Complex fluids with mobile charge-regulating macro-ions

¹ Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University - Ramat Aviv 69978, Tel Aviv, Israel
² DAMTP, Centre for Mathematical Sciences, University of Cambridge - Cambridge CB3 0WA, UK
³ Department of Theoretical Physics, J. Stefan Institute - 1000 Ljubljana, Slovenia
⁴ Department of Physics, Faculty of Mathematics and Physics, University of Ljubljana - 1000 Ljubljana, Slovenia
⁵ School of Physical Sciences, UCAS, University of Chinese Academy of Sciences - Beijing 100049, China

Received: 23 August 2017
Accepted: 12 December 2017

Abstract

We generalize the concept of charge regulation of ionic solutions, and apply it to complex fluids with mobile macro-ions having internal non-electrostatic degrees of freedom. The suggested framework provides a convenient tool for investigating systems where mobile macro-ions can self-regulate their charge (e.g., proteins). We show that even within a simplified charge-regulation model, the charge dissociation equilibrium results in different and notable properties. Consequences of the charge regulation include a positional dependence of the effective charge of the macro-ions, a non-monotonic dependence of the effective Debye screening length on the concentration of the monovalent salt, a modification of the electric double-layer structure, and buffering by the macro-ions of the background electrolyte.