Cao Xulong

Supramolecular vesicles of cationic gemini surfactants modulated by p-sulfonatocalix[4]arene

Supramolecular binary vesicles were constructed by host-guest complex formation between p-sulfonatocalix[4]arene and three cationic gemini surfactants, which were identified by UV-vis, dynamic laser scattering, transmission electron microscopy, scanning electron microscopy, atomic force microscopy, and surface tension experiments. The critical aggregation concentration of gemini surfactants decreased pronouncedly by a factor of ca. 1000 owing to the complexation of p-sulfonatocalix[4]arene.

Molecular Dynamics Simulation of Anionic Surfactant at the Water/ n -Alkane Interface

The structural and dynamic properties of anionic surfactant at the water/n-alkane (nonane,decane,and undecane) interface were investigated by the molecular dynamics simulation. The model anionic surfactant contained a benzene sulfonate group attached to the 4th carbon in the hexadecane backbone and was denoted as 4-C16. We analyzed the interfacial properties (density profile,interfacial tension,and radial distribution function) of the n-alkane-surfactant-water systems in different oil phases and under special inorganic salinity conditions. The simulation results indicate that a well-defined interface exists between the n-alkane and water phases in the equilibrated model systems. The interfacial tensions of the n-alkane-surfactant-water systems show little change when sodium chloride is added to the solutions. We find that a change in the trans-form fraction of the dihedral in 4-C16 is related to a subtle change in the interfacial tension at the water/n-alkane interface. Clearly,the structure of the surfactant at the interface plays an important role in reducing the interfacial tension. In addition,we also find that the polar head group of the surfactant molecules with sodium ions and water molecules undergo stronger interactions.

Multi-scale rheological perspective to polymer solutions and gels in EOR

Polymer flooding for enhanced oil recovery (EOR), especially using polyacrylamide (PAM) based systems, gradually became the largest non-Newtonian fluid process of economic significance. Yet, the mechanistic understanding lags behind. In this paper, the relations of structures — rheological properties — EOR applications were reviewed and some recent laboratory studies on associated PAM and PAM soft gels were introduced. The multi scale understanding of polymer rheology was found to be an essential factor for future developments.

Effects of Surfactants on Interfacial Shear Rheological Properties of Polymers for Enhanced Oil Recovery

The effects of surfactants, namely sodium dodecylbenzenesulfonate(SDBS) and hexadecyltrimethylammonium bromide(CTAB), on the interfacial shear rheological properties of partially hydrolyzed polyacrylamide(PHPAM) and hydrophobically modified polyacrylamide(HMPAM) solutions, which are used in oilfields, were studied using a biconical method. The experimental results show that the interfacial shear complex modulus of HMPAM is significantly higher than that of PHPAM, because an interfacial net structure can be formed by HMPAM molecules through hydrophobic interactions. The SDBS and CTAB molecules can form interfacial aggregates with hydrophobic blocks of HMPAM and destroy the interfacial net structure, which results in a significant decrease in the shear modulus with increasing surfactant concentration. At the same time, the properties of the interfacial film change from viscous to elastic. At low SDBS concentrations, the mixed adsorption film formed by PHPAM and a few SDBS molecules has enhanced strength. However, SDBS molecules can displace PHPAM molecules at the interface and weaken the film at higher surfactant concentrations. The cationic surfactant CTAB neutralizes the negative charge on PHPAM, leading to partial curling of the polymer chain, which decreases the film strength. Relaxation measurements confirmed our mechanism involving destruction of the interfacial netstructure of HMPAM by the surfactant.