Temperature-dependent isotropic-to-nematic transition of charged nanoplates

Studies of temperature-dependent phase behaviors of discotic colloids are found infrequently in the literature. We establish here the isotropic-to-nematic (I-N) transition phase diagram of charged platelets in the temperature-versus-volume fraction plane. We discover that the N phase can be melted by increasing temperature, and that coexistent samples are more sensitive to polydispersity at higher temperature and higher concentration.

Figure 1

$\alpha$-Zirconium phosphate disks. (a) SEM image of pristine ZrP crystals. (b) TEM image of ZrP monolayer platelets. The scale bars in (a) and (b) are $1\mu \mathrm{m}$.

Figure 2

Cross-polarized images of ZrP platelet suspensions 120 h after mixing at different temperatures. From left to right, the ZrP platelet volume fractions were $\varphi =0.00660\left(5\right)$, 0.007 20(5), 0.007 60(5), 0.008 20(5), 0.008 80(5), 0.009 40(5), 0.010 00(5), 0.011 20(5), 0.012 40(5), and 0.014 80(5). The width of each sample is 1.50 ± 0.03 cm.

Figure 3

The I-N transition phase diagram at four temperatures. From top down, the temperatures are 298, 308, 318, and 328 K. Lines are fit to the data using nonlinear functions.

Figure 4

Phase diagram of charged nanoplates in the $T\text{−}\varphi$ plane.