Temperature-Controlled Smart Fluid Achieves Reconfigurable Order in Liquid Crystal Microco

The materials that control light in your phone's display belong to a category of substances called nematic liquid crystals - not quite liquid, not quite solid, but something in between. Their rod-like molecules align with each other in a shared direction, creating a material with both flow properties and optical directionality. Researchers have known for decades that placing small particles in this directional fluid causes those particles to organize according to the crystal's alignment. What they have struggled to do is make that organization reversible.

A study published in Matter in February 2026 by researchers at the University of Colorado Boulder and Hiroshima University's International Institute for Sustainability with Knotted Chiral Meta Matter (WPI-SKCM2) describes a new approach to this problem and, along the way, discovers unexpected ordered states in hybrid liquid crystal-colloid materials.

The Sticking Problem

When conventional solid particles are placed in a nematic liquid crystal, the particles force the nearby crystal molecules to align in a specific way - a phenomenon called surface anchoring. Strong surface anchoring creates large distortions and topological defects in the liquid crystal's orientation pattern. Those distortions attract other particles, promoting irreversible aggregation. The resulting clumps cannot be disassembled by changing temperature or applying fields. The system is stuck.

Solving this problem requires reducing the effective anchoring strength - allowing the crystal molecules at the particle surface to deviate from their preferred alignment without creating large distortions. The surface chemistry of the particle determines whether anchoring is strong or weak, and getting it right requires precise control of surface treatment.

Porous Rods with Slippery Surfaces

The team, led by corresponding author Ivan Smalyukh, Professor of Physics at CU Boulder and director of the WPI-SKCM2 satellite program, developed silica microrods approximately 2-3 micrometers long and 200-300 nanometers in diameter. The rods are etched to be porous and then coated with a perfluorocarbon compound that gives their surfaces a low-energy, "slippery" character.

First author Souvik Ghosh, a research associate at CU Boulder at the time of the study, conducted detailed, systematic optimization of the surface treatment. Even subtle differences in surface chemistry strongly affect how liquid crystal molecules anchor to the rods. The optimized coating achieved the target: weak effective anchoring that produces only small distortions in the surrounding liquid crystal, allowing the rods to remain dispersed and mobile in dense suspensions rather than aggregating.

When dispersed in the common nematic liquid crystal 5CB, these porous slippery microrods form stable, dense suspensions that remain fluid-like - a prerequisite for any practical application that requires the material to flow or be switched between states.

Temperature Switches the Structure

The researchers tracked how rod orientation and the suspension's collective phase behavior change with temperature and rod concentration. As temperature increases or decreases, the coupling between the liquid crystal molecules and the rods changes - because the preferred alignment of the crystal at the rod surface depends on temperature. This change in coupling drives the rods to rotate into a new equilibrium orientation, reorganizing the suspension's internal structure.

In dense samples, the suspension switches between distinct phases as temperature changes. The researchers observed not just the expected uniaxial nematic phase but several unexpected low-symmetry phases - ordered states in which the material has more than one distinguished direction of alignment simultaneously. Standard nematic liquid crystals align along a single direction. The hybrid liquid crystal-colloid system can support more complex arrangements, effectively creating ordered states that neither component could achieve on its own.

Lech Longa, Professor of Theoretical Physics at Jagiellonian University and a WPI-SKCM2 community member, contributed a tensorial Landau de Gennes theoretical framework to explain how host-colloid coupling stabilizes these low-symmetry phases.

Potential Applications and Fundamental Value

Smalyukh described potential application directions: "Materials like this could one day support reconfigurable optical components, potentially changing how screens control light, how photonic chips process information, or how biomedical sensors detect and report conditions." A liquid crystal whose internal structure can be reconfigured with temperature rather than fixed at manufacture could enable new classes of adaptive optical devices.

The low-symmetry phases also have fundamental scientific value. Colloids have long served as "visible analogues" of atoms and molecules - because individual particles are large enough to track directly with microscopy, they allow researchers to observe phase transitions in ways that are impossible at atomic scales. The unusual low-symmetry phases found in these nematic liquid crystal microcolloids could serve as model systems for topological solitons and singular defects relevant to condensed matter physics, with connections to phenomena in magnetism, superconductors, and particle physics.