Visible photomobile response of azobenzene-based polymer/carbon black films

In this work, we developed and characterized composites prepared by dispersing conductive carbon black (CB) at different concentrations in an azobenzene-based photomobile polymer (azo-PMP) matrix. This polymer can move under UV-blue light because its azobenzene moieties undergo a reversible photoisomerization from trans to cis configuration and this nanoscopic structural movement induces a macroscopic movement in the film. We studied the possibility to modify the photomobile properties of azo-PMP by introducing different concentrations of CB (from 0 wt.% up to 1 wt.%) and we investigated morphology, optical properties and photomobile behaviour at different wavelengths. Optical analysis by polarized light shows that the films with CB concentrations up to 0.1wt.% are quite homogeneous and still present birefringence properties. Photoresponsivity measurements at wavelengths in the range 457-747 nm were studied to investigate how the presence of the CB affects the photomobile response inside and outside the absorption spectral region of azo-polymers. Choosing appropriately the CB concentration, we demonstrated that it is possible to enlarge the usable spectral bandwidth of the samples in visible region towards the visible and near infrared spectral region.