Details of the 9th Challenge

There is increasing interest in high temperature and pressure processing of emulsions. Typical conditions of interest are > 100 °C and > 1 bar (pressurized process to maintain liquid state). Dynamic drop tensiometer techniques are available for measuring interfacial tension (IFT) from droplet curvature at high T and P up to 200 °C and 200 bar. See Chaverot et al. as an example.

The 9th Challenge aims to test the ability of molecular modeling approaches to predict water/oil IFT at elevated T and P for three different oils:

• n-dodecane
• toluene
• 50:50 mixture of n-dodecane and toluene

Timeline

• Monday, October 24, 2016 - challenge entries are due
• Sunday, November 13, 2016 - entrants present their work and champions are announced at the AIChE Annual Meeting

Challenge entrants are asked to make a total of 12 predictions of interfacial tension as summarized below (3 oil phases and 4 temperatures). The pressure for all state points is 250 psig.

The n-dodecane (Sigma Aldrich, ReagentPlus >99% purity) was further purified by passing through an alumina column to remove surface-active impurities.  The n-dodecane had a final purity of 99.55%.  The major impurities remaining consisted of isomers of undecane (0.32 %) and isomers of tridecane (0.13 %).

The toluene (Fisher Scientific, HPLC grade) had a purity of 99.95%.

Details of the analytical analysis performed to evaluate the oil compositions are available in the Appendix. It is not required to account for these impurities in the IFT predictions for the challenge, but entrants are free to account for them if they so choose.

Deionized water was used in this study.

The IFT predictions should be reported in units of dyn/cm. Note that the oil blend is 50:50 on a mass basis.

Here are a few references that may be useful for model validation:

• IFT data for n-octane up to 150 °C: Flock et al. (1986)
• IFT data for n-decane up to 120 °C: Michaels et al. (1951)
• IFT data for toluene up to 125 °C: Yu et al. (2014)

Challenge Scoring

Entries will be scored by comparing the predicted interfacial tension values to the measured data. Full credit will be awarded for a prediction that falls within the experimental uncertainty. A linear interpolation of partial credit will be awarded for predictions with an absolute deviation above the minimum threshold and a maximum of X % (to be specified before the challenge concludes). No points will be awarded for prediction above the maximum deviation. The comparison between predictions and experiment will be performed both in terms of the IFT values and in terms of the IFT values relative to whichever one of the 12 IFT values that the entry predicted most accurately the value for dodecane at 110 °C [updated 2016/08/04]. The scores for the relative values will contribute to 2/3 of the total available points, and the raw IFT values will contribute to 1/3.

Rules of the Game

• Any theory/modeling/simulation method can be used as long as it is generally accepted to be a “molecular modeling” approach. For example, strictly empirical correlation will not be considered for the challenge. This is in keeping with the focus and goals of the IFPSC to benchmark and promote molecular modeling and simulation methods. If you are unsure whether or not your method is considered to be “molecular modeling” by the challenge organizers, please ask in advance.
• Any force field (or other model parameterization) previously published in the open literature prior to the announcement of this challenge is acceptable.
• Force fields (or other models) that have not been published previously may not be parameterized for this challenge using interfacial tension data for both the same molecules and state conditions as the challenge problems [i.e. the same molecules but different state conditions...low T and P...is OK; different molecules but the same state conditions...high T and P...is OK. There should be some transferability required - to different molecules or different state conditions - not just fitting to data for the challenge problems if such existed but the organizers failed to find it. By "different state conditions" we mean low T and P, not high T and P at slightly different conditions from the challenge problems - updated 2016/09/27]. Force fields (or other models) may be parameterized using any other published physical property data.
• Estimates of the uncertainty for the predicted properties must be included.
• Participants may choose to take into account the analytical oil composition data that has been provided or may ignore the impurities in the dodecane, toluene, and the mixture. 

Other Entry Guidelines

• Entries are to be submitted to contest@ifpsc.org on or before the deadline
• A submission for this challenge problem is to be in the form of a manuscript suitable for submission to a refereed, archival, scientific journal. The manuscript must contain sufficient detail about the simulation or other method and about the force field (if simulation) so that an experienced simulator could reproduce the results without requiring access to proprietary information. In particular, all potential parameters and molecule geometry parameters must be explicitly specified in the manuscript.
• An analysis of the uncertainty in the calculated results is required and must be included in the manuscript.
• Entries are expected to present results that are statistically significant and to present sufficient supporting evidence to establish this quality. Also, the scientific reasoning behind any new (unpublished) force field parameterizations must be clearly spelled out in the entry. If there is a consensus among the judges that an entry is of poor quality (uses a method commonly accepted to be fundamentally flawed, presents results that are not statistically significant, fails to provide sufficient supporting data and details, violates the various rules and guidelines established for the competition, or for any other reason would be unlikely to be accepted by any peer-reviewed scientific journal in the field), that entry will be rejected and will not be considered in the judging.
• Entries that represent collaborations between multiple research groups are welcomed.