The adsorption of poly(l-lysine) (PLL) from aqueous solution to poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) is investigated. Adsorption is controlled by choice of solvent (and PLL solution conformation) or by FEP surface chemistry. PLL adsorbs from pH 11 buffer solution to FEP: PLL adsorption is concomitant with the liberation of water molecules from the FEP-water interface resulting in a decreased interfacial free energy between organic and aqueous phases. PLL does not adsorb from an aqueous pH 7 solution to FEP unless the FEP surface is carboxylic acid-functionalized (FEPCO2H):an ionic interaction between FEP-carboxylate and PLL-ammonium enhances adsorption.
The surface modifications are charaterized by attenuated total reflectance infrared spectroscopy (ATR IR), ultraviolet-visible spectrophotometry (UV-vis), contact angle, and quantitatively by x-ray photoelectron spectroscopy (XPS). The adsorbed amount of PLL to FEP (from pH 11) is proportional to molecular weight whereas the adsorbed amount of PLL to FEP-CO2H (pH 7) is independent of molecular weight and likely proportional to surface charge density. The modified film samples (relative to the unmodified film samples) show improved characteristics in terms of wettability, chemical reactivity, adhesion, cell growth.