RUI: Thermoreversable hydrogen bonding in mesogenic assembly: enhancing mesogen structure, stability and formation

University Of Wisconsin-Eau Claire, Eau Claire WI

Investigators

Abstract

Non-technical Summary: Liquid crystals (LCs) are in everything that has a digital display: phones, laptops and tablets. They are amongst the most important optically active molecules in the world. Liquid crystalline phases are formed when shaped molecules, called mesogens, align as a liquid. Common wisdom has been that LC phases have a very delicate structure and miniscule amounts of structural or physical defects can destroy it. The ability of a liquid crystalline phase to self-repair or heal would be very significant to understanding how these molecules align under adverse conditions. This project, funded by the Solid State and Materials Chemistry Program in the Division of Materials Research at NSF, investigates new concepts of liquid crystalline networks that are capable of healing and repairing any structural damage that may occur. By changing the type of molecular bonding in the liquid crystal structures, the principle investigator and his group develop a new approach that allows liquid crystal networks to re-form/self-repair, if chemical bonds are broken. Beyond its scientific impact this project enhances the research infrastructure and support human resource development at the University of Wisconsin-Eau Claire. The University of Wisconsin-Eau Claire is a low-cost public institution that has a long-established tradition of strong undergraduate/faculty research collaboration. Almost half of the student body are low-income, first generation students, and about 60% are female, both of which are underrepresented in the scientific communities. This research project greatly enhances student training and intellectual development through hands-on experience with sophisticated equipment and offers the students opportunities to present their findings at national meetings. Technical Summary: The assembly of liquid crystalline materials using non-covalent interactions offers many interesting features involving living polymeric systems and the ability of the mesogens to self-heal and repair macroscale structural defects. Liquid crystalline networks are an area that has received considerable attention due to the ability of the materials to couple the order of the mesogenic directors to the elasticity of the materials. The application of thermoreversible assemblies to liquid crystalline networks is a relatively unexamined area. The ability to combine the healing and reversibility of the hydrogen bond with the characteristics of a crosslinked mesogenic system could produce materials with very intriguing characteristics and properties. This project, funded by the Solid State and Materials Chemistry Program in the Division of Materials Research at NSF, enables the synthesis of a series of liquid crystal precursor networking agents in which the hydrogen bond acceptor is distanced from the central carbon. By varying the functionality of the molecule, the distance from the assembly point to the central carbon (increasing chain length) and the size and rigidity of the hydrogen bond acceptor, the effect of this distal crosslinking on the ability of a hydrogen-bonded liquid crystalline polymer and network to form is investigated. A corollary study determines the effects of using the double hydrogen bond assemblies of the 2-pyridone functionality to create liquid crystalline polymers. In these a series of 2-pyridone aromatic ester tectons are created with variable structure and spacer lengths to determine the effect on mesophase stability and structure, which are studied using spectroscopic, X-ray and thermal analytical techniques. The creation of these new liquid crystalline systems provides valuable insight into the ability of a mesophase to stabilize in unfavorable, constrained (networked) conditions, as well as an understanding of systems assembled through multiple hydrogen bond assemblies. Imparting new characteristics to liquid crystalline systems provides new materials, combining the stabilities of covalent species with the lability and healing capabilities of hydrogen bonded associative chain structures. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.