Effect of inorganic and organic counterions on interfacial properties of oleic acid-based gemini surfactants

Research Progress in Structure Synthesis, Properties, and Applications of Small-Molecule Silicone Surfactants

Silicone surfactants have garnered significant research attention owing to their superior properties, such as wettability, ductility, and permeability. Small-molecular silicone surfactants with simple molecular structures outperform polymeric silicone surfactants in terms of surface activity, emulsification, wetting, foaming, and other areas. Moreover, silicone surfactants with small molecules exhibit a diverse and rich molecular structure. This review discusses various synthetic routes for the synthesis of different classes of surfactants, including single-chain, "umbrella" structure, double chain, bolaform, Gemini, and stimulus-responsive surfactants. The fundamental surface/interface properties of the synthesized surfactants are also highlighted. Additionally, these surfactants have demonstrated enormous potential in agricultural synergism, drug delivery, mineral flotation, enhanced oil recovery, separation, and extraction, and foam fire-fighting.

Structural Change of an α-Gel (α-Form Hydrated Crystal) Induced by Temperature and Shear Flow in an Oleic Acid Based Gemini Surfactant System

We studied the effects of temperature and shear flow on the structures of α-gel bilayers and domains. The α-gel samples were prepared by a carboxylate-type gemini surfactant synthesized from oleic acid and a long-chain alcohol (1-tetradecanol) with water. The structural change as a function of temperature was investigated using small- and wide-angle X-ray scattering (SWAXS) measurements, spin-spin relaxation time (T₂) measurements, and optical microscopy observations. SWAXS measurements suggested that the decreased temperature yielded the α-gel phase from a lamellar liquid-crystal phase. We also found that the lamellar d-spacing drastically decreased at the phase transition temperature. The T₂ measurements suggested that two kinds of protons with different mobilities coexisted in amphiphiles consisting of lamellar bilayers. The abundance of the protons with low mobility increased with decreasing temperature. Optical microscopy results indicated that the size of the α-gel domains increased with decreasing temperature. We assumed that the increased abundance of the low-mobility protons, indicating low flexibility of lamellar bilayers, led to a decreased lamellar d-spacing and increased size of the α-gel domains. Shear-induced structural changes in the α-gel were also studied using simultaneous small-angle neutron scattering and rheological measurements. The α-gel can maintain bilayer structures even at high shear rates. We also found that the lamellar d-spacing was independent of the shear rate.

Characterization of the micelle structure of oleic acid-based gemini surfactants: effect of stereochemistry

In this study, we synthesize a novel oleic acid-based gemini surfactant with carboxylate headgroups, and study the effect of stereochemistry (anti- vs. syn-) on self-aggregation properties in water.