Formulated products in the cosmetic, food, coatings and pharmaceutical industry are typically structured fluids, that is, fluids that are engineered to exhibit desired properties such as texture, spreadability, and stability. This is achieved by carefully designing the product...
Formulated products in the cosmetic, food, coatings and pharmaceutical industry are typically structured fluids, that is, fluids that are engineered to exhibit desired properties such as texture, spreadability, and stability. This is achieved by carefully designing the product composition, so as to obtain a certain internal structure on the microscale, which results in the desired flow properties and performance on the macroscale. Because of an increasing demand for environmentally friendly, healthier, and better performing formulated products, the formulations industry is in need of predictive models for rapid, effective, and sustainable screening of new products.
An outstanding challenge is that the flow conditions during processing of the product, and those during use by the consumer, are very difficult to reproduce in laboratory tests. The realistic conditions of flow of a structured fluid during production or use are â€œextremeâ€ compared to what is accessible with existing experimental methods. As a consequence, the unknown effects of extreme deformation limit the possibility to develop predictive models for sustainable screening of new products. If this understanding becomes available, the cost of development of new products will be reduced, resulting in cost savings for the industry on the one hand, and in the overall increased sustainability of the products.
To deliver this vision, ExtreFlow is introducing a radically innovative approach to explore and characterize the regime of extreme deformation of structured fluids and interfaces. The main goal of the project is to explore the effects of extreme, ultrafast deformation on structured fluids and interfaces. Ultimately it will be possible to reproduce the flow conditions of an industrial plant on a microchip, by combining cutting-edge techniques including acoustofluidics, microfluidics, and high-speed microscopy. This new methodology will enable pioneering, high-precision measurements of macroscopic stresses and evolution of the microstructure under extreme flow conditions that are inaccessible with existing methods. The novel phenomena emerging upon extreme deformation can then be exploited to design new processes and for adding new functionality to formulated products. The results of this research program will guide the development of predictive tools that can tackle the time scales of realistic flow conditions for applications to virtual screening of new formulations.
In the first 18 months of the project, we have made significant progress in the understanding of extreme deformation of structured interfaces. We have elucidated the conditions for particle expulsion during ultrafast, non-spherical deformation of the structured interface. The results revealed the importance of particle inertia, which becomes important even for microscopic particles when the flow conditions are extreme. These findings have been published in the peer-reviewed journal Soft Matter [V. Poulichet, A. Huerre, V. Garbin, Shape oscillations of particle-coated bubbles and directional particle expulsion, Soft Matter 13, 125 (2017)]. In subsequent experiments we have discovered that the ultrafast deformation of the interface results in novel microstructures that are not observed in equilibrium conditions, or under less extreme deformations, because they are due to non-equilibrium interparticle interactions. A theoretical model is currently being developed to describe these surprising experimental results, which have profound implications for the rheological response of structured interfaces. With regards to structured fluids, we have successfully used ultrasound-driven microbubbles to probe the high-frequency rheological properties of a model complex fluid, namely a hydrogel, in two different ways. In the first method, the ultrafast bubble dynamics excites surface elastic waves on the hydrogel. The elastic properties inferred from analysis of the wave propagation differ significantly from those obtained with a conventional rheometer. This result highlights the importance of developing methods to measure rheological properties during extreme deformation, as these can deviate dramatically from the low-frequency properties. This work has been published in the peer-reviewed journal Soft Matter [M. Tinguely, M. G. Hennessy, A. Pommella, O. K. Matar, V. Garbin, Surface waves on a soft viscoelastic layer produced by an oscillating microbubble, Soft Matter 12, 4247 (2016)]. In the second method, we embedded the microbubble probe inside the hydrogel and characterised the shift in resonance frequency of the bubble, as well as the quality factor of the resonance curve. From these measurements we extracted the high-frequency elasticity and viscosity of the material, and confirmed again that the properties differ significantly from those measured at the low frequencies accessible with a rheometer. A journal paper reporting these findings has been submitted.
The research performed so far has confirmed the central hypothesis of ExtreFlow that, upon extreme deformation, novel phenomena of structured fluids and interfaces can emerge. On the one hand, we have observed for the first time new microstructures of particle-modified interfaces that are due to the highly non-equilibrium deformation. On the other hand, we have confirmed in bulk rheological measurements of structured fluids that the rheological properties upon extreme deformation cannot be inferred from knowledge of the properties at the lower frequencies that can be accessed with conventional instruments. The expected impact of the project will be to provide the necessary set of tools for the characterization of structured fluids and interfaces under extreme deformation, with implications that go beyond the processing of formulated products, and include characterization of biomaterials for diagnostic ultrasound applications.
More info: http://garbinlab.ce.ic.ac.uk/extreflow.html.