Wormlike micelles and vesicles prepared from diblock copolymers are attracting great interest for a number of technological applications. Although transmission electron microscopy has remained as the method of choice for assessing the morphologies, fluorescence microscopy has a number of advantages. We show here that when commercially available fluorophores are covalently attached to diblock copolymers, a number of their physicochemical characteristics can be investigated. This method becomes particularly useful for visualizing phase separation within polymer assemblies and assessing the dynamics of wormlike micelles in real time. Near-IR fluorophores can be covalently conjugated to polymers and this opens the possibility for deep-tissue fluorescence imaging of polymer assemblies in drug delivery applications. 1. Introduction In aqueous solution, amphiphilic diblock copolymers can spontaneously self-assemble to form supramolecular morphologies such as spherical and worm-like micelles and vesicles (polymersomes) [1–3]. Due to their unique physico-chemical characteristics these polymeric assemblies have shown potential for various applications such as drug delivery. Wormlike micelles (“worms”) increase the delivered dose of water-insoluble drugs such as Taxol [4, 5], and vesicles (polymersomes) can be used for the encapsulation and delivery of both water-insoluble (Taxol) and water-soluble therapeutics that range from drugs to proteins [6] to siRNA [7]. An understanding of morphologies from amphiphilic diblock copolymers in dilute solution as well as their characteristics would facilitate the generation of even more robust and useful supra-molecular materials. Seminal experiments of Eisenberg and Bates helped to show that classic ideas of surfactant-based morphologies also apply to block copolymers upon varying the relative sizes of the two dissimilar blocks [8, 9]. While such studies used TEM to visualize frozen nano-morphologies, we have emphasized and exploited fluorescence imaging, including the use of dyes covalently conjugated to block copolymers as described here. Fluorescence microscopy helps to clarify many of the unique physical characteristics of polymer assemblies, including the diversity in sizes, shapes, flexibilities and lateral segregation. Fluoroscence microscopy is widely used in cell biology and biophysics for understanding the structure and function of molecules within cells and organelles [10–12]. Although one cannot infer structural information below the diffraction limit, this method nevertheless enables the visualization of spatial
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