Ultraviolet-induced irreversible tensile actuation of diacetylene/nylon microfibers

Photomechanically irreversible tensile-actuated diacetylene-embedding nylon 6/6 microfibers were investigated. 10,12-pentacosadiynoic acid (PCDA) monomer, which have conventionally provided a visual color change by temperature and photo-driven stimuli, was embedded in nylon 6/6 microfibers by wet spinning. By ultraviolet (UV) (254 nm) exposure, we observed irreversible tensile actuation (contraction) of linear (untwisted) and helical (twisted) structural microfibers. The tensile contraction of twisted nylon 6/6-PCDA microfiber containing10 mM PCDA was reached to ∼2% at 60 °C. Such irreversible tensile contraction can be promoted by volume contraction of PCDA monomers during UV exposure along with irregular structural deformation containing gauche conformation with increasing temperature. The kinetics of tensile contraction with temperature and time were shown by the Arrhenius plots. The activation energies were 34.3–35.7 kJ mol⁻¹ as increasing the concentration of PCDA, implies that the nylon 6/6-PCDA microfibers could be applied to show time-temperature integrated device. (paper)