Exploring the influence of coalescing agents in waterborne epoxy amine coatings through thermal and electrochemical characterization

Waterborne (WB) epoxy-amine coatings rely on the incorporation of coalescing agents to achieve proper film formation, yet their specific roles in the thermal evolution, curing behavior, and barrier performance of these systems remain insufficiently understood. In this study, four coalescing agents, including propylene glycol (PG), dipropylene glycol n-butyl ether (DPnB), ethylene glycol butyl ether (EGBE), and butyl glycol acetate (BGA), were incorporated at concentrations ranging from 0.5 to 25 wt% (based on binder solids) to systematically investigate their influence on film formation and coating performance. Differential scanning calorimetry (DSC) of the as-dried base component was used to determine the glass transition temperature (T g ) associated with minimum film forming temperature (MFFT) behavior, while DSC of fully cured films was used to evaluate network development and residual plasticization. Electrochemical impedance spectroscopy (EIS) was performed to evaluate water uptake, dielectric properties, and barrier performance as a function of coalescent type and loading. In addition, an EIS-based two-electrode sensor configuration was used to monitor impedance and capacitance continuously during the transition from wet coating to a fully cured film. The results show that coalescent physicochemical properties strongly influence both film formation dynamics and final barrier performance. Moderate coalescent additions improved particle deformation and coating impedance, whereas excessive loading increased water uptake and reduced coating resistance due to residual plasticization. Among the investigated systems, PG showed minimal long-term plasticization and favorable barrier properties at low concentrations, while DPnB exhibited pronounced concentration-dependent effects associated with higher retention in the polymer phase.