Session G34: Micro/Nano scale Flows: Opto/Electro/Magnetic Manipulation

An Integrated Acoustofluidic Device with Raman Spectroscopy for Process Analytical Technology for Continuous Manufacturing of Vaccines

Viral epidemics and pandemics require rapid development and manufacturing of vaccines to limit the spread of the disease and minimize loss of life. Rapid production of vaccines requires standardized processes for controlling the quality of the product, demanding more innovative and reliable methods in process analytical technology (PAT). In this project, we use Raman spectroscopy as a PAT tool and combine it with machine learning algorithms to characterize viral particles for continuous in-process monitoring of vaccine contents. We use acoustofluidic methods to concentrate particles and improve the Raman signal and establish the basis for a standardized detection method. Different virus-like particles and vaccines were tested and characterized , showing our capability to identify the viral particles using the Raman spectra. Our spectro-acoustic PAT enables the real-time quantification of virus particles necessary for the continuous manufacturing of vaccines.    

Control of cohesive states in colloidal chiral fluids

Active matter systems are composed of autonomous interacting units that continuously dissipate energy, exerting mechanical forces and stresses. Several non-equilibrium phenomena emerge in these systems, governed by the interplay between self-propulsion, thermal fluctuations, and pairwise interactions. In contrast to self-propelling particles, spinning particles in fluids constitute a new class of active matter systems which exhibit coherent dynamical structures through hydrodynamic interactions. A recent experimental realization is a dense chiral fluid composed of spinning colloidal magnets driven by a uniform external rotating magnetic field. These particles couple both via dipolar and hydrodynamic interactions and organize into circulating clusters with unidirectional edge flows. Here we report a mechanism to externally control the collective states of spinning magnetic particles by introducing additional diffusio-osmotic interactions. At a collective scale, we show that this additional interaction leads to a loss in cohesivity in circulating clusters and promotes reversible expansion of the rotating cluster vortex. We identify an activity induced colloidal chain-branching mechanism that mediates the transition between a circulating cluster and its expanded state, which is responsible for the loss in cohesivity. Introduction of chemical activity-based interactions in chiral fluids paves the way for a new paradigm of self-organization routes in chiral active matter.   

Modelling and investigation of magnetic soap films

Adding magnetic particles to a soap film allows for a magnetic field to control the drainage in the film, which has key implications on the film stability since thinner films are less stable and more prone to rupture. Interference colours exhibited by soap films reveal the time evolution of the film thickness. An accurate model for the film thickness, which can be directly compared with experimental results, will allow for predictions of the film lifetime with different magnetic field arrangements. Existing models for the film thickness of magnetic soap films disregard essential physics by assuming a uniform film magnetisation and immobile interfaces. In this study, the lubrication approximation is applied to the Navier-Stokes equations to derive a model for the film thickness that incorporates additional physics compared to previous models. This new model consists of a coupled system of equations for the film thickness, magnetic nanoparticle concentration, surface velocity, and interfacial surfactant concentration. Simulations are performed by solving the system of equations with the finite element method, and results are compared with experiments. Our findings suggest that the migration of nanoparticles and the surface velocity have a significant impact on film thinning. With further research, it is envisaged that magnetic soap bubbles could be used as responsive capsules: magnetic fields could be used to control the capsule location and trigger the release of substances.   

Localized Magnetohydrodynamic-Induced Convection to Control Dendritic Morphologies

The growth of metal dendrites is governed by the ionic concentration and the operating current of an electrochemical reactor. The growth of dendritic structures can be suppressed by forced convection as shown in the literature. However, the bulk force applied requires energy input for its operation. Using a microfluidic reactor, we show an energy-efficient way of suppressing the dendrites using a magnetic field, which can also be applied for the extraction of ionic components. The applied magnetic field modifies the morphology of the deposits locally by exhibiting anisotropy and three-dimensional deposition along a preferred pathway. The magnetic field promotes bulky growth with reduced heights under chronoamperometry and shows enhanced rates of extraction under chronopotentiometry. The growth of dendrites, and the flow of electrolytes around them, create a synergistic effect by inducing localized flows around conductive boundaries. This paves the way for its application in battery systems where dendrites can be controlled and also in electrochemical separation techniques where the energy-efficient electrodeposition is favorable.