Cornucopian cylindrical aggregate morphologies from self-assembly of amphiphilic triblock copolymer in selective media.
ABSTRACT We have investigated, both experimentally and theoretically, the aggregation of ABA amphiphilic triblock copolymers in dilute solution. We observed a number of complex architectures having toroidal and network structures, including some novel ones. The computational analyses of these systems offer some insight into the origins of the self-assembly of these amphiphiles. The results we obtained using real-space self-consistent field theory reveal that the formation of network and toroidal structures from the block copolymers occurs as the result of the breaking of "inhomogeneous vesicles"; the observed polymorphism results from the existence of multiple metastable states.
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ABSTRACT: Self-assembled polymeric aggregates are generally polydisperse in morphology due to the existence of many metastable states in the system. This shortcoming becomes a bottleneck for preparing high quality self-assembled polymeric materials. An important concern is the possibility of controlling morphological polydispersity through the modulation of the metastable states. In this study, both simulative and experimental results show that the metastable states can be modulated. As a typical example, the morphological polydispersity of amphiphilic ABA triblock copolymer vesicles have been successfully controlled by shear flow. A higher shear rate results in more uniform and smaller vesicles. However, if the shear rate is extremely high, small spheres and short rods can be observed. These findings not only give a deeper insight into the metastable behavior of self-assembled polymeric aggregates but also provide a new strategy for improving the uniformity of vesicles.Langmuir 11/2013; · 4.38 Impact Factor
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ABSTRACT: Amphiphilic AB and ABA block copolymers have been demonstrated to form a variety of self-assembled aggregate structures in dilute solutions where the solvent preferentially solvates one of the blocks. The most common structures formed by these amphiphilic macromolecules are spherical micelles, cylindrical micelles and vesicles (polymersomes). Interest into the characterisation and controlled formation of block copolymer aggregates has been spurred on by their potential as surfactants, nano- to micro-sized carriers for active compounds, for the controlled release of encapsulated compounds and for inorganic materials templating, amongst numerous other proposed applications. Research in the past decade has focussed not only on manipulating the properties of aggregates through control of both the chemistry of the constituent polymer blocks but also the external and internal morphology of the aggregates. This review article will present an overview of recent approaches to controlling the self-assembly of amphiphilic block copolymers with a view to obtaining novel micellar morphologies. Whilst the article touches upon multi-compartment micelles particular focus is placed upon control of the overall shape of micelles; i.e. those systems that expand the range of accessible morphologies beyond ‘simple’ spherical and cylindrical micelles namely disk-like, toroidal and bicontinuous micelles.Polym. Chem. 04/2011; 2(5).
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ABSTRACT: The behavior of amphiphilic copolymer chains in a solvent is not the same as that of homopolymers. As an important synthetic biomaterial, poly(ethylene glycol)-b-poly(lactic acid) copolymers are often dissolved in tetrahydrofuran (THF) for study. Few studies have focused on the potential aggregation behavior and compact conformation of the amphiphilic macromolecules in a THF solution. In this study, a series of poly(ethylene glycol)-b-poly(lactic acid) diblock copolymers were synthesized and characterized using fourier-transform infrared spectroscopy, nuclear magnetic resonance, thermogravimetric analysis, and gel permeation chromatography methods. The aggregation behavior of amphiphilic molecular chains in a THF solution was studied using dynamic light scattering and transmission electron microscopy. The results showed that the aggregation size in solutions at a concentration of 2.0 mg/mL is within the range of 50–250 nm. It was further demonstrated that molecular chains exhibit a compact conformation in a dilute THF solution, which leads to a comparatively larger deviation in the characterization of molecular weights using GPC method. Here, a model is proposed to elucidate the dynamic evolution between compact amphiphilic single chains and aggregates. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012Journal of Applied Polymer Science 09/2012; 125(S2). · 1.40 Impact Factor