FlowMat · Exploiting Flow and Capillarity in Materials Assembly: Continuum Modelling and Simulation

Exploiting Flow and Capillarity in Materials Assembly: Continuum Modelling and Simulation

Summary of the project FlowMat has explored new ways in which fluid interfaces and capillarity can be exploited in the field of materials science. The overarching objective of the project is to combine continuum simulations, mathematical modelling, and experiments to investigate the behaviour of multiphase flow mixtures featuring solid particles that adhere to fluid interfaces, the dynamics of drop deposition processes, and the mechanics of anisotropic colloids interacting with fluids or fluid interfaces. Over the past four years we have been developing the Fast Interface Particle Interaction (FIPI) method. This is a conceptually new numerical method that allows the accurate simulation of thousands of particles interacting with fluid interfaces on a common PC. The method can be used to investigate numerous applied problems, from the optimization of the state of dispersion in multiphase polymer blends to drop generation in microfluidic devices. In the second period of the project we have completed a publication exploring the use of FIPI to study a pendant drop experiment, further validated the code, and applied FIPI to simulate the buckling dynamics of particle-covered drops. In collaboration with a government defence agency (the UK Defence Science and Technology Laboratory) we have investigating experimentally mechanisms of spreading in nominally omniphobic textiles. Such textiles defend soldiers in the field to potential chemical attacks. In the second period of the project, we have carried out X-Ray measurements of the penetration of the liquid inside the textile and started working on optical experiments on drop impact on textiles (collaboration with Dr. R. Castrejon-Pita). We have started a new research line on the modeling of elastic deformations of plate-like thin colloids in flow. The preliminary work we have carried out has enabled the Researcher to develop a Starter Grant proposal for the Europear Research Council (ERC) on the hydrodynamics of suspended graphene and other 2D nanomaterials. The proposal has been awarded funding by the ERC, and has started in Apr. 2017. Scientific achievements The most prominent advancement in the past 4 years has been the development of the Fast Interface Particle Interaction (FIPI) method. We have developed FIPI from scratch. This has taken about 1.5 years. We have then applied the FIPI method to the problem of analyzing the surface stress on a pendant drop whose surface is covered with colloidal particles. The analysis was carried out both for static drops and for drops that pinch off. The work has resulted in a publication on Soft Matter. The work is the first analysis of a pendant drop simulation in which the quasi-solid surface layer is not treated as a continuum. We have then applied FIPI to the simulation of a drop covered with particles, to examine the conditions for which the drop sheds particles vs. the condition leading to drop buckling. The work is currently under review in Soft Matter. We have carried out an experimental analysis of liquid pendentration inside a textile. Our work is pioneering: we have been able to visualise the microscopic dynamics of penetration across the textile (in the thickness direction), using oils with ultralarge viscosity to slow down the penetration process. No published work has given accurate data on the normal liquid penetration in textiles, so our work is expected to have significant scientific and technological impact. The work has been published on Langmuir. We have carried out the first numerical analysis of exfoliation by “hydrodynamic peeling”, a microscopic process of relevance to the production of graphene on industrial scales. The work is currently under review. Expected results and impact This CIG-funded project has produced 4 main impact results. - A new numerical method has been developed: the Fast Interface Particle Interaction (FIPI) method. FIPI has received quite a lot of attention from researchers interested in the dynamics of multiphase fluid-fluid systems with suspended particles. Colleagues from Tsinghua University (China) and University of Arkansas (USA) have requested a copy of the software for their research. - Pioneering high-resolution experiments on drops interacting with textiles have been carried out. We have characterised liquid penetration in textiles using dynamic X-Ray experiments, and are currently examining drop impact experiments using high-speed imaging. - Funding from the CIG has enabled the fellow to initiate a research line on hydrodynamics of graphene suspension that has led to an ERC Starter Grant and a promotion to Senior Lecturer as a result. - The fellow has collaborated with researchers from University of Twente on the dynamics of drops deposited on viscoelastic layers. The work has resulted in joint publications in the Journal of Fluid Mechanics and PNAS.

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