Viscoelasticity, nonlinear shear start-up, and relaxation of entangled star polymers

Handle URI:
http://hdl.handle.net/10754/562869
Title:
Viscoelasticity, nonlinear shear start-up, and relaxation of entangled star polymers
Authors:
Snijkers, Frank; Ratkanthwar, Kedar; Vlassopoulos, Dimitris; Hadjichristidis, Nikolaos ( 0000-0003-1442-1714 )
Abstract:
We report on a detailed rheological investigation of well-defined symmetric entangled polymer stars of low functionality with varying number of arms, molar mass of the arms, and solvent content. Emphasis is placed on the response of the stars in simple shear, during start-up, and for relaxation upon flow cessation. To reduce experimental artifacts associated with edge fracture (primarily) and wall slip, we employ a homemade cone-partitioned plate fixture which was successfully implemented in recent studies. Reliable data for these highly entangled stars could be obtained for Weissenberg numbers below 300. The appearance of a stress overshoot during start-up with a corresponding strain approaching a value of 2 suggests that in the investigated shear regime the stars orient but do not stretch. This is corroborated by the fact that the empirical Cox-Merx rule appears to be validated, within experimental error. On the other hand, the (shear) rate dependent steady shear viscosity data exhibit a slope smaller than the convective constraint release slope of -1 (for linear polymers) for the investigated range of rates. The broadness of the stress overshoot reflects the broad linear relaxation spectrum of the stars. The initial stress relaxation rate, reflecting the initial loss of entanglements due to the action of convective constraint release in steady shear flow, increases with Weissenberg number. More importantly, when compared against the relevant rates for comb polymers with relatively short arms, the latter are slower at larger Weissenberg numbers. At long times, the relaxation data are consistent with the linear viscoelastic data on these systems. © 2013 American Chemical Society.
KAUST Department:
KAUST Catalysis Center (KCC); Polymer Synthesis Laboratory; Physical Sciences and Engineering (PSE) Division; Chemical Science Program
Publisher:
American Chemical Society (ACS)
Journal:
Macromolecules
Issue Date:
23-Jul-2013
DOI:
10.1021/ma400662b
Type:
Article
ISSN:
00249297
Sponsors:
We thank R Pasquino for help with the creep analysis and helpful discussions, as well as the reviewers of this work for their very contructive comments. Partial support from the EU (FP7 ITN DYNACOP Grant 214627) is gratefully acknowledged.
Appears in Collections:
Articles; Physical Sciences and Engineering (PSE) Division; Chemical Science Program; KAUST Catalysis Center (KCC)

Full metadata record

DC FieldValue Language
dc.contributor.authorSnijkers, Franken
dc.contributor.authorRatkanthwar, Kedaren
dc.contributor.authorVlassopoulos, Dimitrisen
dc.contributor.authorHadjichristidis, Nikolaosen
dc.date.accessioned2015-08-03T11:13:29Zen
dc.date.available2015-08-03T11:13:29Zen
dc.date.issued2013-07-23en
dc.identifier.issn00249297en
dc.identifier.doi10.1021/ma400662ben
dc.identifier.urihttp://hdl.handle.net/10754/562869en
dc.description.abstractWe report on a detailed rheological investigation of well-defined symmetric entangled polymer stars of low functionality with varying number of arms, molar mass of the arms, and solvent content. Emphasis is placed on the response of the stars in simple shear, during start-up, and for relaxation upon flow cessation. To reduce experimental artifacts associated with edge fracture (primarily) and wall slip, we employ a homemade cone-partitioned plate fixture which was successfully implemented in recent studies. Reliable data for these highly entangled stars could be obtained for Weissenberg numbers below 300. The appearance of a stress overshoot during start-up with a corresponding strain approaching a value of 2 suggests that in the investigated shear regime the stars orient but do not stretch. This is corroborated by the fact that the empirical Cox-Merx rule appears to be validated, within experimental error. On the other hand, the (shear) rate dependent steady shear viscosity data exhibit a slope smaller than the convective constraint release slope of -1 (for linear polymers) for the investigated range of rates. The broadness of the stress overshoot reflects the broad linear relaxation spectrum of the stars. The initial stress relaxation rate, reflecting the initial loss of entanglements due to the action of convective constraint release in steady shear flow, increases with Weissenberg number. More importantly, when compared against the relevant rates for comb polymers with relatively short arms, the latter are slower at larger Weissenberg numbers. At long times, the relaxation data are consistent with the linear viscoelastic data on these systems. © 2013 American Chemical Society.en
dc.description.sponsorshipWe thank R Pasquino for help with the creep analysis and helpful discussions, as well as the reviewers of this work for their very contructive comments. Partial support from the EU (FP7 ITN DYNACOP Grant 214627) is gratefully acknowledged.en
dc.publisherAmerican Chemical Society (ACS)en
dc.titleViscoelasticity, nonlinear shear start-up, and relaxation of entangled star polymersen
dc.typeArticleen
dc.contributor.departmentKAUST Catalysis Center (KCC)en
dc.contributor.departmentPolymer Synthesis Laboratoryen
dc.contributor.departmentPhysical Sciences and Engineering (PSE) Divisionen
dc.contributor.departmentChemical Science Programen
dc.identifier.journalMacromoleculesen
dc.contributor.institutionInstitute of Electronic Structure and Laser, FORTH, Heraklion 71110, Crete, Greeceen
dc.contributor.institutionSchool of Chemical Sciences, Swami Ramanand Teerth Marathwada University, Vishnupuri, Nanded-431606, Indiaen
dc.contributor.institutionDepartment of Chemistry, University of Athens, Athens 15771, Greeceen
dc.contributor.institutionDepartment of Materials Science and Technology, University of Crete, Heraklion 71003, Crete, Greeceen
kaust.authorHadjichristidis, Nikolaosen
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