The Effect of Surface Adsorption and Molecular Geometry on the Determination of Henry's Law Constants for Fluorotelomer Alcohols

Fluorotelomer alcohols (FTOHs) are one important subgroup of perfluorinated compounds (PFCs), yet Henry's law constant (K(H)) of FTOHs, which is also known as the air-water partition coefficient, remains poorly understood with a wide range of reported values. This study measured the K(H) of FTOHs from (309.6 to 334.2) K using the integrated gas-stripping method (IGS) for the first time, which has a lower surface-to-volume ratio comparing to the headspace method (HS). Two different materials, namely, stainless steel and glass, were chosen for constructing the stripping vessels. Results indicated significantly stronger adsorption of long-chained FTOHs on glass surface, which led to a significant bias in K(H) derivation. K(H) values extrapolated to 298 K of 4:2, 6:2, 8:2, and 10:2 FTOH, using a stainless steel vessel, showed no linear increase. A similar tendency was also reported by other groups using the HS approach. The unique molecular geometry of FTOHs was suspected to be responsible for the unusual tendency observed and false predications by modeling software including SPARC and EPI Suite. Compared with HS results reported by others, the K(H) values obtained in this study were higher. The discrepancy might be mainly due to the different extent of surface adsorption engaged in the two approaches.