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What makes particle packings stable? Novel answers to a baffling question

Project Description

Soils, catalysts, nanoporous materials, pharmaceutical tablets, sand dunes: all are packings of particles, with microstructure on scales from nanometre to centimetre. Whether the particle arrangement in packings makes a material stable, or subject to collapse, when a force such as gravity is applied, is a key question in nature (landslides, earthquakes), industry (packed bed reactors, flowable slurries), manufacture (powder flow, tabletting), and new technologies (designer porous materials). In this project we will develop new methods of analysing packing structure, starting with computer simulation and moving to experiments if possible, to explore what structural features of a particle packing determine its stability under forces.

The project seeks to answer a seemingly simple question but one that in fact has baffled scientists and engineers for a long time. Scientists including Kepler, Maxwell and Bernal have puzzled over how the particle configuration in a packing leads to bulk stability. This is important in scenarios from geology to manufacturing, both for making ‘stable’ particulate solids and for improving product efficiencies. An interesting industrial example is the compression of pharmaceutical, food or detergent powders to form solid tablets: you may want to increase packing to densities beyond the point where the tablet first becomes stable and solid, to reduce storage costs. Can this be better achieved by manipulating the packing structure? Alternatively, you may want to reduce packing density to make low-density yet still solid tablets, saving on transport costs (weight) and material cost (amount of ‘bulking’ materials used). Meanwhile geological examples include the 2011 Christchurch earthquake, which saw major damage due to soil ‘liquefaction’: the packing of soil particles became suddenly unstable under earthquake forces.

Despite major research in granular science there remains no clear quantitative link between particle arrangement and bulk material stability: hence landslides and earthquake damage are unpredictable and manufacturing processes are often based on trial and error rather than design. Answering this long-standing question has implications for physics of materials, geology, rheology, construction, packed and fluidised bed chemical reactors, manufacture of advanced porous (nano)materials, food processing, pharmaceutical powders, packaging/transport, and even protein structure.

In the project we will explore new computational structural analysis methods, recently developed from experimental colloidal packing measurements, to find new insight into what features of a packing’s particle arrangement lead to stability and the emergence of solid-like properties. Starting by analysing computationally-generated, simple particle packings, depending on progress we will then go on to apply and test new methods on real experimental packings.

In addition to undertaking cutting edge research, students are also registered for the Postgraduate Certificate in Researcher Development (PGCert), which is a supplementary qualification that develops a student’s skills, networks and career prospects.

Information about the host department can be found by visiting:

Funding Notes

This PhD project is initially offered on a self-funding basis. It is open to applicants with their own funding, or those applying to funding sources. However, excellent candidates may be considered for a University scholarship.

Students applying should have (or expect to achieve) a minimum 2.1 undergraduate degree in a relevant engineering/science discipline, and be highly motivated to undertake multidisciplinary research.

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