Particles In Toluene Research Articles

Small-angle neutron scattering of dilute polystyrene chains at the protein limit of a colloid-polymer mixture

The present work investigates the structure of large polystyrene (PS) chains in solutions of small poly(ethyl methacrylate) (PEMA) microgel particles in toluene. Toluene is a good solvent for the PS chains. The PEMA colloids have an outer radius of R=11 nm which is much smaller in size than the radius of gyration Rg=58 nm of the PS chains. The system is considered to represent the protein limit of polymer-colloid mixtures. Structural investigation is performed by small-angle neutron scattering (SANS) using an appropriate contrast matching. This could be achieved by dissolving fully deuterated PS chains (D8-PS) in solutions of hydrogenated PEMA colloids in hydrogenated toluene (H-toluene). It is first demonstrated that PEMA colloids are satisfactorily contrast matched for SANS in H-toluene if the PEMA concentration does not exceed 200 g/l. Based on these findings, D8-PS is investigated by SANS in pure H-toluene and three different PEMA concentrations in H-toluene. The results indicate a drastic shrinking of D8-PS chain dimensions with increasing PEMA content. Comparison with model curves of star-branched Gaussian chains and Gaussian rings suggest a striking similarity of the respective density-density correlation of those models with the shrunken D8-PS chains. Along with this, a shrinking as large as 0.5 was estimated when the PEMA content reached 200 g/l.

Cryo-TEM observation of 3-dimensionally ordered aggregates of 5-nm gold particles in organic solvents

In this article, we show evidence for the assembly of ordered 3-dimensional aggregates of 5-nm gold particles in toluene, 1-octanol, n-decane, and chloroform. The use of plunge-freezing allows to freeze the solution containing the aggregates at a rate which does not allow reorganisation of the particles during sample preparation. The samples were then observed using cryo-transmission electron microscopy (cryo-TEM) showing that most of the particles were part of ordered aggregates, thus proving that organisation already exists in solution. In some cases, the stability of the sample under the electron beam made it possible to record several pictures of the same aggregate at different angles and build animated tilt series.

Self-Assembly of Glass-Ceramic / CdSe / Protein Aggregations in the Optical Trap

ABSTRACTAggregations, created in 2-component suspension inside the optical trap zone were studied. Particles of porous glass-ceramic of CaO-TiO2-P2O5 composition and 1–50 um size were mixed with BSA molecules in water or with CdSe-TOPO 20 nm particles in toluene. Dynamic aggregations up to 300 um size were created inside the optical trap. These aggregations in comparison with one-component aggregations have a 30% higher growth rate. This effect could be explained by the stronger bonding of the protein molecules and CdSe-TOPO particles inside the glass-ceramic particle aggregations. Micro-Raman spectra, taken from dynamic and stable permanent aggregations show several new peaks, possibly associated with creation of chemical bonds.

Surface modification on time-resolved fluorescences of Fe 2O 3 nanocrystals

The time-resolved studies on the fluorescence properties of Fe 2O 3 nanoparticles prepared by forcing hydrolysis and microemulsion techniques were carried out for the first time. Two different systems of different sized nanocrystals were characterized. Specifically Fe 2O 3 5, 10 and 20 nm particles in water and Fe 2O 3 5, 10 nm particles in toluene demonstrated different fluorescence behavior. We discussed the observed phenomena in terms of surface related effects, attributing the crucial role in optical time response to the surface polarization in these systems. At the same time we clarify some controversial conclusions made in other related studies.

Effect of reaction parameters on the particle size in the dispersion polymerization of 2-hydroxyethyl methacrylate

Poly(2-hydroxyethyl methacrylate) particles in the micron size range were obtained by the dispersion polymerization. Cellulose acetate butyrate and dibenzoyl peroxide were used as steric stabilizer and initiator, respectively. The ultimate particle size could be adjusted by the selection of a suitable polymerization medium consisting of an alcohol added to toluene and by varying their relative amounts. The particle size increased with increasing solubility parameter of the mixture, i.e., by decreasing the toluene/2-methylpropan-1-ol, toluene/butan-2-ol, and toluene/3-methylbutan-1-ol ratio. The particle size decreased with increasing concentration of the stabilizer and/or initiator. At the same time, the particle size distribution became narrower. Particles prepared from polymerization mixtures purged with nitrogen before the start of polymerization were smaller, and of narrower distribution, than those prepared from nitrogen-non-purged mixtures. Equilibrium swelling of particles in toluene decreased with the decreasing content of toluene in the polymerization mixture.

