## 3 Results and Discussion
### Wetting Properties of the Canola Oil Mixture with n-Hexane and Ethanol  
The surface tension of the mixture of canola oil with n-hexane and ethanol plays an important role in the wetting process, which has also influence on the potential application of canola oil as a diesel fuel. Therefore, the contact angle of the studied mixtures on polytetrafluoroethylene (PTFE) and engine valve was measured (Figures 10-12). The contact angle of the canola oil and n-hexane mixture contacted with ethanol on the PTFE and engine valve surface decreases as a function of n-hexane concentration. This decrease is larger than for the canola oil with the n-hexane in the absence of ethanol. The contact angle of ethanol being in the contact with the canola oil and n-hexane mixture also decreases as a function of n-hexane concentration. The contact angle of the canola oil with n-hexane mixture being in contact with ethanol on the engine valve is small and decreases with the n-hexane concentration. It should be stressed that similarly to viscosity there is no linear dependence between the contact angle of the canola oil, n-hexane and ethanol mixture and the composition of the mixture. The decrease in the contact angle as a function of the n-hexane concentration is larger than it results from the values of the canola oil, n-hexane and ethanol surface tension. This indicates that the composition of the surface layer is different from that of the bulk phase. Figure 10: The plot of the contact angle (\(\theta\)) for the canola oil + n-hexane + ethanol mixture on PTFE vs. the n-hexane concentration (\(C_{p}\)). The value of the contact angle on the surface of the given solid depends not only on the total surface tension of liquid and solid but also on the components and parameters of this tension. This dependence results from the Young equation and the approaches to the interface tension proposed by [PERSON] et al. and/or [PERSON] and [PERSON] [27; 48; 49]. The Young equation has the following form [50]:  
\[\gamma_{SV}-\gamma_{SL}=\gamma_{LV}\cos\theta \tag{8}\]  
where \(\theta\) is the contact angle. The subscripts SV, SL and LV refer to the solid-air, solid-liquid and liquid-air interface tension, respectively. Introducing Equation (4) to Equation (8) we obtain the following [27]:  
\[\gamma_{LV}(\cos\theta+1)=2\sqrt{\gamma_{LV}^{\text{LW}}\gamma_{SV}^{\text{LW} }}+2\sqrt{\gamma_{LV}^{+}\gamma_{SV}^{-}}+2\sqrt{\gamma_{LV}^{-}\gamma_{SV}^{ +}} \tag{9}\]  
If the surface tension of solid and liquid results from the Lifshitz-van der Waals interactions, then Equation (9) assumes the form:  
\[\gamma_{LV}(\cos\theta+1)=2\sqrt{\gamma_{LV}^{\text{LW}}\gamma_{SV}^{\text{ LW}}} \tag{10}\]  
Figure 11: The plot of the contact angle (\(\theta\)) of the ethanol phase contacted with canola oil + n-hexane mixture vs. the n-hexane concentration (\(C_{p}\)). Figure 12: The plot of the contact angle (\(\theta\)) for the canola oil + n-hexane + ethanol mixture on the engine valve vs. the n-hexane concentration (\(C_{p}\)). From Equations (5) and (8) we obtain the following results [49]:  
\[\gamma_{LV}(\cos\theta+1)=2\sqrt{\gamma_{LV}^{a}\gamma_{SV}^{a}}+2\sqrt{\gamma_{ LV}^{p}\gamma_{SV}^{p}} \tag{11}\]  
and/or liquid surface tension results from only dispersion interactions [26]:  
\[\gamma_{LV}(\cos\theta+1)=2\sqrt{\gamma_{LV}^{a}\gamma_{SV}^{a}} \tag{12}\]  
Taking into account the contact angle values of the canola oil with n-hexane and the ethanol phase on PTFE and their surface tension as well as that of PTFE (20.24 mN/m) [25] the values of \(\gamma_{LV}^{LW}\) and \(\gamma_{LV}^{a}\) were calculated from Equations (10) and (12), respectively. In fact, the \(\gamma_{LV}^{LW}\) values are equal to \(\gamma_{LV}^{a}\) and they are different only by the definition if they are determined from the contact angle of liquid or solution on the apolar solids surface whose surface tension results from only apolar interactions.