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32 results on '"Pilkington, Georgia A."'

5. Grazing incidence neutron scattering for the study of solid–liquid interfaces

Author

Wolff, Max, primary, Frielinghaus, Henrich, additional, Cárdenas, Marité, additional, Gonzalez, Juan Fransisco, additional, Theis-Bröhl, Katharina, additional, Softwedel, Olaf, additional, von Klitzing, Regine, additional, Pilkington, Georgia A., additional, Rutland, Mark W., additional, Dahint, Reiner, additional, and Gutfreund, Philipp, additional

Published
2023
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7. Elastic deformation during dynamic force measurements in viscous fluids

Author

Wang, Yumo, Pilkington, Georgia, Dhong, Charles, and Frechette, Joelle

Subjects
Condensed Matter - Soft Condensed Matter
Abstract

Understanding and harnessing the coupling between lubrication pressure and elasticity provides materials design strategies for applications such as adhesives, coatings, microsensors, and biomaterials. Elastic deformation of compliant solids caused by viscous forces can also occur during dynamic force measurements in instruments such as the surface forces apparatus (SFA) or the atomic force microscope (AFM). We briefly review hydrodynamic interactions in the presence of soft, deformable interfaces in the lubrication limit. More specifically, we consider the scenario of two surfaces approaching each other in a viscous fluid where one or both surfaces is deformable, which is also relevant to many force measurement systems. In this article the basic theoretical background of the elastohydrodynamic problem is detailed, followed by a discussion of experimental validation and considerations, especially for the role of elastic deformation on surface forces measurements. Finally, current challenges to our understanding of soft hydrodynamic interactions, such as the consideration of substrate layering, poroelasticity, viscoelasticity, surface heterogeneity, as well as their implications are discussed.

Published
2018
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10. Interactions in dendrimer nanofluids

Author

Pilkington, Georgia A.

Subjects
620.1
Abstract

Fluids containing nano-sized structures are being increasingly employed in modern technologies, ranging from lubrication fluids to drug delivery. However, despite their numerous applications, our fundamental understanding of the surface forces mediated by nanofluids is still relatively limited. In particular, due to their nanosize and related characteristics, the applicability of established surface force theories, such as the DLVO theory, remain unclear. With several tunable parameters such as the size, shape and surface chemistry, dendritic macromolecules (or dendrimers) offer a unique model nanofluid for investigating the effect of nanostructures on classic colloidal phenomena. Accordingly small-angle X-ray scattering (SAXS) and X-ray reflectivity (XRR) measurements have been performed to study the interactions between negatively charged poly(amidoamine) (PAMAM) dendrimers in the bulk and at the mica-water interface. In particular, how their interactions can be influenced by the presence of cationic surfactant dodecyl trimethyl ammonium bromide (DTAB) have been studied. Using a version of the surface force apparatus (SF A), the surface forces mediated by these dendrimer-surfactant mixtures under nano-confinement and shear have then also been directly measured. In further work the effect of the surface chemistry on the interactions in dendrimer nanofluids has been studied in two systems: i) as a comparison to the above system, the interactions between positively charged dendrimers with an anionic surfactant have been characterised both in the bulk and at the mica interface using SAXS and XRR, and ii) the interactions between three different surface chemistries of P AMAM dendrimers in an ionic surfactant mesophase have investigated using SAXS. Overall, the results presented demonstrate the tunability of inter-dendrimer interactions via their intramolecular architecture, which in turn may be harnessed to control and tailor the physical properties of dendrimer nanofluids. Such interactions bear fundamental importance to the application of dendrimers, as well as contribute to a better understanding of the surface forces mediated nanofluids.

Published
2015

13. Grazing incidence neutron scattering for the study of solid–liquid interfaces

Author

Wolff, Max, Frielinghaus, Henrich, Gutfreund, Philipp, Cárdenas, Marité, Gonzalez, Juan Fransisco, Theis-Bröhl, Katharina, Softwedel, Olaf, von Klitzing, Regine, Pilkington, Georgia A., Rutland, Mark W., and Dahint, Reiner

Abstract

Neutrons are characterized by a low absorption in many engineering materials. At the same time the scattering cross section of light elements, such as hydrogen and deuterium, may be large. These properties make neutron scattering experiments performed under grazing incidence geometry an excellent tool for the study of solid–liquid interfaces. In this review we describe the basic concepts of neutron reflection and grazing incidence scattering experiments as well as experimental procedures and sample cells. The full power of the method is exemplified on a range of science areas, including polymers, bio- and ionic liquid lubricants, electrolytes as well as bio-membranes or magnetic liquids.

