# Storage Capacity in Dependency of Supercooling and Cycle Stability of Different PCM Emulsions
## 3 Results and Discussion
### PCM Emulsions
#### 3.1.3 Thermal-Mechanical Stability  
P16-97, L17, P18-97, P19-90 and P20Z emulsions are chosen for the stability evaluations. All tested PCM emulsions passed this stability test over 100 thermal-mechanical cycles without optically visible changes like phase separation or creaming. Figures 9-13 depict the results for the measured emulsions. The rheological data show different changes in the viscosity over the 100 cycles, which come with the changes in the particle size distribution. In the viscosity measurements, the lower viscosity value indicates the emulsion's viscosities at 35 \({}^{\circ}\)C and the upper value those at 5 \({}^{\circ}\)C, respectively. At the beginning of the tests, the emulsions show viscosities between 20 and 50 mPa-s, except P19-90, which ranges between 25 and almost 95 mPa-s. Looking at the development of viscosity over the 100 cycles, the samples exhibit quite different changes. For P16-97, the viscosity at 35 \({}^{\circ}\)C is kept more or less constant at 20 mPa-s, while the upper value at 5 \({}^{\circ}\)C rises very linearly with every cycle, up to 80 mPa-s after 100 cycles. This comes with a change in the particle size distribution, from a monomodal distribution at the beginning to a bimodal distribution with a fraction of smaller sizes and a larger fraction at bigger sizes. L17 shows a rise in viscosity at 35 \({}^{\circ}\)C from 20 to 32 mPa-s and from almost 55 mPa-s to 80 mPa-s after 100 cycles at 5 \({}^{\circ}\)C. The particle size increase is minor, and the peak is slightly narrower than at the beginning. P18-97 keeps the lower viscosity at 20 mPa-s, and the upper values are also more or less constant with higher values for single peaks. No significant change in the size distribution is observed. The PCM emulsion P19-90 shows the highest viscosity values in this test. It reaches over 120 mPa-s after 100 cycles. The size distribution also becomes bimodal, but contrary to P16-97, the share that turned to smaller sizes is larger than the one grown to bigger sizes. P20Z also shows a viscosity between 20 and 55 mPa-s at the beginning of the cycle test. While cycled, both values rise, but the upper value at 5 \({}^{\circ}\)C rises faster than the lower value at 35 \({}^{\circ}\)C.  
Figure 8: Storage factors and temperature differences for the melting process and to acquire the total storage capacity for the first phase-transition m-curve (method a), m-curve 6 k (b), m-c-curve (c) and m-c curve (d) (see Section 2.3 Characterisation). Figure 9: Thermal–mechanical stability test of Parafol 16-97: (**a**) viscosity measured between 5 and 35 \({}^{\circ}\)C over 100 cycles, and (**b**) particle size distribution before and after 100 cycles. Figure 10: Thermal–mechanical stability test of Linpar 17: (**a**) viscosity between 5 and 35 \({}^{\circ}\)C over 100 cycles, and (**b**) particle size distribution before and after 100 cycles. Figure 11: Thermal–mechanical stability test of Parafol 18-97: (**a**) viscosity between 5 and 35 \({}^{\circ}\)C over 100 cycles, and (**b**) particle size distribution before and after 100 cycles. Figure 12: Thermal–mechanical stability test of Parafol 19-90: (**a**) viscosity between 5 and 35 \({}^{\circ}\)C over 100 cycles, and (**b**) particle size distribution before and after 100 cycles. Figure 14 shows the comparison of enthalpy curves determined before and after this test. It is visible that all samples show minor changes in the crystallisation curve except P18-97. P16-97, L17 and P19-90 show slightly but not significantly deeper solidification temperatures after the test that might be an indication of an unstable nucleation seed. P20Z reveals an increase in the phase transition temperatures from a liquid to solid, which could be induced by an increase in particle size. Therefore, in general, it can be stated that those emulsions showing minor changes in the viscosity and in the particle size distribution also revealed minor changes in the phase transition behaviour.