InterPore2026

Study on wetting film and apparent contact angle beyond classical DLVO: effects of salinity and finite ion size via a DFT–MSA Poisson–Fredholm model

21 May 2026, 15:35

1h 30m

Poster Presentation (MS06) Interfacial phenomena across scales Poster

Speaker

Wenxing Dai (the University of Manchester)

Description

Wettability is crucial for the simulation of multiphase flow problems such as carbon dioxide storage and shale gas production. Previous studies suggest that a nanometre-scale wetting film can exist in the three-phase contact region and its stability is influenced by surface forces. The presence of the wetting film can further affect the apparent contact angle. DLVO theory has been widely applied to calculate disjoining pressure to study film stability and the electrostatic double layer (EDL) component of disjoining pressure is commonly evaluated with Poisson-Boltzmann (PB) theory, which treats ions as point-charge model and neglects finite ion-size and short-range correlation effects. Therefore, it may lead to inaccuracies in disjoining pressure calculations under high salinity reservoir conditions. This study applies a nonlocal density-functional-theory framework closed by the mean spherical approximation (DFT–MSA), resulting in a coupled Poisson–Fredholm formulation, which accounts for excluded-volume effects and electrostatic correlations to replace the PB-based EDL description within traditional DLVO theory. The resulting disjoining pressure is used to determine the equilibrium film thickness from disjoining–capillary pressure balance, and the equilibrium contact angle is obtained from the augmented Young–Laplace formulation via the Derjaguin–Frumkin relation. By comparing PB- and DFT-based predictions, we evaluate how salinity, ion size, and electrostatic boundary conditions influence the stability of the thin wetting film and equilibrium contact angle under reservoir conditions. Our results indicate that considering ion size effects under high salinity conditions may affects the equilibrium contact angle, with the deviation from PB predictions increasing with salinity. This framework provides a pathway to incorporate finite-size effects into DLVO-based wettability models, with potential implications for predicting wettability evolution and flow behaviour near residual saturation in subsurface CO₂ transport.

Acknowledgment: This PhD project is funded by EPSRC - SHELL.