Melting enthalpies

This method is used to locate phase transitions via measurements of the endothennic enthalpy of phase transition. Details of the teclmique are provided elsewhere [25, 58]. Typically, the enthalpy change associated with transitions between liquid crystal phases or from a liquid crystal phase to the isotropic phase is much smaller than the melting enthalpy. Nevertheless, it is possible to locate such transitions with a commercial DSC, since typical enthalpies are... 

The melting temperature is a function of the melting enthalpy and entropy ... 

A suitable phase change temperature and a large melting enthalpy are the requirements that have always to be met by a PCM. However, there are more requirements that have to be met for most, but not all applications. These are Physical requirements ... 

For applications where the melting point of water at 0 °C is not useful, different material classes have been investigated in the past. Figure 103 shows the typical range of melting enthalpy over melting temperature for the most promising material classes. 

Figure 103. Classes of materials that can be use as PCM with regard to their typical range of melting temperature and melting enthalpy (graph ZAE Bayern)...

Organic materials, as Figure 103 shows, cover a smaller temperature range from about 0 °C to 150 °C. They include mainly paraffins, fatty acids and sugar alcohols. In most cases, their density is smaller than 1 g/cm3. Thus paraffins and fatty acids usually have smaller melting enthalpies per volume than inorganic materials. They tend to be more expensive, but usually do... 

Figure 20.4 The melting temperature ( ) and melting enthalpy ( ) as a function of PEN content for the PEN/PET blends...

Fig. 54. Melting enthalpies of cyclohexane detected in cyanurates cured with various amounts of cyclohexane at T=80 °C...

The melting enthalpy related to the sample mass, represented by the area of this melting peak, increases nearly Hnearly with increasing amount of solvent once phase separation has occurred (Fig. 54). The appearance of such a melting peak has also been observed for cyclohexane-modified epoxies prepared with more than 20 wt % cyclohexane, having domain sizes larger than around 5 pm and a volume fraction of higher than around 13%. 

This equation shows that a high melting temperature is obtained by raising the melt enthalpy AH and/or a lowering of the melt entropy AS. Since and... 

DSC has also been used to evaluate interactions with incorporated drngs. These interactions can be reflected in changes of the melting and recrystallization temperatures or in differences in melting enthalpy [52,68,81]. Direct evidence of the... 

The melting temperature and melting enthalpy are, however, unchanged under poling and are only slightly affected by crystallization conditions since the influence of the preparation conditions is lost during the Curie transition. It is noteworthy that the enthalpy at the Curie transition Ah (up) increases with the... 

Fig. 10. Dependence of the ratio (melting enthalpy)/(Curie enthalpy), Ahm/Ahc, with VF2 mole fractions in %...

The mechanical and thermal properties of a range of poly(ethylene)/ poly(ethylene-propylene) (PE/PEP) copolymers have been examined by Mohajer et al. (1982). They studied the effect of variation of composition and copolymer architecture on the polymer properties by synthesizing a range of PE-PEP-PE and PEP-PE-PEP triblocks and PE-PF.P diblocks with high molecular weights (M > 200 kg mol (.The crystallinity, density and melting enthalpy for all copolymers were found to be linearly dependent on the PE content, indicating microphase separation of PE and rubbery PEP in the solid state. The... 

Figure 1 Melting enthalpy of bulk fat and emulsified fat of ice cream mix with (+E) and without (-E) emulsifier after cooling at 5°C measured by DSC.

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