Dr. Sadati is a scholar of the highest degree, focused on deep and fundamental questions and mentoring graduate students at the forefront of innovations in materials underpinning technologies of the future.
-Hossein Haj-Hariri, College of Engineering and Computing Dean
Solid, liquid and gas are the most well-known states of matter. Liquid crystals are considered the fourth state that exhibit behavior between conventional solids and liquids. Liquid crystals are rod-like molecules that can flow like liquids while at the same time adopt ordered structures like solids. Their alignment can be simply manipulated by external stimuli, including electric field, which makes them the primary component of many displays and electro-optic technologies.
However, the advent of curved and flexible devices has created a knowledge gap since crystallization under curved confinements is a less understood process. Chemical Engineering Assistant Professor Monirosadat (Sanaz) Sadati is in the early stages of a five-year research project to better understand and determine how liquid crystals can adjust and work within the unique properties of curved geometries.
Sadati’s research, “Crystallization of Chiral Liquid Crystal Under Curved Confinement,” is funded through a $524,988 National Science Foundation (NSF) CAREER award. The award funds outstanding junior faculty who exemplify the role of teacher-scholars through research and education and the integration of these endeavors.
“My postdoc research at the University of Chicago was related to liquid crystalline materials, and during my Ph.D. at ETH Zurich, I studied the complex flow of polymers; we call it polymer rheology. My research currently focuses on materials with liquid crystalline behavior and twist and turns, which we call chiral liquid crystals,” Sadati says. “Integrating my postdoc experience and Ph.D. knowledge, I have developed new questions and opened a new line of research exploring chiral liquid crystals’ structures and properties within well-controlled curved geometries and in response to flow forces that have not been investigated before.”
Liquid crystals with properties of both liquids and crystals are the heart of many displays and electro-optic technologies. The fluid nature of these materials makes them responsive to an electric field.
“The electric field can change the alignment and order of the liquid crystal molecules manipulating the amount of light that can pass through. That’s how pixels in Liquid Crystal Displays are designed. Each pixel receives a different voltage and electric field, so the orientation of one pixel to another is different,” Sadati says.
But when the crystallization process occurs within curved spaces, the surface curvature can strain and deform the crystals and cause defects. Sadati wants to provide more knowledge of this little-known process and develop a fundamental understanding of the crystallization and optical behavior of a specific class of liquid crystals. These are so-called “blue phases” within curved confinements. Blue phases are chiral (non-superimposable molecules) liquid crystals which are packed into tiny cubic-crystalline lattices that exhibit refraction of visible light. Sadati’s research aims to understand better how blue phases reconfigure their 3D cubic structure to accommodate curved spaces.
“The twists and turns in blue phase liquid crystals are very strong, so the distance between the twists is short. Within a certain temperature range, these structures start packing together and form 3D submicron cubic lattice structures which can reflect blue and green light” Sadati says. “The blue phase liquid crystals are considered the next generation of the display technology because they have a much faster response time compared to the liquid crystal that has already been used.”
Sadati aims to answer the questions of how will a cubic structure of blue phases interact with curvature, and if it changes, what new structures and properties would emerge? And how would new structures affect the optical features and response time of the liquid crystal?
To address these questions, top-down fabrication strategies, including microfluidic and 3D printing, will be used to systematically confine blue phases in well-defined curved geometries. In addition, reshaping the blue phase lattices through interactions with electric fields, mechanical forces, and chemical species will be examined.
According to Sadati, the fundamental understanding of the crystallization of chiral liquid crystals in different conditions is essential to integrating these materials into new miniaturized flexible devices.
“Once we have a deep understanding of the new structures, evolution mechanism and controlling parameters, we will be able to tune their optical and response behaviors,” Sadati says. “This is a knowledge and design principle which my team will provide over the next five years. Once it is established, it will be exploited as a guideline to engineer new devices and advance the technology.”
Biosensing is another application of liquid crystals. Since they are very responsive to interfacial interaction, liquid crystals are widely used in designing biosensing technologies.
“Anything that can perturb the configuration and alignment of this material can lead to change in optical features, which can easily be detected by an optical microscope. Using this material for biosensing application is also considered a very important area,” Sadati says.
Receiving an NSF CAREER award on her first attempt is an important milestone for Sadati. She is encouraged that the NSF finds her research important and is looking forward to working the next five years on providing a better understanding of the crystallization of chiral liquid crystals in curved confinements.
“Four reviewers looked at my proposal, and their comments were very encouraging. ’It’s now a matter of working, collecting data, analyzing our findings, and disseminating the results,” Sadati says. “I’m not the only one excited about answering the questions I’ve proposed in this proposal since others also want to see the results, so that means I’m on the right track.”
Sadati’s lab uses advanced fabrication technologies to carefully control the location, orientation, and assembly of the anisotropic constituents in 3D printed architectures. Her research mainly focuses on understanding the behavior of anisotropic liquid crystalline materials, particularly chiral liquid crystals, in response to external stimuli, including geometrical confinement, flow forces, and mechanical deformations. Sadati’s research goal is to engineer bioinspired responsive and functional materials for a wide range of applications such as actuation, optics, tough composites as well as biosensing.