Invertible Micelles Based on Ion-Specific Interactions of Sr²⁺ and Ba²⁺ with Double Anionic Block Copolyelectrolytes
2019
Carl, Nico | Prévost, Sylvain | Schweins, Ralf | Houston, Judith E. | Morfin, Isabelle | Huber, Klaus
Polyelectrolytes show diverse ion-specific effects with a wide variety of ions. In the present work, we study the solution behavior of diblock copolymers with polyacrylate (PA) and polystyrenesulfonate (PSS) blocks in the presence of the earth alkaline cations Ca²⁺, Sr²⁺, and Ba²⁺. Micellization can be triggered by a variation in temperature. For Ca²⁺, this micelle formation occurs at high temperatures, while for Sr²⁺ and Ba²⁺, it occurs at high and low temperatures with an intermediate temperature regime of single chains. Small-angle neutron scattering on a partly deuterated block copolymer unambiguously revealed that at low temperatures, PSS/M²⁺ forms the core of the micelles, whereas at high temperatures, PA/M²⁺ forms the core, effectively allowing to reverse the micelle structure by changing the temperature. This inversion of the micellar morphology, induced by a dual-responsive behavior, can be understood by using isothermal titration calorimetry and elucidating the thermodynamics of cation binding.
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