{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"631c233e4cb061b84587744a27ad23022635ff76a8cd9550c50101486dcf9349","created":"2026-10-03T07:18:03Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"4bce647dfdb6a35215de36583ee7e3d4451d7e9f4eee9f3efd321739f649678b","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"identification","assisted_by":[],"external_id":"fluid.contact-lines.singularity-regularization","kind":"phenomenon","literature_status":"open","n":"1","parents":[],"plain":"If liquid sticks perfectly to the solid wall, the friction at a moving contact line becomes infinite and a drop could never spread. Is it slip of molecules along the wall, an invisible thin film ahead of the drop, a smeared-out liquid-gas boundary, or evaporation that removes this infinity in real liquids?","posed_since":"1971","precise":"The no-slip Stokes solution near a contact line moving at speed $U$ gives viscous stress $\\sim \\eta U / r$ and a logarithmically divergent dissipation. For specific liquid-solid pairs (for example silicone oil on silanized glass, water on glass, volatile liquids near saturation), determine which cutoff sets the inner length $L_{\\mathrm{micro}}$ entering the Cox-Voinov law: Navier slip length $\\ell_s$, precursor film, diffuse-interface width with its mobility, evaporation and condensation, or molecular hopping at the line. An answer identifies the dominant mechanism for each class of system and predicts $L_{\\mathrm{micro}}$ and its dependence on $U$, viscosity and wettability.","problem_ref":null,"references":"","settled_by":"Measurements of $L_{\\mathrm{micro}}$ at nanometer resolution for several liquid-solid pairs compared against molecular-dynamics simulations of the same pairs, with each candidate mechanism switched on and off.","status_note":"","title":"Which microscopic physics removes the moving contact-line stress singularity?","topic_ref":"7a825c5c00d33b62e371e3769546f5338a06f02c5d234ce8602c61be90e57f13"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"ce25245bdaeec2e44074ccaddc94fbd3edef44697a84b4614b2bfadbc7e58dff","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"95afa1144e38f3e42059bebffd4b88312c42b8f265378bc226ecf38c0f92bd04","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"wIW4P7zqu9kgD5iye0pBWryGkHHAhtkDtbdjFcyjkYCeZ45B7f4CE3X9mB0K8qYsrSMG8Q4ZZ44GDhFFwHxjBw"},"schema":"pubphys.envelope/1"},"record_hash":"ce25245bdaeec2e44074ccaddc94fbd3edef44697a84b4614b2bfadbc7e58dff","leaf_index":1404}