Search results for "Charge"
showing 10 items of 4686 documents
Collapse of Linear Polyelectrolyte Chains in a Poor Solvent: When Does a Collapsing Polyelectrolyte Collect its Counterions?
2008
To better understand the collapse of polyions in poor solvent conditions the effective charge and the solvent quality of the hypothetically uncharged polymer backbone need to be known. In the present work this is achieved by utilizing poly-2-vinylpyridine quaternized to 4.3% with ethylbromide. Conductivity and light scattering measurements were utilized to study the polyion collapse in isorefractive solvent/nonsolvent mixtures consisting of 1-propanol and 2-pentanone, respectively, at nearly constant dielectric constant. The solvent quality of the uncharged polyion could be quantified which, for the first time, allowed the experimental investigation of the effect of the electrostatic intera…
Synthèse de chalcones à base de tétrathiafulvalène: RC(O)CHC(CH3)TTF, TTFC(O)CHC(CH3)R (R TTF: C6H3S4; Bct: C6H5Cr(CO)3; Fc: C5H4FeC5H5). Propr…
1992
Abstract Novel chalcones that contain tetrathiafulvalene (TTF) and/or metallocene (ferrocenyl or benchrotrenyl) moieties: RC(O)CHC(CH 3 )R′ (R and/or R′ TTF: C 6 H 3 S 4 ; Fc: C 5 H 4 FeC 5 H 5 ; Bct: C 6 H 5 Cr(CO) 3 ) were prepared using TiCl 3 /Et 3 N as the condensation reagent. The 1-1 charge transfer complex with TCNQ (tetracyanoquinodimethane was obtained for the ditetrathiafulvalenic derivative (R R′ TTF). This complex exhibits the semiconducting behaviour.
Growth of fibrous aggregates of silica nanoparticles: Fibre growth by mimicking the biogenic silica patterning processes
2009
We describe the self-assembly of discrete SiO2 nanofibers via grafting of silicatein side chains to a polymer backbone. The covalent binding of silicatein to the backbone of the polymer is based on the affinity of the nitrilotriacetic acid (NTA) side chain, which serves as a ligand for the immobilization of His-tagged silicatein. The surface charge and the bulkiness of the protein moieties prevent the entropically favoured coil formation of the polymer and force it to adopt an open chain structure after hydrolysis of the silica precursors. The probes were characterized by scanning force microscopy (SFM) and optical light microscopy. Surface complexation of the resulting silica nanoparticles…
Quartz Crystal Microbalance for Bioanalytical Applications
2001
The quartz crystal microbalance (QCM) was first introduced as a mass sensor in gas phase and in vacuum. Since oscillator circuits capable of exciting shear vibrations of quartz resonators under liquid load have been developed, the QCM became accepted as a new powerful technique to monitor adsorption processes at solid/liquid interfaces in chemical and biological research rendering the method an attractive low-cost alternative for bioanalytic applications. In the last decade, adsorption of biomolecules on functionalized surfaces turned out to be one of the paramount applications of piezoelectric transducers comprising the interaction of DNA and RNA with complementary strands, specific recogn…
Modified Halloysite Nanotubes: Nanoarchitectures for Enhancing the Capture of Oils from Vapor and Liquid Phases
2013
We prepared hybrid halloysite nanotubes (HNT/sodium alkanoates) in which the inner cavity of the nanoclay was selectively modified. Physicochemical studies evidenced the interactions between HNT and sodium alkanoates, ruled out clay exfoliation, quantified the amount of the loaded substance, and showed an increase of the total net negative charge, allowing us to obtain rather stable aqueous nanoclay dispersions. These dispersions were exploited as inorganic micelles to capture hydrocarbon and aromatic oils in the vapor and liquid states and were revealed to be nonfoaming but very efficient in encapsulating oils. Here, we have fabricated biocompatibile and low-cost inorganic micelles that ca…
2H NMR studies of phase behaviour and molecular motions of doped discotic liquid-crystalline systems
1990
Abstract A discotic triphenylene monomer as well as a dimer and a main chain polymer, all substituted with heptyloxy side groups, were doped with an electron acceptor (2,4,7-trinitrofluorenone (TNF)) to give charge transfer complexes. These doped systems were aligned in a magnetic field, thus proving their liquid crystallinity. 2H NMR measurements show that the electron acceptor molecules are incorporated into the columns built of triphenylene cores. In the charge transfer complex with the triphenylene monomer almost all the electron acceptor molecules stack in the columns even close to the clearing temperature T 1, while for the dimer and especially for the polymer a significant fraction o…
On the Stability of Polymeric Nanoparticles Fabricated through Rapid Solvent Mixing.
2018
We study the stability of polymeric nanoparticles fabricated through the rapid mixing of polymers in a good solvent with a poor solvent that is miscible with the good solvent. In previous experiments where water was used as the poor solvent, a negative surface charge was measured on the precipitated nanoparticles, which led to the long-time stability of the dispersion. It was argued that these charges originate presumably from either water or hydroxide adsorption at the hydrophobic nanoparticle surface or from impurities in the feed streams that preferentially adsorb on the precipitated nanoparticles. To elucidate the origin of this stabilization mechanism, we performed experiments wherein …
Microfluidic Pumping by Micromolar Salt Concentrations
2017
An ion-exchange-resin-based microfluidic pump is introduced that utilizes trace amounts of ions to generate fluid flows. We show experimentally that our pump operates in almost deionized water for periods exceeding 24h and induces fluid flows of um/s over hundreds of um. This flow displays a far-field, power-law decay which is characteristic of two-dimensional (2D) flow when the system is strongly confined and of three-dimensional (3D) flow when it is not. Using theory and numerical calculations we demonstrate that our observations are consistent with electroosmotic pumping driven by umol/L ion concentrations in the sample cell that serve as 'fuel' to the pump. Our study thus reveals that t…
Effect of conductivity of hole injection layer on the performance of a blue light emitting solution processable OLED
2005
The performance of blue emitting OLED devices, using a polyspiro as blue light emitting polymer, were studied as a function of the conductivity of a novel hybrid hole injection material. The hole injection material is based on a polyarylamine using a molecular magnet as oxidant. The charge density and the luminance of the devices changed considerably with increasing conductivity of the hole injection layer. The change in device performance can be attributed to a change from a hole limited device to a balanced charge carrier device and eventually to an electron limited device. The performance of the optimized device configuration is significantly improved with respect to a device making use …
Viscometry of polyelectrolyte solutions: Star-like versus linear poly[[2-(methacryloyloxy)ethyl] trimethylammonium iodide] and specific salt effects
2017
Abstract The intrinsic viscosities, [η], of the 3-arm star polyelectrolyte in pure water are for a given molar mass considerably lower than for the linear product because of the higher monomer concentration and charge density in isolated coils. These effects are much more pronounced than in the case of uncharged macromolecules. Extra salt (NaCl, NaI, CaCl2) reduces the solution viscosities of the 3-arm star polymer less than of the linear product. The transition of [η] from the value in pure water to the minimum saturation value at high salt concentrations follows a Boltzmann sigmoid. In saline solvents the changes of the viscosities with rising polymer concentration depend strongly on the …