Dissipative particle dynamics simulations on inversion dynamics of spherical micelles

Area of Science:

• Soft Matter Physics
• Polymer Science
• Computational Chemistry

Background:

• Spherical micelles formed by diblock copolymers are crucial self-assembled structures.
• Understanding the micelle inversion process is key to controlling their morphology and function.
• Previous studies often lack detailed dynamic insights into the intermediate stages of inversion.

Purpose of the Study:

• To simulate and elucidate the dynamic mechanism of spherical micelle inversion in symmetric diblock copolymers.
• To characterize the intermediate morphologies and determine the scaling of inversion time with chain length.
• To explore the influence of block denaturation on the inversion pathway.

Main Methods:

• Dissipative Particle Dynamics (DPD) simulations were employed to model the micelle inversion.
• Analysis included tracking micelle morphology, calculating radius of gyration and hydrodynamic radius.
• A simplified chemical-potential-driven flow model was used for theoretical comparison.

Main Results:

• Micelle inversion proceeds in two distinct stages: rapid lyophobic block agglomeration followed by slow lyophilic block penetration.
• An intermediate structure with a dilute core and dense shell was observed during inversion.
• Inversion time scales with block copolymer chain length (exponent 1.67–1.89), consistent with the flow model.
• Varying denaturation times led to collapsed intermediates or small, loosely associated clusters, not scattered states.

Conclusions:

• The DPD simulations provide a detailed, stage-by-stage mechanism for diblock copolymer micelle inversion.
• The observed scaling law and intermediate structures offer valuable insights for experimental validation, potentially via light scattering.
• The study highlights the robustness of the inversion pathway, forming defined intermediates regardless of initial block denaturation.