Hysteresis and interfacial energies in smooth-walled microfluidic channels
Water Resources Research 47,(2011)
Hysteresis in the capillary pressure-saturation relationship (P-c-S-w) for a porous medium has contributions from the complex geometry of the pore network as well as the physical chemistry of the grain surfaces. To isolate the role of wettability on hysteresis, we fabricated microfluidic cells that contain a single wedge-shaped channel that simulates a single pore throat. Using confocal microscopy of the three-dimensional interfaces under imbibition and drainage, we demonstrate an accurate balance between mechanical work and surface free energy that was evaluated using measured advancing and receding contact angles. The closed-loop mechanical work per surface water molecule is 95 kJ/mol, which is consistent with physisorption. Therefore, the hysteresis in the P-c-S-w relationship for a single pore throat is defined by advancing and receding contact angles that are controlled by dissipative surface adsorption chemistry.
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