Abstract
Smart cotton fibers with temperature-driven sensitivity were developed by simple finishing with poly(N-vinylcaprolactam-co-tricyanofuranhydrazone);PVCH.Vinyl-bearing tricyanofuranhydrazone was prepared by an azo-coupling of 2-allyloxy-4-nitroaniline diazonium salt with tricyanofuran. Poly(N-vinylcaprolactam) labeled with tricyanofuranhydrazone probe was then prepared in situ by free radical polymerization. The chemical formulae of the hydrazone chromophore and PVCH were examined by FTIR, NMR and CHN elemental analysis. The PVCH-finished cotton functioned as a thermochromic assay producing an instantaneous colorimetric change from yellow to purple when the temperature increases from 34 to 49 degrees C. Changes in color were studied by the CIE Lab color parameters. The absorbance spectra showed a temperature-driven red shift from 429 to 564 nm. This can be attributed to the formation of push-pi-pull hydrazone type chromophore due to temperature-driven proton abstraction leading to intramolecular charge transfer. The surface morphology of cotton immobilized with poly(VC-co-H) nanofibers was examined by scanning electron microscope (SEM) and infrared spectroscopy (FT-IR). The PVCH nanofibers were also inspected by transmission electron microscopy (TEM), showing fibers with diameter of 2-10 nm and length of 148-152 nm. No considerable defects were detected in bending length and permeability to air of the PVCH-finished fibers. In addition, high colorfastness properties were observed for the treated cotton substrates. Upon exposure to gaseous ammonia, the vapochromic cotton was able to rapidly change color from yellow to purple, and then recover back to yellow instantly when removing the vapochromic fabric away from the ammonia source. The current cotton assay showed a detection limit (LOD) of 10 to 250 ppm for aqueous ammonia. The cytotoxic properties of the thermochromic cotton fibers were also examined. Mechanistic study accounting for the thermochromic activity of poly(N-vinylcaprolactam-co-tricyanofuranhydrazone) is proposed.