Description
Fickian non-Gaussian diffusion (FnGD) remains a major open question in soft matter, with its emergence linked to structural or dynamic heterogeneity. Recent model systems show that FnGD is typically preceded by anomalous diffusion, with both regimes closely intertwined. [1, 2].
We investigate colloidal tracer diffusion in heterogeneous environments with static translational disorder of micron-sized pillars. Using maskless photolithography, we fabricated micropillar arrays with tunable randomness, symmetry, and density. Particle tracking of colloidal particles diffusing through the pillar arrays in microfluidic cells extended two orders of magnitude beyond the Brownian time, significantly surpassing previous FnGD studies. We examined particles with varying mass densities and concentrations [3].
We observed the emergence of FnGD behaviour at different timescales at suitable pillar area fraction, depending on the particle’s concentration and the system's aging time. These results provide a foundation to bridge numerical simulations [2], diffusion in optical traps [4], and in complex networks [1].
[1] Guan, Juan, Bo Wang, and Steve Granick. "Even hard-sphere colloidal suspensions display Fickian yet non-Gaussian diffusion." ACS nano 8.4 (2014): 3331-3336.
[2] Rusciano, Francesco, Raffaele Pastore, and Francesco Greco. "Fickian non-Gaussian diffusion in glass-forming liquids." Physical Review Letters 128.16 (2022): 168001.
[3] Chakraborty, Indrani, and Yael Roichman. "Disorder-induced Fickian, yet non-Gaussian diffusion in heterogeneous media." Physical Review Research 2.2 (2020): 022020.
[4] Ciarlo, Antonio, et al. "Fickian yet non-Gaussian diffusion of a quasi-2d colloidal system in an optical speckle field: experiment and simulations." Scientific Reports 13.1 (2023): 7408.