Nucleation and Growth of BPII Liquid Crystals on Chemically Patterned Surfaces: A Surface Anchoring Assisted BPII-Coherence Length

In condensed matter, the correlation length is an essential parameter for describing the distance over which a material maintains its structural properties. In liquid crystals, such a characteristic length is of the order of 10 um while in solid crystals it can be extent up to macroscopic dimensions. Here, we report how to measure the correlation length of blue-phases (BPs), which are chiral liquid crystals with long-range 3D-crystalline structures and submicron-sized lattice-parameters. We design patterned substrates made of a binary array of regions with different anchoring, which facilitate a uniform nucleation and growth of BP-crystals with (100)-lattice orientation and a simple cubic symmetry. Our results indicate that this simple cubic blue-phase (BPII), forms first on the patterned surface, thereby setting the growth of domains in directions that can be parallel or perpendicular to the patterned regions. These results are used to understand the emergence of a surface anchoring assisted BPII-coherence length in terms of time and pattern characteristics. We found that BPII single crystals can be achieved on patterned regions whose lateral dimensions are equal or larger than 10 µm, which is consistent with our measurements of the BPII-coherence length.