Cationic surface polymerization of 1,3-divinylimidazolid-2-one for immobilization on silica gel particles

The cationic polymerization of the bifunctional monomer 1,3-divinylimidazolid-2-one (BVH) is initiated by triphenylmethylium/silica hybrid particles in toluene or 1,2-dichloroethane (DCE) as solvents. Novel poly-BVH/silica hybrid particles are obtained by this procedure. The degree of surface functionalization can be controlled by the BVH concentration and the solvent used. The cationic polymerization of BVH on the surface of silica particles is strongly determined by proton transfer reactions to the monomer. Therefore, the BVH polymer network on the silica particle contains methyl groups and double bonds among the urea units.

Adsorption of triarm starblock copolymers based on polystyrene, poly(ethylene oxide) and poly(ϵ-caprolactone) at the solid-solution interface

Triarm starblock copolymers of ABC type and AB diblock copolymers, where A, B and C are respectively poly(ethylene oxide) (PEO), polystyrene (PS) and poly(ϵ-caprolactone) (PCL) blocks, having molecular weights in the range 24 700–260 000, were prepared by anionic polymerization in tetrahydrofuran. The copolymer adsorption onto titanium dioxide particles in toluene was studied in the concentration range 0.1–30 g dm −3. The proton NMR experimental results indicate that the copolymers were adsorbed by titanium dioxide via the PEO block. For the diblock copolymer the measured maximum adsorbed amount Γ and the surface density σ were larger than those observed for the corresponding star copolymer. For star copolymers having the same number of repeat units of PS and PEO blocks ( N PS and N PEO) Γ and σ were found to increase with decreasing size of PCL block N PCL. Furthermore, the estimated average spacing Σ between the adsorbed chains was found to increase with N PCL, indicating that in the adsorbing layer the PCL arms were close together and stretched.

Formation of Nd2Fe14B hydride by milling of anhydride particles in toluene in a closed reactor

When milling micrometer thin Nd2Fe14B platelets, of an average 1–2 mm diameter, in toluene in a closed reactor, part of the toluene decomposes at the surface of the platelets and yields nascent hydrogen and carbon/low hydrocarbons. The hydrogen diffuses into the Nd2Fe14B platelets and the carbon forms a thin surface passivation layer of the platelets, forming the stable Nd2Fe14BH x ,x ≤ 5, hydride at room temperature. On heating in a calorimeter, the hydrogen desorbs off the sample with a well-defined endotherm between 370 and 425 K. An N2 gas atmosphere, if used during the heating, facilitates the H-desorption process with the modified kinetic parameters. For example, the enthalpy of the H-desorption ΔH and the related activation energyE a have the measured values ΔH = 153 J/g andE a = 58·2 kJ/mol in argon and ΔH = 256 J/g andE a = 41·6 kJ/mol in N2. It is argued that N2 gas has a fast reaction with the H atoms desorbing off the thin sample platelets and forms NH3 gas with an instantaneous decrease of the total external gas pressure at the sample. This supports the fast desorption of H atoms in the sample with the modified desorption kinetics in N2 gas.

Effect of antistatic additives on electrophoresis of ceresine particles in toluene

Effect of antistatic additives on electrophoresis of ceresine particles in toluene

Phase transitions in sterically stabilized silica colloids studied by adiabatic calorimetry

Adiabatic calorimetry measurements were made on colloidal silica particles (designated SJ4) coated with a dense layer of octadecyl chains. A dry powder consisting of these particles shows a phase transition at 284 K. This is attributed to an order–disorder transition in the stabilizing chains. Dispersing the particles in toluene shifts this order–disorder transition to lower temperatures. We propose a model in which the organic layer dissolves in the solvent at high temperatures and solidifies at low temperatures. This eutectic model predicts qualitatively correct the phase behavior of such colloidal dispersions. Particularly the pressure dependence of the phase transition is consistent with the model.

