A study on the contribution of the intermolecular forces to the stabilization of the high internal phase emulsion: A combined experimental and molecular dynamics study

Abstract

The underground formation of the water-in-oil (W/O) high internal phase emulsion (HIPE) plays an important role in the petroleum exploitation from the low permeation zone in the oil reservoir. However, most of the available emulsifier couldn't satisfy the requirement of the underground HIPE. In present study, the model asphaltene (the polyaromatic components, PACs) plus the model wax (n-C30, n-C40, n-C50 and n-C60) and the genuine asphaltene were compared to find out the effect of the emulsifier structural characteristics on the HIPE stability. The interfacial film strength test combined with the molecular dynamics (MD) simulation was carried out to reveal the contribution of the intermolecular forces, including the van der Waals (VdW) force, the hydrogen bond and the π-π stacking between the polyaromatic sheet, to the interfacial film strength. The result revealed that the intermolecular hydrogen bond and the VdW force between the aliphatic groups gave more influence on the EM than the π-π stacking. The PACs with aliphatic side chain (N, N′-Bis(2,6-diisopropylphenyl)-3,4,9,10-perylenetetracarboxylic diimide, DIP and Ditridecylperylene-3,4,9,10-tetracarboxylic diimide, DTP) combined with the wax led to the largest elastic modulus (EM) of the interfacial film up to 22–24 mN/m. The 3,4,9,10-Perylenetetracarboxylic diimide (PyN) and 3,4,9,10-the Perylenetetracarboxylic dianhydride (PyO) who had no side chain, formed the interface film via the π-π stacking and the hydrogen bond. They had lower EM from 15 to 22 mN/m, while the addition of wax had no positive effect on the EM. The all-atom MD simulation revealed that, the DTP and the DIP could fabricate a flexible network with the wax at the interface. The wax played as connector to bridge the node formed by the aggregated PACs. While the PyN and the PyO formed brick wall-like film, but the film could be broken by the wax. The dissipative particle dynamics simulation also indicated that, when the side group inhibited the π-π stacking and increased the dispersion of the asphaltene, the asphaltene could form a water-in-oil emulsion with up to 70% water content. Meanwhile, the stacking of the PACs was still necessary to supply a node for the stabilization of the interfacial film. The study made the first step to establish the relationship between the HIPE stability and the structural characteristics of the emulsifier, that provided a qualitative correlation between the stability of the emulsion and the functional group of the asphaltene, instead of the correlation between the stability of the emulsion and. It would be easier and more practical for the designing of the emulsifier for the underground HIPE.