# Analysis of Nucleation and Glass Formation by Chip Calorimetry
## 3 Results and Discussions
### Glass Formation
#### 3.2.2 In-Situ Formation of Glass in Liquid Crystals  
Liquid crystals (LCs) usually are known to undergo rapid ordering transitions with virtually no hysteresis. These transitions are so fast that almost no supercooling can be observed under ordinary conditions. This allows LCs to serve as standards for temperature calibration at fast cooling rates (up to \(2\times 10^{4}\) K/s) [31,32]. Recently, ITZ was reported as an exceptional case. At slow cooling, the isotropic liquid transforms to a nematic phase and then to a smectic phase, but at fast cooling, smectic ordering can be avoided altogether or avoided partially to produce glassy solids with variable smectic order [5]. To exhibit the smectic ordering in an equilibrium liquid of ITZ, Figure 8a shows that the isotropic liquid of ITZ transforms to a nematic phase (\(T_{N/t}=363\) K) and then to a smectic phase (\(T_{Sm/N}=347\) K) [33, 34, 35]. In the nematic phase, the molecules are aligned with their long axes approximately parallel to each other, while in the smectic phase, the molecules are further organized into layers [5]. Further cooling transforms the smectic liquid to a glassy solid (\(T_{g}=328\) K). Upon reheating, the transitions noted above are reversible. At different cooling rates (\(R_{c}\)), ITZ glasses can be prepared with and without smectic order. When the cooling rate is faster than the relaxation of nematic to smectic transition  
Figure 8: (**a**) Conventional DSC traces of ITZ during cooling and reheating at 10 K/min. (**b**) Fast (red circles) and slow (blue circles) relaxation processes in ITZ from dielectric spectroscopy from Ref. [34], and conventional DSC \(T_{S}\) onset (triangle) is shown as a function of cooling rate \(R_{c}\) (right axis) [5;34]. (**c**) A series of conventional DSC reheating traces with different heating rates, starting from the melt quenched ITZ glass at 10 K/min cooling rate. (**d**) Flash DSC reheating curves with \(10^{3}\) K/s heating rate, and the measured ITZ glass formed upon a series of cooling rates from 10 to \(3\times 10^{3}\) K/s. (**e**) The experimental protocol for the different ITZ glass formation in (**f**). (**f**) Flash DSC reheating curves at \(10^{3}\) K/s heating rate, to examine the ITZ glassy state after the different annealing conditions. (\(R_{c}>20\) K/s), ITZ can be free of smectic order [5]. The rates of molecular rotations in a liquid crystal can be obtained by dielectric spectroscopy, as shown in Figure 8b [36]. Similar to other LCs [37; 38; 39], ITZ shows two relaxation processes [34; 40]. The fast process has been associated with the glass transition detected by DSC [34; 38] and is termed the \(\alpha\) process, where the \(R_{c}\) value for glass formation is given by the right axis in Figure 8b. This process is attributed to molecular rotation about the long axis and precession of the long axis about the nematic director, whereas the slow process (called the \(\delta\) mode) is attributed to molecular rotation about the short axis (end over end). The rates of the two processes can be significantly different in a liquid crystal; this is a result of a nematic potential that favors the alignment of the long axis along the director and reduces the average rate of end-over-end rotation [5]. From Figure 8b, it is evident that if \(R_{c}>10^{3}\) K/s, which is even faster than the rate of the isotropic to nematic transition, the two LC transitions will be avoided, and the liquid can be directly quenched into glassy state. Therefore, to obtain the isotropic glass, the molten sample was quenched at a series of cooling rate from 10 to 104 K/s and then reheated at 103 K/s to determine the different quenched glassy state structures. Unlike the heating curve measured by conventional DSC as shown in Figure 8a, at a high heating rate under Flash DSC the peak of glass transition overlaps with the peak of the smectic to nematic transition. The evolution of the profile of heating curve is guided by the dash line shown in Figure 8c.