Gradual Morphological Tuning in Polymer Microspheres via Pickering Emulsion Synthesis: Architecture-Controlled Dye Adsorption and Encapsulation

Polymeric microspheres synthesized via Pickering emulsion polymerization offer structural tunability, making them attractive platforms for dye adsorption. This study investigates the adsorption behavior of methylene blue onto two classes of polymeric microspheres— poly(methacrylic acid) crosslinked with ethylene glycol dimethacrylate (PM), containing both micro- and nanopores, and poly(methacrylic acid) crosslinked with divinylbenzene (PD), containing only nanopores. The adsorption kinetics were modeled using a dual-process approach that distinguishes between diffusion-controlled transport and surface-controlled kinetic adsorption. The relative contributions of these two mechanisms were quantified and correlated with particle architecture. In the PM particles, diffusion plays a significant role in smaller particles with larger macropores, enabling methylene blue to penetrate the interior. As the particle size increases and macroporosity decreases, adsorption becomes increasingly dominated by surface kinetics. In contrast, the PD particles, which lack macropores, exhibit a different mechanistic transition: smaller particles are primarily governed by fast surface adsorption, while in larger particles, diffusion through nanopores becomes increasingly relevant. Correlation analysis between adsorption rate constants and structural parameters such as particle diameter and pore sizes revealed strong, opposing trends. In PD particles, a near-perfect inverse correlation was observed between the diffusion and kinetic components, indicating competitive suppression, where the dominance of one mechanism limits the contribution of the other. These results demonstrate that internal pore architecture plays a central role in controlling the adsorption mechanism. By tuning particle size and porosity, one can modulate the balance between diffusion and kinetics, enabling the rational design of microparticle adsorbents with tailored uptake behavior for water purification and dye removal applications.