Surface modification of particles

The surface properties of the particles can be modified according to the requirement. Surface modification of particles could be divided into three major categories according to the procedures employed. These are covalent modification, surface adsorption, and encapsulation. 

By injection of refractory powders into RF discharges, it is possible to heat treat the particles. Decomposition, vaporization, melting, or surface modification of particles can be achieved in varying degrees depending on the physical properties of the material, particle residence time, particle surface area, and the enthalpy available in the plasma. 

The industrial development of silica sol manufacturing methods is reviewed. Primary attention is focused on the preparation of monodispersed sols from water glass by the ion-exchange method. Details are given for variations of manufacturing process and for the characteristics of both the processes and sols obtained. Furthermore, the following surface modifications of particles are demonstrated silica sols stabilized with ammonia, amine, and quaternary ammonium hydroxide aluminum-modified or cation-coated silica sol and lithium silicate. Finally, future trends in silica sol manufacturing are discussed from the viewpoint of not only raw materials and improvement of the procedures but also the function of the silica sols and their particle shape. 

Surface modifications of particles which are commonly used as materials for chromatography, as pigments or fillers are of considerable technical interest. By the selection of appropriate monomers and their surface polymerization different chemical functionalities or physical properties are introduced. Silica gel with an extended surface area (Si 60, E. Merc)c) is a useful substrate for the study of photoinitiated surface polymerizations )3ut less porous particles, microcrystalline materials or filjers are the objects of investigations with a more practical bacltground. 

In order to overcome this drawback, there are two main approaches for the surface modification of carbon nanostructures that reoccur in the literature. The first one is covalent functionalization, mainly by chemical bonding of functional groups and the second one is noncovalent functionalization, mainly by physical interactions with other molecules or particles. Both strategies have been used to provide different physical and chemical properties to the carbon nanostructures. Those that will be presented here are only a few examples of the modifications that can be achieved in carbon nanostructure surfaces and composite fabrication. 

An alternative approach to the preparation of bulk Pt bimetallic particles has been the preparation of surface modification of Pt particles with second metals. This approach has been used to prepare partially coated and fully coated Pt particles to give "core-shell" structures. Core-shell structures of Pt or PtM bimetal-lies on alternative metal cores have also been prepared. This approach argues... 

One advantage of sol-gel processing over surface modification is to create the inorganic oxide support in situ. Hence, without the limitation of the surface area of particles, more organic groups can be incorporated, even though their accessibility is not warranted. Another advantage is the possibility to... 

The limiting factors that control photocatalysis efficiency are rapid recombination between photo-generated charge carriers, and the backward reaction leading to recombination of the formed molecular hydrogen and oxygen. To retard these processes efforts have typically focused on surface modification of the semiconductor particles using metals or metal oxides. 

In most practical uses of polymeric particles, their surfaces play a very important role by taking part in interfacial interactions such as recognition, adsorption, catalytic reactions, etc. When we want to use polymer particles, we first check whether the chemical and physical structures of the surfaces meet the purpose. If some of them do not satisfy the criteria, we may seek other particles or try to modify the existing particles. This chapter mainly deals with the modification of surface of existing particles. In addition to chemical modification of particle surfaces, modification of the morphology of particles is also described. 

The surface of polymer particles obtained by emulsion polymerization is occupied by emulsifier molecules, initiator fragments, and hydrophilic comonomer units. Therefore, desirable design of the surface ought to be done by choosing the emulsifier, initiator, and comonomer. Some of them are employed in aiming for postreaction at the surface to convert it into a functional one. When any change is necessary on the particle surface, modification of surface can be done by the following means ... 

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