Effect of Solid Surface Properties on Spreading of a CO₂ Hydrate Film in a Restricted Space between Two Parallel Silicon Substrates

CO2 hydrate formation in a restricted space is studied by conducting in situ visual observation when CO2 gas reacts with a water droplet between two silicon wafers at 2.8-3.8 MPa and -6 to 6 degrees C. It is found that the hydrate film first appears around the gas-liquid interface and then spreads on the surface of silicon wafer by continuous formation at the advancing front. Experiments are also conducted with silicon wafers with different surface properties, prepared by the pretreatment methods of three types, to study the effect of solid surface on CO2 hydrate formation. The results show that no hydrate spreading is observed on the hydrophobic surface pretreated by 1H,1H,2H,2H-perfluorodecyltriethoxysilane solution or crude oil; the hydrate film is observed, and it spreads on the hydrophilic surface pretreated by piranha solution. Quantitative analysis of the results obtained is employed to understand the intrinsic mechanism. It is found that considering the hydrate film spreading on solid surfaces under experimental conditions, the interfacial tension of hydrate and silicon wafer might play a more significant role in hydrate spreading rate and hydrate film thickness compared to pressure and temperature.