Wettability of coal tar pitch surface by aqueous solution of C₁₂-m-C₁₂ cationic Gemini surfactant

Wettability and adsorptive mechanism of coal tar pitch by aqueous solutions of cationic surfactant (C₁₂-m-C₁₂·2Br^-, m=4, 6, 8, 10)were investigated by the sessile drop analysis and electrophoresis. The results indicate that the surface tension decreases with increasing surfactant concentration up to the CMC (critical micelle concentration) of the surfactant solution, which θ and S have the similar trend with surface tension. Within the whole range of concentration, the Zisman theory is in accordance with the wettability on the coal tar pitch when spacer chain length value reaches to 10. Meanwhile, there is a liner dependence between adhesion tension (γ_lgcosθ) and surface tension (γ_lg). Zeta potential on the surface of the coal tar pitch increases with the increasing surfactant concentration from negative to positive, and finally levels off. And the concentration of the zero potential is lower than CMC at least an order of magnitude. C₁₂-8-C₁₂ Gemini surfactants can significantly change the wettability on the surface of the coal tar pitch. According to the wetting data and Zeta potential of Gemini surfactant on coal tar pitch, it can be inferred that wetting is a concerted action result of electrostatic interaction and van der waals adsorption. Therefore, wetting process can be generally divided into three phases.