On May 21st 2018 we welcomed Zelie Brodard, a student from the Institut d’Optique Graduate School in Paris, France, for a three month research project entitled “Whispering-gallery-mode… Read more “We welcome project student Zelie Brodard”
Orienting lipid-coated graphitic micro-particles in solution using AC electric fields: A new theoretical dual-ellipsoid Laplace model for electro-orientation, J.Nguyen, Jonathan G. Underwood and I.Llorente García. Colloids and Surfaces A: Physicochemical and Engineering Aspects 549, 237-251 (2018). Link to published paper. Link to free accepted manuscript in Arxiv.
Graphitic micro-particles coated with thin layers in solution are technologically interesting as they can be manipulated with electric fields. Modeling the electrical manipulation of submerged layered micro-particles analytically or numerically is not straightforward. In particular, the generation of reliable quantitative torque predictions for electro-orientation experiments has been elusive. The traditional Laplace model approximates the coated particle by an ellipsoid with a confocal ellipsoidal layer and solves Laplace’s equation to produce convenient analytical predictions. However, due to the non-uniformity of the layer thickness around the ellipsoid, this method can lead to incorrect torque predictions. Here we present a new theoretical dual-ellipsoid Laplace model that corrects the effect of the non-uniform layer thickness by calculating two layered ellipsoids, each accounting for the correct layer thickness along each relevant direction for the torque. Our model describes the electro-orientation of submerged lipid-coated graphitic micro-particles in the presence of an alternating current (AC) electric field and is valid for ellipsoids with moderate aspect ratios and coated with thin shells. It is one of the first models to generate correct quantitative electric torque predictions. We present model results for the torque versus frequency and compare them to our measurements for lipid-coated highly ordered pyrolytic graphite (HOPG) micro-flakes in aqueous NaCl solution at MHz frequencies. The results show how the lipid shell changes the overall electrical properties of the micro-flakes so that the torque is low at low frequencies and increases at higher frequencies into the MHz regime. The torque depends critically on the lipid-shell thickness, the solution conductivity and the shape of the particle, all of which can be used as handles to control the response of the particles.
On 29-June-2017, we have had four groups of undergraduate students touring our lab and learning about our Biophysics research. Approx. 20 Physics undergraduate and masters students attending the annual Conference of Astronomy and Physics Students (CAPS’17) at UCL passed by and PhD students Johnny Nguyen and Dario Conca, together with project student Basile Khatir, explained their experiments to them:
On May 29th 2017 we welcomed UCL Natural Sciences student Tessa Hughes into our lab.
Tessa is joining us for 8 weeks to work with PhD student Dario V. Conca on experiments of single-molecule force sensing and fluorescence microscopy on living cells to investigate virus entry.
On May 22nd 2017 we welcomed Basile Khatir, a student from the Institut d’Optique Graduate School in Paris, France.
Basile is joining us for three months to work on a project entitled “Whispering-gallery-mode biosensors for early diagnosis of disease“. For this project, our lab collaborates with Prof. Peter Barker and Dr. Lia Li at UCL Physics.
Below, Sophie Minoughan and Pavel Tolar at the new building of the Francis Crick Institute in London, at a social event to welcome new PhD students on Monday 26-September-2016.
PhD student Johnny Nguyen measuring the magnetic properties of graphitic blocks and micro-particle aggregates at the London Centre for Nanotechnology, in collaboration with Dr. Laura Bovo.
This week, PhD student Dario Valter Conca and Isabel Llorente-Garcia are making use of the Optical Tweezer facilities at the Lasers for Science Facility -Central Laser Facility- at the Rutherford Appleton Laboratory.
He is currently working on the alignment of the light-sheet fluorescence optics. See some of his photos of the set-up below: