Search results for "Colloid"

The Role of Order-Disorder Transitions in the Quest for Molecular Multiferroics: Structural and Magnetic Neutron Studies of a Mixed Valence Iron (II)…

2012

Neutron diffraction studies have been carried out to shed light on the unprecedented order-disorder phase transition (ca. 155 K) observed in the mixed-valence iron(II)-iron(III) formate framework compound [NH 2(CH3)2]n[FeIIIFe II(HCOO)6]n. The crystal structure at 220 K was first determined from Laue diffraction data, then a second refinement at 175 K and the crystal structure determination in the low temperature phase at 45 K were done with data from the monochromatic high resolution single crystal diffractometer D19. The 45 K nuclear structure reveals that the phase transition is associated with the order-disorder of the dimethylammonium counterion that is weakly anchored in the cavities …

Confinement effects on phase behavior of soft matter systems.

2008

When systems that can undergo phase separation between two coexisting phases in the bulk are confined in thin film geometry between parallel walls, the phase behavior can be profoundly modified. These phenomena shall be described and exemplified by computer simulations of the Asakura-Oosawa model for colloid-polymer mixtures, but applications to other soft matter systems (e.g. confined polymer blends) will also be mentioned. Typically a wall will prefer one of the phases, and hence the composition of the system in the direction perpendicular to the walls will not be homogeneous. If both walls are of the same kind, this effect leads to a distortion of the phase diagram of the system in thin …

Nanosized shape-changing colloids from liquid crystalline elastomers.

2010

A method to prepare shape-changing nanospheres from liquid crystalline elastomers is reported. The nanosized colloids are prepared by a miniemulsion process. During this process, colloids are prepared from a liquid crystalline (LC) main-chain polyester and subsequently crosslinked into a nanometer-sized LC elastomer. The ability of these LC elastomers to change their shape at the phase transition temperature from the smectic A to the isotropic phase was detected by temperature-dependent transmission electron microscopy. The phase transition-induced shape change leads to strongly shape anisotropic nanosized elastomer particles.

Independent ion migration in suspensions of strongly interacting charged colloidal spheres

1999

We report on sytematic measurements of the low frequency conductivity in aequous supensions of highly charged colloidal spheres. System preparation in a closed tubing system results in precisely controlled number densities between 1E16/m3 and 1E19/m^3 (packing fractions between 1E-7 and 1E-2) and electrolyte concentrations between 1E-7 and 1E-3 mol/l. Due to long ranged Coulomb repulsion some of the systems show a pronounced fluid or crystalline order. Under deionized conditions we find s to depend linearily on the packing fraction with no detectable influence of the phase transitions. Further at constant packing fraction s increases sublinearily with increasing number of dissociable surfac…

Thermoelectric Transport in Cu7PSe6 with High Copper Ionic Mobility

2014

Building on the good thermoelectric performances of binary superionic compounds like Cu2Se, Ag2Se and Cu2S, a better and more detailed understanding of phonon-liquid electron-crystal (PLEC) thermoelectric materials is desirable. In this work we present the thermoelectric transport properties of the compound Cu7PSe6 as the first representative of the class of argyrodite-type ion conducting thermoelectrics. With a huge variety of possible compositions and high ionic conductivity even at room temperature, the argyrodites represent a very good model system to study structure-property relationships for PLEC thermoelectric materials. We particularly highlight the extraordinary low thermal conduct…

Photosensitised Seeding of Thiolate-Stabilised Gold Nanoparticles

2010

Enhancement of visible light photoelectrocatalytic activity of ZnO(core)/TiO2(shell) composite by N-doping and decorating with Au0 nanoparticles

2017

Abstract The composites consisting of ITO-supported ZnO nanorods covered with TiO2 shell were doped with nitrogen and decorated with gold nanoparticles in order to improve their photocatalytic activity under visible light. N-doped TiO2 (TiO2(N)) was prepared under mild conditions through a simple sol-gel synthesis in the presence of NH4Cl. Such procedure results in formation of a highly porous shell of TiO2(N) on the ZnO nanorods. The gold nanoparticles (AuNPs) of the size 7–25 nm were grafted onto the surface of TiO2 as well as TiO2(N) by a photodeposition method from aqueous solution of [AuCl(4-x)(OH)x]− precursor at pH 6.7. The composition and microstructure of the prepared samples were …

Plasmonic versus catalytic effect of gold nanoparticles on mesoporous TiO2 electrodes for water splitting

2014

a b s t r a c t Solar water splitting with metal oxide semiconductors constitutes a promising approach to the conversion of solar energy into chemical energy stored in the atomic bonds of hydrogen molecules. In the present study, we evaluate the effect of the presence of Au nanoparticles on the photoelectrochemical behaviour of mesoporous TiO2 to photo-oxidize water. We observe that the presence of Au nanoparticles leads to enhanced photocurrents for water oxidation and we explore the origin of this enhancement by optical and electrochemical characterization techniques. Our results indicate that although the Au nanoparticles are responsible for a localized surface plasmonic resonance effect…

Plasmon-enhanced photocurrent in quasi-solid-state dye-sensitized solar cells by the inclusion of gold/silica core–shell nanoparticles in a TiO2 phot…

2013

Direct evidence of the effects of the localized surface plasmon resonance (LSPR) of gold nanoparticles (Au NPs) in TiO2 photoanodes on the performance enhancement in quasi-solid-state dye-sensitized solar cells (DSCs) is reported by comparing gold/silica core–shell nanoparticles (Au@SiO2 NPs) and hollow silica nanoparticles with the same shell size of the core–shell nanoparticles. The Au nanoparticles were shelled by a thin SiO2 layer to produce the core–shell structure, and the SiO2 hollow spheres were made by dissolving the Au cores of the gold/silica core–shell nanoparticles. Therefore, the size and morphology of the SiO2 hollow spheres were the same as the Au@SiO2 NPs. The energy conver…

Microwave-assisted synthesis of anhydrous CdS nanoparticles in a water-oil microemulsion.

2006

Abstract Microwave irradiation at a frequency of 2.45 GHz and a power ranging between 22 and 30 W was used, in a water–oil microemulsion at 35 ± 2 ° C , to obtain stable, small, crystalline, anhydrous CdS nanoparticles exhibiting enhanced luminescence properties. The process of nanoparticles growth at different irradiation times was followed by UV–vis spectroscopy. It was observed that irradiated nanoparticles grew faster and their size reached a constant value. The final mean nanoparticle diameter was 2.7 nm, smaller than that observed in a non-irradiated sample, in which particle dimensions slowly increased even after 10 h. This finding was confirmed by high resolution transmission electr…