arXiv subjects

Rowan Walker-Gibbons

Publications and source records attributed to Rowan Walker-Gibbons.

3 recordsLinked to original sources

arXiv2026

Direct measurement of the attractive electrosolvation force between a pair of colloidal particles

In solution, electrically like-charged particles can experience a strong and long-ranged attraction that leads to the formation of stable, slowly reorganizing clusters. The attractive force underpinning this spontaneous organization process has been shown to depend on both the sign of charge of the particle and the nature of the solvent medium. The origin of the attraction has been ascribed to the preferential orientation of solvent molecules at the object-electrolyte interface. Here, we use optical imaging to directly measure the spatial profile of the potential of mean force between isolated pairs of charged microspheres. Working with particles carrying a variety of surface chemistries we find that the range of the electrosolvation attraction is substantially longer than previously held. In particular we show that particles carrying strongly anionic surface coatings composed of DNA or phospholipid bilayers display long-range attraction. We further find that the length scale governing the decay of the attractive force can depend on the properties of the interacting particles. This contrasts with the canonical expectation that the screening length governing the interaction of charged particles in solution depends exclusively on the properties of the intervening electrolyte medium. The observations point to significant departures from current thinking, and the likely need for a model of interactions that accounts for the molecular nature of the solvent, its interfacial behaviour, and spatial correlations. Finally, a strong and long-ranged attraction mediated by anionic matter constituting lipid membranes and chromatin could carry far-reaching implications for biological organization and structure formation.

cond-mat.soft↗

arXiv2025

Chemical control of self-assembly by the electrosolvation force

Self-assembly of matter in solution generally relies on attractive interactions that overcome entropy and drive the formation of higher-order molecular and particulate structures. Such interactions play key roles in a variety of contexts, e.g., crystallisation, biomolecular folding and condensation, pathological protein aggregation, pharmaceuticals and fine chemicals. The electrosolvation force entails a new conceptual paradigm in the known palette of interactions that drive the spontaneous accretion and organisation of matter. However, an understanding of the underlying physical chemistry, and therefore the ability to exert control over and tune the interaction, remains incomplete. Here we demonstrate that this force arises from the structure of the interfacial electrolyte. Neutral molecules such as a different solvent, osmolytes or surfactants, can - even at very low concentrations in the medium - disrupt or reinforce pre-existing interfacial solvent structure, thereby furnishing unanticipated chemical tuning of the ability of matter to self-assemble. The observations further present unexpected mechanistic elements that may explain the impact of co-solvents and osmolytes on protein structure, stability and pathological protein condensation. Our findings shed new light on microscopic mechanisms that drive the emergence of order and structure from molecular to macroscopic scales in the solution phase.

cond-mat.soft↗

arXiv2022

A charge dependent long-ranged force drives tailored assembly of matter in solution

The interaction between charged objects in solution is generally expected to recapitulate two central principles of electromagnetics: (i) like-charged objects repel, and (ii) they do so regardless of the sign of their electrical charge. Here we demonstrate experimentally that the solvent plays a hitherto unforeseen but crucial role in interparticle interactions, and importantly, that interactions in the fluid phase can break charge-reversal symmetry. We show that in aqueous solution, negatively charged particles can attract at long range while positively charged particles repel. In solvents that exhibit an inversion of the net molecular dipole at an interface, such as alcohols, we find that the converse can be true: positively charged particles may attract whereas negatives repel. The observations hold across a wide variety of surface chemistries: from inorganic silica and polymeric particles to polyelectrolyte- and polypeptide-coated surfaces in aqueous solution. A theory of interparticle interactions that invokes solvation at an interface explains the observations. Our study establishes a specific and unanticipated mechanism by which the molecular solvent may give rise to a strong and long-ranged force in solution, with immediate ramifications for a variety of particulate and molecular processes including tailored self-assembly, gelation and crystallization, as well as biomolecular condensation, coacervation and phase segregation. These findings also shed light on the solvent-induced interfacial electrical potential - an elusive quantity in electrochemistry and interface science implicated in many natural and technological processes, such as atmospheric chemical reactions, electrochemical energy storage and conversion, and the conduction of ions across cell membranes.

cond-mat.soft↗