Surface properties and wetting performance of multifunctional cationic surfactants with labile moiety

A series of multifunctional cationic surfactants comprising a tertiary amide linker in their structures and differing in their architecture, i. e. single head-single tail pattern with different hydrophobic tails ([(3-alkanoyilmethylamino)propyl] trimethylammonium bromides (C n Br, n = 12, 14 or 16)), as well as double head-double tail (gemini) analog (dimethyl{{3-[N-(3-{N-[3-(dimethylammonium)propyl] dodecylamido}propyl} dodecylamido}propyl}}ammonium dibromide (2xC 12 BrG 3 )) and double head-single tail (dicephalic) ( N , N -bis[3,3′-(trimethylammonio)propyl]dodecanamide dibromide (C 12 (TAPABr) 2 )), both with the same alkyl chain length, were evaluated for their surface activity at the air/solution interface as well as wettability of the glass and/or polytetrafluoroethylene (PTFE) surfaces. The physicochemical behavior at the air–liquid interface was investigated. Surface tension isotherms of aqueous solutions of the studied multifunctional cationic surfactants were determined by pendant drop shape analysis and interpreted using the modified surface quasi-two-dimensional electrolyte (mSTDE) model of ionic surfactant adsorption, previously developed in our group. The analysis was supported by the molecular dynamics simulations. The wetting properties of the above-mentioned surfactants were evaluated by measuring the advancing and receding contact angles of their aqueous solutions on a bipolar glass surface and the advancing contact angle on an apolar PTFE surface. Based on these results, the influence of surfactants on the surface free energy (surface tension) of water, glass, and PTFE was examined. It was found that changes in the surface free energies of water and glass depend on both the alkyl chain length and the structure of the surfactant molecules. In the case of water, they are related to the reduction of only the acid-base component of this energy. These changes determine the wetting properties of the studied surfactants and indicate that single-chain, single-head surfactants and gemini-type surfactants have the highest wetting properties on hydrophobic solids and the lowest on hydrophilic solids.