Aliphatic flexible spacer length controls photomechanical response in compact, ordered liquid crystalline polymer networks

Abstract The aliphatic spacer length connected to the rigid mesogenic cores is shown to control the structural organization and mechanical actuation in response to light-stimulus in azobenzene-functionalized liquid crystalline polymers networks. The spacer lengths in the mesogenic host (non-photochromic) and in the photo-active azobenzene-functionalized cross linker are parametrically varied to create monodomain liquid crystalline samples. A suite of thermomechanical, photomechanical and structural characterization is used to characterize the binary co-polymers. The photomechanical responses are compared by calculating a figure-of-merit – Photocompliance (Cp). This parameter, Cp, which characterizes the incremental strain generated in response to unit intensity of irradiation (W/cm 2 ), is found to correlate strongly with the S xray order parameter and the D-spacings. We show that compact (smaller D) and higher ordering of the mesogens that result in copolymers with longer flexible spacers manifest greater photomechanical activity.