engleski

Charge-Conformation Behavior of the Spherical Polyamine Brushes

Amphiphilic block-copolymers in aqueous medium spontaneously form micelles in which the water-insoluble core is compacted in the micelle core while the water soluble block forms a spherical shell. In the case of weakly acidic or basic polyelectrolytes, the conformation of the shell strongly depends on the pH and the ionic strength in the bulk solution. The resulting pH-dependent swelling behavior enables tunability that is required in many technological applications (water treatment, pharmaceutical formulations, theranostics, etc.) The mechanism of the swelling is described by the models essentially derived from the scaling theory [1-3], however the number of the experimental studies where the ionization state and the conformation of the polyelectrolyte shell was measured simultaneously, is limited. In the present study, the protonation state a weak polybase spherical brush is experimentally determined by means of potentiometric titrations, for a wide range of bulk solution ionic strengths (0.5 mmoldm3 ≤ I ≤ 1 moldm3). The studied system is prepared from the synthesized block-copolymer poly(styrene)-block-poly(styrene-co-N, N-dimethylaminoethyl methacrylate) pS-b-p(S-co-DMAEMA), whereby the poly-electrolyte shell is featured with a statistical distribution of styrene monomers. The resulting proton binding isotherms are interpreted in terms of the effective pK (pKeff), which allows distinguishing the intrinsic from the cooperative (predominately electrostatic) term in the overall protonation free energy. The size of the micelles was determined by means of the static and dynamic light scattering and the cryo-transmission electron microscopy in the same range of bulk pH and ionic strength conditions, as in the potentiometric titration experiments. The results are compared to the available models based on the scaling theory for spherical polyelectrolyte brushes.

Surface; charge; pK; pH; Electrical; Double; Layer; Model; Polyelectrolyte; Brush; Conformation

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