(698h) Stimuli-Responsive Stabilized Blue Phase Liquid Crystals Microdroplets

Most living organisms’ colors originate from elegant structural arrangements of biopolymers or nanocrystals on their outer skin, which are vital for biological functions such as mating, camouflage, and signal communications. These structures with spatial undulation patterns on a scale of visible light wavelength can selectively reflect light via different mechanisms, including interference, diffraction grating, and scattering. The natural structural colors have inspired the design and advance of novel optically active materials with unique, responsive optical features. Among these materials are chiral liquid crystals which can generate photonic bandgap and selectively reflect the incident light. Blue phase (BP) liquid crystals are a specific class of chiral liquid crystalline materials that self-assemble into 3D soft cuboidal lattice structures. Their 3D crystal symmetry can manipulate the light in more than one direction, while their fluid-like nature makes them responsive to external stimuli. These structures are, however, energetically stable over narrow ranges of temperature (1 or 2 °C), which considerably impede their broad proliferation.

We have coupled the polymerization strategy with geometrical confinements to stabilize BP structures and manipulate molecular organizations. To do so, reactive mesogens were incorporated into the BP liquid crystal, and a lab-built microfluidic device was used to confine the reactive BP mixture within microdroplets with the desired size and dispersity. After photopolymerization of the reactive mixture within spherical droplets, the BP structures were stabilized at room temperature, and the stability window was expanded by 20 °C. The stabilized droplets showed, however, a size-correlated and dynamic optical response upon exposure to temperature, mechanical deformation, and biochemicals. FESEM and TEM imaging were carried out to decipher the polymer-stabilized structures within microdroplets. This study may provide insight toward designing the micro-scale colorimetric biological and strain sensors.