Methane hydrate propagation on surfaces of varying wettability

Methane hydrates were crystallized from water droplets on three different surfaces of varying wettability. Contact angles in air were used to classify substrates in decreasing order of wettability as: glass, sapphire, and polyvinyl chloride (PVC). Hydrates grown on glass appeared to have a rougher texture than those grown on sapphire, and those grown on PVC appeared to have the smoothest texture. Hydrate films formed on sapphire and PVC smoothed over time, and depressions on the clathrate films were observed within 3 h of initial crystal growth. Hydrate films formed on glass did not develop depressions over this 3 h period. On glass and sapphire, methane hydrate propagated beyond the original water droplet boundaries. The hydrate propagation velocity on glass was found to be at least 50% higher than that on sapphire. Methane hydrate did not propagate beyond the water droplet boundaries on PVC. Hydrate growth beyond the original water droplet boundary (halo) was found to proceed through water migration by capillary action: first, water migrated onto the bare substrate (glass or sapphire), and second, hydrate grew on the fresh water surface. We posit that static contact angle measurements of water on a solid substrate in air could be used to infer the potential for hydrate propagation onto a solid substrate.