摘要:

Recently, as an application of the novel synthetic of monodisperse particies named the “gel-sol method”, uniform spindle-like titania particles of anatase type have been produced by a 2-step process, consisting of the first aging of an aqueous solution of a titanium-triethanolamine compound for 24 h at 100°C for the formation of a rigid hydrolyzed gel and the second aging for 72 h at 140°C for the nucleation and growth of the titania particles in the gel network (T. Sugimoto et al., J. Colloid Interface Sci., in press). In this paper, the study is focused on the characterization of the titanium-triethanolamine compound, gel. and final product titania, the formation mechanism of the titania panicles, and their size control.

ISSN:0193-2691    

DOI:10.1080/01932699808913169

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Gelatin is well suited in the preparation of nanosize particles by precipitation of organic substances. Due to their amphiphilic structure, the gelatin molecules exhibit a pronounced surface activity. The surface activity was investigated by means of the Wilhelmy plate and the maximum bubble pressure technique within a time frame of more than five orders of magnitude. The influence of an emulsifier and the gelatin/emulsifier interaction are discussed. By means of laser Doppler electrophoresis, the electrophoretic mobility of A-type and B-type gelatin is measured. The molecular weight distribution of gelatin is measured by size exclusion chromatography. The size of dissolved and adsorbed gelatin molecules is determined by means of dynamic light scattering. It is shown that the surface activity of the gelatin/emulsifier complexes controls the size of the precipitated particles. Furthermore, we show that gelatin is adsorbed by hydrophobic interactions and provides excellent colloidal stability to nanosize particles.

ISSN:0193-2691    

DOI:10.1080/01932699808913170

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Water in oil droplets are used to control the size of silver metal nanoparticles. After synthesis, the silver metal particles are extracted from reverse micelles and redispersed in a non polar solvent. By increasing the size of the water droplets the average size of silver nanoparticles increases from 2 nm to 7 nm with a rather high size distribution. To narrow the panicle distribution a size selected precipitation method is used. By deposition of a dilute solution containing the coated particles on a carbon grid, the particles arrange themselves in a monolayer organized in a hexagonal network. At high particle concentration, the particles are organized in multilayers forming microcrystals arranged in a face centered cubic structure. The optical properties of the silver nanoparticles isolated in micellar solution or self-assembled in 2D or 3D supperlattices are reported.

ISSN:0193-2691    

DOI:10.1080/01932699808913171

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

An analysis of the urea method as a way to synthesize uniform colloidal particles is presented. Various selected cases of precipitation and coprecipitation are reviewed to illustrate the inherent complexities of the method. The importance of the kinetics of urea hydrolysis is recognized. The concept of trajectory is used to rationalized the evolution of the systems upon aging. The influence of thermodynamic and kinetic factors in the definition of the nature of the precipitating solid phases is analyzed; the overriding role of the latter is stressed. The factors that influence particle morphology are also addressed.

ISSN:0193-2691    

DOI:10.1080/01932699808913172

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

This paper presents a theory that links solution complexation equilibria with a model for precipitation predicting the panicle size distribution. This model uses classical nucleation theory and growth rates by various rate limiting steps for the growth of the crystals. This model is compared to forced hydrolysis experiments where dilute Indium nitrate solutions, acidified with nitric acid, were heated to 80°C. The experiments produced cubic particles of Indium hydroxide. The experiments were monitored for temperature, pH. turbidity, indium concentration in solution and particle size distribution, all as a function of lime for comparison with this model. The model gives an accurate prediction of the evolution of the particle size distribution, pH, turbidity, and indium concentration with time.

ISSN:0193-2691    

DOI:10.1080/01932699808913173

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Coated powders offer a variety of different applications. A general description of heterocoagulation and heteronucleation processes and how they are used to prepare well defined coaled participates will be given as an introduction, Following that part will be a number of practical examples. Essential properties of the powder or the final product can be influenced by a specific coaling layer. Examples are the homogeneous distribution of a second component, the protection of the core material towards a reactive environment, the intentional arrangement of electrically conductive or non conductive outer-layers, hydrophilic or hydrophobic behavior, color effects, or the design of controlled microstructures. The present review article will demonstrate how coaled powders can be used to achieve an improved control of numerous properties in composite material systems.

