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When bigger is faster after one century

Since the groundbreaking theory of Einstein and experiments of Perrin in the early 20th century, we know that Brownian particles (such as proteins, polymers, viruses,…) diffuse in a fluid by moving randomly due to thermal fluctuations. Friction with the solvent causes this diffusion to slow down when the particle is big.

This effect amplifies when the particles are embedded in crowded host environment such as biological cells, polymer melts, or colloidal crystals. As a general rule, large guest particles are slower than small host building blocks.

In this work we show, one century after Perrin, that this rule does not hold when long guest rods are immersed in a lamellar structure of self-organized shorter rods, as the size of the guest particles exceeds the typical length scale of the host phase. We foresee that the concept of these non-commensurate diffusers can be generalized for the design of fast diffusers in crowded environment with potential application in cell biology and drug delivery.

Figure1 and Movie 1 : Schematic representation and video microscopy of tracer amounts of long (labeled red) and short (labeled green) fluorescent rods immersed in a lamellar phase (displayed in gray) formed by the short rods. The scale bar indicates 3 µm.

Movie 2 : Analogy with a car packing lot where a bigger truck which does not fit in a single car location has therefore more space to move.

Reference :

Fast diffusion of long guest rods in a lamellar phase of short host particles Phys. Rev. Lett. (2017)

Article published in Physical Review Letters

Article published in arXiv.org

Laura Alvarez, M. Paul Lettinga, and Eric Grelet

Contact :

Mail : Eric Grelet : grelet_at_crpp-bordeaux.cnrs

Phone : 05 56 84 56 13