On the Transition between a Heterogeneous and Homogeneous Corona in Mixed Polymeric Micelles

• Published in: Langmuir 2008-11, Vol.24 (21), p.12221-12227
• Main Authors: Voets, Ilja K, Fokkink, Remco, de Keizer, Arie, May, Roland P, de Waard, Pieter, Cohen Stuart, Martien A
• Format: Article
• Language: English
• Subjects: Chemistry; Colloidal state and disperse state; Colloids: Surfactants and Self-Assembly, Dispersions, Emulsions, Foams; Exact sciences and technology; General and physical chemistry; Micelles. Thin films; Surface physical chemistry
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la801816p

Two-dimensional NMR and small-angle neutron scattering experiments were performed on comicelles of poly(N-methyl-2-vinyl pyridinium iodide)-block-poly(ethylene oxide), P2MVP-b-PEO, and poly(acrylic acid)-block-poly(acryl amide), PAA-b-PAAm, in aqueous solutions to study whether a transition between a heterogeneous (Janus-type) and homogeneous corona can be observed upon a variation of parameters that are anticipated to affect the miscibility of the PEO and PAAm coronal blocks. Investigated were the effect of a salt-induced decrease in micellar aggregation number, P agg for 1 ≤ [NaNO3] ≤ 279 mM, a temperature increase for 25 ≤ T ≤ 80 °C, a variation of the fraction of EO monomers in the corona, f EO, at a fixed corona block length, N corona, for 0 ≤ f EO ≤ 1, a decrease in the PEO block length, N PEO, at a fixed PAAm block length, N PAAm, for 200 ≤ N PEO ≤ 450, and finally, upon a decrease in corona block length at N PAAm = N PEO for 100 ≤ N corona ≤ 400. These parameters should affect the mixing/demixing transition via their effect on the PEO/PAAm interfacial area (e.g., as in the case of f EO and P agg) or the relevant Flory−Huggins interaction parameters (e.g., as in the case of temperature). None of the above parameters was shown to yield a transition toward a homogeneous corona wherein the polymer chains are randomly mixed; i.e., the segregation of PAAm and PEO chains within the micellar corona of comicelles of PAA-b-PAAm and P2MVP-b-PEO appears to be rather robust.