Speaker
Description
Stick-slip is a common phenomenon both in nature and in many engineering applications. It is often observed in out-of-equilibrium disordered systems as a yield response to a smoothly varying external force and is characterized by intermittent bursts of irregular signals of different amplitudes, durations, and separations that result from the spontaneous depinning of mechanical contacts or local rearrangement of material bonds. In this talk, I will report on our recent theoretical and experimental studies of a variety of systems exhibiting stick-slip motion due to complex interactions. Three systems will be discussed: (i) dry friction between two (rough) solid surfaces in contact, with the frictional force in mesoscale monitored by an atomic force microscope; (ii) the depinning dynamics of a circular moving contact line over the rough surface with experiments employing direct atomic force microscopy measurements of a micron-sized vertical hanging glass fiber intersecting a liquid-air interface, in which the measured capillary force acting on the contact line exhibits sawtooth-like stick-slip fluctuations; (iii) the dynamics of intracellular vesicle transport across various cell types and intracellular environments. We find that the local maximal force required for slipping/depinning follows extreme-value statistics, and the measured force drop follows avalanche dynamics with a power-law distribution, in good agreement with the Alessandro-Beatrice-Bertotti-Montorsi model or its generalization. The complex stick-slip and avalanches experimental findings are well-described by theoretical models that connect the Brownian-correlated kinetic friction/drag forces. For the cargo transport powered by molecular motors inside a living cell, we reveal a universal transport mechanism characterized by stick-slip motion. By analyzing an extensive dataset of vesicle trajectories from over 480 live cells across diverse vesicle types, cell lines, and cytoplasmic environments, we show that cargo velocities consistently follow a Gamma distribution, a robust statistical signature that persists despite biological variability. Unlike the Gaussian velocity statistics observed for motor trnsport in vitro, this Gamma distribution emerges from Brownian-correlated kinetic friction between motor-cargo complexes and their surroundings.