Vesicle−Polymer Hybrid Architectures:  A Full Account of the Parachute Architecture

Abstract

We have previously reported that polymerization of styrene in dioctadecyldimethylammonium bromide (DODAB) vesicles leads to so-called parachute-like morphologies where a polymer bead is attached to a vesicle. To learn the constructive principles of these novel polymer colloids, we present here a full characterization study. The dual nature of these particles, combining intrinsic vesicle features with polymer colloid properties, requires characterization methods that address both the morphology (cryo-TEM, AFM, DLS) and the typical vesicle characteristics (micro-DSC, fluorescence techniques, surfactant lysis). It is found that the vesicle characteristics after polymerization are virtually unchanged when compared to the bare vesicles. This observation can be fully accounted for by the putative complete phase separation between polymer and surfactant bilayer matrix. Several methods to release the polymer bead from its parental vesicle are presented. In a second part we investigate the relation between polymerization reaction conditions (i.e., temperature, mode of initiation, molecular weight of the polymer) and the resulting vesicle−polymer hybrid morphology. Unexpectedly, slight modifications in the reaction conditions prove to exert great influence on the produced morphology, resulting in novel vesicle−polymer architectures. It turns out that these variations in morphology are governed by intrinsic vesicle properties. As a general phenomenon, we find that polymerization of styrene in DODAB vesiclesindependent of process parametersinevitably leads to microphase separation between the amphiphilic bilayer matrix and polymer.

A Topology Map for Novel Vesicle-Polymer Hybrid Architectures

“…Additionally, we were able to demonstrate that the phase separation phenomenon in this particular system (DODAB vesicles and polystyrene) is largely independent of process parameters like the molecular weight of the polymer, the initiating chemistry and the polymerization temperature. [11] It could, however, be argued that the expected morphology of polymerization reactions in vesicles would depend on the mutual miscibility of monomer/polymer and surfactant matrix. [3] To investigate the relationship between the chosen surfactant/polymer combination, the applied reaction conditions and the final vesicle±polymer morphology, we performed the present study using a wide variety of polymers and surfactants.…”

“…A similar, albeit less pronounced, behavior has been found for the photopolymerization of styrene in DODAB vesicles at 60 C, i.e., above the phase transition of DODAB vesicles. [11] It is important to note that the DMPC bilayer is visualized here in the so-called rippled phase, [17] P b ¢, just below the main phase transition temperature which gives rise to the faceted contours.…”

Styrene/Maleic Anhydride Macro‐RAFT‐Mediated Encapsulation

“…[6] In attempts to polymerize monomer that is confined within the hydrophobic interior of a vesicle bilayer, van Herk and co-workers found that strongly localized polymerization could occur to form small polymer beads entrapped in the bilayer. [7] The reason for this unexpected behavior was that local initiation of monomer in the bilayer would locally deplete monomer and create a driving force for diffusion towards the site of propagation. This then leads to the growth of a polymer bead at the expense of monomer elsewhere in the vesicle bilayer.…”

Nanostructured Polymers

“…Jung et al have contested this aspect, and in their studies have clearly demonstrated the phase separation of the polymer particle within the vesicular bilayer, forming what they term as ''parachute-like vesicles'' [89]. It is evident that the miscibility of the monomer in the hydrophobic bilayer region does not guarantee the miscibility of the polymer formed and therefore, more often than not one expects that, as the polymerization proceeds, collapse of the polymer chain will occur, leading to nucleation and precipitation of the polymer.…”