Laser-Induced Thermocapillary Reorientation of Liquid Crystal Elastomers

Recent investigation of thermocapillary and thermosolvocapillary forces induced by focused laser spike (FLaSk) annealing has revealed that the interfacial shear generated by highly localized thermal pulses can be employed as a means to align and anneal mesoscale order in soft matter. This work explores the use of FLaSk of a photoabsorbing dye to direct the nematic phases of an RM82-based liquid crystal elastomer, which can be crosslinked either simultaneously or by separate treatment. The director orientation in such nematic systems have a drastic effect on the mechanical properties of the crystal, as mechanical or thermal stress will induce large directional strains along these molecules with only minimal transverse strain, and the deliberate patterning of crosslinked elastomer phases has been used to program the expansion behavior of three-dimensional liquid crystalline soft actuators. Results suggest that both the thermal gradient magnitude and the writing rate effect the overall reorientation for overlapping scans. Compared to previous efforts to optically template these phases, the driving force for this method is decoupled from the polarization of the beam. This allows for patterning of complex paths and even 3D effects.