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21.
Effect of growth conditions on the structure of two-dimensional latex crystals: experiment 总被引:1,自引:0,他引:1
C. D. Dushkin G. S. Lazarov S. N. Kotsev H. Yoshimura K. Nagayama 《Colloid and polymer science》1999,277(10):914-930
The growth kinetics and structure of two-dimensional crystals of fine latex particles on solid substrates have been studied
using a variety of microscopic techniques: optical microscopy, surface plasmon resonance microscopy, transmission electron
microscopy, scanning electron microscopy and atomic force microscopy. A circular-shaped crystal is grown from a thin layer
of a latex suspension by a two-step mechanism: nucleation and crystal growth. Here we report an experimental study of the
factors influencing the crystallization process, especially focusing on the water evaporation rate, the liquid meniscus at
the crystal boundary, the particle size and concentration, the substrate, etc. Crystals of good quality and structure are
grown at a high evaporation rate (low humidity) favoring a convection-dominated influx of particles from the suspension. The
particle diffusion plays a role at suppressed evaporation thus causing an increase in the number of crystal defects. The dynamics
of the meniscus slope leads to growth instability resulting in a sequence of multilayer rings. A hexagonal lattice prevails
in the final crystal whereas a square lattice is observed in the transition regions between two different hexagonal multilayers.
These general trends of the crystallization process are the same for different particle diameters (19 nm, 55 nm, 144 nm and
1.696 μm), volume fractions (0.001–0.01) and substrates (bare and metal-coated glass and mica).
Received: 8 February 1999 Accepted in revised form: 12 May 1999 相似文献
22.
A structural failure problem was solved using an integrated and iterative program of testing and analysis. The steps taken in solving the problem were: analytical calculations; operational testing; qualifications of analytical results; problem identification; design of corrective action; and confirmatory testing. 相似文献
23.
N.I. Maliavski O.V. Dushkin E.V. Tchekounova J.V. Markina G. Scarinci 《Journal of Sol-Gel Science and Technology》1997,8(1-3):571-575
Partially polycondensed γ-aminopropylsilanetriol, (APSTOL) was prepared by hydrolyzing γ-aminopropyltriethoxysilane at a hydrolysis
ratio 8.0. APSTOL contains up to 52% SiO2 and can be easily dissolved in water, forming clear solutions remaining stable practically at any pH value. The thermal evolution
of APSTOL when heating up to 1000°C was examined using TGA and FTIR techniques; the probable mechanism of the oxidative decomposition
of organic groups, with the formation of imino- and carboxyl-containing intermediates, has been discussed. Two magnesium silicates
of the enstatite and forsterite, compositions and two calcium silicates of the wollastonite and rankinite, compositions have
been prepared, using corresponding acetates and APSTOL as MIIO and SiO2 precursors. The crystallization, processes in these systems were studied by TGA and XRD techniques, after heat treatments
up to 1000°C. In all the systems, except rankinite, the parent silicates were found as the main crystalline phases. 相似文献
24.
Georgi?G.?YordanovEmail author Ceco?D.?Dushkin Gospodinka?D.?Gicheva Bocho?H.?Bochev Eiki?Adachi 《Colloid and polymer science》2005,284(2):229-232
Semiconductor nanocrystals are of a great interest for many practical applications which motivates the search of low cost and environmental-friendly methods for their manufacturing. Here we report the synthesis of CdSe and CdS nanoparticles utilizing composite matrix of liquid paraffin as a non-coordinating solvent and stearic acid as a coordinating ligand. The nanoparticle growth kinetics is compared to that of the classical synthesis in trioctylphosphine oxide matrix. It is found that the nucleation and crystal growth are remarkably affected by the coordinating ligand. The CdSe and CdS nanocrystals can be isolated and purified from the matrix which makes it possible their large-scale synthesis for applications. 相似文献
25.
