Non-Isothermal Nucleation
In the development of the non-isothermal nucleation kinetics by spectrophotometry, the values of TCS, TCO and TC, as well as the cooling ramp used in DSC, were taken as a starting point. Figure 4 shows the kinetics obtained for each system. It can be observed that there is a higher absorbance response in the systems with higher MY concentration (SAT), this as a response to the higher formation of MY crystals (solid fraction). It was also observed that there is a higher absorbance response in CN systems compared to CA. The nucleation kinetics initially present a time interval where the system is completely melted (baseline), followed by an almost exponential growth. The point where the increase from the baseline starts is the beginning of nucleation (García-Andrade et al., 2020). Subsequently, the absorbance values present an almost constant trend (Fig. 4). However, it was found that for the CNMGC system there is a second increase after this usual trend. This was not observed in CNSAT because the high concentration of MY in conjunction with the nature of CN gives higher absorbance values in response, which overlies the second increase. This second increase in absorbance values in the CNMGC system corresponds to the crystallization of the oil, which although it has a high crystallization point, it is at a lower temperature than the crystallization of MY (Fig. 2).
From the graphs shown it was possible to determine the most relevant kinetic and thermal parameters during nucleation (Table 3). Shorter nucleation times were obtained in SAT systems compared to MGC, and consequently, higher nucleation rates (J) were obtained. No significant differences were found between the oil variable with high MY concentrations, however, at MGC, the shortest tn was for CN. Shorter nucleation times have been reported with the use of saturated oils, in systems with high concentrations of structurants (Garcia-Andrade et al., 2020), so it was necessary to evaluate the effect of concentration additionally. The differences observed by oil type in MGC systems may be due to the unsaturation of the oils, and the content of free fatty acids (FFA), since FFA require lower activation energy in the crystallization process with respect to TAGs. These compositional differences may be more representative in systems with low gelator concentrations. Due to the inverse correlation between tn andTn , higher values of Tnand lower values of δ were obtained at shorter times, indicating that a lower thermodynamic inductive force is needed in oleogels with higher MY concentration.
The response exhibited by SAT systems is mainly due to a higher amount of attraction and hydrogen bonding interactions of the amphiphilic molecule with the TAGs of the oil. A higher amount of hydrogen bonds promotes a faster orientation of the polar moiety of the MY by aligning its hydrocarbon chains (attractive and hydrophobic interactions) and generating a faster first solid core (Contreras-Ramírez et al., 2021). Regarding the ΔGn values, the values closest to equilibrium were obtained in the SAT systems. Except for theΔGn values that were smaller with CN oil, no significant differences were found by oil type at SAT concentrations. This is due to a higher interaction of SFA content and high MY concentration.