Synthesis of New Sulfobetaine Gemini Surfactants with Hydroxyls and Their Effects on Surface-Active Properties

Sulfobetaine gemini surfactants, bis{[(N-methyl-N-(3-alkoxy-2-hydroxyl) propyl-N-(2-hydroxyl-3-sulfonic acid sodium) propyl] methylene} ammonium chlorides (n = 10, 12, 14), were synthesized by etherification, ring-opening reaction, and quaternization with epichlorohydrin, linear-saturated alcohol, N,N-dimethylethylenediamine, and 3-chloro-2-hydroxypropane sulfonic acid sodium as main raw materials. The structures of the sulfobetaine gemini surfactants with hydroxyls were characterized using Fourier transform infrared spectroscopy (FTIR), H-1-Nuclear Magnetic Resonance (NMR), mass spectroscopy (MS), and elemental analysis. With increasing length of the carbon chain, the values of the critical micelle concentration (CMC) initially decreased. These compounds exhibit superior surface-active properties compared to single-chain sulfobetaine surfactants such as dodecyl dimethyl hydroxyl sulfopropyl betaine surfactants. The efficiency of adsorption at the water/air interface (pC(20)) of these surfactants is very high. The shorter hydrophobic chain length of sulfobetaine gemini surfactants, the faster the surface tension reduction, and the smaller the aggregation number of sulfobetaine gemini surfactants. The micelle diameter and the maximum wetting angle of pure water drop/air increased, but the maximum wetting angle of water phase/n-decane decreased with the increase of the hydrophobic chain length. With the increase of the hydrophobic chain length, salinity resistance went up and the corresponding interfacial tension reduced. Their foam volume and foam half-life were investigated. Our studies have indicated that synthesized gemini surfactants can effectively reduce the oil/water interfacial tension to ultralow interfacial tension of hexane (IFT) (10(-3) mNm(-1) orders of magnitude) under the conditions of high temperature and high salinity.