Subject electrostatic adsorption

In addition to the preparation of Langmuir and Langmuir-Blodgett films, the use of self-assembly techniques also plays an important role in the formation of particle films. Both physisorption, as, for example, electrostatic adsorption of charged particles from colloidal solution, and chemisorption onto a substrate have been investigated. In Section V.A, electrostatic adsorption will be reviewed chemisorption is the subject of Section V.B. 

The material properties of solids are affected by a number of complex factors. In a gas-solid flow, the particles are subjected to adsorption, electrification, various types of deformation (elastic, plastic, elastoplastic, or fracture), thermal conduction and radiation, and stresses induced by gas-solid interactions and solid-solid collisions. In addition, the particles may also be subjected to various field forces such as magnetic, electrostatic, and gravitational forces, as well as short-range forces such as van der Waals forces, which may affect the motion of particles. 

In response to a growing literature on the the subject of adsorption of gases onto solids (including physical adsorption, chemisorption and heterogeneous catalysis) this book was written to examine particularly some of the more fundamental properties of various liquid interfaces. Eight well-referenced chapters describe the physics of surfaces, electrostatic phenomena, electro-kinetic phenomena, adsorption at liquid interfaces, properties of monolayers, reactions at liquid surfaces, diffusion through interfaces, and disperse systems and adhesion. 

Nucleic acids, DNA and RNA, are attractive biopolymers that can be used for biomedical applications [175,176], nanostructure fabrication [177,178], computing [179,180], and materials for electron-conduction [181,182]. Immobilization of DNA and RNA in well-defined nanostructures would be one of the most unique subjects in current nanotechnology. Unfortunately, a silica surface cannot usually adsorb duplex DNA in aqueous solution due to the electrostatic repulsion between the silica surface and polyanionic DNA. However, Fujiwara et al. recently found that duplex DNA in protonated phosphoric acid form can adsorb on mesoporous silicates, even in low-salt aqueous solution [183]. The DNA adsorption behavior depended much on the pore size of the mesoporous silica. Plausible models of DNA accommodation in mesopore silica channels are depicted in Figure 4.20. Inclusion of duplex DNA in mesoporous silicates with larger pores, around 3.8 nm diameter, would be accompanied by the formation of four water monolayers on the silica surface of the mesoporous inner channel (Figure 4.20A), where sufficient quantities of Si—OH groups remained after solvent extraction of the template (not by calcination). 

The removal of Ra by adsorption has been attributed to ion exchange reactions, electrostatic interactions with potential-determining ions at mineral surfaces, and surface- precipitation with BaSO 4. The adsorptive behavior of Ra2+ is similar to that of other divalent cationic metals in that it decreases with an increase in pH and is subject to competitive interactions with other ions in solution for adsorption sites. In the latter case, Ra is more mobile in groundwater that has a high total dissolved solids (TDS) content. It also appears that the adsorption of Ra + by soils and rocks may not be a completely reversible reaction (Benes et al. 1984, 1985 Landa and Reid 1982). 

For more complex molecules a reasonable estimate of the heat of sorption can sometimes be made by considering group contributions. Such an approach works best for nonpolar sorbates on nonpolar surfaces but is subject to considerable error for polar systems in which the electrostatic energies of adsorption are large. 

There are three basic types of contributions to the adsorbate-adsorbent interactions dispersion, electrostatic, and chemical bond. The latter, chemical bond, has been explored for adsorption only recently. Weak chemical bonds, particularly the broad type of bonds involving n electrons, or 7r-complexation, offer promising possibilities for designing new and highly selective sorbents. The subject of Tr-complexation sorbents will be discussed in a separate section. For physical adsorption, the adsorbate-adsorbent potential is... 

At present three theories of adhesion exist—the adsorption theory [9], the diffusion theory [24,25, 26], and the electrostatic theory [10, 23]. The majority of those who have concerned themselves with the subject of adhesion lean toward the adsorption theory, if for no other reason than a recognition that the phenomenon of wetting is intimately related to adhesion. The word "adhesion (unmodified) here means strictly an interfacial phenomenon, while "practical adhesion" means the strength with which two materials stick together—that is, the force required to separate them, or joint strength. 

---