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"Liquid crystals under spherical confinement : a model to study how geometrical frustration can induce patterning"
Spontaneous order or self-organization is ubiquitous in nature, from molecular to ecosystem levels. Examples can be found in crystallization, formation of biological tissues, or animal swarming, where complex organizations arise from local interactions between their constituents. In this talk, I will show you how spontaneous order can be dramatically affected by confinement and curvature. I will use a cholesteric liquid crystal as a model of self-organizing system. In the absence of confinement, the molecules naturally organize themselves in a helical fashion. However, this order gets disrupted when the cholesteric is confined to a spherical shell, that is, a spherical film suspended in water, which we produced using microfluidics. In this arrangement, topological defects—areas where the cholesteric order is ill defined—are required. Using two independent mechanisms, we precisely manipulate both the thickness of the shell and the orientation of the cholesteric molecules at the interfaces, therefore altering the geometry and topology of the system. This results in a series of complex states, where stripes, fingers and skyrmions form organized, hierarchical patterns on the shell surfaces. We shine light on these structures, by inducing transitions between different patterns.
12 octobre 2018
11:00
» 12:00
— A1 (Urbain)