Solid-Surface Micellization of Pluronic P123 on Silica Particles by Mechanochemical Processing and Hydration-State Engineering

Understanding the micellization state of Pluronic P123 immobilized on silica particles is important for applications in detergency, cosmetics, foods, and biomedical fields. The micellization behavior strongly depends on the hydration states of the poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) chains constituting P123. Although previous studies have mainly focused on aqueous solutions, the micellization state of P123 immobilized on solid surfaces through mechanochemical processing remains poorly understood. In this study, Pluronic P123 was immobilized on chlorine-containing silica particles (CS) by a solid-state mechanochemical method, and the micellization state based on the hydration behavior of P123 on the solid surface was evaluated using 1-pyrenecarboxylic acid (1PCA) as a photoluminescence (PL) probe molecule. First, P123 was immobilized on the CS modified with phosphate and sodium ions by a mechanochemical method. The immobilized amount of P123 increased with increasing feed weight concentration of P123, and FE-SEM observations revealed that the interparticle voids between the CS were gradually filled. Subsequently, the hydration state of P123 was evaluated from the FT-IR spectra, demonstrating that the proportion of hydration water associated with PPO chains decreased with increasing immobilized amount of P123, whereas that associated with PEO chains increased. These results suggested the formation of P123 micelles on the CS surface, accompanied by enhanced hydrophobic interactions among the PPO chains. Furthermore, PL properties were evaluated after introducing 1PCA via a solid-state mechanochemical method, and the PL intensity derived from the monomer state of 1PCA markedly increased with increasing immobilized amount of P123. This behavior was attributed to the encapsulation of 1PCA within P123 micelles and stabilization of the monomer state through hydrophobic interactions with PPO chains. Consequently, the use of 1PCA as a PL probe enabled discussion of the micellization state of P123 on the CS surface through its hydration state.