Topic Area: 4e. PFAS Source and Forensic Considerations

Formatted Title:

Practical Implications of PFAS Self-Assembly into Supramolecular Aggregates

Background/Objectives:

The propensity of amphiphilic PFAS to self assemble into supramolecular assemblies such as vesicles, rod-shaped micelles and lamella has been described in multiple scientific publications in physical chemistry journals. Their self organization into stable supramolecular structures in hexagonal, intermediate, and lamellar phases, was first reported in the 1980s.

As a result of the perfluoroalkyl group being stiff, helical, and bulky, as compared to alkyl chains, fluorosurfactant tails are not prone to pack together to form spherical micelles. Whereas hydrocarbon surfactants form micelles, fluorosurfactants self assemble in layered structures, which stack to form multi-layered vesicles and lamella sheets which can grow to form large supramolecular assemblies, some hundreds of microns in size. The omniphobic properties of PFAS, together with low van der Waals interactions, result in their segregation into discrete compartments when dissolved in water. This presentation aims to explain the conditions which cause formation of supramolecular assemblies and their impact on the environmental management of PFAS.

Approach/Activities:

The ordering of films and bilayers made from fluorinated amphiphiles was described to be generally closer to what prevails in crystalline solids. The peculiar physical chemical properties of amphiphilic PFAS and their tendency to aggregate in supramolecular assemblies appear to play a critical role when considering their fate and transport. Amphiphilic PFAS have been described to form multi-layered Langmuir-Blodgett type films on solid surfaces, which could comprise an ongoing source of PFAS following release of firefighting foams.

The powerful driving force for self association conferred by perfluoroalkyl chains is demonstrated by the ability of single-chain amphiphilic PFAS to produce stable vesicles, flexible fibers, and rigid tubules, in the absence of supplementary forces (e.g., hydrogen-bonding, ion-pairing), whereas nonfluorinated analogues yield only micellar solutions. Self-assembled structures formed from amphiphilic PFAS can show remarkable stability, such as surviving heat sterilization.

A detailed review of the physical chemistry of PFAS will be provided to explain their properties and predict their behavior.

marie pierre Krafft

Affiliation

Refine Results

(Group 2, Poster Board #10) Practical Implications of PFAS Self-Assembly into Supramolecular Aggregates