Chemistry

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Science  19 Apr 2002:
Vol. 296, Issue 5567, pp. 431-433
DOI: 10.1126/science.296.5567.431e

Micelles and vesicles form in solution through an interplay of hydrophobic and hydrophilic effects, and their size and shape are highly sensitive to changes in the architecture of the molecules and to small variations in solvent conditions. Most micelles are of the star type, consisting of a thin core surrounded by a thick corona. However, for highly asymmetric triblock copolymers, the reverse occurs, and a large core is surrounded by a thin or “crew-cut” corona. To make these materials, the polymer is dissolved in an organic solvent that accommodates both blocks, and then water is added.

Working with triblock copolymers built on a long polystyrene core and functionalized isoprene end blocks, Riegel et al. have observed a new bowl-shaped morphology that they attribute to the coalescence of bubbles within the micelle, which occurs when the water is added to drive off the solvent. They found that the bowls preferentially formed at higher polymer concentrations and only in solvents that could dissolve both homopolymer materials. A wide dispersion of sizes was seen, indicating that this structure is only kinetically stable and does not represent the equilibrium state.—MSL

Langmuir 10.1021/la015592t (2002).

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