**Phase Diagrams and Related Tammann Plots**

From the integration of the eutectic melting effects at different mixture compositions, the related eutectic melting enthalpy ΔHeut can be obtained. At the eutectic composition, the melting enthalpy is maximum and gradually decreases with composition towards the pure components. Therefore, plotting the ΔHeut values as a function of the composition (Tammann plot), the intersection of the two linearized parts provides a good measure of the eutectic composition in the respective binary system.

**AMG-CAF system**. The presence of the single melting endotherm at 127.2 ◦C (see Figure 3a), lower than that of both the starting components AMG and CAF, indicated the formation of the eutectic composition in the AMG-CAF system at 75 wt.% of AMG. The phase diagram and the Tammann plot for this system are presented in Figure 6a,b. In the phase diagram, the liquidus and solidus temperatures are plotted as a function of weight% (wt.%) of AMG in the CAF-AMG system. It shows the enantiotropic behavior of caffeine and specifies the polymorphic phase transition at ~138◦C confirming the literature data [25,26]. Additionally, this indicates the eutectic composition at ~75 wt.%, which is verified in the Tammann plot (Figure 6b). In addition, the latter indicates a partial solid solution behavior of CAF in AMG in a rather narrow composition range of ~95 ± 2 wt.% of AMG (indicated by the dashed line in Figure 6b). However, since this is based on only two points, it needs to be verified what is hardly to be done in the small existence region of AMG in the phase diagram.

**Figure 6.** (**a**) Binary melt phase diagram and (**b**) Tammann plot of the AMG-CAF system.

**AMG-NIC system**. The DSC profiles in Figure 3b illustrate the melting behavior of solid samples at different AMG-NIC compositions prepared by neat grinding. The system shows simple eutectic behavior; thus, mixtures of both components exhibit two endothermic peaks in DSC curves corresponding to eutectic melting and the subsequent dissolution effect of the excess compound. Figure 7a presents the derived melt phase diagram with a eutectic composition of ~50 wt.% AMG. The eutectic temperature in this system was found on average at 99.2 ◦C (Table 1). The Tammann plot shown in Figure 7b confirms the ~50 wt.% eutectic composition.

**Figure 7.** (**a**) Binary melt phase diagram and (**b**) Tammann plot of the AMG-NIC system.

**AMG-ZMD system**. As for the AMG-NIC system, the melt phase diagram of the AMG-ZMD system is characterized by a simple eutectic, possessing a eutectic point at 101.8 ◦C and composition of ~50 wt.% of AMG. The eutectic composition was derived from the single endothermic event in the DSC thermogram and from the intersection of the ZMD and AMG liquidus curves. Tammann's plot (Figure 8b) for the AMG-ZMD system verifies the eutectic composition close to 50 wt.% AMG and indicates partial miscibility at the solid-state close to the ZMD side (indicated by the dashed line in Figure 8b), but similar to the AMG-CAF system, this needs more detailed studies if important.

**Figure 8.** (**a**) Binary melt phase diagram and (**b**) Tammann plot of the AMG-ZMD system.
