Smart molecular-spring photonic droplets†
Complete solid-state cholesteric liquid crystal (CLCsolid) droplets are fabricated using microfluidics after UV curing and chiral-dopant extraction of monodispersed CLC droplets, which consist of a reactive nematic LC mesogen mixture and a nonreactive chiral dopant. The helical pitch of the CLCsolid droplets is reduced by removing the chiral dopant in proportion to the extracted volume. The CLCsolid droplets exhibit a coloured reflection spot at the centre, with cross-communication dots. These photonic colours indicate that the helical photonic CLC structure is well maintained even after UV curing and dopant extraction. The pitch of the well-defined helical photonic structure depends on the solvent quality, temperature, and humidity, giving rise to a reversible change in the reflection colour of the CLCsolid droplets upon exposure to external stimuli. The CLCsolid droplets are extremely stable for a long time, even in a good solvent. These smart solid-state molecular-spring photonic droplets eliminate the obstacles to CLC-droplet application caused by the fluidic LC state, and thus introduce a new avenue for CLC applications.