Sisi Fang

Investigation of Novel Triple-Responsive Wormlike Micelles

Smart wormlike micelles with stimuli-tunable rheological properties may be useful in a variety of applications, such as in molecular devices and sensors. The formation of triplestimuli-responsive systems so far has been a challenging and important issue. In this work, a novel triplestimuli (photo-, pH-, and thermoresponsive) wormlike micelle is constructed with N-cetyl-N-methylmorpholinium bromide and trans-cinnamic acid (CA). The corresponding multiresponsive behaviors of wormlike micellar system were revealed using cryogenic transmission electron microscopy, a rheometer, and 1H NMR. The rheological properties of wormlike micellar system under different temperatures, pH conditions, and UV irradiation times are measured. As confirmed by 1H NMR, chemical structure of a CA molecule can be altered by the multiple stimulation from an exotic environment. We expect it to be a good model for triple-responsive wormlike micelles, which is helpful to understand the mechanism of triple-responsiveness and widen their applications.

Study on Synthesis and Properties of Gemini Surfactant Used as Viscoelastic Surfactant (VES)

As one kind of the new surfactants with novel structure, higher surface activity, lower critical micelle concentration, and lower Krafft point, the quaternary ammonium gemini surfactants have a promising application prospect in viscoelastic surfactant (VES). In this paper, one kind of viscoelastic cationic gemini surfactant was synthesized through using N,N-dimethyl-1, 3-propane diamine, octadecanoic acid, and 1,4-dibromobutane. The molecular structure of the surfactant was characterized by 1H NMR, the self-assembly structure was observed by atomic force microscopy, and the viscoelasticity behavior was measured through rheological measurements. The study shows that the gemini surfactant can form self-assembled structures in single system, and the molecular self-assembly driven by the non-covalent interactions can provide the foundation for building well-defined structures in the nanometer or micrometer length scale. In addition, stable viscoelastic behavior was observed in the surfactant system, with strong binding energy and electrostatic interactions. This work can reveal the interaction mechanism between the molecules and the synergistic interactions of various non-covalent forces at molecular level, which is significant to study the viscoelastic surfactant used in clean fracturing fluid.

Stability Mechanism of Nitrogen Foam in Porous Media with Silica Nanoparticles Modified by Cationic Surfactants

This work aims at studying the effect of electrostatic interactions between cationic surfactants and silica nanoparticles (NPs) on foam stability in porous media. The physio-chemical property of NPs, the gas-liquid interface properties, the foam flow characteristics, together with the stability under different concentrations of surfactant and NPs were investigated and compared. It was found that the affinity of silica NPs to the surface is tunable by variation of surfactant concentrations. NPs and surfactants as a whole assembling at the surface substantially improve the foam stability in static and dynamic tests. These surfactant-modified NPs accumulate at the bubble surface and remain stable under dilution of brine, providing a barrier effectively preventing coalescence. In addition, foam stability is enhanced since the layer of NPs significantly reduces the mass transfer rate, consequently mitigating the Ostwald ripening.