Deswelling Behavior of Polymer Single-Chain Nanoparticles in Concentrated Solutions and the Resulting Internal Dynamic Heterogeneity

Polymer single-chain nanoparticles (SCNPs) represent a unique class of soft nano-objects, yet their internal dynamics under crowding remain poorly understood. Here, we show that when the polystyrene-based SCNP solutions exceed the critical overlapping concentration ( c * SCNP ), nonuniform deswelling of the SCNPs generates spatially heterogeneous microenvironments, which in turn give rise to two distinct dynamic modes. Intrachain cross-linked polystyrene SCNPs (7% cross-linking degree) were synthesized on the gram scale via an in situ cationic polymerization strategy, and their compact, semiflexible topologies were established through comprehensive structural characterization. Multiangle dynamic light scattering (DLS) measurements reveal a transition from a single relaxation process in dilute solutions to dual relaxation behavior in concentrated regimes: a fast mode corresponding to the cooperative diffusion of chain “blobs” driven by concentration fluctuations, and a slow mode associated with the caged, non-Brownian motion of “blobs” confined within increasingly rigid microdomains. Theoretical analysis, comparison between SCNPs and linear chains, and NMR T 2 relaxation measurements together confirm that this dynamic heterogeneity originates from deswelling-induced variations in local rigidity within individual SCNPs. These findings provide the first experimental demonstration of heterogeneous diffusion dynamics across multiple time scales in concentrated SCNP solutions, highlighting the pivotal role of topological confinement in governing soft nanoparticle behaviors and offering guidance for the rational design of SCNP-based functional materials.