ISSN:0193-2691    

DOI:10.1080/01932699808913174

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The description of electrical double layer at the metal oxide/electrolyte interface requires the determination of the constants of the ionization and complexation of surface groups. These constants allows to determine distribution of surface charge and a potential across the interface region. The different methods of the estimation of these constants at the metal oxide/electrolyte interface, including potentiometric titration, ion adsorption data and zeta potential are compared.

ISSN:0193-2691    

DOI:10.1080/01932699808913175

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Since Professor Matijevité and his colleagues published pioneering work on aerosol chemical reactions, based on experiments with monodisperse aerosol generators and laminar flow reactors, there has been considerable progress in the chemical characterization of aerosol particles and the study of their chemical reactions. This paper surveys recent developments and new research on the application of Raman spectroscopy to gas/liquid and gas/solid aerosol reactions. Of particular interest are applications of the vibrating orifice aerosol generator and electrodynamic and optical levitators coupled to Raman spectrometers to explore aerosol chemistry. The systems examined include the production of polymeric microsphcrcs, the generation of metal oxide particles from alkoxide droplets, SQ2/sorbent particle reactions used for demilitarization of stick gases, chemical characterization of particle arrays, and reactions following collisions of dissimilar particles. The complications associated with the interpretation of Raman data introduced by morphology-dependent resonances in the elastically scattered light are also examined.

ISSN:0193-2691    

DOI:10.1080/01932699808913176

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

In existing theories emulsion desiabilization is considered as the combined processes of irreversible flocculation and coalescence of dispersed droplets. This approach can be justified when the potential pit characterizing the energy of droplet interaction is sufficiently deep, i.e. excluding small droplet dimensions, strong electrosiatic repulsion and low electrolyte concentrations. For smaller droplet dimensions and stronger electrostatic repulsions the emulsion instability must be considered as a combined process of reversible flocculation and coalescence. In this paper a mathematical model that couples the kinetics of flocculation, coalescence and floe fragmentation is developed in order to quantify the kinetic instability of emulsions with charged submicron droplets. The characteristic limes for flocculation (Smoluchowski's time τc) for coalescence (coalescence time τc) and for disaggregation (doublet lifetimeτd) are considered model parameters. The mathematical model applies to the case when and τd<< τc, which corresponds to a situation with a small multiplet concentration compared to the concentration of doublets and a singlet-doublet quasi-equilibrium. It is established that at singlet-doublet quasi-equilibrium the rate of the decline in the total droplet concentration is described by second order kinetics in distinction to the exponential time dependence valid for coalescence at irreversible flocculation. The double disintegration reduces the entire coalescence rate, expressed as τsm/ τd. This reduction is very large at small values of Td. The mathematical model presented can hased on the spontaneous disintegration of doublets predict changes in emulsion stability for model systems and also for technologically important emulsions.

ISSN:0193-2691    

DOI:10.1080/01932699808913177

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

This paper is a review of the points of view of Frank and Evans, Shinoda and the author regarding the hydrophobic hydration of hydrocarbon molecules, with the emphasis on the contribution of the author. It is demonstrated that the enthalpic free energy change, due to the interactions between the hydrocarbon molecules and water, is compensated by the entropic free energy change, due to the ordering caused by the hydrocarbon molecules in the neighboring water molecules. Further, it is shown that the free energy change due to the iceberg formation is negative. Some simplifying assumptions make it possible to conclude that the absolute value of the free energy for iceberg formation can be as large as 1/3 of the free energy change associated with the formation of a cavity. The thermodynamic approach employed can also explain the existence of a minimum in the temperature dependence of the hydrocarbon solubility in water.

ISSN:0193-2691    

DOI:10.1080/01932699808913178

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor