Azobenzene-Doped Liquid Crystals in Electrospun Nanofibrous Mats for Photochemical Phase Control

The encapsulation of liquid crystals (LCs) within semiflexible, nanoscale media has potential use for developing flexible photodisplays, electronic devices, and sensors. Here, coaxial electrospinning is used to fabricate mats of nanofibers consisting of a polyvinylpyrrolidine polymer sheath and an azobenzene-doped, low-molecular-weight LC core. The addition of the azobenzene chromophore into the LC core allows for the nematic to isotropic phase transition to be initiated photochemically. Fiber morphology was investigated by polarized optical microscopy (POM), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). Nanofibrous mats were analyzed using differential scanning calorimetry and polarized optical microscopy. Irradiation with UV light triggers the photoisomerization of the azobenzene dopant and the subsequent nematic to isotropic phase transition in the LC core. This was directly observed by the birefringence in the fibrous mats being turned “off” with UV light. Subsequently, the cis–trans isomerization triggered by visible light allows for the reformation of the nematic state and the birefringence being turned “on”. Encapsulation of the liquid crystal within the nanofibers results in precise spatial control over the optical properties of the nanofibers, which is used to photochemically generate detailed images patterned into nanofibrous mats.