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SUMMARY:Chromonic Twisted Hedgehogs. - Silvia Paparini (Università degli 
 Studi di Pavia)
DTSTART:20230823T130000Z
DTEND:20230823T140000Z
UID:TALK204448@talks.cam.ac.uk
DESCRIPTION:Chromonic liquid crystals (CLCs) are lyotropic materials which
  are attracting growing interest for their adaptability to living systems.
  To describe their elastic properties\, the classical Oseen-Frank theory\,
  which posits a stored energy quadratic in the gradient of the director fi
 led n\, requires anomalously small twist constants and (comparatively) lar
 ge saddle-splay constants\, so large as to violate one of Ericksen&rsquo\;
 s inequalities\, which guarantee that the Oseen-Frank energy density is bo
 unded below. While such a violation does not prevent the existence and sta
 bility of equilibrium distortions in problems with fixed geometric confine
 ment\, the study of free-boundary problems for droplets has revealed a num
 ber of paradoxical consequences. A CLC droplet tactoidal in shape is predi
 cted by the classical theory to be unstable against shape changes: it woul
 d split indefinitely in smaller tactoids while the total energy plummets t
 o negative infinity. To overcome these difficulties\, a novel elastic theo
 ry that extends for chromonics the classical Oseen-Frank stored energy by 
 adding a quartic twist term has been proposed. The total energy of droplet
 s is bounded below in the quartic twist theory\, and paradoxes evaporate. 
 The aim of this talk is to identify a means to differentiate these theorie
 s both qualitatively and quantitatively on the basis of the different stru
 ctures they predict when CLCs are confined to fixed spherical cavities wit
 h homeotropic anchoring.Co-Author: Epifanio G. Virga.
LOCATION:Seminar Room 2\, Newton Institute
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