ADSORPTION OF QUATERNARY AMMONIUM SURFACTANTS ON POLY(TETRAFLUOROETHYLENE) SURFACES

Binding levels and mobilities of cationic surfactants with one, two, or three alkyl chains adsorbed on PTFE surfaces were studied by taking adsorption isotherms and analyzing the ESR spectra of coadsorbed DOXYL and TEMPO spin probes. Isotherms for single-chain and double-chain surfactants exhibited saturation, indicating monolayer formation. The triple-chain surfactant showed no such saturation, evidently due to formation of multilayers. In the dry state, the adsorbates were immobile at all surface densities. Hydrated adsorbates exhibited limited mobility at low surface coverage and became fully mobile above certain critical binding levels. Complete mobility was reached at the same binding levels as those corresponding to full surface coverage. It was concluded that the chains of immobile adsorbates lie flat on the surface, while in mobile adsorbates, the chains are packed normal to the surface plane. Such vertically packed layers provide a means of attaching lipophilic or amphiphilic molecules to the polymer surface.