In Situ Investigation of Swelling Dynamics of Acrylamide-Acrylic Acid Superabsorbent Microparticles at a Single Particle Level

Abstract

Investigating the swelling behavior of superabsorbent polymer microparticles (SAP-MPs) at a single-particle level using traditional methods is constrained by low resolution and insufficient real-time data, especially for particles smaller than 300 µm. To address these challenges, a novel microfluidic device capable is developed of real-time, high-precision single-particle analysis. This platform hydrodynamically traps individual SAP-MPs, enabling continuous monitoring of their swelling dynamics under controlled conditions. SAP-MPs with varying sizes (90–270 µm), crosslinker concentrations (0.25%<Cr<2%), neutralization degrees (50%<ND<100%), and acrylic acid concentrations (10%<AA<90%) are synthesized via inverse suspension polymerization and systematically studied using the response surface method (RSM). Kinetic modeling revealed the dominance of the pseudo-first-order (PFO) model over the pseudo-second-order (PSO) model in describing diffusion-driven swelling dynamics. The PFO model demonstrated superior predictive accuracy (R²>0.98) and minimal equilibrium volumetric swelling ratio deviations (ΔVSR_eq<4%), confirming diffusion as the primary swelling mechanism, particularly for smaller particles. Smaller SAP-MPs exhibited enhanced performance, with VSR_eq of ≈140 m³/m³—40% higher than their larger counterparts—and swelling rates (SR) up to 10 m³ m⁻³·s. This study establishes microfluidics as a transformative tool for single-particle characterization and provides insights into engineering hydrogels tailored for advanced applications in drug delivery, tissue engineering, and environmental sensing.