## 3 Results and Discussion
### Viscosity of the Binary Mixtures  
A comparison of measured viscosity of pure amines in this study with available data in the literature is given in Table 6. The study shows that measured viscosities agree with literature data with around 3.5% AARD. The measured viscosities of the binary aqueous mixtures are shown in Table 6, Table 6, and Table 7. The mixture viscosity varies with the composition and temperature. For the MDEA + H\({}_{2}\)O mixtures at 293.15 K, a maximum viscosity was observed around \(x_{1}\) = 0.7. The study shows that DEEA + H\({}_{2}\)O mixtures have a maximum viscosity around \(x_{1}\) = 0.36 at 293.15 K and the DMEA + H\({}_{2}\)O mixtures exhibit a maximum viscosity around \(x_{1}\) = 0.38 at 293.15 K. The measured viscosities of aqueous mixtures were compared with viscosities presented by [PERSON] et al. [21], [PERSON] et al. [31], [PERSON] et al. [32], and [PERSON] et al. [33] in the supplementary materials. Figure 3 compares viscosity variations of different aqueous amine mixtures at 293.15 K.  
The viscosity deviation \(\eta^{E}\) or the excess viscosity of the mixtures is calculated as shown in Equation (17). The viscosity of pure H\({}_{2}\)O was taken from [PERSON] et al. [34]. \[\eta^{E}=\eta-\sum_{i=1}^{i=2}x_{i}\eta_{i} \tag{17}\] \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Parameters**} & \multicolumn{6}{c}{**Mixtures**} \\ \cline{2-7}  & \multicolumn{2}{c}{**MDEA (1) + H\({}_{2}\)O (2)**} & \multicolumn{2}{c}{**DMEA (1) + H\({}_{2}\)O (2)**} & \multicolumn{2}{c}{**DEEA (1)+ H\({}_{2}\)O (2)**} \\ \cline{2-7}  & \(a_{0}\) & \(a_{1}\) & \(a_{0}\) & \(a_{1}\) & \(a_{0}\) & \(a_{1}\) \\ \hline \(A_{0}\) & 0.3054 & \(-6.25\times 10^{-4}\) & 0.2197 & \(-9.27\times 10^{-4}\) & 0.2491 & \(-11.42\times 10^{-4}\) \\ \(A_{1}\) & \(-0.4206\) & \(8.48\times 10^{-4}\) & \(-0.3892\) & \(12\times 10^{-4}\) & \(-0.4277\) & \(14.91\times 10^{-4}\) \\ \(A_{2}\) & 0.4459 & \(-9.12\times 10^{-4}\) & 0.3690 & \(-10.5\times 10^{-4}\) & 0.5542 & \(-17.69\times 10^{-4}\) \\ \hline AARD (\%) & 0.1 & & 0.03 & & 0.04 \\ AMD (kg\(\cdot\)m\({}^{-3}\)) & 3.0 & & 1.5 & & 2.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Temperature dependency of the Redlich–Kister coefficients (\(A_{i}\)) for the density deviation \(ln(\rho_{\gamma})\) of different aqueous amine mixtures. According to [PERSON] and [PERSON] [35], the viscosity of a mixture strongly depends on the entropy of the mixture that is related to the liquid's structure and bond enthalpy and consequently with the intermolecular interactions between components in the mixture [36]. Hence, viscosity deviation is attributed to the difference in size and shape of the component molecules and molecular interactions between unlike molecules such as H-bonds (strong interactions) and dispersion forces (weak interactions). The value of \(\eta^{\rm E}\) becomes positive due to the presence of strong interactions like H-bond formation [37] and \(\eta^{\rm E}\) is negative where the weak interactions (weak dipole and dispersion forces) are dominant [37; 38]. The semiempirical model suggested by [PERSON] and [PERSON] [39] can be adopted to interpret the strength of the molecular interactions between components in a binary mixture [37]. The model is