{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"3198395f6859c43f963d79e997ced5c54629644b9944c1aee4f83384bfbcf32f","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":["ai:gpt-5.5"],"kind":"seed"},"parents":["334a0ed2845fcb864ceff226ac3480c2238a82201957cb3bc61fef48adb6c1e7","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"87e2d70e4c97716d558cbf07a94283fdaf86a543bc3b26f606b66e686aeb40ce","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":["ai:gpt-5.5"],"external_id":"fluid.contact-lines.air-entrainment-threshold","kind":"well-posed","literature_status":"partially-resolved","n":"2","parents":[],"plain":"When a plate or tape is pushed quickly into a liquid, above a critical speed the liquid can no longer wet the solid and a thin air film is dragged in, which ruins coatings. What sets that critical speed?","posed_since":"","precise":"For a solid plunging at speed $U$ into a liquid of viscosity $\\eta$ and surface tension $\\gamma$, surrounded by gas of viscosity $\\eta_g$ and pressure $p$, predict the critical capillary number $\\mathrm{Ca}* = \\eta U*/\\gamma$ for dynamic wetting failure, including its dependence on the viscosity ratio $\\eta_g/\\eta$, on gas rarefaction when the mean free path approaches the air-film thickness, and on the large increase of $\\mathrm{Ca}*$ when the flow pushes the liquid against the solid (curtain coating). An answer predicts $\\mathrm{Ca}*$ within experimental error for $\\eta_g/\\eta$ from $10^{-6}$ to $10^{-2}$ and across reduced gas pressures.","problem_ref":"334a0ed2845fcb864ceff226ac3480c2238a82201957cb3bc61fef48adb6c1e7","references":"","settled_by":"A comparison of measured $\\mathrm{Ca}*$ for plunging plates and curtain coating over wide viscosity ratios and gas pressures with a single model of the gas film and the contact line.","status_note":"Lubrication models that include gas viscosity capture the weak viscosity-ratio dependence for simple plunging; the roles of gas rarefaction and of flow assistance remain unsettled as of 2026 (not re-verified for 2024-2026).","title":"Threshold speed for air entrainment in forced wetting","topic_ref":null},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"71d8262e87efda11b4021e3dca831682b497536c30a52f76713ba051bf446bec","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"7bd72876f79324cfbee07a485210ba32b4561349482d46b8cc8c7b6958e0b20b","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"NrqDcAVNY0U3x8puy5NnmEbGJaIsGJ-cG573Tdn_vsi0ztoJ6aTS_TkSEMadc69eoUKTMYsMNHR6_3E8mQpzAA"},"schema":"pubphys.envelope/1"},"record_hash":"71d8262e87efda11b4021e3dca831682b497536c30a52f76713ba051bf446bec","leaf_index":3256}