Onion-like morphology

Addition of a graft copolymers is much less frequent. Some blends of this type were reported to have unusual onion-like morphology. This observation is not universally valid — the com-patibilizing effect must depend on the structure and composition of the copolymer. Owing to complexity of the these structures the theoretical analysis has not been attempted. 

Transmission electron microscope (TEM) analysis of nanostructured carbon films shows that, at this scale, the morphology is reminiscent of the precursor clusters. TEM micrographs show the presence of an amorphous matrix with small closed shell particles and bundles of graphene sheets (Figure 2.4a). Large onion-like and tubular particles have also been observed. 

The vesicle family also has a wide range of morphological variations such as simple vesicles with a hydrophobic membrane and hydrophilic corona as shown in Figure 7, onion-like vesicles, elongated tubular vesicles, large compound vesicles, genus vesicles, perforated vesicles with a highly folded membrane, and flower-like vesicles. 

Fig. 8 Micrographs of vesicles with complex morphology, (a) Small uniform vesicles, (b) large polydisperse vesicles, (c) entrapped vesicles, (d) hollow concentric vesicles, (e) onion-like vesicles and (f) vesicles with tubes in the wall. Reproduced with permission from [36]. Copyright (2001) WILEY-VCH Verlag GmbH, Weinheim, Fed. Rep. of Germany...

Besides the well-known core-shell and inverse core-shell [60], or acorn and Janus morphologies obtained with polymers with similar polarities [33], other interesting structures can be formed. Half-spherical structures are accessible by removing the liquid in acorn structures formed with a polymer and a liquid [40, 61]. Onion-like structures are created from block copolymers, for which the phase separation into lamellae causes layered structures that follows the curvature of the particle where they are confined [37,40,62]. The diameter of the particle is in this case also very important. Indeed, if the particle size is low enough, core-shell or Janus stmctures can be obtained [40]. A large variety of different stmctures were predicted from simulations on diblock copolymer/homopolymer blends [63], star-triblock copolymers in spherical nanopores [64], or on diblock copolymers under different confinements [65-67], among which several have already been prepared... 

R = R = OC12H25, R = H) molecular conformations likely predominate to satisfy the geometrical requirements. The supramolecular disks or columns thus result from the molecular association of two or three dendrimers (depending on the aliphatic chain substitution) in the appropriate conformation, as depicted in Fig. 52 and these columns are packed in a hexagonal lattice. Moreover, considering the diblock, alternated chemical nature of these octopus dendrimers, an onion morphology for the columns is most likely probable (Fig. 53) [264]. 

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