Teflon AF Composite Materials in Membrane Separation and Molecular Recognition in Fluorous Media

[摘要] Fluorocarbons are highly non-polar and notoriously poor solvents. The unique nature of fluoropolymers makes them valuable in partitioning based separations and sensing. Molecular diffusion and partitioning are key properties in the scenarios where chemical separation and sensing occur inside a polymer. Unlike in liquid phase where diffusion and partitioning can be estimated by empirical methods, the physical properties as well as dynamics of polymer chainssignificantly impact diffusion and partitioning. Therefore, this work is focused on developing a fundamental understanding of solute transport behavior across Teflon AF 2400 composite films in liquid phase.Three types of Teflon AF 2400 composite films including Teflon AF 2400/FC-70, Teflon AF 2400/fluorophilic silica nanoparticles (FNP), and Teflon AF 2400/FNP/FC-70 wereinvestigated for the selective transport of fluorinated molecules against their hydrocarbon counterparts. Doping FC-70 in Teflon AF 2400 decreases the sorption of organic solvent(CHCl3) in Teflon AF 2400, restores the fluorophilicity of the film, and leads to an increase oftransport selectivity. Teflon AF 2400/FNP composites containing ≥ 50 wt% FNP show significant increase of free volume, sorption of CHCl3, increased solute permeability, and decreased transport selectivity. Teflon AF 2400/FNP/FC-70 composites represent a novel type of composite film: the soft Teflon AF 2400/FC-70 phase which is not dimensionally stable by itself is well supported by the FNPs. The Teflon AF 2400/FC-70 phase in the three-component film shows low CHCl3 sorption, and high solute permeability as well as transport selectivity.Molecular recognition based extractions are highly selective when targets are extracted into a fluorous phase because molecular interactions can be strengthened in fluorocarbons while the partitioning of interferences is minimized. To gain quantitative understanding of noncovalentinteractions in fluorocarbons, the association of perfluorodecanoic acid (PFDA) with pyridine and quinazoline (separately) was investigated via isothermal titration calorimetry (ITC). Thermodynamic data suggests enhanced noncovalent interaction, formation of complexes withacid:base stoichiometry greater than 1:1, and proton transfer in [PFDA3·pyridine] upon the join of the third PFDA. The free energy of complex formation between organic compounds and perfluorinated molecular receptors can serve as the driving force to improve molecular receptorbasedextraction and sensing in fluorous media.

[发布机构] the University of Pittsburgh