Researchers design models in self-propelled liquid crystals


New research shows that the movement of liquid crystals can be harnessed and directed, a step toward developing self-sustaining materials that can sense inputs, amplify signals, and even compute information. Credit: Image courtesy of the Verduzco Laboratory / Rice University

Groundbreaking discoveries could pave the way for new applications of liquid crystals.

Materials capable of performing complex functions in response to changes in the environment could form the basis of exciting new technologies. Think of a capsule implanted in your body that automatically releases antibodies in response to a virus, a surface that releases an antibacterial agent when exposed to dangerous bacteria, a material that adapts its shape when it has to support a particular weight. , or clothing that detects and captures toxic contaminants from the air.

Scientists and engineers have already taken the first step towards these types of autonomous materials by developing “active” materials that have the ability to move on their own. Now, researchers from University of Chicago have taken a new step by showing that the movement of one of these active materials, liquid crystals, can be harnessed and directed.

This proof of concept research, published on February 18, 2021, in the journal Natural materials, is the result of three years of collaborative work between the groups of Juan de Pablo, professor of the Liew family of molecular engineering, and Margaret Gardel, professor Horace B. Horton of physics and molecular engineering, as well as Vincenzo Vitelli, professor of physics, and Aaron Dinner, professor of chemistry.

Exploiting the properties of liquid crystals

Unlike traditional liquids, liquid crystals exhibit a uniform molecular order and orientation which offers potential as building blocks for self-contained materials. Defects in the crystals are basically tiny capsules that could serve as sites for chemical reactions or as transport vessels for cargo in a circuit-like device.

To create self-contained materials that could be used in technologies, scientists had to find a way for these materials to self-propel their flaws while controlling the direction of movement.

To make “active” liquid crystals, the researchers used actin filaments, the same filaments that make up a cell’s cytoskeleton. They also added motor proteins, which are the proteins that biological systems use to exert force in actin filaments. These proteins essentially “walk” along the filaments, causing the crystals to move.

“In this work, we have shown how to master these materials, which could pave the way for applications. “

-Teacher. Juan de Pablo

In this case, in collaboration with the group of Professor Zev Bryant at Stanford University, the researchers developed active liquid crystals powered by photosensitive proteins, the activity of which increases when exposed to light.

Using advanced computer simulations of models developed by de Pablo with postdoctoral fellows Rui Zhang and Ali Mozaffari, researchers predicted that they could create faults and manipulate them by creating local models of activity in a liquid crystal. .

Experiments by Gardel and postdoctoral fellows Steven Redford and Nitin Kumar confirmed these predictions. Concretely, by projecting a laser on different regions, the researchers made these regions more or less active, thus controlling the flow of the defect.

They then showed how this could be used to create a microfluidic device, a tool that researchers in engineering, chemistry and biology use to analyze small amounts of liquids.

Usually, these devices include tiny chambers, tunnels and valves; with a material like this, fluids could be transported autonomously without pumps or pressure, opening the door to programming complex behaviors in active systems.

The findings presented in the manuscript are significant because, so far, much of the research on active liquid crystals has focused on characterizing their behavior.

“In this work, we have shown how to control these materials, which could pave the way for applications,” said de Pablo. “We now have an example where propulsion at the molecular level has been harnessed to control movement and transport at macroscopic scales.”

Creation of new devices from hardware

This proof of concept shows that a liquid crystal system could ultimately serve as a sensor or amplifier reacting to the environment. Next, the researchers hope to demonstrate how to build the elements necessary to turn this system into a circuit capable of performing logical operations much like computers.

“We knew these active materials were beautiful and interesting, but now we know how to manipulate them and use them for interesting applications,” said de Pablo. “It’s very exciting.”

Other authors on the paper include Sasha Zemsky and Paul V. Ruijgrok of Stanford. This collaborative effort was made possible by the UChicago Materials Research Science and Engineering Center. Gardel, Vitelli and Dinner are members of the James Franck Institute.

Reference: “Spatio-temporal control of the structure and dynamics of liquid crystals by activity modeling” by Rui Zhang, Steven A. Redford, Paul V. Ruijgrok, Nitin Kumar, Ali Mozaffari, Sasha Zemsky, Aaron R . Dinner, Vincenzo Vitelli, Zev Bryant, Margaret L. Gardel and Juan J. de Pablo, February 18, 2021, Natural materials.
DOI: 10.1038 / s41563-020-00901-4

Funding: National Science Foundation


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