# Surface Coatings and Treatments for Controlled Hydrate Formation: A Mini Review
## 3 Hydrate-Public Surface Treatments and Coatings
### Superhydrophobic and Omniphobic Coatings  
[PERSON] et al. [47] presented two low-adhesion protective coatings, a superhydrophobic anti-icing coating and an omnipphobic corrosion-resistant coating, and determined their efficiency in reducing the hydrate adhesion on pristine and pre-corroded carbon steel surfaces. Cyclopentane and the methane/ethane mixture both formed sII hydrate structure and were used for testing the effect of both the coatings at atmospheric, high-pressure, and dynamic conditions using a micromechanical adhesion force measurement apparatus and a rocking cell assembly. The MMF experiments performed at atmospheric and high-pressure conditions indicated that the application of the coating resulted in a reduction of adhesive forces between hydrate and solid carbon steel surfaces, more so in the case of the corroded steel. Rocking cell tests indicated that at low-water content the hydrate deposition time reduced significantly. The omniphobic and superhydrophobic coatings decreased the adhesion force by 53% and 29%, respectively, on a pristine surface, whereas the decrease on pre-corroded surfaces was found to be 96% and 95%, respectively. Rocking cell experiments conducted at high pressure indicated that hydrate deposition could be delayed up to 24 h using coated surfaces in a low-water content system. Later, [PERSON] et al. [50], in order to develop a readily applicable robust strategy to reduce the deposition behaviour of various solids (hydrates, wax, asphaltene) within the pipeline, carried out extensive testing of polymeric omniphobic and superomniphobic surface material formulations at atmospheric and high-pressure conditions. Different experimental setups were used to unravel the interactions between the coatings with water, gas hydrate, asphaltene, and crude oil. At atmospheric pressure, on a corroded surface, the omniphobic surface treatment enhanced the water contact angle from 0\({}^{\circ}\) to 91.5\({}^{\circ}\). The low surface energy and water-repellent properties of omniphobic material made the authors test it for its anti-hydrate properties. Compatibility tests were carried out by applying the omniphobic formulation on both sides of the piece of substrate and submerging it into various chemicals representing the substances that might be present in production lines such as kerosene, xylene, and jet propulsion fuel 8 (JP8) for 120 days. The samples were regularly checked for any change in appearance, weight, and adhesion. No detectable changes were noticed, even after 4 months of submersion in the case of kerosene and JP8. However, slight changes in the surface colour were noticed in the case of xylene. Adhesion and weight remained unaltered in all cases. High-pressure measurements were performed using a rocking cell apparatus where the treated/untreated stainless-steel substrates were placed at the bottom of the experimental chambers after filling the desired liquid phase (model oil/water). An isochoric-isothermal method coupled with shear-induced conditions was used to assess the hydrate inhibition ability of the formulation and indicated that the surface treatments inhibit the hydrate deposition for up to 3 days with good repeatability. Omniphobic treatments were also found effective compared to untreated/superomniphobic treatments in reducing the deposition of asphaltene and crude oil on its surface. The authors are looking to scale up the selected formulation and testing in a high-pressure flowloop to produce a robust surface treatment that can be recommended to industries as a strategy to manage solid deposition within the pipelines. [PERSON] et al. [53] created a superhydrophobic (water and hydrate repellent) coating of CuO on the surface of X90 pipeline steel by electrodeposition and hydrothermal treatment of Cu followed by surface modification using stearic acid. The microstructure of the modified surface looks like the structure of a lotus leaf, indicating potential super hydrophobicity.