Liquid-solid contact, particle charge

As we have seen, the electric state of a surface depends on the spatial distribution of free (electronic or ionic) charges in its neighborhood. The distribution is usually idealized as an electric double layer one layer is envisaged as a fixed charge or surface charge attached to the particle or solid surface while the other is distributed more or less diffusively in the liquid in contact (Gouy-Chapman diffuse model, Fig. 3.2). A balance between electrostatic and thermal forces is attained. 

Solid-gas contact Liquid-gas contact No known charging provided solid or liquid does not break up and gas contains no free ions or suspended particles... 

What is the essential difference between the solid form and the liquid form of an ensemble of particles This is a question that is relevant to all processes of fusion, e.g., the process of solid argon melting to form a liquid. In the case of ionic liquids, the problem is more acute. One must explain the great fluidity and corresponding high conductivity in a liquid that contains only charged particles in contact. 

Contact electrification involves the contact and separation of solid-solid, solid-liquid, or liquid-liquid surfaces. Pure gases do not cause charging unless they carry droplets or dust particles. 

We now come to internal metal contacts in ISEs without an internal solution. As discussed above, systems without internal electrolytes are used very often, with both solid and liquid membranes. Obviously, the condition of thermodynamic equilibrium requires that common electrically-charged particles (ions or electrons) be present in electrically-charged phases that are in contact (see chapter 2). ISEs with a silver halide membrane to which a silver contact is attached are relatively simple. In the system... 

This can be accomplished by means of two different processes (1) an electrodeposition process in which z electrons (e) are provided by an external power supply, and (2) an electroless (autocatalytic) deposition process in which a reducing agent in the solution is the electron source (no external power supply is involved). These two processes, electrodeposition and electroless deposition, constitute the electrochemical deposition. In this book we treat both of these processes. In either case our interest is in a metal electrode in contact with an aqueous ionic solution. Deposition reaction presented by Eq. (1.1) is a reaction of charged particles at the interface between a solid metal electrode and a liquid solution. The two types of charged particles, a metal ion and an electron, can cross the interface. 

Atoms on the surface of a colloidal particle are bonded only to other atoms of the particle on and below the surface. These atoms interact with whatever comes in contact with the surface. Colloidal particles often adsorb ions or other charged particles, as well as gases and liquids. The process of adsorption involves adhesion of any such species onto the surfaces of particles. For example, a bright red sol (solid dispersed in liquid) is formed by mixing hot water with a concentrated aqueous solution of iron(III) chloride (Figure 14-19). 

Besides equilibria in the liquid phase (proteolytic, complex forming, etc.) that influence directly the values of effective mobilities of compounds to be separated, it is necessary to also establish, in the electrophoretic system, equilibria between the liquid and solid phase. In electrophoretic techniques which use solid stabilizing media adsorption of solutes on the sorbent surface is the main consideration. In capillary methods, and with colloid particles, similar effects have also to be considered (the surface of the solid phase that is in contact with the liquid phase is, with respect to the volume of the liquid, rather large). In both these latter cases the interaction between the solid and liquid phases participates in the formation of the electric double layer that conditions the electro-osmotic flow, and attributes the electric charge to colloid particles. 

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