# Surface Coatings and Treatments for Controlled Hydrate Formation: A Mini Review
## 6 Conclusions and Future Perspectives  
A systematic review of the area of functionalized surface coatings and treatments for controlled hydrate nucleation and growth was presented. The progress made at this front in the last decade was collected and discussed. At this stage, the research focus is shifting towards managing hydrate formation instead of completely avoiding it within the production pipelines. The recent works reported on this topic are more detailed and improve our understanding of the importance of functionalized surfaces as a hydrate management tool (Figure 5). Some important points can be summarized and highlighted from this review:  
* Surface chemistry (hydrophobicity/hydrophilicity) and physical state (morphology) are both vital in defining a surface as hydrate-phobic or hydratephilic.
* Hydrate formation is a stochastic process, which depends on various parameters (several repetitions are required to obtain statistically significant results), which also make it impossible to compare the results across laboratories.
* Standard protocols indicating clearly the subcooling temperature, composition of THF/CP hydrate forming solutions, and parameters to assess the performance of a coating should be established for round robin measurements so that the results from different laboratories can be compared.
* The results obtained for THF/CP (type sII) model hydrates at atmospheric pressure should only be made with gaseous hydrates that form a similar hydrate structure at high pressure.
* In the future, screening of more robust and environmentally benign surface treatments/coatings, which are economic, can be prepared rapidly at large scale, and be multi-functional in nature, needs to be assessed.
* Systematic molecular modelling studies need to be pursued to unravel the mechanism by which a given surface alters the hydrate adhesion.  
The area of hydrate-promoting functionalized surfaces that can accelerate the rate of hydrate formation and growth is relatively unexplored. Progress at this front will immensely improve various applications based on hydrate technology for energy- and environment-related purposes. We believe that the coming decade will see a surge in research activities in this area.  
Figure 5: From concept to commercialization: Development stages of an anti-hydrate/hydrate-phobic coating.  
**Author Contributions:** Conceptualization, M.T., T.A.; Writing-original draft preparation, T.A.; Writing-review and editing, M.T., J.M.S.S.E.; Fund acquisition, M.T. and J.M.S.S.E. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This work was supported by the Associate Laboratory for Green Chemistry-LAQV, which is financed by national funds from Fundacao para a Ciencia Te Tecnologia, FCT/MCTES (UIDB/50006/2020, UIDP/50006/2020, and LA/P/0008/2020). The support through project PTDC/EQU-EQU/32050/2017, funded by Fundacao para a Ciencia e Tecnologia, FCT/MCTES (Portugal), is also acknowledged.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Not applicable.  
**Conflicts of Interest:** The authors declare no conflict of interest.