Swelling-Controlled Polystyrene Colloids for Structurally Stabilized UVA Absorber Loading

 Organic UV absorbers provide efficient and selective protection in the UVA region but are often plagued by thermodynamic instability, such as unwanted crystallization, localized phase separation, and rapid molecular leaching, especially at high loading levels. Here, we present a swelling-controlled polystyrene (PS) colloidal platform that nanoscale-confines a hydrophobic UVA absorber within a rigid polymer matrix, enabling robust structural stabilization without any chemical modification.

 Monodisperse PS seed particles are systematically transformed into swollen colloids through a precision swelling-fixation process. This approach allows us to fine-tune the internal free volume of the polymer matrix while preserving strict particle uniformity. As a model hydrophobic molecule, diethylamino hydroxybenzoyl hexyl benzoate(DHHB) is successfully incorporated into the swollen PS matrix. We systematically investigate the thermodynamic and kinetic boundaries of this loading process, elucidating how the degree of matrix swelling governs particle morphology, internal loading efficiency, and subsequent colloidal dispersion stability.

 The resulting DHHB-loaded PS colloids preserve the intrinsic UVA absorbance characteristics of DHHB while exhibiting durability. By decoupling molecular loading from colloidal phase stability, this swelling-controlled platform offers a promising strategy for stabilizing hydrophobic functional cargos and provides a general material design rule for durable colloidal carrier systems.