Research

Professor Walba leads an active group working in the general area of supramolecular stereochemistry. This program focuses on liquid crystal science and technology, with an emphasis on ferroelectric liquid crystals. The work is highly interdisciplinary, and the Walba group is a founding member of the interdisciplinary Soft Materials Research Center (SMRC). The Center is an NSF-sponsored Materials Research Science and Engineering Center headquartered at the University of Colorado and led by Professor Noel A. Clark, in the CU Department of Physics.

A retrospective overview of Professor Walba's research can be found at *insert member URL*

Liquid Crystal Conglomerates

A major theme in FLC research has always been the key role of chirality in liquid crystals (LCs) for producing interesting and useful materials properties. The central example: ferroelectricity in chiral tilted smectics.

In work ranked as the "most beautiful chemistry experiment in history" by C&EN [1], Pasteur first showed in 1848 that the sodium ammonium salt of "racemic acid" ((R*,S*)-tartaric acid) can form two macroscopic enantiomers upon crystallization, producing a mixture of right- and left-handed crystals termed a conglomerate [2]. Since then, many examples of conglomerate formation have been demonstrated in 3-D, and even in 2-D crystal systems [3].

Conglomerate formation had never been seen in a thermodynamic liquid phase, however. Stated in another way, all known LC phases produced from achiral or racemic molecules were achiral. This situation changed in 1997 with the report by the Boulder FLCMRC of the formation of chiral smectic phases from the achiral mesogen NOBOW.

the formation of chiral smectic phases from the achiral mesogen NOBOW.

Details of this story can be found in an article in Science [4]. An overview of the discovery of ferroelectric liquid crystal conglomerates can be found in a chapter of the same name in Topics in Stereochemistry [5].

Additional pieces of this ongoing puzzle involve the design and synthesis of the first ferroelectric banana (molecular structure below) [6], and the discovery that such phases exhibit the first example of thermodynamic polarization splay stripes [7].

the first ferroelectric banana (molecular structure

[1] C&EN, Aug 25, 2003,Vol 81, No. 34, , pp. 27-30 (full text (html) - subscription required)

[2] Pasteur, L. C.R. Acad. Sci. Paris 1848, 26, 535-539.

[3] Walba, D.M.; Stevens, F.; Clark, N.A.; Parks, D.C. "Detecting Molecular Chirality by Scanning Tunneling Microscopy," Acc. Chem. Res. 1996, 29, 591-597.

[4] Link, D.R.; Natale, G.; Shao, R.; Maclennan, J.E.; Clark, N.A.; Körblova, E.; Walba, D.M. "Spontaneous Formation of Macroscopic Chiral Domains in a Fluid Smectic Phase of Achiral Molecules," Science 1997, 278, 1924-1927. (full text (html) - subscription required)

[5] Walba, D.M. "Ferroelectric liquid crystal conglomerates;" in Topics in Stereochemistry, Materials-Chirality, M. M. Green, R. J. M. Nolte, E. W. Meijer and S. E. Denmark, Eds.; Wiley, 2003; Vol. 24, pp 457-518. (complete chapter (2.4MB pdf) - with permission of the publisher)

[6] Walba, D.M.; Körblova, 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. (full text (html)) - free registration required)

[7] 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. (full text (html) - free registration required)