Abstract
In this work we constructed a detailed phase diagram for the solutions of ideal diblock-copolymers and compared such diagram with that obtained during polymerization-induced self-assembly (PISA); a wide range of polymer concentrations as well as chain compositions was studied. As the length of the solvophobic block nB increases (the length of the solvophilic block nA was fixed), the transition from spherical micelles to cylinders and further to vesicles (lamellae) occurs. We observed a rather wide transition region between the spherical and cylindrical morphology in which the system contains a mixture of spheres and short cylinders, which appear to be in dynamic equilibrium; the transition between the cylinders and vesicles was found to be rather sharp. Next, upon increasing the polymer concentration in the system, the transition region between the spheres and cylinders shifts towards lower nB/nA values; a similar shift but with less magnitude was observed for the transition between the cylinders and vesicles. Such behavior was attributed to the increased number of contacts between the micelles at higher polymer volume concentrations. We also found that the width of the stability region of the cylindrical micelles for small polymer volume concentrations is in good quantitative agreement with the predictions of analytical theory. The obtained phase diagram for PISA was similar to the case of presynthesized diblock copolymer; however, the positions of the transition lines for PISA are slightly shifted towards higher nB/nA values in comparison to the presynthesized diblock copolymers, which is more pronounced for the case of the cylinders-to-vesicles transition. We believe that the reason for such behavior is the polydispersity of the core-forming blocks: The presence of the short and long blocks being located at the micelle interface and in its center, respectively, helps to reduce the entropy losses due to the insoluble block stretching, which leads to the increased stability of more curved micelles.
Highlights
Structured block copolymer systems have attracted great attention due to a large number of application areas, including targeted drug delivery systems, nanoreactors, nanolithography, nanostructured membranes and emulsion stabilizers [1]
In this work we performed an extensive study of the micelle formation in solutions of presynthesized monodisperse diblock-copolymers as well as during polymerization-induced self-assembly (PISA) by means of dissipative particle dynamics (DPD) simulations
A wide range of polymer concentrations as well as chain compositions was studied in order to construct comprehensive phase diagrams, and special care was taken in order to ensure that the observed morphologies are in equilibrium
Summary
Structured block copolymer systems have attracted great attention due to a large number of application areas, including targeted drug delivery systems, nanoreactors, nanolithography, nanostructured membranes and emulsion stabilizers [1]. A great advantage of PISA in comparison with the classical method of obtaining micelles from diblock-copolymers prepared in advance is that it is possible to use substantially higher polymer concentrations [1,5]. Two classes of systems can be distinguished: emulsion PISA [2,3,6] and dispersive PISA [7,8,9] In the former case, the monomer is initially insoluble in the selected solvent, so the polymerization takes place in the droplets enriched with it, whereas in the latter case, the incompatibility between the solvent and the solvophobic monomer is not so large, and only its segments of a certain length are insoluble. There are already a number of works on applying PISA in various fields [16], including pharmacology [17,18] and even artificial biology [19]
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