Structuring Colloidal Gels via Micro-Bubble Oscillations

Abstract: Locally (re)structuring colloidal gels $\unicode{x2013}$ micron-sized particles forming a connected network with arrested dynamics $\unicode{x2013}$ enables precise tuning of the micromechanical and -rheological properties of the system. A recent experimental study [B. Saint-Michel, G. Petekidis, and V. Garbin, Soft Matter $\boldsymbol{18}$, 2092 (2022)] showed that rapid restructuring can occur by acoustically modulating an embedded microbubble. Here, we perform Brownian dynamics simulations to understand the mechanical effect of an oscillating microbubble on the structure of the embedding colloidal gel. Our simulations reveal a hexagonal-close-packed restructuring in a range that is comparable to the amplitude of the oscillations. However, we were unable to reproduce the unexpectedly long-ranged modification of the gel structure $\unicode{x2013}$ dozens of amplitudes $\unicode{x2013}$ observed in experiment. This suggests including long-ranged effects, such as fluid flow, should be considered in future work.