23 research outputs found
Shaping thin nematic films with competing boundary conditions
Free interfaces of liquid crystals tend to minimise both capillarity and
anchoring forces. Here we study nematic films in planar and radial geometries
with antagonistic anchoring boundary conditions and one deformable interface.
Assuming a perturbation ansatz we study possible couplings of the director
configuration with the shape of free interfaces. In the long-wavelength limit
independent of the surface tension, we find analytically threshold thickness
when flat film becomes unstable. Next we quantify the bifurcation of a circular
ring towards structures with -fold rotational symmetry, induced by elastic
anisotropy of nematic director in the bulk. We believe that our simplified
approach can give additional insight into elastic and capillary phenomena of
materials with inherent liquid crystalline order and free interfaces.Comment: 5 pages, 3 figures; reference is added and stability criterion is
stated; final version accepted for publication in EPJ
Slow dynamics in a model of the cellulose network
We present numerical simulations of a model of cellulose consisting of long
stiff rods, representing cellulose microfibrils, connected by stretchable
crosslinks, representing xyloglucan molecules, hydrogen bonded to the
microfibrils. Within a broad range of temperature the competing interactions in
the resulting network give rise to a slow glassy dynamics. In particular, the
structural relaxation described by orientational correlation functions shows a
logarithmic time dependence. The glassy dynamics is found to be due to the
frustration introduced by the network of xyloglucan molecules. Weakening of
interactions between rod and xyloglucan molecules results in a more marked
reorientation of cellulose microfibrils, suggesting a possible mechanism to
modify the dynamics of the plant cell wall.Comment: 13 pages, 7 figures, accepted in Polyme
Cell motility: a viscous fingering analysis of active gels
The symmetry breaking of the actin network from radial to longitudinal
symmetry has been identified as the major mechanism for keratocytes (fish
cells) motility on solid substrate. For strong friction coefficient, the two
dimensional actin flow which includes the polymerisation at the edge and
depolymerisation in the bulk can be modelled as a Darcy flow, the cell shape
and dynamics being then modelled by standard complex analysis methods. We use
the theory of active gels to describe the orientational order of the filaments
which varies from the border to the bulk. We show analytically that the
reorganisation of the cortex is enough to explain the motility of the cell and
find the velocity as a function of the orientation order parameter in the bulk.Comment: 15 pages, 4 figures, accepted for publication in EPJ - Plu
Instability patterns in ultrathin nematic films: comparison between theory and experiment
Motivated by recent experimental observations [U. Delabre et al, Langmuir 24,
3998, 2008] we reconsider an instability of ultrathin nematic films, spread on
liquid substrates. Within a continuum elastic theory of liquid crystals, in the
harmonic approximation, we find an analytical expressions for the critical
thickness as well as for the critical wavenumber, characterizing the onset of
instability towards the stripe phase. Comparing theoretical predictions with
experimental observations, we establish the utility of surface-like term such
as an azimuthal anchoring.Comment: 6 pages, 3 figures, LaTeX macros EPL draft, accepted for publication
in EP