Quantification of the Effect of an Impurity Addition on the Interaction Between Unlike Molecules in Mixed Liquids: A Theoretical Study

Abstract

The aim of this work is to develop a simple theory to study the effect of the addition of an impurity on the interaction between unlike molecules in mixed liquids. For the viscosity of a binary liquid mixture, the interaction between unlike molecules is quantified by the Grunberg–Nissan constant $d_{{}}^{'}$. When an impurity is added, the ternary system can be considered as quasi-binary. Thus, the interaction between unlike molecules in the presence of an impurity is quantified by a pseudo Grunberg–Nissan constant $d_{\text{p}}^{'}$. Several other quantities are introduced to describe the effect of an impurity addition: the deviation of the Grunberg–Nissan constant, $\delta d_{{}}^{'} = d_{\text{p}}^{'} - d^{'}$, and the relative deviation of the Grunberg–Nissan constant $\left| {{{\delta d_{{}}^{'} } \mathord{\left/ {\vphantom {{\delta d_{{}}^{'} } {d^{'} }}} \right. \kern-0pt} {d^{'} }}} \right|$ A critical concentration, $c_{\text{c}}$, is also introduced, above which the impurity presence affects the interaction between unlike molecules in mixed liquids. The developed approach was applied for specific impurities: neutral polymer, nonelectrolyte, and electrolyte. Thus, the introduced quantities are connected to the impurity characteristics in each liquid and their mixture.