Nanocomposite Teflon AF 2400 films as tunable platforms for selective transport

The performance of polymeric film-based sensors, separations, including extractions, depends on solute transport rates and selectivity. The membrane's chemical composition, its state (e.g, crystalline, glassy, rubbery), and its fractional free volume are all important in defining performance attributes. Other properties of films important in sensors are robustness in the environment, chemical inertness and biocompatibility, thermal stability, and optical transparency. With the long-term goal of selective transport/extraction based on molecular recognition, we have focused on fluorous media such as Teflon AF 2400. We present a novel approach to create nanocomposite Teflon AF 2400 films with the polymer in different states to facilitate permeation and fluorous selectivity in liquid phase transport. Films cast from stable suspensions of the fluorocarbon polymer Teflon AF 2400 (T(g) ∼ 240 °C), fluoroalkylsilane-modified solid, low polydispersity silica nanoparticles (FNPs: 116 nm diameter), and with or without a plasticizer (perfluorotripentylamine, FC-70) are macroscopically homogeneous. The nanocomposite films with glassy polymer absorb considerable solvent, CHCl(3), when in contact with solutions. Thus, the films are very permeable to solutes (toluene and octafluorotoluene) from CHCl(3) solution with poor selectivity for the fluorinated solute. Plasticized Teflon AF nanocomposite films show very low solvent sorption, improved fluorocarbon/hydrocarbon selectivity, and excellent transport rates. This is an unprecedented example demonstrating the effect of a plasticizer to create polymer nanocomposites with different chemical and barrier properties. The state of the polymer in the nanocomposites dictates chemical properties. The chemical properties dictate the transport behavior. In all cases, the films are dimensionally and thermally quite stable, making them ideal materials for applications in separations and sensors.