Published
2023

17. Electro-responsivity of ionic liquid boundary layers in a polar solvent revealed by neutron reflectance.

Author

Pilkington, Georgia A., Harris, Kathryn, Bergendal, Erik, Reddy, Akepati Bhaskar, Palsson, Gunnar K., Vorobiev, Alexei, Antzutkin, Oleg. N., Glavatskih, Sergei, and Rutland, Mark W.

Subjects
*IONIC liquids, *BOUNDARY layer (Aerodynamics), *NEUTRON reflectivity, *POLAR solvent analysis, *MEASUREMENT of viscosity, *ION scattering
Abstract

Using neutron reflectivity, the electro-responsive structuring of the non-halogenated ionic liquid (IL) trihexyl(tetradecyl)phosphonium-bis(mandelato)borate, [P6,6,6,14][BMB], has been studied at a gold electrode surface in a polar solvent. For a 20% w/w IL mixture, contrast matched to the gold surface, distinct Kiessig fringes were observed for all potentials studied, indicative of a boundary layer of different composition to that of the bulk IL-solvent mixture. With applied potential, the amplitudes of the fringes from the gold-boundary layer interface varied systematically. These changes are attributable to the differing ratios of cations and anions in the boundary layer, leading to a greater or diminished contrast with the gold electrode, depending on the individual ion scattering length densities. Such electro-responsive changes were also evident in the reflectivities measured for the pure IL and a less concentrated (5% w/w) IL-solvent mixture at the same applied potentials, but gave rise to less pronounced changes. These measurements, therefore, demonstrate the enhanced sensitivity achieved by contrast matching the bulk solution and that the structure of the IL boundary layers formed in mixtures is strongly influenced by the bulk concentration. Together these results represent an important step in characterising IL boundary layers in IL-solvent mixtures and provide clear evidence of electro-responsive structuring of IL ions in their solutions with applied potential. [ABSTRACT FROM AUTHOR]

Published
2018
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26. A multifunctional force microscope for soft matter with <italic>in situ</italic> imaging.

Author

Roberts, Paul, Pilkington, Georgia A., Wang, Yumo, and Frechette, Joelle

Subjects
*ATOMIC force microscopy, *FINITE element method, *X-ray diffraction, *MAGNETIC force microscopy, *POLYDIMETHYLSILOXANE
Abstract

We present the multifunctional force microscope (MFM), a normal and lateral force-measuring instrument with in situ imaging. In the MFM, forces are calculated from the normal and lateral deflection of a cantilever as measured via fiber optic sensors. The motion of the cantilever is controlled normally by a linear micro-translation stage and a piezoelectric actuator, while the lateral motion of the sample is controlled by another linear micro-translation stage. The micro-translation stages allow for travel distances that span 25 mm with a minimum step size of 50 nm, while the piezo has a minimum step size of 0.2 nm, but a 100 μm maximum range. Custom-designed cantilevers allow for the forces to be measured over 4 orders of magnitude (from 50 μN to 1 N). We perform probe tack, friction, and hydrodynamic drainage experiments to demonstrate the sensitivity, versatility, and measurable force range of the instrument. [ABSTRACT FROM AUTHOR]

Published
2018
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30. Quiescent bilayers at the mica–water interface

Author

Speranza, Francesca, primary, Pilkington, Georgia A., additional, Dane, Thomas G., additional, Cresswell, Philip T., additional, Li, Peixun, additional, Jacobs, Robert M. J., additional, Arnold, Thomas, additional, Bouchenoire, Laurence, additional, Thomas, Robert K., additional, and Briscoe, Wuge H., additional

Published
2013
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32. Amontonian frictional behaviour of nanostructured surfaces

Author

Pilkington, Georgia A., primary, Thormann, Esben, additional, Claesson, Per M., additional, Fuge, Gareth M., additional, Fox, Oliver J. L., additional, Ashfold, Michael N. R., additional, Leese, Hannah, additional, Mattia, Davide, additional, and Briscoe, Wuge H., additional

Published
2011
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