Ionomers are a class of materials consisting of a polymer matrix with ionic groups dispersed throughout their structure. These ionic groups, usually in the form of metal cations, play an important role in the unique properties exhibited by ionomers. An important variant of ionomers is ionomer dispersion, in which the polymer matrix is dispersed as a colloidal suspension in a liquid medium. This dispersion form provides additional advantages in handling, processing, and application.
Ionomers (dispersions) are used in a wide range of industries due to their excellent properties, such as superior adhesion, high clarity, and improved toughness. Their dispersion properties allow them to be easily incorporated into coatings, films, adhesives, and other formulations, making them versatile materials.
Fig. 1 The monomeric unit of the Nafion ionomer. (Ji Hye Lee, et al., 2015)
Classification of Ionomers (Dispersions)
Dispersions can be broadly categorized into two main groups based on their function:
Functional dispersions are systems of ionomers in which ionic groups actively participate in chemical reactions or interactions. Cation- or anion-exchange dispersions are prime examples of functional dispersions, as they can exchange various cations or anions, respectively. The reactive nature of functional dispersions allows cross-linking, which enhances the mechanical properties and stability of the resulting material.
- Non-functional (Inert) Dispersions
Non-functional or inert ionomer dispersions do not actively participate in chemical reactions or interactions. They are not ionically functional and therefore cannot exchange ions. These dispersions are primarily used as additives or modifiers in formulations to improve specific properties.
Polytetrafluoroethylene dispersions are a good example, and their primary function is to provide binding sites for the catalyst particles, provide hydrophobicity to remove by-product water and regulate the porosity of the portion they have.
Ionomers (Dispersions) Applications
Dispersions have a wide range of applications in various industries. Some notable applications include:
Preparing catalyst slurries with the right dispersions will increase the ionic conductivity of the catalyst layer to achieve high performance.
Fig. 2 The catalyst layer structure of anion exchange membrane fuel cells can be tailored by controlling the size of ionomer aggregates in the dispersion. (Jonghyun Hyun, et al., 2022)
- Specialty Films and Sheets
Dispersions enable the fabrication of specialty films and sheets with specific properties, such as optical clarity, gas barrier properties, and impact resistance. They can be used to prepare mechanically enhanced films that are self-supporting.
The unique adhesive properties of ionomer dispersions make them ideal for use as adhesives and sealants, for example, to immobilize catalyst particles on the surface of a gas diffusion layer or the surface of a membrane. During the evaporation of the catalyst ink solvent, microporous structures are left behind, which help to carry gaseous or liquid reactants to the catalyst layer or facilitate the removal of the resulting gaseous by-products from the catalyst layer.
Ionomer dispersions are used as binders or additives in coatings and paints to improve adhesion, chemical resistance, and film formation. They are particularly suitable for demanding applications that require excellent adhesion to different substrates, such as automotive, metal, and packaging coatings.
References
- Ji Hye Lee, et al. Dispersion-Solvent Control of Ionomer Aggregation in a Polymer Electrolyte Membrane Fuel Cell[J]. Scientific Reports, 2018.
- Jonghyun Hyun, et al. Tailoring Catalyst Layer Structures for Anion Exchange Membrane Fuel Cells by Controlling The Size of Ionomer Aggreates in Dispersion[J]. Chemical Engineering Journal, 2022.
Home