Anomalous dynamics of intruders in a crowded environment of mobile obstacles

Abstract

Many natural and industrial processes rely on constrained transport, such as proteins moving through cells, particles confined in nanocomposite materials or gels, individuals in highly dense collectives and vehicular traffic conditions. These are examples of motion through crowded environments, in which the host matrix may retain some glass-like dynamics. Here we investigate constrained transport in a colloidal model system, in which dilute small spheres move in a slowly rearranging, glassy matrix of large spheres. Using confocal differential dynamic microscopy and simulations, here we discover a critical size asymmetry, at which anomalous collective transport of the small particles appears, manifested as a logarithmic decay of the density autocorrelation functions. We demonstrate that the matrix mobility is central for the observed anomalous behaviour. These results, crucially depending on size-induced dynamic asymmetry, are of relevance for a wide range of phenomena ranging from glassy systems to cell biology.

Dynamically arrested micelles in a supercooled sugar urea melt

“…As compared to micelles formed in 95% water, a six order of magnitude decrease in the diffusion coefficient of the micelles is observed when the micelles are present in 20% water, the rest being glucose, urea and surfactant. The evolution of the micelles' correlation function with a decrease in water concentration is analogous to that observed in colloids under jammed state 25,26 . In particular, the correlation function changes from a single exponential to a double exponential function as is observed in the case of arrested macromolecules in a crowded environment 27 .…”

Differential dynamic microscopy microrheology of soft materials: A tracking-free determination of the frequency-dependent loss and storage moduli

“…These data are treated via an image processing algorithm [22] or equivalent versions of it [23] that combines image differences and spatial Fourier transformations to obtain as a result the intermediate scattering function f (q,t) that is typically probed in DLS experiments as a function of the scattering wave vector q and time t [24]. Since its introduction, DDM has been profitably used and also extended by several groups [25][26][27][28][29][30][31][32][33][34] for a variety of applications [35]. In particular, DDM has been recently proven to be an effective tool to measure also the rotational dynamics of anisotropic colloidal particles in solution.…”

Complex dynamics induced by strong confinement – From tracer diffusion in strongly heterogeneous media to glassy relaxation of dense fluids in narrow slits

“…Recently, it has been shown that the ISF can also be obtained from advanced image correlation spectroscopy such as dynamic differential microscopy (DDM) [36,68,69], a method that is also suited to resolve the motion of active particles [70,71]. Here we focus again on tracer particles that are located on the infinite cluster only and modify the definition of the ISF accordingly to…”

“…For example, for the alkali silica melts [26][27][28][29] the preferential diffusion pathways for the alkali ions emerge as a quasi-arrested defect structure of a tetrahedral network. Similarly, for size-disparate soft [31] or hard spheres [36] the interaction between the particles leads to strong short-range correlations which modify locally the structure of the pores. Nevertheless fingerprints of the anomalous dynamics as predicted for the Lorentz models are clearly found in all these systems.…”

“…Within MCT this is connected to a delocalization transition for the small particles [35] which diffuse through an arrested matrix of big particles. An experimental realization of such a strongly size-disparate mixture has been achieved for colloids only recently by Sentjabrskaja et al [36]. There the experimental challenge was to resolve the dynamics of the small particles which rearrange too fast for conventional particle tracking.…”