Colloidal dispersions direct dispersion method

Principally purification and characterization methods of monometallic nanoparticles are directly applied to those of bimetallic nanoparticles. Purification of metal nanoparticles dispersed in solution is not so easy. So, in classical colloid chemistry, contamination is carefully avoided. For example, people used pure water, distilled three times, and glass vessels, cleaned by steam, for preparation of colloidal dispersions. In addition, the reagents which could not byproduce contaminates were used for the preparation. Recently, however, various kinds of reagents were used for the reaction and protection. Thus, the special purification is often required especially when the nanoparticles are prepared by chemical methods. 

The migration of colloidally dispersed particles in a direct current field was reported as early as 1809. From then on the phenomenon received attention only every 30 or 50 years as an analytical method, culminating in 1948 when Arne Tiselius received the Nobel Prize for his experimentations, particularly electrophoretic separation of proteins. 

In determining the colloidal heavier of a latex, the surfoce properties play a very important role, and these are directly relaied to the preparative method employed. They frequently depend on (i) groupings arising from the initiator used (ii) adsorbed or grafted surfoctants and (iii) adsorbed or grafted polymers, particularly, those soluble in the dispersion medium. 

After an aqueous dispersion of monodispersed spherical colloids was injected into the cell, a positive pressure was applied through the glass tube to force the solvent (water) to flow through the channels. The beads were accumulated at the bottom of the cell, and crystallized into a three-dimensional opaline lattice under continuous sonication. So far, we have successfully applied this approach to assemble monodispersed colloids (both polystyrene beads and silica spheres) into ccp lattices over areas of several square centimeters. This method is relatively fast opaline lattices of a few square centimeters in area could be routinely obtained within several days. This method is also remarkable for its flexibility it could be directly employed to crystallize spherical colloids of various materials with diameters between 200 nm and 10 pm into three-dimensional opaline lattices. In addition, this procedure could be easily modified to crystalhze spherical colloids with diameters as small as 50 nm. ... 

The next direct method used to characterize the colloidal properties of crude oil is the sedimentation method. It is obvious from the name of the method that this method is based on the sedimentation effect. There are two possibilities to carry out this method the first is the sedimentation under the influence of gravitational force and the second sedimentation under influence of centrifugal force. The choice between these methods depends on the viscosity of the sample and the size of the particles of the disperse phase. Viscous samples or samples with relatively small particles should be analyzed by the second method. 

The last direct method often used for determination of the colloidal properties of crude oils is gel permeation chromatography. The principles of this method were described in section 2.1.2. Normally, this method is used for analyzing the molecular weight distribution of substances. However, it is possible to use it to analyze colloidal properties as well if an appropriate solvent is used as the mobile phase. This solvent must not change the native disperse particles. Almost all the solvents that can be used in this analysis as a mobile phase change the size of native particles. This is why this analysis is usually used for estimating the particle size in the sample solution. 

Interfacial phenomena at metal oxide/water interfaces are fundamental to various phenomena in ceramic suspensions, such as dispersion, coagulation, coating, and viscous flow. The behavior of suspensions depends in large part on the electrical forces acting between particles, which in turn are affected directly by surface electrochemical reactions. Therefore, this chapter first reviews fundamental concepts and knowledge pertaining to electrochemical processes at metal oxide powder (ceramic powder)/aqueous solution interfaces. Colloidal stability and powder dispersion and packing are then discussed in terms of surface electrochemical properties and the particle-particle interaction in a ceramic suspension. Finally, several recent examples of colloid interfacial methods applied to the fabrication of advanced ceramic composites are introduced. 

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