Delayed solidification of soft glasses: new experiments, and a theoretical challenge

Area of Science:

• Colloid science
• Rheology
• Materials science

Background:

• Aqueous Laponite suspensions exhibit complex rheological behavior under stress.
• Understanding delayed solidification is crucial for predicting material properties.

Purpose of the Study:

• Investigate the delayed solidification transition in Laponite suspensions.
• Determine the dependence of delay time on stress, frequency, and initial material properties.
• Evaluate the applicability of soft-glassy rheology (SGR) models.

Main Methods:

• Large amplitude oscillatory shear stress applied to Laponite suspensions.
• Measurement of delay time (t(c)) dependence on stress amplitude and frequency.
• Analysis of age-dependent initial loss modulus.
• Comparison with a soft-glassy rheology (SGR) model.

Main Results:

• Aqueous Laponite suspensions show abrupt solidification after a long delay time (t(c)).
• Observations are initially consistent with an SGR model where strain induces barrier crossings.
• Data suggests a power-law distribution for barrier heights, deviating from the typical SGR exponential form.
• The SGR model's assumptions are irreconcilable with the large experimental strain amplitudes.

Conclusions:

• The study provides insights into the delayed solidification of Laponite suspensions.
• A modified SGR model with a power-law barrier height distribution may better describe the phenomenon.
• Explaining delayed solidification at large strain amplitudes remains an open theoretical challenge.