Dispersion of carbon nanotubes (CNTs) into liquids typically requires ultrasonication to exfoliate individuals CNTs from bundles. Experiments show that CNT length drops with sonication time (or energy) as a power law t −m . Yet the breakage mechanism is not well understood, and the experimentally reported power law exponent m ranges from approximately 0.2 to 0.5. Here we simulate the motion of CNTs around cavitating bubbles by coupling Brownian dynamics with the Rayleigh-Plesset equation. We observe that, during bubble growth, CNTs align tangentially to the bubble surface. Surprisingly, we find two dynamical regimes during the collapse: shorter CNTs align radially, longer ones buckle. We compute the phase diagram for CNT collapse dynamics as a function of CNT length, stiffness, and initial distance from the bubble nuclei and determine the transition from aligning to buckling. We conclude that, depending on their length, CNTs can break due to either buckling or stretching. These two mechanisms yield different power laws for the length decay (0.25 and 0.5, respectively), reconciling the apparent discrepancy in the experimental data.T he dispersion of carbon nanotubes (CNTs) in liquids is critical for the use of CNTs in applications ranging from biomedical sensors to structural composites (1). However, CNTs form insoluble bundles and ropes during production due to van der Waals attraction. Commonly, CNTs are exfoliated and dispersed in liquids by sonication, where energy is supplied to the system as ultrasonic waves. These waves induce cavitation, which leads to progressive exfoliation of bundles into individual CNTs. Understanding dispersion by sonication is critical for the use of CNTs in biological and materials applications (2).Prior studies have monitored the effects of sonication on CNT dispersion quality and length (3-7). Most of these studies sonicated a sample under controlled conditions and monitored bundle diameter and length. Although sonication decreases bundle diameter at short times as individual CNTs are exfoliated, it also cuts the CNTs. Shortening has been observed for both singlewalled and multiwalled CNTs (SWNTs and MWNTs) (4, 5).Similar shortening occurs during sonication of polymer solutions (5,(8)(9)(10)(11)(12), where the mechanism is well established; cavitation induces high strain rates in the liquid, stretching polymer molecules to failure. Although the mechanism of CNT shortening remains unclear, there are some similarities between sonicated polymers and CNTs. Like polymers, CNTs show a nonrandom cutting pattern; i.e., they break near their center of mass (CoM) (5). Similar to polymers, the kinetics of CNT shortening are length-dependent, and sonicated CNTs approach a limiting length, below which no shortening occurs (6, 13). Evidence suggests that thermal effects (due to local temperature rise during bubble collapse) are negligible and mechanical effects dominate (6,14,15).Experiments consistently report a power law relation between CNTs' average length and sonication time L ∼ t −m . Th...