Self-consistent field description of polyelectrolyte-grafted colloidal actuators

We present a theoretical description of actuators in prototype artificial muscle tissue by means of a self-consistent (mean field) lattice computational scheme. The actuators are composed of pH-responsive polyelectrolytes grafted at both ends between plate- or rod-like colloidal particles and immersed in an aqueous solution. We build on a model developed for grafted rods [A. Ianiro, J. A. Berrocal, R. Tuinier, M. Mayer and C. Weder, J. Chem. Phys., 2023, 158, 14901], but we specifically include weakly acidic monomers to incorporate the effects of a pH variation to trigger the expansion of the material. As a first toy model, we consider strong polyelectrolyte chains: for both plate- and rod-like colloidal particles, we obtain pressure differences of the order of tens of MPa; sufficient to generate volume variation. During actuation, the system expands and contracts by approximately one third of the polymer contour length and about 100kT of work per polymer chain is performed. Secondly, we show that for weakly charged polyelectrolyte chains the salt concentration can be used to tune the actuation window by multiple pH units, which is important to obtain a biocompatible range of pH values. In this scenario, we find smaller actuation pressures than for strong polyelectrolytes, but still sufficient expansion and contraction for practical purposes.