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Bent-Core Liquid Crystals exhibit Twisted Nanofilament and Plumber's Nightmare Phases (September 2009)

The mysterious B4 and dark conglomerate phases of bent-core liquid crystals have been explained by Center researchers in two papers published in the journal Science. In 1997, a year after the rediscovery of banana liquid crystals by scientists at the Tokyo Institute of Technology, Center researchers showed that achiral, bent-core liquid crystal molecules form polar, chiral smectic phases when the molecules are tilted in the layers, the first example of spontaneous chiral resolution in a fluid phase. The B4 phase was also observed around this time, and the dark conglomerate a few years later, but their underlying structures, though the subject of much speculation, were not understood. Under the direction of Noel Clark, doctoral student Loren Hough, together with colleagues in the Center and collaborators from Germany, Japan and Santa Barbara, combined optical microscopy, x-ray scattering, AFM and freeze-fracture transmission electron microscopy to put together the first complete picture of these phases. In both phases, the layers have significant saddle splay curvature.The B4 phase is a unique variant of the twist grain boundary phase, being made of bundles of twisted, rope-like smectic ribbons (helical nanofilaments) of finite lateral extent, which pack together to produce macroscopic left- and right-handed domains that rotate plane-polarized light and can typically be resolved in the microscope. The dark conglomerate (DC) phase is an optically isotropic, three-dimensional assembly of curved smectic layers that form the sponge-like structure filled with smectic layers that minimizes the global free energy. The dark conglomerate phase exhibits little birefringence but is optically active and exhibits large homochiral domains in cells.

banana phases

The B4 banana phase (top) is a nanoporous assembly of helically twisted smectic layers. The sponge-like organization of the layers in the dark conglomerate phase (bottom) is analogous to the plumber's nightmare structure of lytotropic liquid crystals.

 

This work was published in L. E. Hough et al., Science 325, 452 (2009) and L. E. Hough et al., Science 325, 456 (2009). The issue includes a Perspectives article (D. Amabilino, Science 325, 402 (2009)). The research is also featured in Chemistry World, Chemical & Engineering News, and in Nature Chemistry.

Nanoimprinted Polymer Films control the Alignment of Liquid Crystal Molecules (June 2009)

Polymer films nanoimprinted with checkerboard patterns of square wells between 200 nm and 800 nm in width have been shown by Center researchers to align calamitic (rod-like) liquid
crystals vertically, horizontally or tilted depending on the depth/width ratio of the wells. The LCs prefer to orient parallel to the surface when the
polymer films are smooth but when the polymer is topographically patterned, post-doc Youngwoo Yi and collaborators have demonstrated that the preferred average orientation of the LC director depends on the pattern profile, the increasing elastic energy density as the wells become narrower eventually overcoming the surface anchoring of the polymer and changing the average orientation in cells from planar to homeotropic. Nanoimprinting, a technique in which a spin-coated monomer film is polymerized while pressing against a finely-patterned master mold, can be used to produce topographically-patterned surfaces rapidly and at low cost. Yi's experiments suggest that suitably topographically-patterned polymer films could be used to control the alignment of a variety of anisotropic soft matter in advanced electrooptic devices including liquid crystal displays, where alignment of the liquid crystal director is


Polarized light photomicrograph of a hybrid nematic cell with checkerboard patterns of different square well widths (200, 600, and 400 nm, from top to bottom) on one surface and an OTES SAM-coated glass slide as the other. The director orientation changes from homeotropic to planar as the well width increases. The white scale bar is 20 μm. The insets show a sketch of the director field in a homeotropic well and an AFM image of a checkerboard pattern of 400 nm square wells imprinted on a polymer replica.


essential in controlling the optical properties of the pixels. This work was published in Y. Yi, G. Lombardo, N. Ashby, R. Barberi, J. E. Maclennan, and N. A. Clark, Phys. Rev. E 79, 041701 (2009).

Boulder Workshop on Light-Controlled Liquid Crystalline Complex Adaptive Materials (August 2008)

This Center workshop brought together researchers from across the world working at the forefronts of materials science & optics to discuss the emerging uses of light for control of ordered soft materials and advances in the use of liquid crystals to control light. The LC2CAM program included tutorial lectures, professional development presentations, and poster sessions. The workshop was featured in Nature Photonics and in an ICAM news release. The complete workshop presentations are available on the web.

lc2cam image
Liquid Crystals a Sensitive Probe of DNA Hybridization (June 2008)

Liquid crystals that realign in response to DNA can reveal subtle sequence alterations, even a single base mutation. Center investigator Dan Schwartz.and doctoral student Andrew Price showed that nematic liquid crystals, which naturally align themselves perpendicular to the surface of a surfactant-coated glass slide, tilt slightly following the addition of short lengths of single stranded DNA. The addition of complementary strands of DNA - with a base sequence that would bind to the strands on the slide - triggers the tilted molecules to return to their perpendicular alignment. However, adding a non-complementary DNA strand - with a sequence that differs by just one base - causes no such response. These differing responses of the liquid crystals are easily observed in polarized light. The finding could lead to cheap, portable alternatives to current lab-based analytical detectors. This work was published in A. Price and D. Schwartz, Journal of the American Chemical Society 130, 8188-8194 (2008) and has recently been featured in Chemistry World.

DNA detection by nematic


The texture of a liquid crystal film to which single-stranded DNA has been added (a) changes progressively with the addition of complementary single-stranded DNA (b-d).

Two Center Graduates awarded ILCS Glenn Brown Prizes (May 2008)

Two young scientists who performed graduate research in the Center have been selected by the International Liquid Crystal Society as winners of the prestigious 2008 Glenn Brown Prize: Loren Hough for his study of the B4 and dark conglomerate phases of banana liquid crystals (directed by Noel Clark), and Giuliano Zanchetta for his studies of a novel class of liquid crystal assemblies based on short-chain DNA (directed by Center collaborator Tommaso Bellini, of the University of Milan). Both laureates are currently pursuing post-doctoral research.

 


Glenn Brown Laureates Hough (l) and Zanchetta (r).
Tiny DNA Molecules show Liquid Crystal Phases (November 2007)

Center members and a team of collaborators have discovered some unexpected forms of liquid crystals of ultrashort DNA molecules immersed in water, providing a new scenario for a key step in the emergence of life on Earth. The research is described in a paper published in the Nov. 23 issue of Science (download Abstract or Full Text from Science). Read more in the press release.

Microscope image shows that a solution of tiny DNA molecules has formed a liquid-crystal phase

Cool Chemistry wows Audience at Pueblo Super Science Saturday (April 2007)

Cool and Creative Chemistry, an interactive K-12 outreach program designed by Center faculty and students, was presented to an enthusiastic audience of children and their parents as part of Super Science Saturday at the Steelworks Museum of Industry & Culture in Pueblo, Colorado. Read more in this news story.

kids doing chemistry
Photo: John Jaques/Pueblo Chieftain

Noel Clark elected to National Academy of Sciences (April 2007)

Center Director Noel Clark has been elected to the National Academy of Sciences. Read more in the press release.

NAS Logo

21st International Liquid Crystal Conference
(July 2006)

The Center organized the 21st ILCC held in Keystone, in the Colorado Rockies, from 2-7 July 2006. See the ILCC2006 archive website.

ILCC logo

Noel Clark wins 2006 Buckley Prize
(October 2005)

University of Colorado at Boulder physics Professor Noel Clark has been awarded the American Physical Society's 2006 Oliver E. Buckley Prize for Condensed Matter Physics in recognition of his work in liquid crystals. Read more in the press release.

noel clark portrait

 

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