This thesis describes work done to investigate the effects of flow on concentrated suspensions. The work is largely about the effects of flow on concentrated colloidal suspensions, however, a short section on the effects of flow on concentrated granular suspensions is also given. Concentrated suspensions show a variety of complex flow behaviour. They can show Newtonian, shear thinning or shear thickening behaviour, depending on the applied stress or shear rate and concentration. The shear thickening behaviour may be discontinuous and this is characterised by a dramatic increase in viscosity above a certain threshold of stress. This is thought to be closely related to flow induced jamming, which can be defined as the conversion of a liquid system into a solid by imposed stress. This behaviour is not well understood and can cause significant complications in industry. It also has potential applications, for example in shock absorption. Due to their complexities and potential applications, gaining a better understanding of how shear thickening and jamming materials behave is of interest and forms the basis of this thesis. In this work, bespoke shear cells and a novel method to detect flow induced jamming were designed and utilised. This allowed jamming to be visualised and evaluated quantitatively. Conditions where jamming occurs were mapped out and the effects of parameters such as concentration, shear stress, system geometry and system confinement were investigated. This, and an analysis of jamming statistics, allowed ways to prevent and control jamming to be identified and a better understanding of the system to be achieved. Such an analysis is lacking in literature. The conditions where jamming was detected using the novel equipment matched well with measurements using a commercial rheometer. This supported the idea of discontinuous shear thickening and flow induced jamming being closely related. The studies allowed a mechanism for flow induced jamming and discontinuous shear thickening to be proposed. By designing and using novel equipment that is not commercially available, a better understanding of the effects of flow on concentrated suspensions was achieved. This could ultimately lead to a better understanding of complex flow systems and lead to more efficient processes.
|Date of Award||1 Jul 2015|
- University Of Strathclyde