Emergence of biaxial nematic phases in solutions of semiflexible dimers.
Physical review. E
MetadataShow full item record
Vaghela, A., Teixeira, P. I., & Terentjev, E. M. (2017). Emergence of biaxial nematic phases in solutions of semiflexible dimers.. Physical review. E, 96 (4-1), 042703. https://doi.org/10.1103/physreve.96.042703
We investigate the isotropic, uniaxial nematic and biaxial nematic phases, and the transitions between them, for a model lyotropic mixture of flexible molecules consisting of two rigid rods connected by a spacer with variable bending stiffness. We apply density-functional theory within the Onsager approximation to describe strictly excluded-volume interactions in this athermal model and to self-consistently find the orientational order parameters dictated by its complex symmetry, as functions of the density. Earlier work on lyotropic ordering of rigid bent-rod molecules is reproduced, and extended to show explicitly the continuous phase transition at the Landau point, at a critical bend angle of $36^\circ$. For flexible dimers with no intrinsic biaxiality, we nevertheless find that a biaxial nematic phase can form at sufficiently high density and low bending rigidity. For bending stiffness $\kappa > 0.86 k_BT$, this biaxial phase manifests itself as dimer bending fluctuations occurring preferentially in one plane. When the dimers are more flexible, $\kappa < 0.86 k_BT$, the modal shape of the fluctuating dimer is a `V' with a sharp opening angle, and the biaxial order parameter changes sign. These two regions are separated by a narrow strip of uniaxial nematic in the phase diagram, which we generate in terms of the variables spacer stiffness and particle number density.
External DOI: https://doi.org/10.1103/physreve.96.042703
This record's URL: https://www.repository.cam.ac.uk/handle/1810/270384