# Surface Coatings and Treatments for Controlled Hydrate Formation: A Mini Review
## 3 Hydrate-Public Surface Treatments and Coatings
### Functionalized Hydrate-Phobic Surfaces
Other modifications using AEAPTMS coupled with glycerol at the 1 or 2 position did not show any significant change compared to unmodified glass tubes. However, the test tube modified with APTES and succinic acid enhanced the THF hydrate formation. [PERSON] et al. [46] treated the smooth and textured silicone surfaces with octadecyltrichlorosilane (OTS) or tridecalfluoro-1,1,2,2 tetrahydrorocytl trichlorosilane (FS) in order to design passive hydrate-phobic surfaces and measured the cyclopentane hydrate adhesion and accumulation on them. Among the silane-modified surfaces, the one treated with OTS exhibited almost null hydrate adhesive strength and lower accumulation. Although the FS-modified surfaces exhibited low surface energies, one useful parameter that was taken into account in this work was the measurement of contact angle hysteresis, i.e., the difference between the advancing and receding angles that provides information on the interaction between the liquid and solid surface under scrutiny. A large hysteresis indicates a larger pinning and higher roll-off angles. For instance, the untreated silicon surfaces in cyclopentane showed a \(\sim\)24\({}^{\circ}\) hysteresis for water; this value was \(\sim\)55\({}^{\circ}\) for FS-treated ones and was much lower for OTS-treated surfaces compared to other two. This indicates that the water droplet will stick to the untreated and FS-treated ones even at a tilt angle of 90\({}^{\circ}\), whereas on OTS-treated surfaces, it will roll down just at an inclination of 2\({}^{\circ}\). Another interesting aspect of this work was to study the spreading of the cyclopentane barrier film between the hydrate and solid surfaces. The spreading coefficients were measured, which  
Figure 2: (**A**) Correlation between hydrate adhesion strength with the practical work of adhesion evaluated using the 19.1 wt.% THF in water solution on various functionalized surfaces. (**B**) A linker-grafted pPFDA/pDVB polymeric ice-phobic, hydrate-phobic, and hydrophobic coating. (**C**) Representation of water contact angles on solid surfaces (s), indicating two zones of spreading coefficient, S\({}_{\text{os(w)}}\) of cyclopentane (o) in presence of water (w). (**A**) Reprinted with permission from ref. [40]. ©2012 Royal Society of Chemistry. (**B**) Reprinted with permission from ref. [43]. ©2015 American Chemical Society.and (**C**) Reprinted with permission from ref. [46]. ©2017 American Chemical Society. gave information about the relative spread of this interfacial film and its effect on hydrate adhesion (Figure 2C). The role of surface chemistry and texture plays a significant role in the spreading of such films. Although the surface energy criteria were found consistent in predicting the poor performance of untreated silicon, the spreading coefficient captured a complete picture of the performance for all the studied systems. In the case of a positive spreading coefficient for cyclopentane, the solid/water contact area reduced drastically due to the formation of a barrier film by cyclopentane that exhibited much lower hydrate accumulation and adhesion. OTS-coated samples resulted in almost negligible accumulation and a 2-fold reduction in adhesion compared to the FS-coated surfaces.