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 ${\phi }_{\mathrm{I},\mathrm{N}}$ $=$ $m{\xi }^{1.36\pm 0.07}$, where the prefactor $m$ strongly depends on size polydispersity for ${\phi }_{\mathrm{N}}$ but does not depend on size polydispersity for ${\phi }_{\mathrm{I}}$ with ${\phi }_{\mathrm{I}}$ and ${\phi }_{\mathrm{N}}$ being the volume fractions of the isotropic and the nematic phases on the cloud curves, respectively.

• Received 22 March 2012

DOI:https://doi.org/10.1103/PhysRevE.85.061708