Simulations of nematic-isotropic transition of liquid crystals in two
dimensions are performed using an O(2) vector model characterised by non linear
nearest neighbour spin interaction governed by the fourth Legendre polynomial
P_4. The system is studied through standard Finite-Size Scaling and
conformal rescaling of density profiles of correlation functions. A topological
transition between a paramagnetic phase at high temperature and a critical
phase at low temperature is observed. The low temperature limit is discussed in
the spin wave approximation and confirms the numerical results