Breakup of carbon nanotube flocs in microfluidic traps

The critical stress to break flocs of multiwalled-carbon nanotubes suspended in low-molecular-weight polymer fluid is measured in planar elongational flow. Through image analysis of aggregates and their fragments, the extension rate of the flow and the size and aspect ratio of the aggregates are measured in real time. While trapping an aggregate at the stagnation point of the device, the flow rate is increased continually and breaking events are recorded, establishing a correlation between aggregate size and the critical elongation stress for fragmentation sigma. This relationship resembles that for the breakup of flocs comprising spherical particles, yet it indicates that the strength of these fibrous flocs depends much more strongly on the local particle concentration. Fracture avalanches (or cascades) are also observed.