Search results for "Colloid"

Novel core–shell (TiO2@Silica) nanoparticles for scattering medium in a random laser: higher efficiency, lower laser threshold and lower photodegrada…

2013

There has been growing interest in scattering media in recent years, due to their potential applications as solar collectors, photocatalyzers, random lasers and other novel optical devices. Here, we have introduced a novel core-shell scattering medium for a random laser composed of TiO2@Silica nanoparticles. Higher efficiency, lower laser threshold and long photobleaching lifetime in random lasers were demonstrated. This has introduced a new method or parameter (fraction of absorbed pumping), which opens a new avenue to characterize and study the scattering media. Optical chemical and colloidal stabilities were combined by coating a suitable silica shell onto TiO2 nanoparticles.

Hydrodynamic chromatography of macromolecules on small spherical non-porous silica particles

1990

Abstract Non-porous silica spheres with sizes in the range 1.4–2.7 μm were applied as packings for the hydrodynamic chromatography (HDC) of macromolecules. Highly efficient columns, with a reduced plate height below 2, were packed with these small particles. Up to molecular weights of 10 6 the elution behaviour of polystyrenes agreed very well with existing theoretical models. However, for larger polystyrenes the flow-rate exerted an influence on the relative peak positions. The applicability of HDC to rapid separations of soluble macromolecules and inorganic colloids was demonstrated.

Phase behaviour of deionized binary mixtures of charged colloidal spheres.

2009

We review recent work on the phase behaviour of binary charged sphere mixtures as a function of particle concentration and composition. Both size ratios and charge ratios are varied over a wide range. By contrast to hard spheres the long ranged Coulomb interaction stabilizes the crystal phase at low particle concentrations and shifts the occurrence of amorphous solids to particle concentrations considerably larger than the freezing concentration. Depending on size- and charge ratios we observe upper azeotrope, spindle, lower azeotrope and eutectic types of phase diagrams, all known well from metal systems. Most solids are of body centred cubic structure. Occasionally stoichiometric compound…

Packing polydisperse colloids into crystals: when charge-dispersity matters

2019

Monte-Carlo simulations and small-angle x-ray scattering experiments were used to determine the phase diagram of aqueous dispersions of titratable nano-colloids with a moderate size polydispersity over a broad range of monovalent salt concentrations, 0.5 mM $\leq c_s \leq$ 50 mM and volume fractions, $\phi$. Under slow and progressive increase in $\phi$, the dispersions freeze into a face-centered-cubic (fcc) solid followed unexpectedly by the formation of a body centered cubic (bcc) phase before to melt in a glass forming liquid. The simulations are found to predict very well these observations. They suggest that the stabilization of the bcc solid at the expense of the fcc phase at high $\…

Nonlinear Optical Characterization of InP@ZnS Core-Shell Colloidal Quantum Dots Using 532 nm, 10 ns Pulses

2021

InP@ZnS core-shell colloidal quantum dots (CQDs) were synthesized and characterized using the z-scan technique. The nonlinear refraction and nonlinear absorption coefficients (γ = −2 × 10−12 cm2 W−1, β = 4 × 10−8 cm W−1) of these CQDs were determined using 10 ns, 532 nm pulses. The saturable absorption (β = −1.4 × 10−9 cm W−1, Isat = 3.7 × 108 W cm−2) in the 3.5 nm CQDs dominated at small intensities of the probe pulses (I ≤ 7 × 107 W cm−2) followed by reverse saturable absorption at higher laser intensities. We report the optical limiting studies using these CQDs showing the suppression of propagated nanosecond radiation in the intensity range of 8 × 107–2 × 109 W cm−2. The role of nonline…

Electrophoretic mobility of electrostatically interacting colloidal spheres

2004

We have measured the electrophoretic mobility μ = vE/E (where E is the electric field strength and vE the electrophoretic velocity) of highly charged colloidal spheres in deionized aqueous suspension at particle number densities n between 0.15 and 150 µm−3. Under these conditions the system exhibits fluid or crystalline order. We used laser Doppler velocimetry to determine the electrophoretic velocities vE as spatially averaged particle velocities from both integral and spatially resolved measurements. With this approach we were for the first time able to extend measurements far into the crystalline region of the phase diagram. We found μ to be constant at low n while at large n we observe …

Chiral Inversion of Thiolate-Protected Gold Nanoclusters via Core Reconstruction without Breaking an Au-S Bond

2019

On the basis of density functional theory computations of the well-known chiral Au38(SR)24 nanocluster and its Pd- and Ag-doped derivatives, we propose here a mechanism for chiral inversion that does not require the breaking of a metal-sulfur bond at the metal-ligand interface but features a collective rotation of the gold core. The calculated energy barriers for this mechanism for Au38 and Pd-doped Au38 are in the range of 1-1.5 eV, significantly lower than barriers involving the breakage of Au-S bonds (2.5 eV). For Ag-doped Au38, barriers for both mechanisms are similar (1.3-1.5 eV). Inversion barriers for a larger chiral Au144(SR)60 are much higher (2.5-2.8 eV). Our computed barriers are…

Zr, Hf and REE fractionation between dissolved pool and sediments in river waters. Effect of changing ionic strength conditions in element partitioni…

Die Synthese reiner Oligo[hydroxy-5-nitro1,3-phenylen)-methylen]e, Verbindungen mit mehreren ortho- bzw. para-Nitrophenolbausteinen im Molekül

1976

Zur Synthese der Oligo[(hydroxy-5-nitro-1,3-phenylen)methylen]e dienten chlormethylierte Nitrophenole sowie mono- und bischlormethylierte Bis- und Tris[(hydroxy-5-nitro-1,3-phenylen)methylen]e. Die Chlormethylierung erfolgte durch Umsetzung mit Chlormethylmethylather in Gegenwart von Zinkchlorid. Die Synthese der Oligomeren gelang mit guten Ausbeuten, wenn die chlormethylierten Verbindungen mit stark uberschussigem Nitrophenol und Zinkchlorid als Katalysator kondensiert wurden. Reaktionsbedingungen und unterschiedliche Reaktionsfahigkeiten werden mitgeteilt. Einige Verbindungen wurden in ihrer Struktur bestatigt, indem sie auf zwei voneinander unabhangigen Wegen dargestellt wurden. Damit wa…

Highly stable Cp*-Ir(III) complexes with N-heterocyclic carbene ligands as C-H activation catalysts for the deuteration of organic molecules.

2006

The preparation of a series of complexes of the type CpIrX2(NHC) provides effective catalysts for the H/D exchange of a wide range of organic molecules in methanol-d4. The reaction proceeds with higher yields under milder reaction conditions than previous CpIr systems reported thus far. For comparative purposes, we also studied the catalytic activity of CpIrCl2(PMe3) under the same reaction conditions. The molecular structures of two of the new CpIr(NHC) complexes are described.