High-<i>χ</i>, low-<i>N</i> micelles from partially perfluorinated block polymers.

Williams, Eric R; van den Bergh, Wessel; Stefik, Morgan · Soft Matter · 2022

basic_science · Level V

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Abstract

Kinetically trapped ("persistent") micelles enable emerging applications requiring a constant core diameter. Preserving a <i>χN</i> barrier to chain exchange with low-<i>N</i> requires a commensurately higher <i>χ</i><sub>core-solvent</sub> for micelle persistence. Low-<i>N</i>, high-<i>χ</i> micelles containing fluorophobic interactions were studied using poly(ethylene oxide-<i>b</i>-perfluorooctyl acrylate)s (O<sub>45</sub>F<sub><i>X</i></sub>, <i>x</i> = 8, 11) in methanolic solutions. DLS analysis of micelles revealed chain exchange only for O<sub>45</sub>F<sub>8</sub> while SAXS analysis suggested elongated core block conformations commensurate with the contour lengths. Micelle chain exchange from solution perturbations were examined by characterizing their behavior as templates for inorganic materials <i>via</i> SAXS and SEM. In contrast to the F<sub>8</sub> analog, the larger <i>χN</i> barrier for the O<sub>45</sub>F<sub>11</sub> enabled persistent micelle behavior in both thin films and bulk samples despite the low <i>T</i><sub>g</sub> micelle core. Careful measures of micelle core diameters and pore sizes revealed that the nanoparticle distribution extended through the corona and 0.52 ± 0.15 nm into the core-corona interface, highlighting thermodynamics favoring both locations simultaneously.