We simulate agglomeration in different fuel cell catalyst ink solutions using Discrete Element Method. Carbon support is modelled as particles in various inks with ionomer and various solvents. The particles interact with particle-pair forces resulting in agglomerate build-up. The classical colloidal theory with van der Waals and electric double layer forces underestimates the ink stability, which motivates the development of a new model of polymer force between particles. The force is activated when there is a bridging of polymer between the carbon black particles, and the strength is dependent on the ionomer interaction with the solvent by the dielectric constant. A critical dielectric constant was defined for which ionomer form a web-like polymer network that increases the ink stability. This modification can explain the trend of the ink stability, and the model can simulate the effect of different solvents on the agglomerate size distribution with good agreement with experimental results. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.