RUI: Investigations of the cybotactic nematic phase in bent-core liquid crystals

University Of Puget Sound, Tacoma WA

Investigators

Abstract

Non-technical summary Liquid crystal displays (LCD) are found in devices such as cell phones and television and computer screens. These devices are constructed using compounds that exhibit a liquid crystal phase. Molecules in this phase can be reoriented in the presence of an electric field, which changes their optical properties. With support from this grant by the Solid State and Materials Chemistry Program compounds are prepared and studied that exhibit a unique type of liquid crystal phase in which the molecules can potentially undergo faster reorientation. This could lead to faster liquid crystal displays, which would improve the optical quality of the devices, and lower the amount of energy consumed by the devices. Undergraduate students at the University of Puget Sound are directly involved in all aspects of the NSF-funded research. Participation in research offers an excellent opportunity for students to enhance their critical thinking skills. These experiences provide students with strong technical training that will serve them well as they enter the workforce in a scientific field or pursue graduate studies in Chemistry or a related area. At the University of Puget Sound, 57% of the students are women, and 25% of the students identify as students of color. This support from NSF helps the PI to provide research opportunities to students from groups who are typically underrepresented in STEM fields. Technical summary There has been intense interest in the biaxial nematic phase (Nb) since it was reported in high melting bent-core compounds; liquid crystal displays fabricated using this phase have the potential to undergo faster electro-optic switching. However, there is controversy as to whether this phase is truly a biaxial nematic phase; recent evidence suggests the phase consists of layered (smectic) domains (cybotactic clusters) that show nematic order only across larger length scales. This grant from the Solid State and Materials Chemistry Program supports the synthesis of a variety of oxadiazole-based compounds, and analysis of their liquid crystalline behavior. These studies provide critical insight into how various structural factors affect the stability and nature of the nematic phase in bent-core compounds. The preparation of series of compounds with 1) various lateral groups, 2) highly polar substituents, and 3) amide linkages allow the PI and his students to generate structure-property relationships, with the intention to learn what structural features yield a nematic phase with a low onset temperature. Synthesis of the target compounds and initial analysis of phase behavior (using polarizing microscopy and differential scanning calorimetry) are carried out at the University of Puget Sound. Collaborators of the PI study the compounds by X-ray diffraction, which provides detailed information about the molecular organization within the nematic phase. They also carry out electro-optic experiments on the derivatives with highly polar groups as these are candidates for ferroelectric switching. Having derivatives with low temperature nematic phases would facilitate both fundamental study by physicists and investigation of possible applications. This support from NSF helps the PI to provide research opportunities to undergraduate students from groups who are typically underrepresented in STEM fields.