Memorizing UV exposure energy in resistance — A smart patch based on conductive polymer

We have successfully demonstrated a smart UV patch to memorize the accumulative energy from the exposure to UV light over a period of time. The sensing principle is based on changes in the electrical resistance of a composite made of photo-acid generator triphenyl sulfonium triflate (TST), polyaniline emeraldine (PANI-EB), polyethylene glycol (PEG) and carbon nanotubes (CNTs). The sheet resistance of the composite can drop five orders of magnitude within 30 minutes of exposure to the UV light using an LED light source of 10Mw/cm
²
. The photo-induced protonation process can release protons from photo acid generators. With the help of the polyethylene glycol and CNTs, protons can diffuse across the film and cause the doping of polyaniline emeraldine base into a conductive polyaniline salt state to increase the conductivity.