(86c) Smectic Flowers As Compound Eyes

Smectic Flowers as Compound Eyes

Kathleen Stebe

Department of Chemical and Biomolecular Engineering, Laboratory for the Structure of Matter, the University of Pennsylvania, Philadelphia, PA, U.S.A.

Liquid crystalline molecules arrange in a variety of bulk phases owing to the molecules anisotropic shape. In the smectic phase, the molecules tend to form equally spaced layers in which the molecules have both orientational and translational order.   At boundaries, the orientation of the molecules can be influenced by imposing chemistries or textures that favor one orientation over the another-foe example, favoring planar anchoring or homeotropic (perpendicular) anchoring of the molecules at the surfaces. By imposing boundaries with interesting geometries, liquid crystals can self-assemble into highly organized hierarchical structures which may prove useful as functional materials.

We have recently studied an astonishingly beautiful self-assembled structure, a ‘smectic flower’ formed by a thin film of a smectic liquid crystal around a micropost.  The liquid crystal pins to the edges of the post; its height decays with distance to reach a limiting film thickness.  Faced with antagonistic boundary conditions, the liquid crystal spontaneously forms focal conic domains (FCDs). The size of the FCDs is related to the film height, so the curved liquid-vapor interface guides the FCDs to form a ‘flower’ structure.  Within this structure, FCDs of large radii and pronounced eccentricity form near the post, and defects of decreasing size and eccentricity form far from it.  The FCDs are arranged with their focal hyperbolæ diverging radially outward from the texture center.  We present a model for this system which applies the law of corresponding cones, and shows how FCDs can be embedded smoothly within a “background texture” of large FCDs and concentric spherical layers (1).

Isolated FCDs are known to focus light as gradient-index lenses. This motivates the question- can we exploit the self-assembled flower structure as a compound eye comprising many FCDs as lenses acting in concert?   We are able to demonstrate that our flowers are indeed compound eyes with several important features, including a wide range of focal lengths, determined by the FCD size, a wide depth of field, and sensitivity to polarization. Furthermore, our smectic compound eye can be reconfigured by heating and cooling at the LC phase transition temperature (2).  Finally we show that, by imposing more complex confinement, we can mold these flowers into “gardens” with broad potential as reconfigurable lenses (3). 

1.  Focal conic flower textures at curved interfaces, D. A. Beller, M. A. Gharbi, A. Honglawan, K. J. Stebe, S. Yang, and R. D. Kamien, Phys. Rev. X. 3, (2013) 041026,  DOI: 10.1103/PhysRevX.3.041026

2. One-step assembly of a (reconfigurable) smectic liquid crystal “compound eye” on a curved interface F. Serra, M.A. Gharbi, Y. Luo, I. Liu, N.D. Bade, R.D. Kamien, S. Yang, K.J. Stebe, Article first published online: 5/3/15;  DOI: 10.1002/adom.201500153, Advanced Optical Materials

3.Garden of Smectic Liquid Crystal Flowers M. A. Gharbi, I. B. Liu, Y. Luo, F. Serra, N. D. Bade, R. D. Kamien, S. Yang, K. J. Stebe, , in review