## 3 Results
### Density and Viscosity
[PERSON] and [PERSON] [43] proposed an equation based on a parameter:  
\[ln\eta=x_{1}ln\eta_{1}+x_{2}ln\eta_{2}+x_{1}x_{2}d \tag{10}\]  
The [PERSON] [44] equation with two parameters is:  
\[ln\eta=x_{1}ln\eta_{1}+x_{2}ln\eta_{2}+x_{1}lnM_{1}+x_{2}lnM_{2}-ln(x_{1}M_{1} +x_{2}M_{2})+x_{1}x_{2}[\alpha_{12}+\alpha_{21}(x_{1}-x_{2})] \tag{11}\]  
By the application of the [PERSON] [45] equation, viscosity of the binary mixtures can be expressed as:  
\[\ln(\eta V)=x_{1}\ln(\eta_{1}V_{1})+x_{2}\ln(\eta_{2}V_{2})+x_{1}\ln\left(x_{ 1}+x_{2}\frac{V_{2}}{V_{1}}\exp\left(-\frac{\lambda_{12}}{RT}\right)\right)+x _{2}\ln\left(x_{2}+x_{1}\frac{V_{1}}{V_{2}}\exp\left(-\frac{\lambda_{21}}{RT} \right)\right) \tag{12}\]  
[PERSON] and [PERSON] [46] proposed the following semi-empirical equation:  
\[\ln(\eta V)=x_{1}\ln(\eta_{1}V_{1})+x_{2}\ln(\eta_{2}V_{2})+x_{1}x_{2}\left[ \frac{w_{12}}{x_{2}+x_{1}\exp\left(-\frac{w_{21}}{RT}\right)}+\frac{w_{21}}{x _{1}+x_{2}\exp\left(-\frac{w_{21}}{RT}\right)}\right] \tag{13}\]  
The Eyring-NRTL [47] correlative model is given by the relation:  
\[\ln(\eta V)=x_{1}\ln(\eta_{1}V_{1})+x_{2}\ln(\eta_{2}V_{2})+x_{1}x_{2}\left[ \frac{\tau_{21}\exp(-\alpha\tau_{21})}{x_{1}+x_{2}\exp(-\alpha\tau_{21})}+ \frac{\tau_{12}\exp(-\alpha\tau_{12})}{x_{2}+x_{3}\exp(-\alpha\tau_{12})}\right] \tag{14}\]  
In these equations \(\eta\), and \(\eta_{1}\), \(\eta_{2}\) are the dynamic viscosities of the liquid mixtures and of the pure components 1 and 2, \(x_{1}\), \(x_{2}\) are the mole fractions, \(M_{1}\), \(M_{2}\) are the molecular masses, \(V\) is the molar volume of the mixtures, \(V_{1}\) and \(V_{2}\) are the respective molar volumes of the pure components, \(T\) is the temperature, \(R\) is the gas constant; \(d\), \(\alpha_{12}\), \(\alpha_{21}\), \(\lambda_{12}\), \(\lambda_{21}\), \(w_{12}\), \(w_{21}\), \(\tau_{12}\) and \(\tau_{12}\) are interaction parameters (viscosity coefficients) and reflect the non-ideality of the systems. The Eyring-NRTL equation has three parameters, including \(\alpha\), which is a measure of non-ideality of the systems, considered here to be fixed at 0.20 [48]. The parameters were estimated using the experimental viscosity data and a non-linear regression analysis employing the Levenberg-Marquardt algorithm [42]. The ability of these models to correlate viscosity data was tested by calculating the average absolute deviation (\(ADD\%\)), between the experimental and calculated values, using the equation:  
\[ADD\%=\frac{100}{m}\sum_{i=1}^{m}\left|\frac{\eta_{exp}-\eta_{cal}}{\eta_{exp}} \right|_{i} \tag{15}\]  
where \(n\) is the number of experimental data points. The presented data in Table A3 show that, for the DEG + DMSO system, ADD% values of maximum 2% are obtained for the Grunberg-Nissan and Noda-Ishida equations, and for the MDEA + DMSO system, the ADD% values for the two equations are very high (10%). For the Heric-Brewer equation, ADD% values of maximum 1.5% are obtained for the DEG + DMSO system and of maximum 6.0% in the case of the system formed by MDEA and DMSO. Approximately the same values are obtained for the Wilson equation. The Eyring-NRTL equation presents the best results, with ADD% values of maximum 0.8% for the DEG + DMSO system and maximum 3.3% for the MDEA + DMSO system. The higher ADD% in the MDEA + DMSO system than in the DEG + DMSO system can be attributed to higher deviation of the system from ideality. The obtained ADD% values lower than 5% are regarded to be acceptable for engineering calculations [49].