Spatial and temporal inhomogeneities in the flow of dense colloidal suspensions into geometrical constrictions
- Event time: 1:00pm
- Event date: 23rd January 2006
- Speaker: Lucio Isa (University of Edinburgh)
- Location: Room 2511, James Clerk Maxwell Building (JCMB) James Clerk Maxwell Building Peter Guthrie Tait Road Edinburgh EH9 3FD GB
The flow of material into geometrical constrictions is widely present both in nature and in technological applications. Despite the great deal of interest in such phenomena for the case of polymer solutions and granular media, very little is known for the case of colloidal suspensions. We propose a study on the pressure-driven flow of PMMA spheres (1.5m radius) suspended in a density matched solvent into glass capillaries of different sizes. For high volume fractions (above 60%), a very rich flow behaviour is observed with strong analogies with the granular case. Thanks to fast Confocal Microscopy, we are able to track the motion of the particles inside the capillaries and obtain quantitative information on the local structure and velocities. According to the presence or the absence of local shear, two different kinds of velocity fluctuations are observed. In addition to this, such fluctuations are strongly dependent on the local speed; increasing the speed leads to higher frequencies and amplitudes. Finally, the flow is not only inhomogeneous in time (velocity fluctuations), but but also spatially. Due to self-filtration effects caused by a difference between the velocity of the solvent and the one of the particles, the volume fraction of the suspension decreases in the flow direction, leading to substantial differences in the flow profiles and local structure.
This is a weekly series of informal talks given primarily by members of the soft condensed matter and statistical mechanics groups, but is also open to members of other groups and external visitors. The aim of the series is to promote discussion and learning of various topics at a level suitable to the broad background of the group. Everyone is welcome to attend..