Abstract:

Internal olefin sulfonates are efficient surfactants for oil displacement with good application prospects in high-temperature and high-salinity reservoirs. To explore the interfacial behavior of internal olefin sulfonate molecules, two kinds of internal olefin sulfonates with different alkyl chain lengths, IOS-C₁₄ and IOS-C₁₈, were selected, and their dilational rheological properties at gas-liquid and oil-water interfaces were investigated. The results showed that the branched structure and carbon-carbon double bond in hydrophobic group of internal olefin sulfonate endowed it with higher interfacial film strength than conventional anionic surfactants. With the increase of chain length, the adsorption amount of internal olefin sulfonate increased, but the interfacial steric hindrance between the molecules also increased. During the dilation-compression process at gas-liquid interface, the IOS-C₁₈ molecules who had longer alkyl chain tended to desorb from the surface and diffuse into the bulk phase, and meanwhile, the dilational modulus significantly decreased and the phase angle increased. The presence of oil molecules would weaken the intermolecular interactions of internal olefin sulfonate at the interface, but meanwhile inhibited the diffusion-exchange of surfactant molecules between the interface and the bulk phase. For IOS-C₁₄ with higher surface film strength, the strength of interfacial film slightly decreased. For IOS-C₁₈ with lower surface film strength, the strength of interfacial film significantly increased, and the intra-film relaxation process dominated the properties of interfacial film.

Key words: internal olefin sulfonate, branching, chain length, dilational modulus, phase angle