Colloidal Stability of PFSA-Ionomer Dispersions. Part I. Single-Ion Electrostatic Interaction Potential Energies

Area of Science:

• Colloid and Surface Chemistry
• Electrochemistry
• Materials Science

Background:

• Charged colloidal particles stabilized by single counterions are vital for technologies like hydrogen fuel cells and water electrolyzers.
• Perfluorinated sulfonic acid polymer (PFSA) ionomers in aqueous/alcohol solutions form catalyst layers, stabilized by proton-dissociated diffuse double layers.
• Classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory fails for these single-ion systems due to the absence of added electrolyte.

Purpose of the Study:

• To propose a new theoretical formulation for interparticle interaction potentials in single-counterion colloidal suspensions.
• To investigate the impact of this new model on the size distribution and stability of PFSA ionomer dispersions.
• To provide a general framework for predicting colloidal behavior in ionizing solvents without added electrolytes.

Main Methods:

• Development of a new theoretical model for single-counterion diffuse double layer interactions.
• Application of the new model to predict aggregated size distributions and solution pH of PFSA in n-propanol/water mixtures.
• Analysis of interparticle repulsive forces and osmotic forces in single-ion systems.

Main Results:

• Single-counterion diffuse layers create a non-neutral solvent environment and exert both repulsive and backside osmotic forces.
• The proposed single-ion electrostatic pair potential yields significantly larger repulsive energies than classical DLVO potentials.
• Observed dramatic changes in dispersion behavior, including volume fraction-dependent stability and particle size-dependent stability.

Conclusions:

• The new formulation accurately describes colloidal interactions in single-ion systems, crucial for understanding PFSA ionomer behavior.
• The model predicts unique dispersion characteristics not captured by existing theories, offering insights into material stability.
• This generalized electrostatic pair potential can predict colloidal behavior in various charged particle dispersions within ionizing solvents lacking added electrolytes.