**Author details**

**7. Recommendations for future work**

180 Carbon Capture, Utilization and Sequestration

**8. Conclusions**

data relevant to CO<sup>2</sup>

**Acknowledgements**

**Conflict of interest**

We believe that the potential reasons for the scatter in the CA data are due to the differences in: substrate types used (e.g., muscovite mica and phlogopite mica, quartz and silica), their preparation methods, and surface roughness values and patterns; fluid types (i.e. purities of droplet and external phase fluids and whether the fluids had been mutually saturated in the presence of substrate material); chemical compatibility of the materials used in the experimental facilities with the cleaning and process chemicals; types of CA data reported (e.g., static or dynamic CAs, sessile or captive, one droplet/bubble for a given pressure range or new droplet/bubble at each pressure). Repeatability in the data is necessary but not sufficient. Reproducibility is what is important. So, comparisons should only be made among the data collected using same system of solid and fluids, purities and preparation methods, measurement techniques, and especially type of CA data. We suggest microCT-based in-situ CA measurement with automated three-phase contact line detection for simultaneously obtaining several hundreds of thousands of CA values, as performed by AlRatrout et al. [81]. The method may also provide relative permeability and capillary pressure data for indirect estimation of wettability. One disadvantage of the suggested method is the requirement of doping the fluids. We also suggest in-situ surface chemical analysis as performed by Tripps and Combs [75] during the CA measurement in order to know any surface chemical alterations responsible for CA changes.

A detailed overview on the published IFT and CA (experimental and molecular simulation)

research groups are found to be in good agreement, but there exists significant scatter in the reported CA data. Potential reasons for the disagreements in CA data are discussed, and

The authors convey their sincere gratitude to Intergovernmental Panel on Climate Change (IPCC), Geneva, Switzerland, for kindly providing the permission to use Figure TS.7; Figure 5.9 from IPCC 2005: IPCC Special Report on Carbon Dioxide Capture and Storage, prepared by Working Group III of the IPCC (Metz, B., O. Davidson, H.C. de Coninck, M. Loos, and L. A. Meyer (eds.)). Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. The authors would like to convey their sincere appreciation to ACS publishers for

recommendations are made for future research to obtain reproducible CA data.

kindly granting the permission to use Figures 8(a), 10, and 12 from [15].

The authors declare no competing financial interest.

sequestration is presented. Overall, the IFT trends reported by various

Prem Bikkina\* and Imran Shaik

\*Address all correspondence to: prem.bikkina@okstate.edu

Oklahoma State University, Stillwater, USA
