{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"c98d3bc8255956ac3d981788c8ec3690af4669506c3de4b31c147c9811fd2220","created":"2026-10-03T07:17:57Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"504c751678930dc1d03c2e81f735da6c97056972ddb09d6aa51a975b76fbebbc","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":[],"external_id":"bio.polymer-dynamics.viscosity-exponent","kind":"well-posed","literature_status":"contested","n":"1","parents":[],"plain":"The viscosity of melts of long linear chains grows as chain length to the power 3.4, while the basic sliding-in-a-tube picture (reptation) predicts power 3. Corrections explain the gap, but it is unconfirmed whether very long chains finally reach power 3.","posed_since":"","precise":"For monodisperse linear polymer melts, eta_0 ~ $M^3$.4 is observed while pure reptation gives M^3; contour-length fluctuations and constraint release account for the difference at moderate $M / M_e$. Determine whether $\\eta_0$ crosses over to $M^3$ at very high $M / M_e$, and at what $M / M_e$, in experiment and in simulation.","problem_ref":null,"references":"","settled_by":"Measurements of $\\eta_{0}$ for narrowly distributed melts extending to $M / M_{e}$ of order 1e3 or more, or equivalent simulations, showing the local exponent approaching 3 or not.","status_note":"Exponents near 3 were reported for very high M polybutadiene (Colby, Fetters and Graessley 1987) and ultrahigh-molecular-weight polyethylene (Vega et al. 2004), but polydispersity and equilibration make these claims disputed; tube theory explains the 3.4 regime quantitatively.","title":"Does melt viscosity cross over to pure reptation scaling","topic_ref":"aeb1d914c5245c3ac0eb6390c11efb8e31b123b88f6954758542aa7f4dbb81e4"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"ffe2467ca38d5704eb06f65ac16b6117099d08f0f221c175560d4da5d327849f","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"68dbeae37e4b24439dcb8ccf518fc886a8c715e040e2ae0810455ae18985087c","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"EsfuBQmwCnHcTB3NuwR5CoIXyf12bi-0onXDnSTOLMBN1hBTikCl4vYFLShb0ylOuO5yypReDRdumuPgXAhMDQ"},"schema":"pubphys.envelope/1"},"record_hash":"ffe2467ca38d5704eb06f65ac16b6117099d08f0f221c175560d4da5d327849f","leaf_index":827}