Effects of polymer concentration and molecular weight on the dynamics of visco-elasto-capillary breakup

Capillary-break-up measurements of viscoelastic polymer solutions are performed using a Capillary Breakup Extensional Rheometer (CABER). The device consists of two coaxial plates which are used to form and hold a liquid bridge of the test fluid. An axial step strain is applied to the fluid by raising the top plate and the elongated fluid thread then evolves towards breakup under the combined action of viscous, elastic and capillary forces. The test fluids used in the present study are a series of diluted polystyrene Boger fluids ('PS025' and its dilutions) and a new polystyrene Boger fluid (labelled 'MV1') comprising of a lower molecular weight solute. This fluid is less susceptible to gravity, and allows us to observe the coil-stretch transition of high molecular weight polymers. The persistent dependence of the measured relaxation time on concentration, even in the dilute regime predicted from theory, is demonstrated both experimentally and numerically. Indeed, numerical simulations of the evolution of the stress contributions and of the radius using a single mode FENE-P model based on the one-dimensional analysis of Entov and Hinch for transient extensional flows are compared to the experimental observations of the radius of the liquid filament. Below a critical dilution, the stress in the necking thread is carried solely by the solvent with no appreciable contribution from the polymer chains, and the dynamics of the necking process change appreciably. A sensitive force transducer is also added to the CABER. This allows us to measure the initial tensile stress resulting from the axial step strain. Existing one dimensioned models for analyzing capillary breakup measurements have assumed this to be identically zero.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Aeronautics and Astronautics.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2004

Author dc:creator

• Verani, Matthieu, 1977-

Advisor dc:contributor.advisor

• Gareth McKinley.

• Aeronautics and Astronautics.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/17837

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/17837