# Crystallization Kinetics of an Equimolar Liquid Crystalline Mixture and Its Components
## 3 Results and Discussion
### Dielectric Relaxation Processes
Figure 7: BDS results for MHPOBC obtained upon slow cooling: dielectric increment (**a**), activation plot of relaxation times (**b**), and activation plot for ionic conductivity (**c**). The activation energies in (**b,c**) are in kJ/mol. There is an alternative way for determining \(m_{f}\), based on DSC thermograms [58]:  
\[m_{f}=\frac{cT_{g}\Delta C_{p}}{\Delta H_{m}}, \tag{6}\]  
where \(\Delta C_{p}\) is the jump in the heat capacity at \(T_{g}\), and \(\Delta H_{m}\) is the enthalpy of melting. Based on the experimental data for more than 40 glassformers, the empirical \(c\) parameter was usually ca. 56 [58]. The modulated-temperature DSC results were used to determine the \(m_{f}\) parameter of MIX2 HF6 (Figure 10). The MTDSC technique separates the non-reversing and reversing parts of the heat flow [59]. For MIX2 HF6, these parts of the heat flow correspond to the cold crystallization and glass transition, overlapping in the standard DSC thermogram. The glass transition occurs at \(T_{g}\) = 245.3 K, with \(\Delta C_{p}\) = 0.16 kJ/(mol\(\cdot\)K). As the melting enthalpy, the summed melting enthalpies of the Cr1 and Cr2 phases were included, giving \(\Delta H_{m}\) = 9.2 kJ/mol. Using Equation (6) and \(c\) = 56, one obtains \(m_{f}\) = 233, which is an exceptionally high value [57]. However, for a few substances presented in [58], \(c\) deviated strongly from 56, which can also be the case for MIX2 HF6. Recently, we published the DSC  
Figure 9: BDS results for MIX2 HF6 obtained upon slow cooling (**a**–**c**), heating after slow cooling (**d**–**f**), and heating after fast cooling at 10 K/min (**g**–**i**): dielectric increment (**a**,**d**,**g**), activation plot of relaxation times (**b**,**e**,**h**), and activation plot for ionic conductivity (**c**,**f**,**i**). The activation energies in (**b**,**c**,**e**,**f**,**h**,**i**) are in kJ/mol. and BDS results for the 3F/FPhH6 compound [37]. 3F/FPhH6 has a molecular structure similar to MIX2 HF6 components, and it forms the SmCa* glass. The fragility index obtained from the \(\alpha\)-relaxation time is \(m_{f}=72\). Using the \(T_{g}=233.9\) K, \(\Delta C_{p}=0.18\) kJ/(mol\(\cdot\)K), and \(\Delta H_{m}=15.7\) kJ/mol values determined from the DSC thermograms of 3F/FPhH6, one can conclude that the kinetic fragility agrees with the thermodynamic fragility for \(c=26\). If the same \(c\) parameter is applied for MIX2 HF6, then \(m_{f}=108\), a more reasonable value, within the 72-149 range obtained for similar compounds [36; 37; 38; 56]. Returning to the BDS spectra of MIX2 HF6, one can see that the P\({}_{\rm H}\)-relaxation time has a nonlinear dependence in the activation plot, and it is expected to reach 100 s at a temperature only slightly higher than \(T_{g}\). Moreover, P\({}_{\rm H}\) appears at much lower frequencies than the cr-process from the crystal phase; therefore, upon cooling, it is less affected by crystallization than the \(\alpha\)-process. The P\({}_{\rm H}\)-relaxation time fits the VFT formula well (Figure 9b). The approximate \(T_{g}\) obtained from the fitting parameters is 249 K, close to the calorimetric 245.3 K. The fragility index obtained from the P\({}_{\rm H}\)-relaxation time is 100, also surprisingly close to the calorimetric 108. However, it does not mean that P\({}_{\rm H}\) can always be used to determine \(m_{f}\). In publication [56], in which both P\({}_{\rm H}\) and \(\alpha\)-relaxation times were analyzed by the VFT formula, the obtained \(T_{g}\) values differed only by 2 K. At the same time, the \(m_{f}\) values were less consistent (117 and 149, respectively). The last relaxation process in MIX2 HF6 is the cr-process from the Cr3 phase, which is absent in Cr2 and Cr1. Its relaxation time also follows the VFT equation. While the fitting parameters are similar for slow cooling and subsequent heating (Figure 9b,e), they are different for heating after fast cooling (Figure 9h)--one can see that in the latter, the cr-relaxation time is longer, and diverges at higher temperatures.