Adsorption Behavior of Cationic and Zwitterionic Surfactants on Poly(methyl methacrylate)

The wetting behavior of poly(methyl methacrylate) (PMMA) surfaces by aqueous solutions of cationic surfactants, hexadecanol glycidyl ether ammonium chloride (C16PC), hexadecanol polyoxyethylene (3) glycidyl ether ammonium chloride (C-16(EO)(3)PC), and zwitterionic surfactants, hexadecanol glycidyl ether glycine betaine (C16PB) and hexadecanol polyoxyethylene(3) glycidyl ether glycine betaine (C-16(EO)(3)PB), were investigated by sessile drop analysis. The influence of surfactant type and concentration on contact angle was determined. The PMMA surface is modified hydrophobically only slightly at low bulk concentration because the surfactant molecules are parallel to the substrate surface and the hydrophilic groups are close to the surface. However, at high concentration, the surfactant molecules can adsorb onto the PMMA surface through Lifshitz-van der Waals interactions and hydrophilic groups directed towards the bulk phase of solution, which increases the hydrophilic character of the PMMA surface. The contact angles of cationic surfactants show little variation following the insertion of polyoxyethylene units. However, the presence of polyoxyethylene units in the zwitterionic surfactants leads to an obvious decrease of contact angle because of the formation of hemimicelles on the PMMA surface.