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.