Dynamics of a Colloidal Dynamics of a Colloidal Glass During Stress- Glass During Stress- Mediated Structural Mediated Structural Arrest Arrest (“ (“ Relaxation in Relaxation in Reverse Reverse ”) ”) Ajay Singh Negi and Chinedum Osuji Department of Chemical Engineering, Yale University, New Haven, CT.
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Ajay Singh Negi and Chinedum Osuji Department of Chemical Engineering,
Dynamics of a Colloidal Glass During Stress-Mediated Structural Arrest (“ Relaxation in Reverse ”). Ajay Singh Negi and Chinedum Osuji Department of Chemical Engineering, Yale University, New Haven, CT. Motivation. Structural Glass. Colloidal Glass. Under high shear, the system flows. - PowerPoint PPT Presentation
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Dynamics of a Colloidal Glass Dynamics of a Colloidal Glass During Stress-Mediated During Stress-Mediated
Structural ArrestStructural Arrest(“(“Relaxation in ReverseRelaxation in Reverse”)”)
Ajay Singh Negi and Chinedum OsujiDepartment of Chemical Engineering,
Yale University, New Haven, CT.
MotivationMotivation
Structural Glass
• At high temperatures (above Tg), system is liquid.
• Below Tg, the viscosity is very high.
• Below Tg, the system shows aging behavior.
Colloidal Glass
• Under high shear, the system flows.
• At low shear rates or rest, the system does not flow.
• Aging behavior is seen at rest or low shear.
Is shear temperature ?
MotivationMotivation
EXPERIMENTS: Ediger et al, Science, 323, 231 (2009)At higher creep stresses, the dynamics was faster and distribution narrower.
SIMULATIONS: Warren and Rottler, 2010: At higher stresses, dynamics is accelerated and distribution is narrowed.
How does stress influence the structural arrest of a colloidal glass?
MotivationMotivation
What is the role of stress on the arrest timescale?
How does stress affect the trajectory of the system during arrest? (peak-width in time-dependent viscosity)
System and MethodSystem and Method
• Laponite XLG
(a) Electrostatic screening length at
pH 10 ≈ 30 nm.
(b) Non-ergodic state at concentration
of 1 wt %.
• Bulk Rheology
(a) Constant stress measurements.
(b) Oscillation over a background steady flow.
time (s)Solid lines: Controlled variable Dashed lines: Measured variable
Schematic of Protocol Schematic of Protocol (constant stress)(constant stress)
t=0
Dynamical ArrestDynamical Arrest
0.1 1 10 100
1E-4
1E-3
0.01
0.1
1
10
100
3 Pa 4 Pa 6 Pa 9 Pa 13 Pa 18 Pa 24 Pa 31 Pa
shea
r ra
te (
1/s)
t (s)
Increasing Stress
Shear rate measured
as a function of time
for a constant applied
stress.
The time for arrest
increase with increase
in the applied stress.
Above a certain stress the system will NOT arrest.
Viscosity Bifurcation Coussot et al, PRL 2002
time (s)Solid lines: Controlled variable Dashed lines: Measured variable