Frustrated nematic order in spherical geometries

• Published in: Nature physics Vol. 7; no. 5; pp. 391 - 394
• Main Authors: Lopez-Leon, T., Koning, V., Devaiah, K. B. S., Vitelli, V., Fernandez-Nieves, A.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.05.2011; Nature Publishing Group
• Subjects: Atomic; Bioengineering; Carbon; Classical and Continuum Physics; Colloids; Complex Systems; Condensed Matter Physics; Crystal defects; Crystals; Fluid dynamics; letter; Liquid crystals; Materials science; Mathematical and Computational Physics; Microstructure; Molecular; Molecular structure; Nematic; Optical and Plasma Physics; Physics; Physics and Astronomy; Polymers; Theoretical; Thin walled shells; Tuning
• ISSN: 1745-2473; 1745-2481; 1476-4636
• DOI: 10.1038/nphys1920

Coating a spherical colloid with a nematic liquid crystal causes frustration-induced defects in the crystal. The thickness of this coating can be used to systematically control the number and orientation of these defects, which could be useful for engineering the microstructure of colloidal materials. The prospect of mimicking molecular chemistry with colloidalrather than molecular building blocks could enable unprecedented control over the properties of microstructured materials 1 . The usual absence of directionality to the interaction between colloids has limited the complexity of the structures they can spontaneously form. One way to address this is to coat spherical colloid particles with a thin layer of nematic liquid crystal 2 and functionalize 3 the unavoidable defects or bold spots that arise when nematic order is established on the surface of a sphere 4 , 5 . The number and arrangement of these defects can vary 2 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , providing flexibility for tuning directional interactions that are more difficult to achieve by other methods 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 . Yet, many theoretically predicted structures have not been observed and control over defect location remains elusive. In this work, we show that varying the thickness of a nematic liquid crystal shell enables us to systematically control the number and orientation of defects formed. For thin shells, these defects can be engineered to emulate the linear, trigonal and tetrahedral geometries of s p , s p 2 and s p 3 carbon bonds, respectively. Such control opens up the possibility to engineer particles with tunable-valence and directional-binding capabilities.