Constant viscosity elastic liquids, known as Boger fluids, are unique fluids that behave like elastic solids when stretched, yet flow like liquids with constant viscosity. Unlike most elastic fluids that exhibit shear thinning due to polymer solutions, Boger fluids are highly dilute, minimizing this effect. They are typically made by adding a small amount of polymer, such as polyacrylamide, to a viscous Newtonian fluid like corn syrup. This simplicity makes Boger fluids invaluable in rheology, allowing clear distinction between elasticity and shear effects in non-Newtonian flow, enabling experiments that isolate the impact of elasticity on fluid behavior.
Research
Original Boger fluid
Boger fluids are named after David V. Boger, who in the late 1970s was the primary researcher pushing for the study of constant viscosity elastic liquids.2 He released his first paper on Boger fluids in 1977, titled "A Highly Elastic Constant-Viscosity Fluid", where he described the ideal fluid for experimentation as a fluid that is "highly viscous and highly elastic at room temperature and at the same time is optically clear". The main purpose of the paper was to experiment on the highly viscous and highly elastic fluid and record the fundamental rheometric properties of the fluid. Such a fluid would allow for experimentation under conditions not affected by inertia and shear thinning effects, and influence of inertia would easily be distinguishable.3
He began his research using maltose syrups (corn syrups) mixed with a small amount of water. He then tested shear stress versus shear rate of the solution to prove that the solution was a Newtonian fluid. This was done by using a R16 Weissenberg rheogoniometer4 (a rheogoniometer calibrated to measure specifically the behavior of a viscoelastic polymer solution) for the low range shear stress rates, and the high rates were measured using a capillary rheometer, a device used to measure shear stress rates under high stress. The data proved that there was a linear relationship between shear stress and shear rate with the slope being very close to one, meaning the maltose syrup was indeed a Newtonian fluid. Once 0.08% of the polymer polyacrylamide was added, the flow properties drastically changed. Elastic properties were introduced to the fluid while only a slight amount of shear thinning was observed, small enough to be ignored. The syrup solution had properties very similar to a polymer melt, but there was no shear thinning and the materials could be produced at room temperature.
Subsequent Boger fluids
The original Boger fluid was an aqueous solution, as were all the solutions synthesized until 1983, when organic Boger fluids were produced using a dilute solution of polyisobutylene (PIB) in a mixture of polybutene (PB) with a small quantity of kerosene oil added. From then on, most Boger fluids have been PIB - PB solutions. Other recipes include:
- polystyrene in oligomeric glycol (Solomon and Muller 1996)
- polyethylene oxide in polyethylene glycol (Dontula et al. 2004)
- polystyrene in dioctyl phthalate (Odell & Carrington 2006)
Commercial use
Waste disposal
The best application so far for Boger fluids is solving the problem of disposal for the waste produced in the processing of bauxite to alumina for use in producing aluminium, and there is normally two or three times more "red mud" produced than alumina. Normally, the waste, known as "red mud", was disposed of by being flushed down dams with millions of liters of water. The dams continue to hold the "red mud", because it does not work as a building foundation and also can't be used as farm land. Companies needed to find a way to efficiently dispose of it all onto the dams without clogging the tubes it was being transferred in. With the development of Boger fluids, aluminum giant Alcoa developed a way to convert the waste into a thick matter that could still flow down pipes. Using this method, the dangers of tubes erupting was cut out, leading to a more sustainable practice.5
References
James, David F. (2009). "Boger Fluids". Annual Review of Fluid Mechanics. 41 (1): 129–142. Bibcode:2009AnRFM..41..129J. doi:10.1146/annurev.fluid.010908.165125. /wiki/Bibcode_(identifier) ↩
"David V. Boger". Archived from the original on 29 July 2015.[unreliable source?] https://web.archive.org/web/20150729162123/http://www.che.ufl.edu/faculty/boger/ ↩
Boger, D.V. (September 1977). "A highly elastic constant-viscosity fluid". Journal of Non-Newtonian Fluid Mechanics. 3 (1): 87–91. Bibcode:1977JNNFM...3...87B. doi:10.1016/0377-0257(77)80014-1. /wiki/Bibcode_(identifier) ↩
MacSporran, W. C.; Spiers, R. P. (March 1982). "The dynamic performance of the Weissenberg Rheogoniometer: I. Small amplitude oscillatory shearing". Rheologica Acta. 21 (2): 184–192. Bibcode:1982AcRhe..21..184M. doi:10.1007/BF01736417. /wiki/Bibcode_(identifier) ↩
"$300,000 'Boger' fluid prize not on the nose". The Age. 5 October 2005. https://www.theage.com.au/national/300-000-boger-fluid-prize-not-on-the-nose-20051005-ge0zrm.html ↩