The aqueous self-assembly behavior of polydisperse poly(ethylene oxide-b-1,4-butadiene-b-ethylene oxide) (OBO) macromolecular triblock amphiphiles is examined to discern the implications of continuous polydispersity in the hydrophobic block on the resulting aqueous micellar morphologies of otherwise monodisperse polymer surfactants. The chain length polydispersity and implicit composition polydispersity of these samples furnishes a distribution of preferred interfacial curvatures, resulting in dilute aqueous block copolymer dispersions exhibiting coexisting spherical and rod-like micelles with vesicles in a single sample with a O weight fraction, w O , of 0.18. At higher w O = 0.51−0.68, the peak in the interfacial curvature distribution shifts and we observe the formation of only American football-shaped micelles. We rationalize the formation of these anisotropically shaped aggregates based on the intrinsic distribution of preferred curvatures adopted by the polydisperse copolymer amphiphiles and on the relief of core block chain stretching by chain-length-dependent intramicellar segregation. M anipulating the micellar aggregate morphologies adopted by amphiphilic block copolymers (ABCs) in aqueous media is a fundamental problem in self-assembly, which has critical implications for the applications of these materials. Comprised of at least one hydrophobic segment covalently linked to a water-soluble polymer block, macromolecular amphiphiles self-assemble in water to form spherical and worm-like micelles and vesicles, depending on their overall degree of polymerization (N) and their specific chemical compositions. 1,2 By virtue of their vanishingly small critical micelle concentrations, ABCs form persistent aggregates with more complex morphologies than their small-molecule congeners. 3,4 Persistent worm-like micelles and their branched variants are known to entangle in aqueous solutions, resulting in viscoelastic fluids useful in personal care products and in enhanced oil recovery. 5−7 Spherical micelles and vesicles ("polymersomes") exhibit potential in the delivery of chemotherapeutics and peptide-based drugs, albeit with variable efficiencies. 8,9 Recent biological studies indicate that cells uptake high-aspect ratio particles more rapidly than spherical ones, which motivates the quest for ABCs that form persistent and nonspherical shapes as more effective drug delivery vehicles. 10 These examples illustrate the sensitive dependence of the physical properties of aqueous ABC dispersions and their applications on their self-assembly into micellar aggregates exhibiting well-defined shapes and sizes.The search for new methods of controlling the micellar morphologies adopted by ABCs has profited immensely from the development of polymer syntheses that enable delicate tuning of the balance of noncovalent interactions that govern aqueous macromolecular assembly. 11 The preferred equilibrium morphology adopted by the simplest, monodisperse AB diblock or ABA triblock copolymer surfactants may be rationalized in terms ...

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Accurate imaging of nanometer-sized structures and morphologies is essential to characterizing amyloid species formed at various stages of amyloid aggregation. In this report, we examine the effect of different drying procedures on the final morphology of surface-mediated fibrils formed during the incubation period, which may be then mistaken as oligomers or protofibrils intentionally formed in solution for a particular study. AFM results show that some artifacts, such as globules, flake-like structures, and even micrometer-long fibrils, can be produced under various drying conditions. We also demonstrate that one can prevent drying artifacts by using an appropriate spin-coating procedure to dry amyloid samples. This procedure can bypass the wetting/dewetting transition of the liquid layer during the drying process, and preserve the structure of interest on the substrate without generating drying artifacts.

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