Diffusometric Fingerprinting of Geometrically Similar Amphiphilic Molecular Assemblies

Experimental identification of self-assembled surfactant/copolymer nanomorpholgies in their native solution state is a challenging task. Indirect inferences from rheological measurements, cryogenic transmission electron microscopy which subjects fluid samples to invasive thermal/flow deformation cycles, X-ray/neutron scattering and diffusion-ordered NMR spectroscopy have been employed for micelle characterization. The latter relies on the deduction of micelle shapes based on the measurements of diffusion coefficients of the constituent molecules. Identification of geometrically similar, yet topologically distinct assemblies, e.g., a spherical micelle (SM) vs. a unilamellar vesicle (UV), requires the interpretation of diffusivity data based on high-fidelity theoretical/computational analysis. We utilize coarse-grained molecular dynamics simulations of self-assembling triblock copolymers in explicit water (Liu and Sureshkumar, Langmuir, 41, 5083–96 (2025)) to probe the diffusion mechanisms of individual molecules within an SM and a UV of pactically identical diameters. The two structures are clearly differentited by the significantly slower copolymer diffusion within the UV. The role of geometic confinement and the dynamics of copolymer chain configurations which determine the overall diffusion behavior will be discussed.