On-demand pitch tuning of printed chiral nematic liquid crystal droplets

Identifying facile means with which to tune the pitch of, and therefore the reflected colour from, chiral nematic liquid crystals (CLC) is of interest for many different photonics applications including optical filters, coloured displays, and mirrorless lasers. Precise control of the pitch of the helix, however, can be challenging. Here, we demonstrate the ability to tune the pitch, and consequently the reflection band, by depositing picolitre volumes of nematic LC into printed CLC droplets with a short pitch. Results are presented that demonstrate mixing of the nematic LC and CLC droplets such that the pitch elongates causing the reflection band located at blue wavelengths (430 nm) to redshift to longer wavelengths. The magnitude of the redshift can be controlled by varying the number of nematic LC droplets deposited into each CLC droplet. We consider the process of diffusion of these two separate mixtures using inkjet printing and showcase how this process of tuning the pitch can be employed to create coloured images in the form of an alphanumeric logo.