1. NSLS-II Friday Lunchtime Seminar

    "Phase Transition Kinetics of Close-Packed Block Copolymer Micelles"

    Presented by Sangwoo Lee, Rensselaer Polytechnic Institute, Troy, NY

    Friday, February 1, 2019, 12 pm
    NSLS-II Bldg. 743 Room 156

    Hosted by: Ignace Jarrige

    In the past decades, the structures of spherical particle packing have been intensively investigated to understand the origin of materials structures and associated properties. However, despite its equal importance, the phase transformation kinetics of spherical particles has been relatively poorly understood. We investigated close-packed structures of spherical block copolymer micelles induced by rapid cooling of disordered micelles using small angle X-ray scattering experiments conducted at the 11-CMS and 12-SMI lines. We found that depending on the depth of quenching, disordered block copolymer micelles self-assemble into three different close-packed structures: face-centered cubic (fcc), random stacking of hexagonal-close packed layers (rhcp), and hexagonal-close-packed (hcp) structures as the depth of temperature quenching increases. Cooling and heating of these close-packed micelle solutions reveal that the hcp and rhcp structures are long-lasting metastable structures that eventually transform to stable fcc. Close-inspection of the 2D small angle X-ray scattering patterns shows that the formation of these metastable structures is correlated with the size of crystallites. The Laplace pressure is attributed to the origin of the formation of the metastable structures.