Surface force oleophilicity

Two different liquids may compete with each other, if each of them individually wets a solid surface. In this case the resulting contact angle corresponds to that of a better wetting liquid with nature similar to that of the solid surface. If the surface is better wetted by water than by a hydrocarbon ( 0<9O°), it is referred to as hydrophilic (oleophobic) in the case when the surface is better wetted by non-polar hydrocarbon (0>9O°), it is referred to as hydrophobic (oleophilic). For selective wetting, as opposed to wetting in air, the contact angle, 0, can assume any value between 0° and 180°. When 0 = 0°, the more polar liquid spreads over the solid surface, forcing the less polar liquid away when 0 = 180° the situation is opposite the non-polar liquid phase completely forces the polar liquid away from the solid surface. 

Silica particles are polar and porous (Section 1.4.6). The silica particles show not only significant interparticle van der Waals forces, but also strong polar and dipole bonds. This results in much higher viscosities than in carbon black compounds (Eq. 8.3) and more complex rheological properties generally. Silica compounds are hard to process and silica agglomerates are difficult to disperse in rubber matrices [ 12]. The surface of silica is hydrophilic, which is incompatible with oleophilic rubber matrices. There has been much research on breakup of silica agglomerates [13 to 20]. 

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