Nanoconfined competitive adsorption and wettability transition
Wenzhen Chu, Kaiqiang Zhang
Abstract
Adsorption-driven wettability transitions are fundamental to understanding fluid–solid interfacial phenomena and their impacts on diverse processes in nature and industry. In systems with multiple fluid species, competitive adsorption introduces additional complexity by altering interfacial energy and fluid behavior. This study employs molecular simulations and atomic force microscopy to investigate the CO 2 – n- decane competitive adsorption dynamics, serving as a model for geological surface sciences. At a typical geological temperature of 323.15 K, as pressure gradually increases to 1 MPa, CO 2 molecules begin to displace the adsorbed n- decane. Due to interfacial energy effects, CO 2 preferentially adsorbs at the solid–liquid–gas three-phase contact line and gradually penetrates the solid–liquid contact interface. With further pressure increases, CO 2 molecules progressively form an adsorption layer at the solid–liquid interface, reaching a stable thickness of 1.14 nm at the pressure of 5 MPa. Beyond this value, the adsorption layer thickness decreases with increasing pressure as an indicative of the miscibility onset. A three-dimensional surface model F ad T P is constructed to quantify critical thresholds of adhesion forces, identifying the conditions driving wettability transitions. Analysis of the Gaussian curvature of the F ad surface reveals critical thresholds corresponding to the wettability transition line in the T - P space, T P = 1.00 − 1.62 × 10 7 · P + 1.71 · P 2 . These quantitatively detailed observations deepen our understanding of the mechanisms underlying competitive adsorption-induced wettability transitions. Additionally, the study underscores the role of competitive adsorption in geological CO 2 -involved activities, where CO 2 -induced wettability transitions enhance utilization efficiency and storage security. This study contributes to optimizing processes across earth and environmental, industrial, as well as carbon neutrality efforts, advancing the understanding and application of competitive adsorption and wettability transition.