# Jamming and unjamming of concentrated colloidal dispersions in channel flow

A.I. Campbell, M.D. Haw

Research output: Contribution to journalArticle

23 Citations (Scopus)

### Abstract

We investigated the pressure driven flow of concentrated colloidal dispersions in a converging channel geometry. Optical microscopy and image analysis were used to track tracer particles mixed into dispersions of sterically stabilized poly(methyl methacrylate) (PMMA) spheres. The dispersions were drawn into a round \unit[0.5]{mm} capillary at one of two pump speeds ($\equiv$ applied pressure): $v_1=\unit[0.245]{ml\,\, min^{-1}}$ and $v_2=\unit[0.612]{ml\,\, min^{-1}}$. We observed that the dispersions at particle volume fractions $\phi\leqslant0.50$ followed Hagen-Poiseuille flow for a simple fluid; i.e. the mean flow rate $\langle V\rangle$ is approximately proportional to pressure drop (pump speed) and inversely proportional viscosity $\eta$. Above this concentration ($\phi\geqslant0.505$), the dispersions exhibit granular-like jamming behavior with $\langle V\rangle$ becoming independent of the pressure drop. However, at the highest applied pressure ($v_2$), the dispersions are able to unjam and switch from granular-like behaviour back to a simple hard-sphere liquid like system, due to the formation of rotating vortices in the spatial flow pattern. This mechanism is consistent with computer simulations of granular systems and supports for example proposed explanations of anomalously low friction in earthquake faults.
Original language English 4688-4693 6 Soft Matter 6 19 6 Aug 2010 https://doi.org/10.1039/C0SM00110D Published - 2010

### Keywords

• jamming
• unjamming
• concentrated
• colloidal
• dispersions
• channel flows

## Flow induced heterogeneity in applications of complex fluids" - Transfer of Mark Haw's grant from Nottingham

Haw, M.

EPSRC (Engineering and Physical Sciences Research Council)

15/09/0814/10/09

Project: Research

## Research Output

• 23 Citations
• 1 Article

## Impact of concentrated colloidal suspension drops on solid surfaces

Bertola, V. & Haw, M. D., 1 Jan 2015, 270, Part B, p. 412-417 6 p.

Research output: Contribution to journalArticle

Open Access
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• 7 Citations (Scopus)