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Recent studies of electrostatics in colloidal systems have increasingly addressed the complexity that inhomogeneous surface charge distributions introduce into self-assembly processes. However, approaches based on extensions of DLVO-like models remain valid only within the mean-field regime and are therefore mainly applicable to environments dominated by monovalent salts, [1]. In the work we present, we move beyond this limitation by developing a theory for anisotropically charged colloids that is applicable in regimes where mean-field theory fails, such as in salt mixtures containing polyvalent ions.
When polyvalent ions are present, strong coupling effects emerge, leading to unconventional electrostatic phenomena such as like-charge attraction. While these effects are well documented for uniformly charged systems, their role in systems with anisotropic charge distributions remains largely unexplored.
To address this problem, we consider a simplified model of Janus colloids immersed in a mixed ionic solution containing both monovalent and multivalent salts. Using a field-theoretic, path-integral approach, we derive effective electrostatic interactions that explicitly account for strong correlations and ionic asymmetry. This framework enables exploration of the full orientational dependence of pair interactions and provides a foundation for incorporating these effects into coarse-grained simulations. Our results contribute to a more comprehensive understanding of electrostatic self-assembly in complex ionic environments.
[1] A. Gnidovec, E. Localtelli, S. Čopar, A. Božič and E. Bianchi, Natt. Comm., 16, 4277, 2025.