Abstract:
Wetting of solids by aqueous surfactant is important for many commercialapplications such as coatings, detergency, and printing. The surface tension of solution is usually considered as a main factor in wetting, whereas the adsorption of surfactant onto solid/liquid interface is generally ignored. In this work, the adsorption isotherm and contact angle measurement of three representative surfactants : sodium Octyl benzene sulfonate (NaOBS), cetylpyridinium chloride (CPC) and polyoxyethylene octyl phenyl ether (Triton X-100) on high-density polyethylene (HDPE), polystyrene (PS) and polyethyleneterephthalate (PET) were conducted as a function of surfactant concentration and salinity. For all cases, the solid/liquid interfacial tension (ysL) decreased with surfactant concentration. Together with the adsorption isotherm, YsL was also observed to decrease with surfactant adsorption on plastic. Surfactant decreased not only the liquid surface tension (yLv) but also YsL. The reduction in both interfacial tension resulted in lower value of contact angle. In case of PS and PET, the presence of NaCl hindered the ability to reduce the contact angle of CPC solution that has the same yLv. The possible reason is the difference in the nature of solid/liquid interface and liquid/air interface, which caused CPC to differently distribute among the two interfaces. However, this effect was not observed for NaOBS, possibly due to the difference in the length of hydrophobic tail of CPC and NaOBS.
