Solvent-induced glassy-state relaxation behavior in poly(2,5-benzimidazole) (ABPBI) polymer electrolyte membranes investigated by broadband dielectric spectroscopy
Year: 2026
Type: article
Abstract: The molecular dynamics of benzimidazole-based membranes play a vital role in deciding its proton transport behavior and electrochemical performance. Although many studies have focused on the chemical structure and proton conductivity of Poly benzimidazole (PBI) membranes, the effect of polymer membrane casting solvents on sub-glassy relaxation dynamics and their effect on the proton conduction mechanism remains poorly understood. A detailed dielectric investigation over a wide temperature and frequency range that links molecular relaxation processes to charge transport pathways has not yet been reported. In this study, poly(2,5-benzimidazole) (ABPBI) membranes were prepared using the solvent casting method using four chemically distinct solvents, namely methanesulfonic acid, trifluoroacetic acid, formic acid, and sulfuric acid, and investigated using broadband dielectric spectroscopy (BDS) over a broad temperature range (-100–300 °C). The objective of this work is to determine how solvent-assisted membrane fabrication affects the molecular dynamics of sub-glassy relaxations and the connectivity of proton transport pathways. Three secondary relaxations (δ, γ, and β) were distinctly observed in all membranes. The dielectric loss (ε″) curve exhibited increasing relaxation intensity with temperature up to 10⁵ Hz. Membranes produced at higher casting temperatures and with longer casting times exhibited stronger molecular cohesion, reduced chain mobility, and consequently improved thermal and mechanical stability. Wide-angle X-ray diffraction further confirmed differences in polymer chain packing arising from solvent selection. The Havriliak–Negami (HN) model successfully deconvoluted the dielectric response after removing the dc conductivity contribution, enabling the extraction of the connecting parameter (N). A strong correlation between the derived connecting parameter and the experimentally determined proton conductivity confirmed that dielectric relaxation analysis can effectively quantify the connectivity of charge-migration pathways in ABPBI membranes. These observations provide unique insights into the role of solvent engineering in tailoring the molecular dynamics and proton transport characteristics of high-temperature polymer electrolyte membranes.
Source: Next Materials
Language: English
Subfield: Electrical and Electronic Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,280
OpenAlex ID: W7202128751