Close-packed block copolymer micelles induced by temperature quenching.

Area of Science:

• Materials Science
• Soft Matter Physics
• Crystallography

Background:

• Close-packed structures of uniform spheres are common in various materials like elements and colloidal assemblies.
• Controlled formation of specific symmetries in self-assembled spherical particles remains a challenge.

Purpose of the Study:

• To investigate the ordering of spherical block copolymer micelles induced by rapid temperature changes (quenching).
• To understand the formation and stability of different close-packed structures (fcc, rhcp, hcp) as a function of quench depth.

Main Methods:

• Utilized rapid temperature changes (quenching) to induce self-assembly and ordering of block copolymer micelles.
• Employed time-resolved scattering experiments to monitor structural transitions.
• Analyzed the stability and transformation pathways of the formed close-packed structures.

Main Results:

• Quenching induced three distinct close-packed structures: face-centered cubic (fcc), random stacking of hexagonal-close-packed layers (rhcp), and hexagonal-close-packed (hcp).
• The induced hcp and rhcp structures were metastable, transforming to fcc upon heating or cooling, indicating they are intermediate states.
• Time-resolved scattering confirmed rhcp structures do not arise from rapid growth of competing structures.

Conclusions:

• Metastable hcp and rhcp structures are likely stabilized by small crystal grain sizes and Laplace pressure.
• Observed transitions (hcp to rhcp to fcc) demonstrate Ostwald's rule in the crystallization of uniform spheres.
• This work provides controlled access to non-cubic close-packed structures in self-assembled systems.