tailieunhanh - Coatings of Polymers and Plastics Part 5

Tham khảo tài liệu 'coatings of polymers and plastics part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Formulating Plastics for Paint Adhesion 89 YS the surface energy of the solid the energy necessary to increase the surface of the solid YL the surface energy of the liquid the energy necessary to increase the surface of the liquid which is valid at equilibrium. Figure 1 shows a representation of the physical situation. When 0 is zero cos 0 is 1 and wetting occurs with the surface energy of the solid being equal to or greater than the liquid depending on the interfacial energy. The surface energies of the solid the liquid and the interface are material properties the contact angle is measured. One can see that liquids with low surface energy will wet out onto solids with high surface energy because the vector force is to pull the liquid down. This means that oil low surface energy spreads out on water high surface energy but water paint in this case doesn t spread out on oil solid oil like polyolefins . For a given YSL interfacial energy a high surface-energy solid is necessary because the surface energy of the liquid is reduced by the cos 0 which varies from 0 to 1. The interfacial surface energy is an important component of this equation but can not be measured directly 9 . The surface energy of the solid can be determined by extrapolation from liquid homologs 8 or by wettability data with various surface-tension liquids. A theoretical model is needed to relate the interfacial energy to the surface energy of the two components. Good and Girifalco developed a very early model however this model did not include the fact that the surface energy has two components a dispersion component Yd and a polar component Yp for each material. The term dispersion comes from the fact that the perturbation of electronic motion that creates this force is related to the perturbation of light with frequency or dispersion of light 8 . The adhesion between the two materials is described by the following equation where WAB is the work of adhesion YA YB and YAB are the surface Fig. 1 .