Since they first appeared on wristwatches in the early 1970s, liquid crystal displays have made the leap to TVs, smartphones, household appliances and automobile dashboards.
Now an even more responsive type of LCD technology, called blue phase liquid crystals, is getting closer to commercial use, and a USC chemical engineering professor’s research in that field is attracting notice.
Sanaz Sadati, an assistant professor of chemical engineering in the Molinaroli College of Engineering and Computing, has developed a novel method for making blue phase liquid crystals more stable so that they can be used at room temperature while maintaining their fast dynamics. Their narrow high-temperature operating range — about 100 to 104 degrees Fahrenheit — has long been a limiting factor in their development. The journal Advanced Functional Materials featured Sadati’s blue phase liquid crystal research on the cover of its June 2025 issue. Her collaborators include scientists at the Universidad Autónoma de San Luis Potosi and the University of Chicago.
“The response time of blue phase liquid crystals is two orders of magnitude faster than the common class of liquid crystals, so they’ve been considered as candidates for the next generation of display and sensor technology,” says Sadati, who is using her NSF CAREER Award to conduct research in the field of photonic crystals. “The biggest limitation to their commercial development has been that blue phase liquid crystals appear only in a narrow temperature range.”
In recent years, some researchers have experimented with polymers as a solution to that limitation. These long chains of molecules can be introduced into the blue phase liquid to scaffold the large 3-D crystals in place while operating temperature is reduced and extended.
But that approach reduces the speed at which the liquid crystals respond to stimuli such as an electric field and increases the voltages required to achieve the same optical changes, Sadati says. That’s a problem because their fast reaction to a low-energy electric field is what makes liquid crystals so functional in display devices.
“The biggest limitation to their commercial development has been that blue phase liquid crystals appear only in a narrow temperature range.”
Sadati’s approach, outlined in her front-cover article in Advanced Functional Materials, has been to create a nano-architected polymer shell that covers the blue phase liquid crystals but is not inside the liquid itself.
“We have a nano-structured polymer shell encapsulating the liquid crystal, which stabilizes the blue phase, enabling it to change structure quickly over a 35-degree range from below room temperature to above room temperature,” she says. “So, we were able to retain the faster reaction speed while gaining a much wider range of operating temperatures.”
Blue phase liquid crystals quickly change color from blue to green and red in response to external stimuli such electric field energy, chemicals and biochemicals, making them ideal for fast-response sensor technology that provides an immediate visual cue to the user. In Sadati’s experiments with polymer shells around the liquid crystals, she has demonstrated that smaller inputs of electric voltage are needed to emit a response from the crystals.
“When we stabilize the crystals with the polymer shell, the amount of voltage needed to change the crystals’ shape is very low — 20 times less than blue phase crystals stabilized internally with polymers,” she says. “With our approach, they change shape much more dynamically with only a fraction of the energy.”