Biopolymer mimicry with polymeric wormlike micelles: Molecular weight scaled flexibility, locked-in curvature, and coexisting microphases

Giant and stable wormlike micelles formed in water from a series of poly(ethylene oxide) (PEO)-based diblock copolymer amphiphiles mimicked the flexibility of various cytoskeletal filaments. The worm diameter (d) was found by cryo-transmission electron microscopy to scale with the length of the hydrophobic chain (N-h) of the copolymer as d similar to N-h(0.61). By fluorescence video imaging of worm dynamics, we also showed that the persistence length (l(P)) of wormlike micelles scaled as l(P) similar to d(2.8), consistent with a fluid aggregate (similar tod(3)) rather than a solid rod (similar tod(4)). By polymerizing the unsaturated bonds of assembled copolymers, fluid worms were converted to solid-core worms, extending the bending rigidity from that of intermediate filament biopolymers to actin filaments and, in principle, microtubules. Through partial crosslinking, polymerized worms further locked in spontaneous curvature at a novel fluid-to-solid percolation point. The dynamics of distinct, branched conformations were also imaged for recently discovered Y-junctioned wormlike micelles composed of diblocks of high molecular weight ( > 10-15 kg/mol). Finally, block copolymers of hydrophilic weight fraction close to the transition between a vesicle- and worm-former assembled into both structures, allowing encapsulation of wormlike micelles in giant vesicles reminiscent of cytoskeletal filaments enclosed within cells. (C) 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 168-176, 2004.