## 3 Results
### Physicochemical Properties of Cosmetic Oils  
3.2.1. Spreading Properties of Body Oils  
One of the important factors affecting the quality of the final product in the case of cosmetics is their ability to spread on the skin, which, similar to raw materials, depends on the surface tension, dynamic viscosity, and contact angle of the cosmetics [49]. Figure 5 shows the results of testing the surface tension, dynamic viscosity, and contact angle of the developed cosmetic oils.  
There is a significant difference in the results of dynamic viscosity, surface tension, and contact angle between the tested cosmetic oils made according to recipes F1-F3 and F4-F6. Recipes F1-F3, in which the predominant percentage was vegetable oils, were characterized by a significantly higher viscosity (6-10 times) than recipes F4-F6, in which synthetic emollients predominated (Figure 5A). There is also a noticeable difference in the viscosities of the F1-F3 recipes with a high percentage of natural oils. The highest viscosity \(\eta\) = 223.7 mPa\(\cdot\)s is characterized by body oil (F2), which contains 50% castor oil and 30% macadamia nut oil. In formulations F4-F6, with the main share of synthetic emollients,the difference in the dynamic viscosity results was insignificant. \(\eta\) values ranged from 23 to 27 mPa-s.  
Formulations with a predominance of vegetable oils (F1-F3) are characterized by significantly higher contact-angle values (Figure 5C) than formulations with synthetic emollients (F4-F6). The values of contact angles (\(\theta\)) on the PMMA surface for cosmetic oils based on natural oils range from 22.7\({}^{\circ}\) to 25\({}^{\circ}\), while those based on synthetic emollients range from 10.6\({}^{\circ}\) to 14.7\({}^{\circ}\). The lowest value of the contact angle (\(\theta\) = 10.6\({}^{\circ}\)) was recorded for the F4 formulation containing mainly (50%) Dicaprylyl Carbonate and 30% Dibutyl Adipate. However, the highest value of the contact angle (\(\theta\) = 25) was recorded for the F2 formulation containing mostly (50%) castor oil and 30% macadamia nut oil.  
For formulations F1-F3, the surface-tension values (Figure 5B) are higher than for formulations F4-F6, with the highest value of the tested parameter (\(\sigma\) = 32.16 mN/m) characteristic of the cosmetic oil F2. However, the lowest value was observed for F4 body oil and is 25.1 mN/m.  
Figure 4: Three-dimensional clustering of colorimetric parameters of emollients. (**A**)—synthetic/semi-synthetic emollients: CCTG—Caprylic/Capric Triglyceride, DA—Dibutyl Adipate, OD—Octyldodecanol, DC—Dicaprylyl Carbonate; (**B**)—natural emollients: MTSO—_Macadamia Ternifolia Seed Oil_, PADO—_Pruuns Amygdala Dulcis (Sweet Almond) Oil_, RCSO—_Ricinus Communis (Castor) Seel Oil_, VVSO—_Vitis Vinfera (Grape) Seel Oil_.  
Figure 5: Physicochemical properties of body oils. (**A**)—dynamic viscosity, (**B**)—surface tension, (**C**)—contact angle. F1–F3 and F4–F6 specific recipes. For F1–F3, the predominant ingredient was vegetable oils, whereas for F4–F6, the predominant ingredient was synthetic/semi-synthetic emollients, ***-significance level \(p<0.001\), ***-significance level \(p<0.0001\).