Aspect ratio and polydispersity dependence of isotropic-nematic transition in discotic suspensions.

We demonstrate the strong dependency of the isotropic-nematic (I-N) transition of discotic suspensions on the aspect ratio (ξ = thickness/diameter) via control of the sizes of pristine ZrP crystals and subsequent exfoliation to monolayers. The size fractionation of the I-N transition facilitates the analysis of the effect of polydispersity. A systematic variation in the aspect ratio in the low aspect ratio region (0.001 < ξ < 0.01) showed that the I-N transition volume fraction increases with the aspect ratio in agreement with computer simulations. It was found that the transition volume fractions scale with aspect ratio φ_{I,N} = mξ^{1.36±0.07}, where the prefactor m strongly depends on size polydispersity for φ_{N} but does not depend on size polydispersity for φ_{I} with φ_{I} and φ_{N} being the volume fractions of the isotropic and the nematic phases on the cloud curves, respectively.