Surface properties of flat poly(tetrafluoroethylene) plates grafted with poly(N-isopropylacrylamide)

Flat poly(tetrafluoroethylene) (fPTFE) plates grafted with N-isopropylacrylamide (NIPAAm) were prepared by the combined use of the oxygen plasma treatment and photografting. The amounts of PNIPAAm grafted onto fPTFE plates were evaluated from N1s/C1s values of NIPAAm-g-fPTFE plates by ESCA. Their surface properties were followed up by contact angles with water and several organic liquids. As a result, it was found that the hydrophobic and non-wettable surfaces of fPTFE plates were made highly hydrophilic and wettable. The wettabilities of NIPAAm-g-fPTFE plates increased with an increase in the amount of PNIPAAm grafted onto fPTFE plates. A discontinuous decrease in wettabilities of NIPAAm-g-fPTFE plates was observed between 30 and 35 degrees C, corresponding to LCST (the lower critical solution temperature) of PNIPAAm in an aqueous solution. The surface free energies gamma(s) of NIPAAm-g-fPTFE, PNIPAAm and NIPAAm gel plates at 25 and 40 degrees C were calculated on the basis of the modified Fowkes equation and the components of hydrogen bonding gamma(s)(h) were found to decrease at 40 degrees C compared to those at 25 degrees C. It was made clear that the hydrophobic interaction between isopropyl groups in PNIPAAm chains at higher temperatures brought about the decrease in the hydrogen bonding between grafted PNIPAAm chains and water molecules.