Analysis of Local Free Volume and Hydration in Pharmaceutical Polymer Films Using Positron Annihilation Lifetime Spectroscopy
Year: 2026
Type: article
Abstract: The relationship between the nanoscale free volume of pharmaceutical polymer films and their hydration behavior remains poorly understood. Eight pharmaceutical polymers were screened at three concentration levels within a quality-by-design framework; only two poly(vinyl alcohol) grades (PVA EG-30P and EG-40P), hydroxypropyl cellulose (HPC), and sodium alginate (Na-alginate) formed continuous films. These were characterized by positron annihilation lifetime spectroscopy (PALS), loss on drying (LOD), and swelling analysis. PALS clearly differentiated HPC, Na-alginate, and PVA, whereas the two PVA grades were similar and the concentration had only a minor effect. HPC showed the largest free volume holes (86.7–89.5 Å3), and Na-alginate the smallest holes (36.9–39.6 Å3) together with the highest LOD (20.2–21.6%). Across the 12 polymer–concentration combinations, the free volume hole volume correlated inversely with LOD (Spearman ρ = −0.85) but not with the equilibrium swelling index, as both HPC and Na-alginate swelled considerably more than PVA. Thus, PALS discriminates film-forming pharmaceutical polymers and reflects their residual water content, but the free volume of the air-dried films does not predict their swelling capacity.
DOI: 10.3390/ijms27219518
Institutions: Semmelweis University, Eötvös Loránd University
Language: English
Subfield: Condensed Matter Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $3,499
OpenAlex ID: W7223919466