Counter Anion Type Influences the Glass Transition Temperature of Polyelectrolyte Complexes

Area of Science:

• Materials Science
• Polymer Chemistry
• Physical Chemistry

Background:

• Salt acts as a plasticizer in polyelectrolyte complexes (PECs), affecting their physical, thermal, and mechanical properties.
• Added salt disrupts intrinsic ion pairs in hydrated PECs, lowering their glass transition temperature (Tg).
• The specific influence of counterion type on PEC Tg is not well understood.

Purpose of the Study:

• To investigate the effect of different salt anion types on the Tg of hydrated poly(diallydimethylammonium) (PDADMA)-poly(styrenesulfonate) (PSS) PECs.
• To understand how the chaotropic nature of anions impacts PEC Tg.
• To explore the relationship between ion pairs, water content, and Tg in PECs.

Main Methods:

• Investigated the Tg of hydrated PDADMA-PSS PECs with varying salt anion types (NaCl, NaBr, NaNO3, NaI).
• Analyzed the effect of increasing anion chaotropic nature on Tg.
• Examined the scaling relationship between Tg, intrinsic ion pairs, and water content.

Main Results:

• The Tg of hydrated PECs decreased with increasing chaotropic nature of the salt anion.
• Anion type influenced Tg due to doping level, bound water, water mobility, and polymer interactions.
• Tg followed the scaling of -1/Tg ≈ ln([IP]/[H2O]) across all salt types and concentrations.

Conclusions:

• The Tg of solid-like, hydrated PECs is significantly impacted by the type of salt anion.
• The underlying mechanism of the glass transition in these PECs remains consistent regardless of salt type.
• The study provides a quantitative estimate for the disruption of ion pairs required for glass transition in PECs.