# Analysis of Nucleation and Glass Formation by Chip Calorimetry
## 3 Results and Discussions
### Glass Formation  
#### 3.2.1 New Polyamorphous Material-D-Mannitol  
Polyamorphism refers to the existence of two amorphous phases of the same composition separated by a first-order transition. This phenomenon is analogous to crystal polymorphism exemplified by diamond and graphite but is less well understood and even controversial [30]. [PERSON] et al. reported that the melt-quenched glass of D-mannitol  
Figure 6: (**a**) A series of Flash DSC heat flow curves corresponding to different annealing times ranging \(t_{a}\) from 2 to 12 s at 50 \({}^{\circ}\)C for amorphous PBT sample; (**b**) plot of \(T_{g}\) and \(t_{a}\) at 50 \({}^{\circ}\)C (\(t_{1}\) and \(t_{2}\) are two selected annealing times before and after the break point of 6.6 s); (**c**) the isothermal test for PBT sample at 50 \({}^{\circ}\)C; and (**d**) XRD patterns for annealed samples corresponding to the annealing times of \(t_{1}\) and \(t_{2}\). can transit into another apparently amorphous state by continuous heating or isothermal annealing, with a first-order characteristic [2]. In agreement with this report, the first-order transition can be completed by annealing the melt-quenched sample at 310 K for 180 s in the conventional DSC. Figure 7a shows when heating the melt-quenched glass (GN) sample with a 20 K/min heating rate, the sample begins the glass transition to a supercooled liquid (SCL-1) at 287 K, but further heating results in an exothermic transition from SCL-1 to amorphous phase X (GX) beginning at 298 K. When heating a sample that has been aged at 310 K for 180 s, the sample shows neither a glass transition at 287 K nor a sharp exothermic peak at 298 K [3]. This is identical to the DSC heating trace of the GX sample, which is obtained by first being heated to 313 K (above the first exothermic transition) and then quenched [2]. The X-ray diffraction patterns of GN, GX, and the \(\alpha\) crystal polymorph are shown in Figure 7b. It is evident that GX does not have crystal-like diffraction features, which  
Figure 7: (**a**) Conventional DSC measurements on a normal glass (GN) and a phase X (GX) D-mannitol sample [31; 32; 33]. (**b**) X-ray diffraction patterns of GN and GX [31; 33]. (**c**) The experimental protocol for the sample preparation in (**d**). (**d**) Transition path during heating. Sample was annealed at 309 K for 16 s, preheated to 340 K, and quenched down before this heating. Sample starts as a mixture of normal (melt-quenched) glass and phase X, and shows three endothermic transitions: (1) glass transition of GN (298 K); (2) glass transition of GX (328 K); and (3) liquid–liquid from SCL-2 to SCL-1 (340 K) [33]. (**e,f**) Enthalpy change with different annealing conditions; (**e**) is 3-D plot of the enthalpy change with \(T_{a}\) and \(\mathrm{In}(t_{a})\); (**f**) is the result of projecting the profile onto T-t plane, and the boundaries between adjacent plateaus are the Time–Temperature–Transition curves of the corresponding transition [33]. strongly indicates that the GX is an amorphous state. Additionally, the diffraction pattern of GX is distinct from that of GN. The GX has a featured broad maximum that appears at lower 20 than that for the GN, with an additional small peak around 15, which likely results from a different local structure with long range correlation. This is consistent with the report that the GN has a smaller specific volume than GX at 273 K, which is the measuring temperature of the X-ray diffraction experiments [3,4]. Due to the slow heating rates of the conventional DSC, GX can form from SCL-1 of GN to produce an exothermic peak. In the Flash-DSC, however, the 100 K/s or even a 10 K/s heating rate is too fast to allow for this transition so that no exothermic peak can be observed on the heating trace of a melt-quenched GN sample.