9:30–10:30 am
Please Join us:
Kha-I To's PhD Thesis Defense
Wednesday November 9, 2022 at 9:30 am CDT
RIFTS IN RAFTS: DISTRIBUTED FAILURE AND CLUSTER FORMATION OF PARTICLE RAFTS UNDER EXPANSION
Particle rafts are single-layers of aggregated sub-millimeter polydisperse particles floating at an air-liquid interface. When pulled from opposing sides, these rafts fail with an interesting morphology that depends on the rate of expansion. The failure is uniformly distributed throughout the raft. When the pulling velocity is low, the resulting cluster size, that is the number of particles in between adjacent cracks, is large and approaches the original dimension of the system; upon increasing the velocity, the cluster size continuously decreases until it reaches the size of a single particle. Between these two limits, the average cluster size varies approximately inversely with the pulling speed. At later times, after the initial clustering occurs, nonlinear relaxation and particle rearrangement is also observed. This behavior is found both in experiments performed with isotropic radial expansion as well as in experiments where the rafts are stretched along only a single axis.
We modeled this phenomenon with a one-dimensional (in)stability analysis in which the relaxation rate for clustering, which depends on the cluster size, competes with the difference of velocity between neighboring particles caused by the expanding fluid. This competition selects the cluster size. This model agrees with experimental measurements from both uniaxial and radial expansion. With its easily accessible particle dynamics, this system provides an experimental analog to material failure that occurs over a wide range of length scales – from small-scale porous membranes to the formation of structure left behind by cosmological expansion.
Committee members:
Sidney Nagel (Chair)
Heinrich Jaeger
Abigail Vieregg
Stephanie Palmer
Kha-I will be a postdoc working with Prof. Mahesh Bandi at Okinawa Institute of Science and Technology in Okinawa, Japan.