| Abstract
| - With a view to describe the structural arrangement of the tetramethylammonium (TMA+)counterions in simple salt-free aqueous poly(styrene-block-acrylic acid) [PS(20)-b-PA(85)] solutions, thepartial structure factors pertaining to PS−PS, PS−TMA, and TMA−TMA density correlations wereobtained with small-angle neutron scattering and isotopic labeling of the counterion. The contributionsto the scattering related to the PA-blocks are blanked by contrast matching in water. The copolymersself-assemble with an aggregation number ∼100 into spherical micelles made of a PS-block core,surrounded by a coronal layer formed by the PA-blocks. At the present level of ionization (50%), the PAchains are almost fully stretched in the radial direction away from the core. A comparison of the counterioninvolved partial structure factors with the previously reported relevant structure factors pertaining tothe PA-blocks shows that the counterion distribution along the radius is very close to the one for thesegments of the corona-forming blocks. Within a 10% error margin, all counterions are trapped in thecoronal layer, and there is no indication for charge annealing effects and/or counterion migration towardthe outer corona region.
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