Time dependence of nonlinear flow dynamics of near hard sphere suspensions

Kumar, Mansi Agarwal

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https://hdl.handle.net/2142/98110 Copy

Description

Title

Time dependence of nonlinear flow dynamics of near hard sphere suspensions

Author(s)

Kumar, Mansi Agarwal

Issue Date

2017-06-08

Director of Research (if dissertation) or Advisor (if thesis)

Zukoski, Charles F.

Doctoral Committee Chair(s)

• Zukoski, Charles F.
• Ewoldt, Randy H.

Committee Member(s)

• Schweizer, Kenneth S.
• Braun, Paul
• Sottos, Nancy

Department of Study

Materials Science & Engineerng

Discipline

Materials Science & Engr

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Nonlinear rheology
• Rheology and small-angle neutron scattering (Rheo-SANS)
• Hard spheres

Abstract

The mechanical properties of near hard sphere suspensions are studied from low frequency to high frequency terminal regions as a function of frequency and strain. The volume fraction dependence of experimentally observable characteristic time scales are reported- the longest relaxation time and two cross over times: the first denoting the end of the low frequency terminal region where the linear storage modulus first exceeds the loss modulus and the high frequency cross over time where loss modulus exceeds the storage modulus. At low frequencies where the viscous behavior dominates, the onset of nonlinearities is driven by increases in rate of strain. At higher deformation frequency, where suspension mechanics is dominated by an elastic response, the nonlinear responses occur when deformation exceeds a characteristic strain. This strain is associated with the transient confinement of particles by nearest neighbors and its volume fraction dependence is through cage parameters derived from the high frequency elastic modulus. The onset of nonlinear responses takes on a universal behavior when deformation frequency is normalized by the characteristic time governing the shift from viscous to elastic behavior at low frequency indicating that this transition is associated with transient particle localization and is expected to be observed for all volume fractions where pair interactions are important. Small angle neutron scattering experiments were used to characterize the suspension microstructure under steady shear and in the low frequency terminal region and the resulting scattering was expanded using spherical harmonics. The coefficients of the spherical harmonics are successfully used to predict the stress response of the microstructure under steady shear, and, for the first time, for near hard sphere suspensions, under oscillatory shear.

Graduation Semester

2017-08

Type of Resource

text

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http://hdl.handle.net/2142/98110

Copyright and License Information

Copyright 2017 Mansi Kumar

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