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SUMMARY:A tale of swirling layers and twisting columns - Swapnil Jaideo Ko
 le (Indian Institute of Science)
DTSTART:20231120T150000Z
DTEND:20231120T160000Z
UID:TALK208594@talks.cam.ac.uk
DESCRIPTION:At thermal equilibrium\, chiral molecules form a range of liqu
 id-crystalline phases\, such as the cholesteric which presents a helical s
 tructure of the molecular orientation. Chirality\, though essential to the
  construction of the cholesteric\, is totally absent in its long-wavelengt
 h hydrodynamics\, which is identical to that of the achiral smectic&nbsp\;
  A liquid crystal. This cloaking of chirality\, however\, relies on the ex
 istence of an energy function for the dynamics.&nbsp\; We show here that t
 he macroscopic mechanics of active layered phases carries striking chiral 
 signatures. We start by constructing\, in two and three dimensions\, the c
 hiral and active variants of model H. Thanks to the mix of solidand liquid
 -like directions\, we predict that chiral active stresses create a force d
 ensity tangent to contours of constant mean curvature of the layers. This 
 non-dissipative force in a fluid direction &ndash\; odder than odd elastic
 ity &ndash\; leads\, in the presence of an undulational instability create
 d by non-chiral active stresses normal to the layers\, to spontaneous vort
 ical flows arranged in a two-dimensional array with vorticity aligned alon
 g the pitch axis and alternating in sign in the plane. This vortex-lattice
  state can be switched on or off by means of an externally imposed uniaxia
 l stress\, due to an exact equivalence of the active buckling instability 
 and the passive Helfrich-Hurault instability of achiral layered phases.We 
 further show that two-dimensional odd elasticity\, an effect that is attra
 cting much current attention\, is naturally realised in three-dimensional 
 material for polar and chiral columnar systems. The resulting oscillatory 
 mode\, thanks to the Stokesian hydrodynamic interaction\, has a nonzero fr
 equency on macroscopic scales\, set by the ratio of the coefficient of chi
 ral and polar active stress and the viscosity. In effect\, the two compone
 nts of the in-plane displacement field mimic a position-momentum pair. We 
 also show that a bulk active columnar phase is spontaneously unstable to a
 n extensile activity along the column direction via a buckling instability
  and predict singular stiffening or softening &ndash\; depending on whethe
 r the active achiral stress is contractile or extensile &ndash\; of the bu
 ckling of fluid columns in all active columnar materials\, irrespective of
  whether they are chiral or polar. The instability is mediated by a twist-
 bend mode resulting in helical columns &mdash\; the same as those that ari
 se from a Helfrich-Hurault instability of passive columnarmaterial. If the
  active units composing the columnar state are\, in addition\, chiral\, th
 e buckled and twisted state beyond the spontaneous Helfrich-Hurault instab
 ility in an apolar system hosts large-scale shear flows due to a new form 
 of odd elasticity.
LOCATION:Seminar Room 2\, Newton Institute
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