Crew cut

Abstract: Crew-cut micelle-like aggregates of various morphologies prepared from polystyrene-b-poly(acrylic acid), PS-b-PAA, diblock copolymers under near-equilibrium conditions, were studied by transmission electron microscopy (TEM). The insoluble block (PS) contents in the copolymers ranged from 80 to 98 wt %. In spherical micelles, the micelle cores, formed by aggregation of the PS blocks, were generally monodisperse. A comparison between star and crew-cut micelles showed that the latter are distinguished by a low density of corona chains on the core surface and a low degree of stretching of the PS blocks in the cores. As the PAA content in block copolymer decreased, the morphology of the aggregates changed progressively from spheres to cylinders, to bilayers (both vesicles and lamellae), and eventually to compound micelles consisting of an assembly of inverted micelles surrounded by a hydrophilic surface. The compound micelles are believed to be a new morphology for block copolymers. The addition of homopolysty...

Abstract: The addition of ions in micromolar (CaCl2 or HCl) or millimolar (NaCl) concentrations can change the morphology of "crew-cut" aggregates of amphiphilic block copolymers in dilute solutions. In addition to spherical, rodlike, and univesicular or lamellar aggregates, an unusual large compound vesicle morphology can be obtained from a single block copolymer. Some features of the spontaneously formed large compound vesicles may make them especially useful as vehicles for delivering drugs and as models of biological cells. Gelation of a dilute spherical micelle solution can also be induced by ions as the result of the formation of a cross-linked "pearl necklace" morphology.

Abstract: The morphology of crew-cut aggregates of amphiphilic block copolymers in dilute solutions can be controlled by the addition of ions in micromolar (HCl, NaOH, CaCl2, Ca(Ac)2) or millimolar (NaCl) concentrations. The copolymers are highly asymmetric polystyrene-b-poly(acrylic acid) diblocks, PS-b-PAA, in which the lengths of the insoluble PS blocks are much longer than those of the soluble PAA blocks. In addition to spherical, rodlike, and univesicular or lamellar aggregates, large compound vesicles (LCVs), a new morphology, can be obtained from a single block copolymer. The morphogenic effect of different added ions on the crew-cut aggregates can be ascribed to the changed repulsive interactions among the hydrophilic PAA segments, due to neutralization by NaOH, protonation by HCl, ion-binding or bridging by Ca2+, and electrostatic screening by NaCl, respectively. The formation of the LCVs may involve a secondary aggregation of individual vesicles and a subsequent fusion process. Some features of the sponta...