## 3 Results and Discussion
When increasing the concentration of carvacrol, the bulk SA did not show any changes in the lattice spacing (which remained d \(\sim\) 4 nm). For both waves (BW and CW), the \"d\" value increased with the increase in monoterne concentration. [PERSON]'s equation (\(2d\)-sin\(\theta=n\lambda\)) was used to determine the interlayer distance (d) in the lipid lattice, where \(\theta\) is the angle of diffraction, \(\lambda\) the wavelength and n the order of the crystalline plane [51]. When compared with the bulk lipid, the increase in the distance with the loading with a drug, anticipates the assumption that the drug molecules are within the lipid lattice. As shown in the patterns of Figure 5, the experimental lattice spacing of bulk stearic acid, beeswax and carnauba wax was, respectively, 4.15 nm, 7.25 nm and 8.50 nm. The mixing with increasing concentrations of carvacrol increased the interlayer spacing of beeswax and carnauba wax, but not of stearic acid. This result anticipates the assumption that both waves would improve the loading capacity (LC) and encapsulation efficiency (EE) of carvacrol in NLCs composed of one of those lipids. The higher the concentration of carvacrol in the wax mixtures, the higher the lamellar spacing and thus the higher the LC and EE. According to [PERSON] et al., the amount of interface (and lamellae) decreases with the increase in the \"d\" value and, thus, increases the spacing between lamellae [50]. This result indicates that carvacrol is most likely to be placed in between the solid lipid lamellae of both waves, increasing the \"d\" value, thus promoting a less ordered structure, which also confirms the DSC results. An amorphous polymorphic form (\(\alpha\)-form) is associated with a less ordered structure of the lipid core, thus also improving both LC and EE [52]. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Samples** & **Melting Peak (\({}^{\circ}\)C)** & **Onset (\({}^{\circ}\)C)** & **Width of Melting Event 1 (\({}^{\circ}\)C)** \\ \hline Bulk SA & 57.0 & 37.0 & 28.0 \\ SA 10\% & 56.5 & 36.0 & 29.0 \\ SA 25\% & 54.9 & 34.3 & 30.0 \\ SA 50\% & 50.2 & 34.0 & 30.0 \\ Bulk BW & 63.0 & 55.8 & 32.6 \\ BW 10\% & 61.4 & 50.0 & 32.7 \\ BW 25\% & 58.5 & 48.1 & 32.7 \\ BW 50\% & 50.9 & 48.0 & 24.5 \\ Bulk CW & 82.0 & 39.5 & 35.5 \\ CW 10\% & 81.4 & 38.6 & 36.5 \\ CW 25\% & 77.3 & 38.2 & 37.1 \\ CW 50\% & 72.9 & 36.2 & 39.2 \\ \hline \hline \end{tabular} \({}^{1}\) WME, width of the melting event, i.e., difference between endset and onset temperatures.  
\end{table} 
Table 3: Melting peak, onset temperature and width of the melting event of the bulk solid lipids and their binary mixtures with carvacrol obtained by differential scanning calorimetry (see Table 1 for composition). The optical behavior of solid lipids and their mixtures with carvacrol was checked by PLM. Materials can be classified either as anisotropic or as isotropic, depending on the effect that the material causes under polarized light. In the characterization of solid lipids, PLM can be used to observe microstructural changes [35]. Figure 4: Scattering X-ray diffraction patterns _l(q)_ as a function of scattering vector _(q)_ for stearic acid (SA, upper left), beeswax (BW, upper right), carnauba wax (CW, bottom) and their binary mixtures containing 10%, 25% and 50% of carvacrol (see Table 1 for composition). Figure 5: Value of lattice spacing _“d”_ measured by small-angle X-ray scattering of bulk solid lipids (stearic acid, beeswax and carnauba wax) plotted as a function of carvacrol concentration (10%, 25% and 50%). Figure 6 shows the optical micrographs recorded at room temperature of bulk lipids (SA, BW and CW) and their binary mixtures with increased concentration of carvacrol (10%, 25% and 50%). The bulk solid lipids showed highly ordered crystalline microstructures, as previously demonstrated by DSC and SAXS analysis. SA exhibited a needle-shaped structure, while both waves (BW and CW) clearly showed a maltese cross symbol of lamellar structure, confirming the results recorded with SAXS [43].