Open Conference Systems, StatPhys 27 Main Conference

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On the impact of controlled surface roughness shape on the slippage of a soft material
Andrea Scagliarini

##manager.scheduler.building##: Edificio Santa Maria
##manager.scheduler.room##: Auditorio San Agustin
Date: 2019-07-10 12:00 PM – 03:45 PM
Last modified: 2019-06-14

Abstract


An assembly of soft jammed particles ("soft material")
usually exhibits a complex rheology characterized by the
existence of a yield stress, i.e. a threshold value below
which the material responds elastically to external perturbations
while behaving as a non-Newtonian fluid above
it. When driven by a constant force (pressure gradient)
in a confined channel, the material flows and exhibits
an effective slippage at the walls. Slippage becomes the
dominant contribution to the flow below or close to yield,
while the material flows as an elastic plug in the rest of
the channel. It is commonly accepted that wall roughness
decreases slippage, however a detailed picture of how
such geometrical corrugations change the near-wall flow
properties is still lacking. By means of numerical simulations,
we sistematically assess this problem, by performing
a quantitative analysis of scaling laws that relate the
wall slippage, estimated from the averaged mass flow-rate,

to the wall stress. In particular, we will
address, for the first time in the literature, the importance
of roughness shape. Results show the existence of two
regimes of slippage: a linear scaling, for small values
of stress, and a quadratic one, for large values of
stress. Interestingly, we find also that, while the two scaling
laws are relatively robust, across different realizations of
roughness, for a given stress, the slip-roughness relation
depends on geometry.
We will address how the amplitude and frequencies
of time oscillations of the mass flow-rate depend on the wall roughness geometry and how they correlate to the topological characteristics of the droplet assembly constituting the soft material.