THE TUMBLING OR FLOW-ALIGNING NATURE OF NEMATICS AS PREDICTED FROM THE SLIGHTLY BENDING ROD MOLECULAR-MODEL

Existing calculations of the Leslie coefficients for rigid rods endowe d with the Maier-Saupe potential are here extended to investigate the consequences of relaxing the constraint of a complete molecular rigidi ty. In particular, the recently proposed model of the Slightly Bending Rod (SBR) is used to calculate the ratio alpha(3)/alpha(2), the sign of which controls whether the nematic is of the tumbling or flow-align ing type. The results show that SBRs are more prone to tumbling than f ully rigid rods. The flow-aligning to tumbling transition, which lakes place by increasing the order parameter (e.g. by decreasing the tempe rature) is shifted, for SBRs, to a smaller value of the order paramete r.