Most of us have probably used the words “liquid crystals” when talking about our newly purchased flat-panel television sets. The scientific key to this display technology lies in the amazing fundamental ability of liquid-crystal materials to form a range of structural “textures” that display different contrasts under the illumination of polarized light. Such textures correspond to different physical states, in which the constituent anisotropically shaped molecules—rodlike molecules, for example—collectively, and spontaneously, orient and spatially arrange themselves. It turns out that the ability of liquid crystals to self-assemble does not stop at the molecular level: Even the defects in them are capable of self-organizing into ordered arrays. Such defect-based self-assemblies have found applications in optically selective photomasks and microlens arrays. In this experimental paper, informed by fundamental theoretical insights, we demonstrate a new experimental route to generating “flower textures” through controlled, defect-induced self-assembly in liquid crystals.

The class of liquid crystals we investigate are the so-called smectics, stacked layers of rodlike molecules well aligned along a common direction. It has been known that a colloidal particle inserted into a smectic liquid-crystal layer works as a defect by forcing the liquid-crystal molecules next to it to anchor themselves in particular orientations that differ from the orientations of those far away, giving rise to complicated geometries. Of particular interest are “focal conic domains,” geometric arrangements of layers studied nearly 150 years ago by Maxwell.

The key to our experiment is to generate these domains as desired by controlling the molecular alignment along the boundary of our smectic liquid-crystal sample using both nanoscale colloidal particles and the meniscus that forms between air and the liquid crystal. It is like finding a way to stack mattresses on an uneven bed frame—how do the lumps, bumps, and “peas” change the way they stack? Based on our insight of how to manipulate the local geometric properties of the “focal conical domains” created by such specially engineered settings, we can generate desired textures of radially distributed “flowers.” We have developed a concrete model to understand this flower geometry based on the elastic description of smectic liquid crystals.

Our findings provide local control over the geometrical properties of focal conic domains, meeting the great technological interest in manipulating these textures. In particular, our theoretical model should serve as a fundamental guideline to crafting smectic configurations of increased complexity.