Yttria stabilized zirconia (YSZ) thin films are obtained using both spray-pyrolysis and dip-coating. The ability of YSZ films
incorporated with platinum nanospecies (Pt-YSZ) to detect oxygen is compared with that of pure YSZ thin films using a new
experimental setup. With this system, the surface electrical resistance of the films as a function the oxygen content is measured
at a fixed temperature. In addition, the effects of thermal annealing on the oxygen sensitivity of the films are observed.
Platinum doped samples, Pt-YSZ, show different kinetics of carrier diffusion as compared to pure YSZ samples. 相似文献
26.
The kinetics of adsorption from micellar surfactant solutions is considered theoretically from a uniform point of view. Three boundary value problems for the adsorption on flat and on spherical interface are solved analytically by means of the method of the Green functions. In this way the bulk concentration and the adsorption of surfactant monomers are expressed as functions of time. The contribution of the micelles (surfactant aggregates) to the diffusion of the monomers is accounted for as pseudo-first order reaction. The adsorption from surfactant solutions without micelles turns out to be the particular case of the problems considered here. Being general in form, the derived equations can be applied also to other practical problems in heterogeneous chemical kinetics, adsorption of gases, heat transfer, etc. 相似文献
27.
N. Maliavski E. Tchekounova O. Dushkin 《Journal of Sol-Gel Science and Technology》1994,2(1-3):503-505
The spinnability conditions for concentrated aqueous solutions of polysilicates of aliphatic amines, were investigated. The spinnable state was shown to be characteristic for the temperature regions of the reversible increase of viscosity with heating caused by a displacement of polycondensation equilibrium of polysilicate anions. The gel fibers were drawn from the viscous solutions and converted to silica fibers by heating above 700°C. The thermal evolution of the fibers was studied using TGA, XRD and SEM techniques. 相似文献
28.
29.
Emin SM Denkova PS Papazova KI Dushkin CD Adachi E 《Journal of colloid and interface science》2007,305(1):133-141
(1)H NMR spectroscopy was used to investigate the aggregation of the surfactant di-isobutyl-phenoxy-ethoxy-ethyl-dimethyl-benzyl ammonium methacrylate (Hyamine-M) in benzene. Adding water makes swollen reverse micelles (microemulsion droplets). The droplets also contain cadmium ions and the sodium salt of the methacrylic acid. The critical micelle concentration of Hyamine-M was determined by NMR to be 3.95 mM under the current conditions. Two-dimensional NMR NOESY spectra were used to study the conformation of the surfactant in the micelle and the spatial localization of water and counterions. We found that the surfactant molecules are folded with both phenyl fragments oriented toward the micelle exterior and the oxyethylene and NCH(3) groups in the micelle core. The water molecules and counterions are distributed around the surfactant polar groups in the micelle interior and penetrate up to both aromatic rings. The investigated system can be further utilized as a microemulsion matrix for the synthesis of cadmium-containing semiconductor nanocrystals, eventually capped with a polymer shell, or of polymer nanoparticles. 相似文献
30.
Saim M. Emin Ceco D. Dushkin Seiichiro Nakabayashi Eiki Adachi 《Central European Journal of Chemistry》2007,5(2):590-604
We first focus on the kinetics of nanoparticle growth in a microemulsion synthesis of CdSe semiconductor nanocrystals. The
process consists of a fast initial stage of typical time constant of the order of 103 s followed by a slow stage of time constant of the order of 104s. Growth proceeds similarly to that described for the hot-matrix synthesis of CdSe, underlining the generality of the two-stage
growth mechanism, irrespective of the matrix type and synthesis conditions. However, the time constant of each stage in the
microemulsion synthesis is much larger than in the hot-matrix one. Also, the ratio between the fast and slow time constant
is appreciably bigger. We also prove that larger size reverse micelles, obtained by increasing the water:surfactant ratio,
generally lead to larger CdSe nanoparticles. Bis(trimethylsilyl) selenium is the crucial precursor for the CdSe nanoparticle
synthesis. An intermediate stage of the chemical reaction limiting the bis(trimethylsilyl) selenium production is described
theoretically.
相似文献