Effects of anionic surfactants containing polyether group on wettability of polymethyl methacrylate surface
In order to explore the wettability regulation mechanism of extendable surfactant molecules with both polyoxyiso-propyl(PO)and polyoxyethylene(EO)groups on the surface of polymethyl methacrylate(PMMA),the wettabil-ity of sodium octadecyl-(polyoxyisopropyl)m-(polyoxyethylene)n-carboxylate(C18POmEOnCOONa,m=5,10,15,and n=5,10,15)solutions of five anionic extendable surfactants with PO and EO groups on the surface of PMMA was tested and analyzed.The effects of PO groups,EO groups,and surfactant concentrations on surface tension(γLV)and contact angle(θ)were investigated and the adsorption parameters such as adhesion tension(γLV cos θ),adhesion work(WA),and solid-liquid interfacial tension(γSL)were calculated.The results show that when the concentration of surfactant is less than the critical micelle concentration(CMC),the C18POmEOnCOONa molecules adsorb at the solution-air interface and PMMA-solution interface,resulting in a decrease in γLV,hy-drophobic alkyl chains facing the aqueous phase,and an increase in γSL.The θ stays consistent at about 75° due to these two important considerations.When the concentration is greater than CMC,C18POmEOnCOONa molecules form saturated adsorption films at both the solution-air and PMMA-solution interface,the interface adsorption parameters remain constant.As the level of concentration keeps increasing,C18POmEOnCOONa molecules con-tinue adsorbing at the PMMA-solution interface and aggregate structure is formed through hydrophobic interac-tion.The hydrophilic group confronting the aqueous phase leads to a rapid decrease in γSL and θ,the θ of C18PO5EO15COONa can be reduced to roughly 43°.The γLV at CMC and the θ at high concentration gradually in-crease with the increase in the number of PO groups.However,the γLV and the θ barely alter when the number of EO groups increases.
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