Search results for "Colloid"
showing 10 items of 1288 documents
Synthesis and characterization of catalytic iridium nanoparticles in imidazolium ionic liquids
2006
Abstract The reduction of [Ir(cod)Cl]2 (cod = 1,5-cyclooctadiene) dissolved in 1-n-butyl-3-methyl tetrafluoroborate, hexafluorophosphate and trifluoromethane sulphonate ionic liquids in the presence of 1-decene by molecular hydrogen produces Ir(0) nanoparticles. The formation of these nanoparticles follows the two-step [A → B, A + B → 2B ( k 1 , k 2 )] autocatalytic mechanism. The same mean diameter values of around 2–3 nm were estimated from in situ TEM and SAXS analyses of the Ir(0) nanoparticles dispersed in the ionic liquids and by XRD of the isolated material. XPS and EXAFS analyses clearly show the interactions of the ionic liquid with the metal surface demonstrating the formation of …
Characterization of the Oxidation of Magnetite Nanoparticles during Their Synthesis by Different Structural Analysis Techniques
2020
Water colloidal solutions of iron oxide nanoparticles coated with tetramethylammonium hydroxide were synthesized by co-precipitation methods. Dimensional analyses were accomplished by transmission ...
Conformation of a chain polyelectrolyte in solution with low molecular weight salt: small angle neutron scattering measurements
1986
Small angle neutron scattering measurements have been carried out on the tetramethylammonium salt of the polystyrenesulfonic acid withDP w =310 and 1060 in water solution with tetramethylammonium chloride with ionic strength between 0.02 M and 1.0 M. The scattering curves in the scattering vector range 0.05 nm−1≤Q≤1.8nm−1 have been fitted using the form factor of a worm-like chain of finite thickness. The conformational parameters mean square radius of gyration, statistic chain element, mass per unit length and mean square radius of the cross-section have been determined experimentally and used for describing the conformation of the coils. By these molecular weights and ionic strengths, exc…
Ion Pair Recognition of Quaternary Ammonium and Iminium Salts by Uranyl-Salophen Compounds in Solution and in the Solid State
2007
Efficient ditopic receptors for quaternary ammonium and iminium salts have been obtained upon functionalization of the uranyl-salophen unit with conformationally flexible side arms bearing phenyl or beta-naphthyl substituents. Binding affinities in chloroform solution have been measured for a large number of quaternary salts comprising tetramethylammonium (TMA), tetrabutylammonium (TBA), acetylcholine (ACh), N-methylpyridinium (NMP), and N-methylisoquinolinium (NmiQ) cations. Recognition of the anion partner is ensured by coordination to the hard Lewis acidic uranyl center, whereas cation-pi/CH-pi interactions of the quaternary ions are established with the aromatic pendants. The role of th…
Active colloidal suspensions: Clustering and phase behavior
2014
We review recent experimental, numerical, and analytical results on active suspensions of self-propelled colloidal beads moving in (quasi) two dimensions. Active colloids form part of the larger theme of active matter, which is noted for the emergence of collective dynamic phenomena away from thermal equilibrium. Both in experiments and computer simulations, a separation into dense aggregates, i.e., clusters, and a dilute gas phase has been reported even when attractive interactions and an alignment mechanism are absent. Here, we describe three experimental setups, discuss the different propelling mechanisms, and summarize the evidence for phase separation. We then compare experimental obse…
Structure relaxation after temperature jumps in homogeneous polystyrene/poly(styrene-co-bromostyrene) blends
1988
Concentration fluctuations in polymer blends and their change after a temperature jump were studied by time-dependent small angle X-ray scattering experiments. Measurements were conducted on homogeneous mixtures of polystyrene and a partially brominated derivative. Structure factors in thermal equilibrium show the form given by the random phase approximation, thus enabling a direct determination of theχ-parameter and the mean radius of gyration. TheT-dependence ofχ can be understood as the result of superposed enthalpic contributions and a free volume term. In theT-jump experiments, samples were quenched to temperatures near Tg. Relaxation occurs on the time scale of minutes and is nonexpon…
Effect of Isovalent Substitution on the Thermoelectric Properties of the Cu2ZnGeSe4–xSx Series of Solid Solutions
2013
Knowledge of structure–property relationships is a key feature of materials design. The control of thermal transport has proven to be crucial for the optimization of thermoelectric materials. We report the synthesis, chemical characterization, thermoelectric transport properties, and thermal transport calculations of the complete solid solution series Cu_2ZnGeSe_(4–x)S_x (x = 0–4). Throughout the substitution series a continuous Vegard-like behavior of the lattice parameters, bond distances, optical band gap energies, and sound velocities are found, which enables the tuning of these properties adjusting the initial composition. Refinements of the special chalcogen positions revealed a chang…
Carbon Nano-onions: Potassium Intercalation and Reductive Covalent Functionalization
2021
Herein we report the synthesis of covalently functionalized carbon nano-onions (CNOs) via a reductive approach using unprecedented alkali-metal CNO intercalation compounds. For the first time, an in situ Raman study of the controlled intercalation process with potassium has been carried out revealing a Fano resonance in highly doped CNOs. The intercalation was further confirmed by electron energy loss spectroscopy and X-ray diffraction. Moreover, the experimental results have been rationalized with DFT calculations. Covalently functionalized CNO derivatives were synthesized by using phenyl iodide and n-hexyl iodide as electrophiles in model nucleophilic substitution reactions. The functiona…
One step grafting of monomethoxy poly(ethylenglycol) during synthesis of maghemite nanoparticles in aqueous medium
2008
Abstract Grafting of silanated monomethoxy poly(ethylene glycol) (m-PEG) onto maghemite nanoparticles surface in aqueous medium through one step procedure was investigated. The major characteristic of this work is that the grafting of m-PEG was produced during the synthesis of maghemite nanoparticles. The maghemite nanoparticles were characterized by photon correlation spectroscopy (PCS), zeta potential measurement, X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), Fourier transform infrared spectrometer (FTIR), and X-ray photoelectron spectroscopy (XPS). The spinel structure of maghemite nanoparticles was verified and successful grafting of m-PEG was evid…
Effect of halloysite nanotubes filler on polydopamine properties
2019
Abstract Hypothesis Polydopamine (PDA) is widely used as hydrophilic coating for several applications. However, most of the methods studied to improve or manipulate PDA properties are multistep and time-consuming, and there is a need for versatile strategies aimed at controlling and modifying the properties of PDA. Experiments PDA-halloysite nanocomposites were produced under different oxidation conditions in alkaline and acidic media and were characterized by UV–visible and attenuated total refraction- Fourier Transform Infrared spectroscopies, thermogravimetric analysis, porosimetry, scanning electron microscopy, X-ray diffraction and contact angle measurements against the reference PDA p…