Dependence of clay–water contact angle on surface charge and ambient temperature: A study from molecular dynamics perspective

The clay-water contact angle emerges as a pivotal parameter essential for elucidating various engineering challenges. Its variability is closely linked to surface charge and ambient temperature, thereby exerting significant influence on soil's hydraulic properties. However, current research on the joint effects of ambient temperature and surface charge on clay's contact angle is incomplete, lacking insights from molecular dynamics perspective. Focusing on static contact angle, this study has established diverse montmorillonite-water systems under varying surface charge conditions (cation exchange capacity = 0, 27.60, 54.84, 108.38, and 134.73 meq/100 g) and ambient temperatures (277, 293, 313, 353, 393, and 433 K) through the molecular dynamics (MD) method. The liquid phase boundary is determined by extracting density contour plots and a unified conical curve is introduced to quantitatively analyze the contact angle calculated by MD simulations. This approach led to the development of a nonlinear equation for estimating contact angle variations under different surface charges and ambient temperatures. Finally, the proposed equation is validated against literature data, demonstrating a strong correlation with experimental findings. It exhibits remarkable accuracy in predicting the variations of contact angles induced by ambient temperature under various surface charge conditions. These findings offer valuable insights and practical equation for designing clay impermeable layers in engineering applications.