembly and morphology were studied using cryo-TEM and SEM, and the secondary structures, using FT-IR. Highly volatile chloroform led to the major fraction of α-helical conformation of PLL­(DBSA), whereas less volatile solvents or higher drying temperatures led to the increasing fraction of β-sheets. Added drugs budesonide and ketoprofen prevented β-sheet formation and studied PLL­(DBSA)–drug nanoparticles were in the α-helical conformation. Preliminary studies showed that ketoprofen released with a slower rate than budesonide which was hypothesized to result from different localization of drugs within the PLL­(DBSA) nanoparticles. These results instruct to prepare polypeptide aerosol nanoparticles with internal self-assembled structures and to control the secondary structures by aerosol solvent annealing, which we foresee to be useful, e.g., toward controlling the release of poorly soluble drug molecules

Fabrication of Dual-Type Nanowire Arrays on a Single Substrate

A novel method for fabricating dual-type nanowire (NW) arrays is presented. Two growth steps, selective-area epitaxy (SAE) in the first step and vapor–liquid–solid (VLS) in the second step, are used to grow two types of NWs on the same GaAs substrate. Different precursors can be used for the growth steps, resulting in sophisticated compositional control, as demonstrated for side-by-side grown GaAs and InP NWs. It was found that parasitic growth occurs on the NWs already present on the substrate during the second growth step and that the SAE NWs shadow the growth of the VLS NWs. Optical reflectance measurements revealed the dual-type array having improved light trapping properties compared to single-type arrays. Dual-type NW arrays could be practical for thermoelectric generation, photovoltaics and sensing where composition control of side-by-side NWs and complex configurations are beneficial

Visualization 4: Nonlinear microscopy using cylindrical vector beams: Applications to three-dimensional imaging of nanostructures

Visualization 4. 3D SHG images of the vertically-aligned semiconductor nanowires using azimuthal polarization Originally published in Optics Express on 29 May 2017 (oe-25-11-12463

Thermally Sensitive Block Copolymer Particles Prepared via Aerosol Flow Reactor Method: Morphological Characterization and Behavior in Water

This work describes properties of thermosensitive submicrometer-sized particles having the same chemical composition but different morphologies. These particles have been prepared with an aerosol technique using dimethylformamide solutions of linear polystyrene-<i>block</i>-poly­(<i>N</i>-isopropylacrylamide)-<i>block</i>-polystyrene, PS-<i>b</i>-PNIPAM-<i>b</i>-PS. The particles were characterized by cryo-electron microscopy, microcalorimetry, and light scattering. Block copolymers self-assembled within the particles forming onion-like, gyroid-like, and spherical morphologies having poly­(<i>N</i>-isopropylacrylamide) matrix and physically cross-linking polystyrene domains. The particles were dispersed in aqueous media, and their behavior in water was studied both below and above the lower critical solution temperature of poly­(<i>N</i>-isopropylacrylamide). We found out that the particles with spherical and gyroid-like morphologies swell considerably in water at 20 °C, whereas at 40 °C the particles resemble more of those studied without water treatment. Light scattering experiments showed that the particles gradually aggregate and precipitate with time at 40 °C. Microcalorimetric studies revealed for all three studied morphologies that PNIPAM undergoes a two-step transition due to the different hydration levels of PNIPAM inside and outside the particles. Thicknesses of the PS and PNIPAM layers within the onion-like particles were analyzed using the TEM micrographs by fitting a model of electron density to the integrated electron intensity data. The surface layer of the particles was found out to be PNIPAM, which was supported by light scattering and microcalorimetry. It was also found out from the TEM micrograph analysis that the width of the outmost PS layer is considerably thinner than the one in the dry state prior to immersion in water, and a degradation scheme is proposed to explain these results

Thermally Sensitive Block Copolymer Particles Prepared via Aerosol Flow Reactor Method: Morphological Characterization and Behavior in Water

This work describes properties of thermosensitive submicrometer-sized particles having the same chemical composition but different morphologies. These particles have been prepared with an aerosol technique using dimethylformamide solutions of linear polystyrene-<i>block</i>-poly­(<i>N</i>-isopropylacrylamide)-<i>block</i>-polystyrene, PS-<i>b</i>-PNIPAM-<i>b</i>-PS. The particles were characterized by cryo-electron microscopy, microcalorimetry, and light scattering. Block copolymers self-assembled within the particles forming onion-like, gyroid-like, and spherical morphologies having poly­(<i>N</i>-isopropylacrylamide) matrix and physically cross-linking polystyrene domains. The particles were dispersed in aqueous media, and their behavior in water was studied both below and above the lower critical solution temperature of poly­(<i>N</i>-isopropylacrylamide). We found out that the particles with spherical and gyroid-like morphologies swell considerably in water at 20 °C, whereas at 40 °C the particles resemble more of those studied without water treatment. Light scattering experiments showed that the particles gradually aggregate and precipitate with time at 40 °C. Microcalorimetric studies revealed for all three studied morphologies that PNIPAM undergoes a two-step transition due to the different hydration levels of PNIPAM inside and outside the particles. Thicknesses of the PS and PNIPAM layers within the onion-like particles were analyzed using the TEM micrographs by fitting a model of electron density to the integrated electron intensity data. The surface layer of the particles was found out to be PNIPAM, which was supported by light scattering and microcalorimetry. It was also found out from the TEM micrograph analysis that the width of the outmost PS layer is considerably thinner than the one in the dry state prior to immersion in water, and a degradation scheme is proposed to explain these results

Visualization 1: Nonlinear microscopy using cylindrical vector beams: Applications to three-dimensional imaging of nanostructures

Visualization 1. 3D SHG images of the vertically-aligned semiconductor nanowires using linear x polarization Originally published in Optics Express on 29 May 2017 (oe-25-11-12463

Visualization 3: Nonlinear microscopy using cylindrical vector beams: Applications to three-dimensional imaging of nanostructures

Visualization 3. 3D SHG images of the vertically-aligned semiconductor nanowires using radial polarization Originally published in Optics Express on 29 May 2017 (oe-25-11-12463