Freezing-Induced Modulation of Molecular Motion and Self-Assembly in the Water/Dimethyl Sulfoxide/Polyoxyethylene...

Freezing of multicomponent aqueous systems generates pronounced compositional gradients and interfacial heterogeneity that strongly influence molecular dynamics and self-assembly. Here, we investigate the effects of ice formation on molecular motion and micellar organization in a water/dimethyl sulfoxide (DMSO)/polyoxyethylene (20) oleyl ether (C18:1EO20) system by combining solution-state nuclear magnetic resonance (NMR) and small-angle X-ray scattering (SAXS). Spin-spin relaxation (T2) measurements show that cooling progressively suppresses molecular mobility of ethylene oxide (EO) moieties and alkyl chains, while the coexistence of ice at - 20 °C induces an additional reduction of their T2 values compared with unfrozen conditions of equivalent solvent composition. Nuclear Overhauser effect spectroscopy (NOESY) further reveals spatial correlations between the EO chains and DMSO molecules exclusively under freezing conditions, indicating freezing-induced localization of DMSO in the vicinity of the micellar corona. SAXS analysis demonstrates that the core-shell micellar structure of C18:1EO20 is largely preserved upon freezing, whereas the effective hard-sphere volume fraction increases markedly. Taken together, these results show that ice formation modifies molecular dynamics and local organization in micellar solutions through interfacial effects that cannot be explained solely by cooling or bulk concentration changes. This combined NMR-SAXS approach provides a molecular-level framework for elucidating freezing-induced reorganization processes in the frozen soft-matter systems.