Rheological characterization of polymers via dissipative particle dynamics

Dissipative particle dynamics (DPD) is a mesoscale simulation technique which uses soft potentials between large particles to reproduce liquid behavior. In form, DPD is similar to molecular dynamics, as all matter is represented by point particles which interact with each other via, pairwise forces. The method was first introduced in the early 1990's, and has since undergone a number of refinements which have put it on a firm thermodynamic footing. DPD is notable for the flexibility it presents the modeler for building complex fluid systems. DPD has been used to study simple molecular liquids, polymer and colloid solutions, and phase behavior of block copolymer melts. Recently, a number of workers have used DPD to study the flow of polymer solutions in various geometries such as microchannels, pores, and sudden contractions. While these types of flows are well-suited to DPD's relative strengths, an important step has been skipped. Before the results of these complex flows can be accepted, it is necessary to demonstrate that the rheological predictions made by DPD are generally reliable. The principle aim of this thesis is to demonstrate that the rheology of polymer solutions can be simulated successfully with DPD. The rheology of a solution of DPD dumbbells using a FENE spring force law is studied in the first part of this thesis via simulation of steady shear flow and steady planar elongational flow. The rheological results are compared to dilute Brownian dynamics simulations of the same FENE dumbbell model. The level of coarse-graining of the DPD fluid is varied by changing the length of the DPD dumbbell relative to the particle size, while maintaining a constant extensibility parameter. Broadly speaking, the viscosity, first normal stress coefficient, and dumbbell extension in shear flow calculated with DPD are in agreement with the BD results. The two methods are not perfectly alike however, and two systematic differences between the DPD and BD results are observed. An excluded volume effect which occurs naturally in DPD and is not present in the BD simulations results in elevated viscosity and dumbbell extension in the zero-shear-rate regime.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Chemical Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2008

Author dc:creator

• Clarke, Theis Forman

Advisor dc:contributor.advisor

• Robert C. Armstrong.

• Chemical Engineering.

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/1721.1/45927

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/45927