Versatile Diblock Polyampholytes Can Form Two Types of Charged and Internally Structured Core–Shell Particles by Complexation with Cationic or Anionic Surfactants

Abstract

We used diblock poly­(acrylic acid)-b-poly­(2-dimethylamino ethyl methacrylate) (PAA-b-PDMAEMA) polyampholytes to prepare core–shell complexes with ionic surfactants. The dispersions have been characterized by means of small-angle X-ray scattering (SAXS), cryogenic transmission electron microscopy (Cryo-TEM), dynamic light-scattering, and zeta potential methods. Using cationic or anionic surfactants it is possible to produce particles with either positively or negatively charged shells, both having an internal liquid-crystalline core structure. For the different systems, different preparation protocols were found to be successful to produce stable and reproducible particles. The particle morphologies depend on the surfactant used. Complexes with the cationic surfactant hexadecyltrimethylammonium (CTA+) form oblate particles, while complexes with dodecyl sulfate (DS–) form cylindrical rods. In both complexes, the smallest dimension of the core does not exceed twice the block length of the core-forming polymer block. For the particles with CTA+, nonelectrostatic attractive interactions among the PDMAEMA chains in the shells seem to be present, affecting the particle shape. In both types of particles, the surfactant in the core forms rod-like aggregates, arranged in a two-dimensional hexagonal structure with the surfactant rods aligned with the axis of rotational symmetry in the particle. With charged polymer chains in the shell, the aggregates present a striking stability over time, displaying no change in particle size over the time scale investigated (10 months). Nevertheless, the aggregates are highly dynamic in nature, and their shapes and structures can be changed dramatically in dispersion, without intermediate precipitation, by changes in the composition of the medium. Specifically, a transition from aggregates with cationic surfactant to aggregates with anionic surfactant can be achieved.

Complexes of Charged-Neutral Block Copolymers and Surfactants: Process-Dependent Features and Long-Term Stability of Their Aqueous Dispersions

“…The combination of light and X-ray scattering techniques for the dispersions prepared by the CS approach, with or without added simple salt, indicated internally structured anisometric particles (Figure A and Tables and ). This is consistent with previous results on similar polyion-surfactant dispersed particles. − By contrast, MS-based particles were here found to be spherical, lacking an ordered internal structure. In agreement with these results, Berret et al previously reported cryo-TEM images of spherical particles based on the same components prepared by the MS approach.…”

Virtual Issue: Interfacial Science Developments in Latin America

“…Apart from metallic compounds, NPs can be prepared from the complexation of diblock copolymers with ionic surfactants. Trindade et al used small-angle X-ray scattering and cryogenic transmission electron microscopy to characterize NPs formed from the complexation of the diblock copolymer PAA- b -PDMAEMA, in a pH window in which both the polyacid and the polybasic blocks are charged, with anionic and cationic surfactants . They showed that the charge of the surfactant defines the morphology of the NPs (oblate or cylindrical rods) as well as the shell charge.…”

Comparative study of the co-assembly behaviour of 3-chloro-4-hydroxy-phenylazo dyes with DTAB

“…15 In a recent example it was shown, that the addition of ionic surfactants to an amphoteric diblock-copolyelectrolyte resulted in the formation of core-shell complexes, with an internal crystalline core structure and either positive or negative surface charge, dependent on the charge of the surfactant. 16 Moreover, like the addition of inorganic counter ions or amphiphilic molecules, the introduction of charged dye molecules into polyelectrolyte systems yields supramolecular structures. These structures may be responsive to light as a trigger for morphological changes.…”