{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"df0b6541c3dc7b0ac55da8163e34b6ee2d76fddae06e18e18c33d45e653c93a3","created":"2026-10-03T07:17:57Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"05391add45ecc0bc63074f8c55c48952908d27ba33f5dc583c677b487f07fb6e","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"mechanism","assisted_by":[],"external_id":"bio.electrolytes-confined.like-charge-attraction","kind":"phenomenon","literature_status":"contested","n":"1","parents":[],"plain":"Objects with the same electric charge should repel, and standard theory of salt solutions forbids attraction when the salt ions carry a single charge. Yet experiments repeatedly report like-charged colloids (microscopic suspended particles) attracting in such solutions.","posed_since":"","precise":"Poisson-Boltzmann theory forbids attraction between like-charged bodies in a $1:1$ electrolyte, and correlation-driven attraction requires the coupling parameter $\\Xi = 2\\pi z^3 l_B^2 \\sigma_s >> 1$, where $z$ is counterion valence, $l_B = e^2/(\\epsilon k_B T) \\sim 0.7\\,\\mathrm{nm}$ in water is the Bjerrum length and $\\sigma_s$ is the surface charge number density; monovalent systems have $\\Xi <\\sim 1$. Observed attractions between like-charged microparticles in monovalent salt, near walls or in confinement, include reports that depend on the sign of the particle charge and on the solvent. An answer identifies the mechanism (interfacial solvent structure, ion correlations beyond mean field, hydrodynamic or optical artifacts) and predicts the pair potential versus salt concentration and charge sign.","problem_ref":null,"references":"","settled_by":"Direct pair-potential measurements for isolated particle pairs far from walls, with opposite charge signs and several solvents, reproduced by a molecular-solvent calculation.","status_note":"Experiments around 2024 reported sign-dependent like-charge attraction in water and alcohols attributed to interfacial solvation; mean-field explanations remain excluded for monovalent ions.","title":"Why like-charged particles attract in monovalent salt solutions","topic_ref":"157a1ba9426f0d60e33212293f1b767b543732401ec3d0153c6ca684819a4974"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"7f4c34c7328fe79e6bf239220eef9244983ce778917289e0376eda4c0282a4fd","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"a01f08b1e677d7e22bfa257f8e0a693faaa074e04f014ec47487e6d34bf224a1","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"d1g451B2YLpc9TLq4qzjaaV43RmMEGyCuLFBlS1LOjJRVjeaeqXQnldU1izCArg6V1N6akSwiJVJWNSH5q37BA"},"schema":"pubphys.envelope/1"},"record_hash":"7f4c34c7328fe79e6bf239220eef9244983ce778917289e0376eda4c0282a4fd","leaf_index":762}