Periodic Reporting for period 4 - ExtreFlow (Extreme deformation of structured fluids and interfaces. Exploiting ultrafast collapse and yielding phenomena for new processes and formulated products)
Reporting period: 2019-10-01 to 2021-04-30
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 increasingly in need of predictive models for rapid, effective, and sustainable screening of new products.
One reason why it remains difficult to provide such predictive models, is the challenge of reproducing the flow conditions during processing of the product, and those during use by the consumer, in laboratory tests. The realistic conditions of flow of a structured fluid during production or use are “extreme” 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, the ExtreFlow project has introduced a radically innovative approach to explore and characterize the regime of extreme deformation of structured fluids and interfaces. After the successful completion of the project it is now possible to reproduce the flow conditions of an industrial plant on a fluidic chip, by combining cutting-edge techniques including acoustofluidics, microfluidics, and high-speed microscopy. This new methodology enables high-precision measurements of macroscopic stresses and evolution of the microstructure under extreme flow conditions that were so far inaccessible with existing methods.
In the course of the project we revealed emerging phenomena of structured interfaces that have no counterpart at lower strain rates, and had so far eluded observation. For instance we discovered dynamic capillary interactions between colloids bound to the surface of an ultrasound-driven bubble, which lead to unique microstructures.
The novel phenomena emerging upon extreme deformation can 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.
One reason why it remains difficult to provide such predictive models, is the challenge of reproducing the flow conditions during processing of the product, and those during use by the consumer, in laboratory tests. The realistic conditions of flow of a structured fluid during production or use are “extreme” 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, the ExtreFlow project has introduced a radically innovative approach to explore and characterize the regime of extreme deformation of structured fluids and interfaces. After the successful completion of the project it is now possible to reproduce the flow conditions of an industrial plant on a fluidic chip, by combining cutting-edge techniques including acoustofluidics, microfluidics, and high-speed microscopy. This new methodology enables high-precision measurements of macroscopic stresses and evolution of the microstructure under extreme flow conditions that were so far inaccessible with existing methods.
In the course of the project we revealed emerging phenomena of structured interfaces that have no counterpart at lower strain rates, and had so far eluded observation. For instance we discovered dynamic capillary interactions between colloids bound to the surface of an ultrasound-driven bubble, which lead to unique microstructures.
The novel phenomena emerging upon extreme deformation can 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.
The work performed during the ExtreFlow project can be divided into two application areas, namely structured interfaces and structured fluids.
Overview of results for extreme deformation of structured interfaces:
we developed a new methodology for high-frequency, controlled deformation of structured interfaces, based on acoustic forcing of bubbles. The gas-liquid interface of the bubbles was modified with a monolayer of colloidal particles to study the effect of high-frequency deformation on interface microstructure. During acoustic forcing, and ensuing high-frequency bubble deformation, we observed specific regimes of monolayer buckling and particle expulsion, including patterned expulsion for the case of non-spherical bubble shapes. In controlled experiments where the bubble remains spherical and particles are not expelled from the interface, precision measurements of the evolution of the interface microstructure revealed the emergence of a new microstructure which could not be explained with existing theory. We pinpointed a unique interaction arising in this regime of extreme deformation, namely dynamic capillary interactions, which are due to the extremely high acceleration of the interface, thousands of times larger than the acceleration due to gravity. These observations pinpoint that new mechanisms can occur in extreme deformation regime that have no counterpart in normally accessible conditions. In addition to revealing specific phenomena of extreme deformation, we provided a modelling framework to analyse the experimental data in order to measure high-frequency mechanical properties of the interface from bubble dynamics data. This methodology can be exploited for characterization of interfaces in complex multiphase systems undergoing flow and deformation.
Overview of results for extreme deformation of structured fluids:
we applied the approach based on acoustic forcing of bubbles to high-frequency rheology of structured fluids in bulk. In this case, the gas-liquid interface is bare, and the bubble is completely surrounded by a fluid with a complex microstructure in three-dimensions. We first developed the framework to measure high-frequency rheology in the linear regime from bubble dynamics data. We then tested the hypothesis that for yield-stress fluids, which behave as solids below a minimum stress called the yield stress, the deformation imparted by bubble dynamics may provide a new strategy for bubble removal from formulated products. We developed a theoretical model and performed initial tests of the most common yield-stress fluid, Carbopol. Finally we moved on to colloidal gels and used confocal microscopy to directly visualise the evolution of the microstructure during acoustic forcing of bubbles at 10000 Hz. We evidenced a local restructuring of the gel in the vicinity of the bubble.
The methodology developed in ExtreFlow, for applications in both structured interfaces and structured fluids, will ultimately provide the necessary experimental data for validation of predictive models of formulation processing and performance. The dynamic restructuring of both interfaces and bulk materials opens new avenues for tuning of material properties with a remote, programmable trigger.
Overview of results for extreme deformation of structured interfaces:
we developed a new methodology for high-frequency, controlled deformation of structured interfaces, based on acoustic forcing of bubbles. The gas-liquid interface of the bubbles was modified with a monolayer of colloidal particles to study the effect of high-frequency deformation on interface microstructure. During acoustic forcing, and ensuing high-frequency bubble deformation, we observed specific regimes of monolayer buckling and particle expulsion, including patterned expulsion for the case of non-spherical bubble shapes. In controlled experiments where the bubble remains spherical and particles are not expelled from the interface, precision measurements of the evolution of the interface microstructure revealed the emergence of a new microstructure which could not be explained with existing theory. We pinpointed a unique interaction arising in this regime of extreme deformation, namely dynamic capillary interactions, which are due to the extremely high acceleration of the interface, thousands of times larger than the acceleration due to gravity. These observations pinpoint that new mechanisms can occur in extreme deformation regime that have no counterpart in normally accessible conditions. In addition to revealing specific phenomena of extreme deformation, we provided a modelling framework to analyse the experimental data in order to measure high-frequency mechanical properties of the interface from bubble dynamics data. This methodology can be exploited for characterization of interfaces in complex multiphase systems undergoing flow and deformation.
Overview of results for extreme deformation of structured fluids:
we applied the approach based on acoustic forcing of bubbles to high-frequency rheology of structured fluids in bulk. In this case, the gas-liquid interface is bare, and the bubble is completely surrounded by a fluid with a complex microstructure in three-dimensions. We first developed the framework to measure high-frequency rheology in the linear regime from bubble dynamics data. We then tested the hypothesis that for yield-stress fluids, which behave as solids below a minimum stress called the yield stress, the deformation imparted by bubble dynamics may provide a new strategy for bubble removal from formulated products. We developed a theoretical model and performed initial tests of the most common yield-stress fluid, Carbopol. Finally we moved on to colloidal gels and used confocal microscopy to directly visualise the evolution of the microstructure during acoustic forcing of bubbles at 10000 Hz. We evidenced a local restructuring of the gel in the vicinity of the bubble.
The methodology developed in ExtreFlow, for applications in both structured interfaces and structured fluids, will ultimately provide the necessary experimental data for validation of predictive models of formulation processing and performance. The dynamic restructuring of both interfaces and bulk materials opens new avenues for tuning of material properties with a remote, programmable trigger.
The research performed 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 both particle-modified interfaces and bulk colloidal gels, due to the effects of high-frequency oscillatory deformation. On the other hand, we have developed a methodology to perform bulk rheological measurements of structured fluids under oscillatory elongation at high-frequency, well above the frequencies that can be accessed with conventional instruments. Theproject will has provided a new 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, and the fundamental study of physical phenomena like freezing, fracture and shock.