Unveiling the Role of Oil-Water Interfacial Elasticity Mediated by Colloidal Assembly in Fluid Control

Abstract

Controlling oil-water interfaces is crucial for optimizing various well production processes, including liquid/gas flooding, water control, emulsion formation, foam generation, and modifying wettability and spreading behavior. The modulation of the interface can be achieved by tuning interfacial tension and viscoelastic properties, which are controlled by two primary methods: molecular assembly (e.g., surfactants) and particle decoration. The latter approach offers enhanced stability against perturbations and increases the interfacial area, enabling an elastic response and improved overall emulsion performance. In this study, a novel colloidal system is developed with a subsequent surface functionalization route to graft polymeric brushes, defined as dense array of polymeric chains, leading to the formation of external surface protrusions with tunable pendant charges. This physiochemical modulation of the colloidal surface enables a wide range of interfacial properties, including the ability to control oil-water interfacial elasticity upon assembly. Oscillatory shear rheological measurement is adopted with a double-wall-ring pinned at the oil-water interface. This technique enables a time-dependent observation of the evolution of the loss modulus (G″) and storage modulus (G′) following particle assembly coupled with a frequency sweep and varying the oscillation amplitudes to capture the intra- and inter-particle interaction. Atomic Force Microscopy with quantitative nanomechanical mapping (AFM-QNM) is utilized with the oscillating probe pinned at the oil-water interface to capture the stiffness and adhesive behavior of the interfacial layer. Particle concentration as well as local environmental conditions can influence surface charge density on the colloidal surface which plays a crucial role on the inter-particle interaction dictating the strength of the assembly. In low reservoir salinity conditions where the particles are highly-charged with minimum charge screening, the interparticle repulsive forces are maximized where the particle-laden interface exhibits a viscous, liquid-like film characterized by a dominant viscous modulus (G″>G′). This repulsive behavior can also be observed at high particle concentration at the interface. In contrast, at low particle concentrations or at high ionic strengths, strong inter-particle association and attraction are observed. As a result, this gives rise to a dominant elastic, solid-like behavior (G′>G″) of the interfacial film driven by the frictional interlocking of surface patches. Elastic interfaces achieved at low colloidal charged density or low particle concentrations facilitate various applications, including enhanced sweep efficiency, improved resistance to rupturing leading to more stable emulsions, and controlled mobility. Additionally, they facilitate the redistribution of flow into upswept zones, thereby optimizing fluid flow in complex environments. By leveraging the multifunctional and switchable nature of the colloidal design and particle concentrations, manipulation of interfacial properties can be achieved to exert robust control of fluid flow, enabling tailored solutions for challenging applications.