4 research outputs found
Tensile Deformation and Failure of Thin Films of Aging Laponite Suspension
In this paper we study deformation, failure and breakage of visco-elastic
thin films of aging laponite suspension under tensile deformation field.
Aqueous suspension of laponite is known to undergo waiting time dependent
evolution of its micro-structure, also known as aging, which is accompanied by
an increase in the elastic modulus and relaxation time. In the velocity
controlled tensile deformation experiments, we observed that the dependence of
force and dissipated energy on velocity and initial thickness of the film is
intermediate to a Newtonian fluid and a yield stress fluid. For a fixed waiting
time, strain at break and dissipated energy increased with velocity, but
decreased with initial thickness. With increase in age, strain at break and
dissipated energy showed a decrease suggesting enhanced brittle behavior with
increase in waiting time, which may be caused by restricted relaxation modes
due to aging. In a force controlled mode, decrease in strain at failure at
higher age also suggested enhanced brittleness with increase in waiting time.
Remarkably, the constant force tensile deformation data up to the point of
failure showed experimental time- aging time superposition that gave an
independent estimation of relaxation time and elastic modulus dependence on
age.Comment: 30 pages, 17 figure
Time-aging time-stress superposition in soft glass under tensile deformation field
We have studied the tensile deformation behaviour of thin films of aging
aqueous suspension of Laponite, a model soft glassy material, when subjected to
a creep flow field generated by a constant engineering normal stress. Aqueous
suspension of Laponite demonstrates aging behaviour wherein it undergoes time
dependent enhancement of its elastic modulus as well as its characteristic
relaxation time. However, under application of the normal stress, the rate of
aging decreases and in the limit of high stress, the aging stops with the
suspension now undergoing a plastic deformation. Overall, it is observed that
the aging that occurs over short creep times at small normal stresses is same
as the aging that occurs over long creep times at large normal stresses. This
observation allows us to suggest an aging time - process time - normal stress
superposition principle, which can predict rheological behaviour at longer
times by carrying out short time tests.Comment: 26 pages, 7 figures, To appear in Rheologica Act
Squeeze flow behavior of (soft glassy) thixotropic material
We study the flow behavior of a model soft glassy material − an aqueous suspension of Laponite − when it is squeezed between two circular parallel plates of different roughness. Aqueous suspension of Laponite shows a time dependent aging behavior as reflected in increased elastic modulus as well as yield stress, both of which however also decrease with an increase in the strength of deformation field thereby demonstrating typical thixotropic character. In a squeeze flow situation, under both force as well as velocity controlled modes; we find the behavior to be independent of the initial gap between the plates. In a constant force mode, the gap between the plates decreases until it reaches a finite limiting value, which is found to increase with an increase in age of the material as well as with a decrease in the applied force. In constant velocity experiments, at large gaps between the plates, normal force varies inversely with plate separation. The normal force is higher for a sample aged for a longer time as well as for a larger velocity of the top plate. We observe that the experimental behavior follows prediction of Herschel–Bulkley model solved for the squeeze flow (with different friction coefficients at the two plates) reasonably well under weak deformation fields. However, under strong deformation fields, experimental behavior deviates significantly from the prediction of Herschel–Bulkley model. This deviation arises due to melting or partial yielding of Laponite suspension under large deformation fields causing decrease in the viscosity, elastic modulus and the yield stress