University of Chicago
Chameleons are famous for their color-changing abilities. Depending on their body temperature or mood, their nervous system directs skin tissue that contains nanocrystals to expand or contract, changing how the nanocrystals reflect light and turning the reptile's skin a rainbow of colors.
Inspired by this, scientists at the Pritzker School of Molecular Engineering (PME) at the University of Chicago have developed a way to stretch and strain liquid crystals to generate different colors.
By creating a thin film of polymer filled with liquid crystal droplets and then manipulating it, they have determined the fundamentals for a color-changing sensing system that could be used for smart coatings, sensors, and even wearable electronics.
The research, led by Juan de Pablo, Liew Family Professor of Molecular Engineering, was published July 10 in the journal Science Advances.
Stretching liquid using thin films
Liquid crystals, which exhibit distinct molecular orientations, are already the basis for many display technologies. But de Pablo and his team were interested in chiral liquid crystals, which have twists and turns and a certain asymmetrical "handedness" -- like right-handedness or left-handedness -- that allows them to have more interesting optical behaviors.
These crystals can also form so-called "blue phase crystals," which have the properties of both liquids and crystals and can in some cases transmit or reflect visible light better than liquid crystals themselves.
The researchers knew that these crystals could potentially be manipulated to produce a wide range of optical effects if stretched or strained, but they also knew that it's not possible to stretch or strain a liquid directly. Instead, they placed tiny liquid crystal droplets into a polymer film.
"That way we could encapsulate chiral liquid crystals and deform them in very specific, highly controlled ways," de Pablo said. "That allows you to understand the properties they can have and what behaviors they exhibit."
Creating temperature and strain sensors
By doing this, the researchers found many more different phases -- molecular configurations of the crystals -- than had been known before. These phases produce different colors based on how they are stretched or strained, or even when they undergo temperature changes.
"Now the possibilities are really open to the imagination," de Pablo said. "Imagine using these crystals in a textile that changes color based on your temperature, or changes color where you bend your elbow."
Such a system could also be used to measure strain in airplane wings, for example, or to discern minute changes in temperature within a room or system.
Changes in color provide an excellent way to measure something remotely, without the need for any sort of contact, de Pablo said.
"You could just look at the color of your device and know how much strain that material or device is under and take corrective action as needed," he said. "For example, if a structure is under too much stress, you could see the color change right away and close it down to repair it. Or if a patient or an athlete placed too much strain on a particular body part as they move, they could wear a fabric to measure it and then try to correct it."
Though the researchers manipulated the materials with strain and temperature, there's also the potential to affect them with voltage, magnetic fields, and acoustic fields, he said, which could lead to new kinds of electronic devices made from these crystals.
"Now that we have the fundamental science to understand how these materials behave, we can start applying them to different technologies," de Pablo said.
Prolate and oblate chiral liquid crystal spheroids
Monirosadat Sadati, Jose A. Martinez-Gonzalez, Ye Zhou, Nader Taheri Qazvini, Khia Kurtenbach, Xiao Li, Emre Bukusoglu, Rui Zhang, Nicholas L. Abbott, Juan Pablo Hernandez-Ortiz and Juan J. de Pablo
Science Advances Vol. 6, no. 28, eaba6728 (10 Jul 2020)
Contact information:
Juan de Pablo
Professor of Molecular Engineering, Pritzker School of Molecular Engineering (PME), University of Chicago
depablo@uchicago.edu
Phone: 773.702.7791
Waste polyamide-derived CQDs show continuous photoluminescence tuning from 308 to 552 nm through sequential defect-state engineering, with optical transition energies decreasing from 4.32 to 2.50 eV. @Christian Ebere Enyoh from Saitama University Carbon quantum dots (CQDs) are fluorescent carbon nanomaterials with potential applications in sensing, optoelectronics, displays, anti-counterfeiting, and environmental technologies. Their optical properties can be adjusted by modifying the carbon...
The researchers used circularly polarized light at normal incidence and found that helicity-dependent photocurrents appeared perpendicular to the crystal’s polarization but vanished when measured parallel to it, supporting a bulk origin of CPGE. @Institute of Science Tokyo The circular photogalvanic effect (CPGE), a phenomenon that generates helicity-dependent photocurrents in noncentrosymmetric materials, can originate purely from a crystal's internal structure without contribution from the...
Summary of gold nanoparticle growth programming in liposome based on localization of biomineralization peptide The position of biomineralization peptides within liposomes can influence how gold nanoparticles grow, reports a research team from Institute of Science Tokyo. Peptides localized at the membrane interface promote branched structures, while those confined to the liposome interior favor spherical nanoparticles. The findings offer a new strategy for controlling nanoscale reaction...
