Rheology studies how matter flows, usually in its liquid state but also as “soft solids”. The technique has been applied in the last century in fields as diverse as materials science, engineering, geophysics, physiology, human biology, and pharmaceutics. In more recent decades, it has been a key part of the rise of green technology.
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Green technology, clean technology, and cleantech are used to refer to research, technology, policies, and practices being developed to reduce and counteract humanity’s negative impact on the environment.
One of the least sustainable industries must necessarily be a part of any green technology solution to environmental damage. In the construction industry, rheology has enabled significant reductions in carbon fuel consumption, and materials being wasted or unnecessarily replaced.
Making concrete more durable and long-lasting – and reducing the need to renovate or even demolish and replace buildings – is an important direction of research for green technologists. Rheology has been used to study superplasticizers, which are added to cement to make it less prone to yield to stress formation and to retain viscosity before it has set (Ferrari et al., 2011). By improving the properties of concrete in this way, rheology has contributed to longer-lasting buildings and therefore fewer finite resources used in the construction industry.
Rheology has also been used to make finished buildings greener in terms of their energy usage (Lucas et al., 2010). The green technology development of phase change materials (PCMs) introduced mortars for walls that would better retain thermal energy inside the building. This emphasis on latent heat storage results in buildings with few energy demands, especially in cooler climates. The rheological study also found that lime mortars that incorporate PCMs can be applied even in old buildings during renovation. In this way, rheology contributes to construction’s ongoing sustainability conundrum.
An early application of rheology was in the development of the “sol-gel” process. Sol-gel is a method for fabricating metal oxides. In the process, monomers are converted into a colloidal solution (sol) which is the chemical precursor to an integrated network (gel) of the desired material. In this way, discrete molecules can be formed as solid materials.
An early application of the sol-gel process was in nuclear energy. Nuclear energy is a key element of green technology, as it presents a means to meet modern energy requirements without extracting and burning limited fossil fuels such as oil and coal. However, it is by no means without its environmental problems, due to the extremely high radioactivity of materials it requires.
The sol-gel method enabled nuclear energy generators to manufacture uranium and thorium – essential elements for nuclear energy generation – as powders and avoid the extremely harmful by-product of radioactive dust that other methods released. In this way, rheology was an important step in moving energy generation away from burning fossil fuels, and in a safer way.
One of the major causes of environmental damage is aircraft travel (contributing between 2% and 3% of anthropogenic greenhouse gas emissions), and rheology researchers are paying attention. It is widely accepted that improved aircraft and engine design will help drive forward the necessary efficiencies in air travel. However, research and design are limited by the cost of physical testing.
Computational field dynamics (CFD) – which draws from classical rheology and advanced computer modeling – is poised to remove these barriers to improved aircraft technology. In a recent study, NASA laid out the technological developments in CFD required to ensure aircraft reach emissions (and noise pollution) targets by 2030: “Vision 2030” (Slotnick et al., 2014).
NASA’s vision outlines the techniques of classical and computer-assisted rheology that will play a key part in the development of green technology for the aerospace industry in the coming years.
Lucas, S., Senff, L., Ferreira, V., Barroso de Aguiar, J.L. and Labrincha, J.A. (2010). Fresh state characterization of lime mortars for latent heat storage. Applied Rheology, 20(6), pp. 63162–63169.
Ferrari, L., Kaufmann, J., Winnefeld, F., and Plank, J. (2011). A multi-method approach to study the influence of superplasticizers on cement suspensions. Cement and Concrete Research, 41(10), pp.1058–1066.
Slotnick, J.P., Khodadoust, A., Alonso, J.J., Darmofal, D.L., Gropp, W.D., Lurie, E.A., Mavriplis, D.J. and Venkatakrishnan, V. (2014). Enabling the environmentally clean air transportation of the future: a vision of computational fluid dynamics in 2030. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 372(2022), p.20130317.