Electrospun polymer nanofibers of P(NIPAAm-co-SA-co-FBPY): Preparation, structural control, metal ion sensing and thermoresponsive characteristics

Multifunctional electrospun (ES) nanofibers prepared from random copolymers of poly{(N-isopropylacrylamide)-co-(stearyl acid)-co-[9,9-dihexylfluorene-2-bipyridine-7-(4-vinylphenyl)]} (poly(NIPAAm-co-SA-co-FBPY) were successfully prepared from the electrospinning technique with a single-capillary spinneret. FBPY demonstrated blue or red shift in emission wavelength and fluorescence quenching when chelating with different metal ions. With appropriate composition of SA in the copolymer, films and nanofibers could maintain their morphology in aqueous solution at different thermal treatments. Polymers in three states, solution, film and nanofiber, were prepared and their effects on sensing ability were investigated. The smooth nanofibers prepared from P2 (with copolymer composition of NIPAAm:SA:FBPY = 93:6:1) demonstrated superior sensitivity as low as 10−5 M in sensing zinc ions as compared to polymer films (10−3 M) due to the high specific surface area of nanofibers. The porous nanofibers of P2 were also manufactured to further enhance sensing performance and showed the best sensitivity (10−6 M) among three states when sensing with zinc ions (sensitivity of polymer solution in THF was about 10−5 M). These nanofibers also exhibit an interesting “on/off” switch behavior with decreasing temperature from 40 to 10 °C due to the hydrophobic-hydrophilic transition of NIPAAm moieties which cause the gradual swelling of nanofibers. These results indicated that the new nanofibers could have potential applications in multifunctional sensory devices.