Electrostatically Driven Coassembly of a Diblock Copolymer and an Oppositely Charged Homopolymer in Aqueous Solutions

Abstract

Electrostatically driven coassembly of poly(acrylic acid)-block-poly(acrylamide), PAA-b-PAAm, and poly(2-methylvinylpyridinium iodide), P2MVP, leads to formation of micelles in aqueous solutions. Light scattering and small angle neutron scattering experiments have been performed to study the effect of concentration and length of the corona block (N PAAm ) 97, 208, and 417) on micellar characteristics. Small angle neutron scattering curves were analyzed by generalized indirect Fourier transformation and model fitting. All scattering curves could be well described with a combination of a form factor for polydisperse spheres in combination with a hard sphere structure factor for the highest concentrations. Micellar aggregation numbers, shape, and internal structure are relatively independent of concentration for C p < 23.12 g L -1 . The Guinier radius, average micellar radius, hydrodynamic radius, and polydispersity were found to increase with increasing N PAAm . Micellar mass and aggregation number were found to decrease with increasing N PAAm.

Towards a structural characterization of charge-driven polymer micelles

“…The scaling behaviour of structural parameters such as micellar size and aggregation number with respect to, for example, core and corona block length, is sparsely investigated [6,7]. One may anticipate similar dependencies as the ones experimentally reported and theoretically derived for micelles consisting of polymeric amphiphiles.…”

“…The apparent micellar aggregation number, P agg , and more specifically, the number of anionic, P − agg , and cationic, P + agg polymers per micelle can be calculated from M micelle , M building block (see ref. [6] for the definition of a "building block"), and f + . Toluene was used as a reference.…”

“…For two samples (see below), a hard-sphere structure factor (PercusYevick closure, decoupling approximation using an average particle radius) was included. Detailed data analysis procedures have been described elsewhere [6]. Table 2 presents an overview of the relevant coherent scattering length densities, ρ.…”

Electrostatic hierarchical co-assembly in aqueous solutions of two oppositely charged double hydrophilic diblock copolymers

“…Finally, we would like to remark that these dependencies might be investigated quantitatively in for example Cryo-TEM experiments on a system where one of the coronal blocks could be stained selectively, which is not the case in the present system. Moreover, we suppose that a more symmetric PEO/PVOH system would consist of ellipsoidal Janus-micelles, as was found for the rather symmetric P2MVP 42 Consider a strict core-shell segregation where all PAA/ PVOH and P2MVP/PEO junctions are locked to the core/ corona interface, restricting the number of possible chain conformations. It is likely that the short cationic blocks are incapable of compensating all charges of the much longer anionic blocks, i.e., it would involve a considerable stretching penalty if at all possible, so that small, monovalent counterions are taken up by the micellar core to establish charge neutrality.…”

“…This concept has been explored in a series of recent papers [11,12,[24][25][26] where we observed that a pair of relatively miscible hydrophilic blocks yielded spherical C3Ms with a mixed shell and a pair of relatively immiscible hydrophilic blocks yielded ellipsoidal micelles with a laterally segregated corona (Janus-micelles). A combination of poly(2-(N,N-dimethylamino)ethyl methacrylate)-blockpoly(glyceryl methacrylate), PDMAEMA 45 -b-PGMA 90 and poly(acrylic acid)-block-poly(acrylamide), PAA 42 -bPAAm 417 resulted in spherical micelles with a mixed corona [11], while the Janus-type segregation was achieved in aqueous mixtures of poly(N-methyl-2-vinyl pyridinium iodide)-block-poly(ethylene oxide), P2MVP 42 -b-PEO 446 and poly(acrylic acid)-block-poly(acrylamide), PAA 42 -bPAAm 417 [12,24,25]. Within the corona of these micelles, the relatively immiscible PAAm and PEO blocks were approximately of equal size and abundance.…”