Ph.D.: California Institute of Technology, 1975
Postdoctoral Fellow: NIH fellow at University of California at Los Angeles, 1975-77
Awards:Camille and Henry Dreyfus Teacher-Scholar, 1984-86Alfred P. Sloan Fellow, 1982-83Fellow of the AAAS, 1999
Liquid Crystals, Polymers, and Gels
Materials Chirality, Electro-Optic Materials, Ferroelectric Liquid Crystals
Research in the Walba group focuses on supermolecular stereochemistry and materials chirality in the context of liquid crystal science and technology. Most projects in the group are interdisciplinary; runing in collaboration with CU students and Professors in the Physics. These include synthesis of molecules designed to provide new liquid crystal phases, design and synthesis of ferroelectric liquid crystals and polymers for nonlinear optics applications, development of computational approaches for understanding and predicting liquid crystal properties from molecular structure, and exploration of new approaches for controlling liquid crystal macroscopic stereochemistry using novel liquid crystal/solid surface interfaces.
Ferroelectric liquid crystals represent a unique "soft matter" system possessing polar symmetry and a spontaneous macroscopic electric dipole moment. One illustrative project involves synthesis and characterization of new banana phases, named after the shape of the molecules forming the phases. Until recently all ferroelectric liquid crystals were composed of enantiomerically enriched molecules. Recently, however, we have shown that achiral or racemic banana-shaped molecules (see Figure 1) can form ferroelectric liquid crystals. More interestingly, these phases are chiral, even thought the molecules are achiral or racemic. This is analogous to Pasteur's famous discovery of the macroscopic chirality of racemic tartrate crystals in the nineteenth century, but for the first time observed in a liquid.
Figure 1: Molecular structure of ferroelectric banana MHOBOW
A photomicrograph, taken with the liquid crystal sample between crossed polarizers, shows below (in Figure 2) the beautiful texture observed for one of the new phases of the racemic compound MHOBOW, the material exhibiting the first ferroelectric banana phase.
Figure 2: Photomicrography of the first ferroelectric banana phase
Walba, D. M.; Yang, H.; Shoemaker, R. K.; Keller, P.; Shao, R.; Coleman, D. A.; Jones, C. D.; Nakata, M.; Clark, N. A. "Main-chain chiral smectic polymers showing a large electroclnic effect in the SmA* phase," Chem. Mater. 2006, ASAP Article; DOI: 10.1021/cm0606373.
Walba, D. M.; Korblova, E.; Huang, C. C.; Shao, R. F.; Nakata, M.; Clark, N. A. "Reflection symmetry breaking in achiral rod-shaped smectic liquid crystals?," J. Am. Chem. Soc. 2006, 128, 5318-5319.
Walba, D. M.; Eshdat, L.; Körblova, E.; Shoemaker, R. K. "On the nature of the B4 banana phase: Crystal or not a crystal?," Cryst. Growth Des. 2005, 5, 2091-2099.
Walba, D. M.; Xiao, L.; Korblova, E.; Keller, P.; Shoemaker, R.; Nakata, M.; Shao, R.; Link, D. R.; Coleman, D. A.; Clark, N. A. "Main-chain ferroelectric liquid crystal polymers for electronic nonlinear optics applications," Ferroelectrics 2004, 309, 77-82.
Coleman, D. A.; Fernsler, J.; Chattham, N.; Nakata, M.; Takanishi, Y.; Korblova, E.; Link, D. R.; Shao, R. F.; Jang, W. G.; Maclennan, J. E.; Mondainn-Monval, O.; Boyer, C.; Weissflog, W.; Pelzl, G.; Chien, L. C.; Zasadzinski, J.; Watanabe, J.; Walba, D. M.; Takezoe, H.; Clark, N. A. "Polarization-modulated smectic liquid crystal phases," Science 2003, 301, 1204-1211.
Walba, D.M.; Korblova, E.; Shao, R.; Maclennan, J.E.; Link, D.R.; Glaser, M.A.; Clark, N.A. "A ferroelectric liquid crystal conglomerate composed of racemic molecules," Science, 2000, 288, 2181-2184.
Link, D. R.; Natale, G.; Shao, R.; Maclennan, J. E.; Clark, N. A.; Korblova, E.; Walba, D. M. "Spontaneous formation of macroscopic chiral domains in a fluid smectic phase of achiral molecules," Science 1997, 278, 1924-1927.