# SKM 2023 – wissenschaftliches Programm

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# DY: Fachverband Dynamik und Statistische Physik

## DY 27: Statistical Physics: Far From Equilibrium I

### DY 27.3: Vortrag

### Mittwoch, 29. März 2023, 10:15–10:30, ZEU 250

Colloidal monolayers: bridging the gap between two and three spatial dimensions — Johannes Bleibel^{2}, •Alvaro Domínguez^{1}, and Martin Oettel^{2} — ^{1}Univ. Sevilla, Spain — ^{2}Univ. Tübingen

It is well established that, unlike for a three-dimensional fluid, particle interactions prevent the hydrodynamic transport coefficients from being defined for a two-dimensional fluid due to the notorious “long-time tail” feature of the velocity autocorrelation.

A colloidal monolayer formed at a fluid interface builds a bridge between these two limiting cases, and it provides insight on the transition from three down to two spatial dimensions: the particle positions are constrained to a plane and the colloid thus resembles a two-dimensional fluid. But the exchange of particle momentum takes place in three-dimensional space through hydrodynamic interactions in the ambient fluid.

Here we study the colloidal diffusivity starting from
the Smoluchowski equation. We show that the diffusivity exhibits an
intermediate behavior between purely two-dimensional and fully
three-dimensional fluid: on the one hand, Fick’s law, which pertains
to *collective diffusion*, breaks down altogether, as
confirmed experimentally. On the other hand, the coefficient of
*self-diffusion* is finite, but the transitional nature of
the monolayer shows up in a non-analytic dependence on the colloidal
packing fraction, at odds with the case of a fully
three-dimensional colloid.