Sphere, Cylinder, and Vesicle Nanoaggregates in Poly(styrene-b-isoprene) Diblock Copolymer Solutions

Abstract

An asymmetric poly(styrene-b-isoprene) diblock copolymer with block molecular weights of 13 000 and 71 000 g/mol, respectively, was dissolved at 1 vol % in a series of solvents with varying selectivity for styrene: dibuthyl phthalate (DBP), diethyl phthalate (DEP), and dimethyl phthalate (DMP). The degree of solvent selectivity was adjusted by mixing DBP/DEP and DEP/DMP in various proportions. With increasing solvent selectivity, the predominant micellar shape changes from spheres to cylinders to vesicles, reflecting the changing interfacial curvature. The detailed micellar morphologies were characterized by small-angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (cryo-TEM). Recently developed form factors were used to characterize the micellar structures in detail, and a vesicle form factor was derived for this system. From the core dimensions, the packing properties, such as the interfacial area per chain and the core chain stretching, were determined. The cryo-TEM results demonstrate the suitability of the technique for these glass-forming solvents and gave micellar core dimensions in quantitative agreement with those from SAXS. The universality of the shape sequence sphere/cylinder/vesicle, well-established for aqueous solutions of surfactants and block copolymers, is thus confirmed for organic systems.

Self‐Assembled Block Copolymer Aggregates: From Micelles to Vesicles and their Biological Applications

“…However, entropic demands and molecular frustration induces the formation of defects such as end caps (which are more energetically favourable) and branch points (which are less favourable). [13] Literature reports of giant [14] and short worms, [15,16] y-junction and end cap defects, [17,18] and even worm-like micellar networks [19] illustrate the increasing complexity associated with macromolecular amphiphilic self-assemblies. The wide array of intramolecular and intermolecular interactions within block copolymer assemblies generates even more sophisticated structures.…”

Polymerization-induced self-assembly of block copolymer nanoparticles via RAFT non-aqueous dispersion polymerization

“…In principle, the morphology of the resulting diblock copolymer nanoparticles [2][3][4][5] is dictated by the relative block volume fractions, as defined by the so-called packing parameter ( Figure 1) [6][7][8]. In practice, the copolymer concentration can also influence the morphology in some cases [9][10][11][12].…”

Design of block copolymer membranes using segregation strength trend lines

“…As the solvent selectivity increased, the solvent--core block interactions decreased, and the interfacial tension increased, which resulted in various aggregate morphologies. 61 In a similar way the solvents can be adjusted to fit the trend line in Fig. 3.…”