Pressure-induced phase transition in sterically stabilized colloids

Increasing the pressure on stable dispersions of sterically stabilized silica particles in toluene induces a phase transition. This transition can also be induced by lowering the temperature. The dispersion separates into two phases with different particle densities. The origin of the phase behavior cannot be explained with the classical Flory-polymer-physics model. Here we attribute the observed behavior to a ‘‘local ordering’’ or ‘‘liquid-crystalline-like phase transition’’ of the stabilizing moieties grafted to the particles. Through such an effect we can consistently explain the observed phenomena and particularly the high value of the differential quotient dp/dTtrans =+77 bars/K for the phase transition temperature at which the dispersion separates into two liquid phases of different particle concentrations.

Hydrodynamics of sedimentation of multisized particles

A one-dimensional hydrodynamic model for the sedimentation of multisized particles was developed. The basic model was solved by the ICE numerical method, using a modified K-FIX computer code. The predicted settling rates agree with Selim's et al. settling data of two heavy species and Fessas and Weiland's experiments of heavy, buoyant two-species settling. The model also computes reasonable concentration profiles in the settler. To effectively simulate the sedimentation of multisized fine colloidal particles in non-aqueous media, the model was modified to be a diffusion-type matrix equation and solved by the method of characteristics. Surface charge effect of colloidal particles was included in the model The predicted concentration profiles for the settling of fine illite particles in toluene with asphaltene agree well with the recent experimental data reported by Shih et al.

Self-transparency effects in heterogeneous nonlinear scattering media and their possible use in lasers

Transmission of intense laser beams through heterogeneous scattering media is considered. Effects of intensity limitation, self-recovery of the wave front of a transmitted beam, and bistable reflection associated with the laser-induced self-transparency (suppression of scattering) of such media are predicted because of the compensation of the linear refractive-index difference ΔnL of the heterocomponents of a medium by nonlinear change ΔnNL for different mechanisms of nonlinearity. Applications of these effects in lasers for Q switching and mode locking are discussed. The observation of self-transparency effects in several heterogeneous media (glass particles in toluene and nitrobenzene, and lead molybdenite powder) for cw Ar- and pulsed Nd- and CO2-laser radiation is reported. Q switching and mode locking have also been demonstrated with a YAG:Nd laser using nonlinear scattering in a heterogeneous cell as a control element in a laser resonator.

Dilution induced instability in ferrofluids

The effect of dilution on the stability of a ferrofluid consisting of cobalt particles in toluene has been measured. The ferrofluid was found to have a median particle diameter determined from magnetic measurements, of 5 nm. Prior to dilution the fluid was found to have long term gravitational stability, and the application of a uniform magnetic field induced only a small amount of aggregation. On dilution the fluid was found to become unstable due to the formation of large aggregates of particles. Measured settling velocities indicate that the agglomerates consisted of up to 106 particles and had radii of the order of 1μ. The effect is interpreted in terms of the equilibrium between adsorbed surfactant on the surface of the particles and free surfactant in solution in the base fluid. The implications of this effect as regards magnetic and physical measurements of the properties of ferrofluids as a function of concentration are discussed.

Small-angle X-ray scattering on ferromagnetic colloids

The size distribution and the structure of colloidal cobalt particles in toluene, as well as interparticle correlations, have been studied.

Measurements of particle size distribution parameters in ferrofluids

A method is presented by means of which (for a ferrofluid with a lognormal distribution of particle size) it is possible to determine the standard deviation (σ) and median particle diameter (D <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">v</inf> ) from the room temperature magnetisation curve. The method has been applied to several commercial ferrofluids, containing ferrite particles, and to fluids consisting of cobalt particles in toluene prepared by the method of Hess and Parker. The particle size distributions have also been measured by using an electron microscope. It has been found that the magnetic data gives estimates of the 'magnetic size distribution' parameters D <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">vm</inf> and σ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</inf> , which differed from the 'physical size distribution' parameters D <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">vp</inf> and σ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</inf> obtained from electron microscope data. It is found that D <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">vp</inf> > D <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">vm</inf> , and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\sigma_{p} &lt; \sigma_{m}</tex> . These observations are consistent with the results of Kaiser and Miskolczy and Granqvist and Buhrman.