Zhiqing Zhang

Investigations on NaDEHP and AOT: computer simulation and surface tension measurements

Abstract This paper studies two structurally related surfactants NaDEHP and AOT with the surface tension measurements and the computer simulation. The surface activities of AOT and NaDEHP with different temperatures and different NaCl concentrations are investigated. The interaction parameters (βM) of NaDEHP–CTAB and AOT–CTAB molecules in their respective mixed micelles are obtained according to the equation proposed by Rubingh et al. (Solution Chemistry of Surfactants 1 (1979) 337) The mixing energy and Huggins parameter of AOT–CTAB mixed system and NaDEHP–CTAB mixed system are also obtained by computer simulation and the results are consistent with our surface tension measurements. The following results are obtained: (i) the surface tension of AOT is reduced with the increase of temperature when the temperature is below 40xa0°C, but it has the opposite trend above 40xa0°C; this phenomenon is not observed in the NaDEHP case; (ii) the lower βM value of AOT–CTAB suggests the stronger interaction between AOT and CTAB molecules in their mixed system. It is novel to find that the βM of NaDEHP–AOT mixed systems is also a negative value, which suggests there is a weak attractive interaction between NaDEHP and AOT molecules. Comparing the experimental values with those obtained from theoretical calculation we find the CMCs of NaDEHP–AOT mixed systems do not agree well with the ideal mixed model, whereas the effect of NaCl on AOT agrees well with the empirical formula.

Adsorption of sodium oleate at the interface of oil sand/ aqueous solution

This paper explores the effects of several factors such as the ratio of liquid/solid, temperature and additives on the adsorption of sodium oleate at the interface of oil sand/aqueous solution. The results indicate that adsorbed amount is almost unchanged with the ratio of liquid/solid under the experimental conditions, and the rise of temperature favors the adsorption process. In addition, the adsorption behaviors are different in the presence of different additives. The adsorbed amount of sodium oleate increases considerably when polymers are added to the solution, the same trend with the addition of NaCl. The maximum is found in the adsorption isotherm with the addition of alcohol. From the IR spectra, zeta potential and atomic energy spectrum we discuss the mechanism of adsorption of sodium oleate onto the oil sand in order to control the surfactants adsorption and the loss in chemical flooding.