School of Chemistry - Research Publications

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    Precise measurements of capsule mechanical properties using indentation
    Berry, JD ; Mettu, S ; Dagastine, RR (ROYAL SOC CHEMISTRY, 2017-03-14)
    Application of elastic theory to experimental data of capsule and particle compression under-predicts the value of material properties such as the Young's modulus by up to 100% when the effect of the rigid substrate is neglected, as is commonly done in the literature. Results of numerical simulations, spanning the range from thin-shelled capsules to solid particles, are presented in terms of correction factors that account for the substrate. In addition, the scaling relationship between indentation force and displacement is characterised for arbitrary shell thicknesses and indenter radii.
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    Dynamic forces between emulsified water drops coated with Poly-Glycerol-Poly-Ricinoleate (PGPR) in canola oil
    Mettu, S ; Wu, C ; Dagastine, RR (ACADEMIC PRESS INC ELSEVIER SCIENCE, 2018-05-01)
    The dynamic collision of emulsified water drops in the presence of non-ionic surfactants plays a crucial role in many practical applications. Interaction force between water drops coated with non-ionic food grade surfactants is expected to exhibit rich dynamic behavior that is not yet explored. The collision forces between immobilized water drops in canola oil in the presence of a well-known food grade surfactant polyglycerol polyricinoleate (PGPR) are measured at concentrations well below typically used to form stable emulsions. An extension or kink, attributed to a short-range attractive interaction due to PGPR bridging between the drops, was observed in the retract portion of the force curves at higher applied forces or slower collision velocities. The Stokes-Reynolds-Young-Laplace (SRYL) model was used to calculate theoretical force curves. For higher collisions velocities, the agreement between the calculated and experiment data was acceptable, but the SRYL model failed to describe the extension or kink feature observed at slower velocities below. Both the AFM data and the comparison to the model calculation indicated the presence of a short-range attractive force, not of a hydrodynamic origin, attributed to the bridging and extension of PGPR molecules on the surface of water drops below saturation of the interface.
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    Hydrodynamic boundary conditions and dynamic forces between bubbles and surfaces
    Manor, O ; Vakarelski, IU ; Tang, X ; O'Shea, SJ ; Stevens, GW ; Grieser, F ; Dagastine, RR ; Chan, DYC (AMER PHYSICAL SOC, 2008-07-11)
    Dynamic forces between a 50 microm radius bubble driven towards and from a mica plate using an atomic force microscope in electrolyte and in surfactant exhibit different hydrodynamic boundary conditions at the bubble surface. In added surfactant, the forces are consistent with the no-slip boundary condition at the mica and bubble surfaces. With no surfactant, a new boundary condition that accounts for the transport of trace surface impurities explains variations of dynamic forces at different speeds and provides a direct connection between dynamic forces and surface transport effects at the air-water interface.