Electrically Charged Surfaces

Some of the functional groups (e.g., OH) on the clay surface exhibit electrical charges. The magnitude of the electrical charge, as well as its character, are controlled by the properties of the surfaces to which the functional groups are bound and by the composition of the surrounding hquid. Sposito (1984) classified the surface charge density of soils as follows  

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The next four chapters provide an introduction to the concepts and techniques needed to study and understand dispersion stability. Some approaches to the characterization of emulsions, foams and suspensions, and of their dispersed species (droplets, bubbles and particles)are described in Chapter 2. The concepts of surface tension, wettability and surface activity, which are important to the stability and properties of all types of dispersion, are described in Chapter 3. To this is added the nature of electrically charged surfaces in Chapter 4. All of these aspects are brought together in Chapter 5 in an introduction to the stability of dispersions. 

All polymer films were used as prepared, i.e. the samples were not mechanically rubbed. Samples that were contacted with other polymer sheets and afterwards separated, showed highly electrically charged surfaces which cannot be studied by the AFM techniques mentioned below. 

Water purification can be achieved by decomposition or destruction of the pollutant on contact with an electrically charged surface. In several cases permeable electrodes are used in a flow-through mode to ensure contact between the pollutant and the electrode. The type of electrode ranges from metal meshes and carbon cloths to ceramic membrane supports coated with a porous layer of electroconductive material. 

When most of the materials (e.g., glass) come into contact with the aqueous solutions, their surfaces become electrically charged. This electrically charged surface attracts the co-ions and repels the counterions of the aqueous solution and builds up an electrically charged layer that is called the electric double layer EDL). 

Motion is generated by electrostatic attraction force between electrically charged surfaces. Examples of electrostatic MEMS actuators are in-plane comb drives (Fig. la) and out-of-plane parallel plate actuators (Fig. lb) [4]. Both types of actuators require large driving voltages... 

Electro-osmosis motion of a buffer solution in contact with an electrically charged surface such as fused silica at pH > 3 (deprotonated silanol groups) under the influence of an external electric field. The resulting movement of the bulk liquid is called electro-osmotic flow (EOF). 

Many results indicate that SERS or SERRS spectroscopy is also useful in the investigation of molecules in interfacial situations. This feature seems to be of particular importance since many functions of biological molecules are realized through their association with biological or other electrically charged surfaces. 

Study of interaction of nucleic acids with electrically charged surfaces. 

An understanding of electro-osmosis goes back to Schmoluchowski (Figure 10.14). An electrically charged surface (surface potential 0 exposed to a layer of almost pure water develops a double layer (surface -h counter-ions), the thickness of which is the screening radius where the counter-ions collect. 

Transfer of charge with surface melted fluid [86]. If each ice surface is covered with a film of electrically charged surface melted fluid then transfer of that fluid from one particle to another transfers charge. 

We have found 17 different systems of any IL with water. In Figure 19 we present rj data for BMIM-Cl and EMIM-Br (Liu et al., 2008), which concentration as molarity, m(mol/L). As observed the viscosity is bigger for the smallest ion (Cl), probably due to the fact that its electrical charge surface density is higher and so electrostatic interactions with the cation are also higher. In Fig. 20 we plot three systems with common Q anion and cation of the same... 

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