## 3 Results
### Excess Properties
#### 3.2.2 Viscosity Deviation  
The viscosity deviation (\(\Delta\eta\)) values were calculated from the experimental data of viscosity using the equation:  
\[\Delta\eta=\eta-(x_{1}\eta_{1}+x_{2}\eta_{2}) \tag{17}\]  
where \(\eta\) is the dynamic viscosity of the mixture, \(x_{1}\), \(x_{2}\) and \(\eta_{1}\), \(\eta_{2}\) are the mole fractions and the dynamic viscosities of pure components 1 and 2, respectively.  
The \(\Delta\eta\) values are shown in Figures 3 and 4. The viscosity deviation values are negative at all investigated temperatures for both systems. The viscosity deviations may be generally explained by considering the following factors: (1) the difference in size and shape of the component molecules and the loss of dipolar association to a decrease in viscosity; (2) specific interactions between unlike molecules, such as H-bond formation, and charge transfer complexes may cause an increase in the viscosity of mixtures rather than in pure components. The former effect produces negative excess viscosity, and the latter effect produces positive excess viscosity [56]. For the DEG + DMSO system, the negative values of viscosity deviation indicate that the strength of specific interactions is not the only factor influencing the deviation in viscosity. The molecular size and shape of the components also play an important role [57]. For these systems the negative values of viscosity deviation indicate that the molecular size and shape of the components is a more important factor than the strength of specific interactions for determining the viscosity deviation.  
The negative values of viscosity deviation for MDEA + DMSO corroborated with positive \(V^{\rm E}\) values demonstrate that there were no strong molecular interactions.  
The values of viscosity deviation decrease with an increase in temperature. An increase in temperature decreases self-association as well as the association between unlike components because of the increase in thermal energy [58].  
The excess molar volumes and viscosity deviation of the binary systems can be represented by the Redlich-Kister [59] (Equation (18)) and Hwang [60] (Equation (19)) equations:  
\[X^{E}=x_{1}x_{2}\sum_{k=0}^{3}a_{k}(2x_{1}-1)^{k} \tag{18}\]  
\[X^{E}=x_{1}x_{2}\Big{(}A_{0}+A_{1}x_{1}^{3}+A_{2}x_{2}^{3}\Big{)} \tag{19}\]  
where \(X^{E}\) represents either of the following properties: \(V^{E}\), \(\Delta\eta\); \(x_{1}\), \(x_{2}\) are the mole fractions of the components 1 and 2, respectively, and \(a_{k}\), \(A_{0}\), \(A_{1}\), \(A_{2}\) denote the polynomial coefficients.  
In addition, the excess molar volumes were also correlated with the Myers and Scott [61] equation:  
\[X^{E}=x_{1}x_{2}\frac{\sum_{k=0}^{p}B_{k}z_{12}^{k}}{1+\sum_{l=1}^{m}C_{l}z_{1 2}^{l}} \tag{20}\]  
where \(X^{E}\) is \(V^{E}\) and \(z_{12}=x_{1}-x_{2}\). \(B_{k}\) and \(C_{l}\) are polynomial coefficients.  
The values of polynomial coefficients are given in Table 1 along with the standard deviation, \(\sigma\), calculated with Equation (9). From the presented data it can be seen that, for both systems, the excess molar volume is best correlated using the Myers and Scott equation. The Redlich-Kister equation shows better results than the Hwang equation for correlating the viscosity deviation for both systems.