This RUI award to University of Wisconsin-Eau Claire by the Solid State Materials Chemistry program in the Division of Materials Research is to study the creation of new liquid crystalline systems, which will provide valuable insight into the ability of a mesophase to stabilize using multiple hydrogen bonding associations. Initial investigations by Professor Wiegel in this field have pointed to three ideal systems for this study: a) benzoic acid/pyridine associations (single hydrogen bonds); b) pyridone dimers (double hydrogen bonds); and c) imide/diaminotriazine assemblies (triple hydrogen bonds). Each of these systems forms a strong overall association and conceptually possesses the linearity and rigidity to form calamitic, discotic and banana-shaped liquid crystals. In order to study the effects of various mesogenic shapes and sizes, the project will alter the rigidity of the mesogens, as well as the flexibility and length of the tails/spacer groups and forming both small molecules (for each of the mesogen types) and polymers (for the calamitic and banana mesogens). These systems will be studied using spectroscopic, X-ray and thermal analytical techniques. Results from this project are expected to provide insight into the nature of the formation of a mesophase, and a comparison of the quantity and strength of supramolecular forces involved in the formation of liquid crystals. In particular, we will learn how the mesophase is stabilized when the number of hydrogen bonds is increased. In addition, these data could have a broad impact on the field of supramolecular liquid crystals. The applications of hydrogen bonded mesogens are limited by the fragility of the associative chain structure. An understanding of the stability of a mesophase as a function of hydrogen bond strength and multiplicity could have considerable impact on the optical display industry. The multiple hydrogen bond polymer and network assembles have shown physical properties superior to their covalent analogs. Imparting similar characteristics to supramolecular liquid crystalline systems would provide new materials, combining the stabilities of covalent species with the lability and healing capabilities of hydrogen bonded associative chain structures.
Liquid Crystals have become a mainstay of the scientific and technological community, emerging as one of the most important optical materials of the past decade. The assembly of liquid crystalline materials using non-covalent interactions offers many interesting areas involving living polymeric systems and the ability of the mesogens to self ?heal? and repair macroscale structural defects. A study of liquid-crystalline systems capable of forming one, two or three hydrogen bonds per association will lead to an understanding of the stability of liquid crystalline phases as related to the assembly of the associative chain structures. In addition, this research will be used to enhance research infrastructure and support human resource development at University of Wisconsin- Eau Claire, which is a low-cost public institution that has a long-established tradition of strong undergraduate/faculty research collaboration. Almost half of the students at the University are of first generation students from low-income families, and about 60% female. The research activities described could greatly enhance student training and intellectual development through hands-on experience with sophisticated equipment and the opportunity to present their findings at regional and national meeting. These experiences will be valuable steps in the training of the next generation of scientists
Our work has focused on making liquid crystals, materials found almost everywhere our society, stronger, and more resistant to heat and impact. These substances are very commonly used in computer, telephone and televisions. One of the main weaknesses of liquid crystals is fragility: they are very shock and thermally sensitive. Any work that can be done to improve the service lifetime of these devices would have a very significant impact on the display industry, as well as promoting environmental stewardship and sustainability. Our specific area of research involved making very high molecular weight liquid crystal but using hydrogen bonds (a weak adhesion between hydrogen bond donors and acceptors) for the assembly. This may seem an odd choice: how can a weak association be useful for making liquid crystalline displays les fragile? The advantage that hydrogen bonds provide is directly linked to that weakness. The materials can heal when damaged or disrupted. Molecules with normal covalent bonds are permanent in almost all regards, including damage that cannot be easily fixed. Such materials are very limited in the extreme applications, and once it’s damaged it is effectively destroyed. Liquid crystals that can heal could have more robust usage lifetime. Our principal research design was in making hydrogen bonded networks that were capable of forming liquid crystalline materials. We approached this by introducing an additional hydrogen bond acceptor that would not form liquid crystal when introduced. Our results indicated there was a direct link between the rigidity and flexibility of the molecules and the liquid crystalline behavior of the network. Increasing the flexible groups between rigid portions made networks that could contain more than 50% of the non-liquid crystalline component and still maintain strong liquid crystalline characteristics. The introduction of the hydrogen bonding network didn’t disrupt the presence of liquid crystallinity in the materials we studied. I’d like to add that I feel one of the most important products of the research is he training the undergraduates received while working on this project. 15 undergraduates participated in this research, 11 of whom were first generation college students. Eight of these fifteen have matriculated to graduate or professional schools. I’m very lucky to have been able to work with these bright, talented students.
