Equilibration of Surface State Electrons on Contact

The concept of equilibration of surface states at an interface may be illustrated by the case in which the two contacting phases are solids. In such a case, the energy levels of the surface state electron can be used to explain the surface state equilibration that occurs on contact. When two dissimilar surfaces contact each other, the transfer of surface state electrons occurs to equilibrate the energy levels of surface state electrons at the newly created interface. When two surfaces are separated, each surface retains the equilibrium electron level, which has been just attained on the contact, leading to the creation of the static charge, if a material is, or both materials are, nonconducting. In such a case, the two surfaces stick together by the coulombic attraction and it is necessary to apply force to separate them. 

The peak current and the total area under the curve for the contact current and for the separation eurrent are nearly identical, differing only in the sign. From the contact and separation current value a triboelectric series, which shows not only the position but also quantitative separation between two positions, is constructed as shown in Table 24.1. Triboelectric series based on the average current on contact and separation is given in Table 24.2, in which the zero point is set at nylon. 

The electronegativities of elements involved in a surface state seem to dominate the overall eleetronegativity of the surfaee, i.e., the high electronegativity of F and the absence of other pending group in Teflon are responsible for the most 

The problem associated with static charge of polymers is a good example for why the polymer surface should be treated as a polymer/air interface. The humidity of air changes the surface state of a polymer due to the adsorption of water molecules on the surface state of the polymer. The reduction of static charge by an increase in the humidity is not due to the dissipation of charge to the gas phase, i.e., humid air, but due to the change of surface state in equilibration with humid air. 

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