  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.
