@article{MajeeBierBlosseyetal., author = {Majee, Arghya and Bier, Markus and Blossey, Ralf and Podgornik, Rudolf}, title = {Charge symmetry broken complex coacervation}, series = {Physical Review Research}, volume = {2}, journal = {Physical Review Research}, number = {4}, abstract = {Liquid-liquid phase separation has emerged as one of the important paradigms in the chemical physics as well as biophysics of charged macromolecular systems. We elucidate an equilibrium phase separation mechanism based on charge regulation, i.e., protonation-deprotonation equilibria controlled by pH, in an idealized macroion system which can serve as a proxy for simple coacervation. First, a low-density density functional calculation reveals the dominance of two-particle configurations coupled by ion adsorption on neighboring macroions. Then a binary cell model, solved on the Debye-H{\"u}ckel as well as the full nonlinear Poisson-Boltzmann level, unveils the charge symmetry breaking as inducing the phase separation between low- and high-density phases as a function of pH. These results can be identified as a charge symmetry broken complex coacervation between chemically identical macroions.}, language = {en} } @article{MajeeBierDietrich, author = {Majee, Arghya and Bier, Markus and Dietrich, Siegfried}, title = {Electrostatic interaction of particles trapped at fluid interfaces: effects of geometry and wetting properties}, series = {Soft Matter}, volume = {14}, journal = {Soft Matter}, pages = {9436 -- 9444}, abstract = {The electrostatic interaction between pairs of spherical or macroscopically long, parallel cylindrical colloids trapped at fluid interfaces is studied theoretically for the case of small inter-particle separations. Starting from the effective interaction between two planar walls and by using the Derjaguin approximation, we address the issue of how the electrostatic interaction between such particles is influenced by their curvatures and by the wetting contact angle at their surfaces. Regarding the influence of curvature, our findings suggest that the discrepancies between linear and nonlinear Poisson-Boltzmann theory, which have been noticed before for planar walls, also occur for spheres and macroscopically long, parallel cylinders, though their magnitude depends on the wetting contact angle. Concerning the influence of the wetting contact angle θ simple relations are obtained for equally sized particles which indicate that the inter-particle force varies significantly with θ only within an interval around 90°. This interval depends on the Debye length of the fluids and on the size of the particles but not on their shape. For unequally sized particles, a more complicated relation is obtained for the variation of the inter-particle force with the wetting contact angle.}, language = {en} } @article{MajeeBierBlosseyetal., author = {Majee, Arghya and Bier, Markus and Blossey, Ralf and Podgornik, Rudolf}, title = {Charge regulation radically modifies electrostatics in membrane stacks}, series = {Physical Review E}, volume = {100}, journal = {Physical Review E}, number = {5}, pages = {050601}, abstract = {Motivated by biological membrane-containing organelles in plants and photosynthetic bacteria, we study charge regulation in a model membrane stack. Considering (de)protonation as the simplest mechanism of charge equilibration between the membranes and with the bathing environment, we uncover a symmetry-broken charge state in the stack with a quasiperiodic effective charge sequence. In the case of a monovalent bathing salt solution our model predicts complex, inhomogeneous charge equilibria depending on the strength of the (de)protonation reaction, salt concentration, and membrane size. Our results shed light on the basic reorganization mechanism of thylakoid membrane stacks.}, language = {en} }