Blue phases (BPs) are unique subset of soft liquid crystalline materials with a three-dimensional ordered cubic structure analog of rigid atomic crystals. BP crystals are thermotropic and undergo phase transition by increasing temperature from BPI with a body-centered cubic structure to BPII with a simple cubic structure. These soft crystals offer numerous advantages such as tunable selective Braggs reflection, sharp reflectivity and sub-millisecond response times. Moreover, their fast response to external stimuli such as electric fields, mechanical and hydrodynamic forces, as well as geometrical constraints makes them an attractive candidate for a wide range of applications spanning from electro-optical devices to photonic crystals and lasers. BPs, however, appears at narrow ranges of temperature, 1 or 2 °C, which impede their versatile practical applications. Introducing the UV reactive polymers is one of the promising strategies to lock-in BP structures over a extended temperature ranges. Here, we study the coupling of the geometrical confinement and polymerization on the crystalline structure and stability of the BP liquid crystals in order to design the optically active microstructures.
In this research work, we have used microfluidic technology to produce mono-disperse polymer-stabilized BP microdroplets with controlled size and dispersity (Figure 1(a)). The morphologies, phase behavior, and stability range of stabilized BP droplets were investigated before and after polymerization as a function of confinement size, level of chirality, polymer content, and UV curing conditions. Our results demonstrate that optical properties of BP phases residing in microdroplets can be controlled by tuning the droplet size and level of chirality (Fig. 1b) which provides a toolbox for designing advanced soft photonic crystals.