**6. Thermal span adjustment of binary mixture C16/C20**

The study of simple compound made it possible to thermally characterize the different kinds of paraffin likely to be suitable for textile thermoregulation. However, none of them have a sufficiently wide thermal span between 19 and 30°C. Odd n-alkanes appear to be of little interest given the existence of a solid/ solid transition with low energy and a lower enthalpy of solid/liquid phase change than for even n-alkanes. Also, their cost is four times higher than that of even n-alkanes, justifying the fact that these two compounds do not appear to be ideal candidates for this research. Of the remaining three n-alkanes, we focused on the

binary mixture C16/C20, due to their respective melting temperatures on either side of those required for the application. Also, the objective is to obtain a succession of phase transitions, which can be induced by the superposition of crystals of different sizes and the partial miscibility of n-alkanes. It is hoped that all transitions will be

**85**

**Figure 12.**

*Enthalpy variation vs. TEOS content.*

*Phase Change Materials for Textile Application DOI: http://dx.doi.org/10.5772/intechopen.85028*

not suitable for textile application [41–43].

stances and 190 J g<sup>−</sup><sup>1</sup>

ing the thermal span.

contained within a single, relatively large peak. The binary diagrams C16/C18 and C18/C20 presented in Métivaud's work show that solid/solid and solid/liquid transitions occur over relatively narrow and distinct temperature ranges and are therefore

The enthalpy characterization of the C16/C20 mixture in different proportions was performed with 3 mg samples and a temperature ramp of 0.5°C/min, allowing the peaks for the different transitions to be dissociated. All the thermograms relating to this mixture are presented in **Figure 11**. The superposition of the endotherms shows that when one of the compounds is in the majority in the mixture, the thermal phase transition windows are narrow and tend towards those of the alkane fusion in a higher proportion. On the other hand, for mass fractions between 0.3 and 0.7, there is an expansion of the endotherms between 0 and 35°C, implying the appearance of new solid/solid transitions within the material during the temperature rise. The measurement of enthalpies shows that they vary between those of pure sub-

ane/eicosane). Thus, the widening of the thermal window is accompanied by a decrease of about 20% in the total enthalpy of phase changes. This "loss" is related to the increase in the number of solid/solid transitions that are less energetic than solid/liquid transitions. We finally chose the 50/50 mixture, which allowed us to load the material over a

The binary mixture of the two kinds of paraffin disrupts the cohesion of the crystal, which results in a succession of solid/solid transitions inducing the widening of the thermal window and the decrease of the overall enthalpy. Based on this hypothesis, we focused on the introduction into the mixture of a "soluble" charge in any proportion whatsoever in hexadecane and eicosane. We chose tetraethyl orthosilicate. The measurements of the overall enthalpies of the mixture as a function of the charge ratio show that the latter makes it possible to increase the energy balance to values comparable to those of pure substances, then from 4% in weight,

Among the five n-alkanes selected, based on their melting temperatures, the even n-alkanes have a higher enthalpy of phase change and are less expensive. The binary mixing of n-hexadecane with n-eicosane allows the thermal window to widen with a decrease in phase transition enthalpies. The addition of a "miscible" charge in the pre-selected mixture consolidates the energy balance without modify-

larger thermal window observed from 3 to 32°C for enthalpy of 190 J g<sup>−</sup><sup>1</sup>

the enthalpy decreases until reaching its basic level at 20% (**Figure 12**).

, except in the particular case of mixing in a 30/70 ratio (hexadec-

.

**Figure 11.** *Heating and cooling curves of C16/C20 binary mixture at various ratio.*

#### *Phase Change Materials for Textile Application DOI: http://dx.doi.org/10.5772/intechopen.85028*

*Textile Industry and Environment*

binary mixture C16/C20, due to their respective melting temperatures on either side of those required for the application. Also, the objective is to obtain a succession of phase transitions, which can be induced by the superposition of crystals of different sizes and the partial miscibility of n-alkanes. It is hoped that all transitions will be

**84**

**Figure 11.**

*Heating and cooling curves of C16/C20 binary mixture at various ratio.*

contained within a single, relatively large peak. The binary diagrams C16/C18 and C18/C20 presented in Métivaud's work show that solid/solid and solid/liquid transitions occur over relatively narrow and distinct temperature ranges and are therefore not suitable for textile application [41–43].

The enthalpy characterization of the C16/C20 mixture in different proportions was performed with 3 mg samples and a temperature ramp of 0.5°C/min, allowing the peaks for the different transitions to be dissociated. All the thermograms relating to this mixture are presented in **Figure 11**. The superposition of the endotherms shows that when one of the compounds is in the majority in the mixture, the thermal phase transition windows are narrow and tend towards those of the alkane fusion in a higher proportion. On the other hand, for mass fractions between 0.3 and 0.7, there is an expansion of the endotherms between 0 and 35°C, implying the appearance of new solid/solid transitions within the material during the temperature rise.

The measurement of enthalpies shows that they vary between those of pure substances and 190 J g<sup>−</sup><sup>1</sup> , except in the particular case of mixing in a 30/70 ratio (hexadecane/eicosane). Thus, the widening of the thermal window is accompanied by a decrease of about 20% in the total enthalpy of phase changes. This "loss" is related to the increase in the number of solid/solid transitions that are less energetic than solid/liquid transitions. We finally chose the 50/50 mixture, which allowed us to load the material over a larger thermal window observed from 3 to 32°C for enthalpy of 190 J g<sup>−</sup><sup>1</sup> .

The binary mixture of the two kinds of paraffin disrupts the cohesion of the crystal, which results in a succession of solid/solid transitions inducing the widening of the thermal window and the decrease of the overall enthalpy. Based on this hypothesis, we focused on the introduction into the mixture of a "soluble" charge in any proportion whatsoever in hexadecane and eicosane. We chose tetraethyl orthosilicate. The measurements of the overall enthalpies of the mixture as a function of the charge ratio show that the latter makes it possible to increase the energy balance to values comparable to those of pure substances, then from 4% in weight, the enthalpy decreases until reaching its basic level at 20% (**Figure 12**).

Among the five n-alkanes selected, based on their melting temperatures, the even n-alkanes have a higher enthalpy of phase change and are less expensive. The binary mixing of n-hexadecane with n-eicosane allows the thermal window to widen with a decrease in phase transition enthalpies. The addition of a "miscible" charge in the pre-selected mixture consolidates the energy balance without modifying the thermal span.

**Figure 12.** *Enthalpy variation vs. TEOS content.*
