Molecular Structure of Canonical Liquid Crystal Interfaces

Numerous applications of liquid crystals rely on control of molecular orientation at an interface. However, little is known about the precise molecular structure of such interfaces. In this work, synchrotron X-ray reflectivity measurements, accompanied by large-scale atomistic molecular dynamics simulations, are used for the first time to reconstruct the air-liquid crystal interface of a nematic material, namely, 4-pentyl-4′-cyanobiphenyl (5CB). The results are compared to those for 4-octyl-4′-cyanobiphenyl (8CB) which, in addition to adopting isotropic and nematic states, can also form a smectic phase. Our findings indicate that the air interface imprints a highly ordered structure onto the material; such a local structure then propagates well into the bulk of the liquid crystal, particularly for nematic and smectic phases. This research is a collaboration between the Institute of Molecular Engineering at the University of Chicago (including members of ChemMatCARS), the University of Illinois at Chicago, and the University of Wisconsin at Madison. 

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Monirosadat Sadati1,6Hadi Ramezani-Dakhel1,2Wei Bu3Emre Sevgen1Zhu Liang4Cem Erol4Mohammad Rahimi1Nader Taheri Qazvini1,6Binhua Lin3Nicholas L. Abbott5Benoı̂t Roux2Mark L. Schlossman4, and Juan J. de Pablo1

1Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637, United States

2Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois 60637, United States

3Center for Advanced Radiation Sources, University of Chicago, Chicago, Illinois 60637, United States

4Department of Physics, University of Illinois at Chicago, Chicago, Illinois 60607, United States

5Department of Chemical and Biological Engineering, University of Wisconsin−Madison, Madison, Wisconsin 53706, United States

6Argonne National Laboratory, Argonne, Illinois 60439, United States

J. Am. Chem. Soc., 2017, 139, pp 3841-3850

DOI:  10.1021/jacs.7b00167