title: Lattice model for biaxial and uniaxial nematic liquid crystals.
abstract: We use a lattice gas model to describe the phase transitions in nematic liquid crystals. The phase diagram displays, in addition to the isotropic phase, the two uniaxial nematics, the rod-like and discotic nematics, and the biaxial nematic. Each site of the lattice has a constituent unit that takes only six orientations and is understood as being a parallelepiped brick with the three axes distinct. The possible orientations of a brick are those in which its axes are parallel to the axes of a Cartesian reference frame. The analysis of the model is performed by the use of a mean-field approximation and a Landau expansion of the free energy.
authors.affiliation: Departamento de Física, Universidade Federal de Santa Maria, 97105-900 Santa Maria, RS, Brazil.
authors.forename: Ricardo A
authors.initials: RA
authors.lastname: Sauerwein
authors.affiliation: Instituto de Física, Universidade de São Paulo, Rua do Matão, 1371, 05508-090 São Paulo, São Paulo, Brazil.
authors.forename: Mário J
authors.initials: MJ
authors.lastname: de Oliveira