Hélène Yockell-Lelièvre

Optical tests of nanoengineered liquid mirrors

We describe a new technology for the fabrication of inexpensive high-quality mirrors. We begin by chemically producing a large number of metallic nanoparticles coated with organic ligands. The partides are then spread on a liquid substrate where they self-assemble to give optical quality reflective surfaces. Since liquid surface can be modified by a variety of means (e.g., rotation, electromagnetic fields), this opens the possibility of making a new class of versatile and inexpensive optical elements that can have complex shapes and that can be modified within short time scales. Interferommetric measurements show optical quality surfaces. We have obtained reflectivity curves that show 80% peak reflectivities. We are confident that we can improve the reflectivity curves because theoretical models predict higher values. We expect nanoengineered liquid mirrors to be useful for scientific and engineering applications. The technology is interesting for large optics, such as large rotating parabolic mirrors, because of its low cost. Furthermore, because the surfaces of of ferrofluids can be shaped with magnetic fields, one can generate complex, time-varying surfaces that are difficult to make with conventional techniques.

Nanoengineered astronomical optics

We describe a technology for the fabrication of inexpensive and versatile mirrors through the use of a new type of nanoengineered optical material composed by the spreading of a self-assembling reflective colloidal film spread at the surface of a liquid. These new reflecting liquids offer interesting possibilities for astronomical instrumentation. For example, they can replace mercury in conventional rotating liquid mirrors. The main advantages offered include extremely low cost and, by coating a viscous liquid, the possibility of tilting the mirror by a few tens of degrees. We also have coated ferromagnetic liquids with these reflecting films. The resulting surfaces can be shaped by the application of a magnetic field, yielding reflecting surfaces that can have complicated shapes that can rapidly shift with time. These inexpensive and versatile optical elements could have numerous scientific and technological applications. Among possible astronomical applications, they could be used to make large inexpensive adaptive mirrors exhibiting strokes ranging from nanometers to several millimeters.

Ferrofluid-based deformable mirrors: a new approach to adaptive optics using liquid mirrors

The trend towards ever larger telescopes and more advanced adaptive optics systems is driving the need for deformable mirrors with a large number of low cost actuators. Liquid mirrors have long been recognized a potential low cost alternative to conventional solid mirrors. By using a water or oil based ferrofluid we are able to benefit from a stronger magnetic response than is found in magnetic liquid metal amalgams and avoid the difficulty of passing a uniform current through a liquid. Depositing a thin silver colloid known as a metal liquid like film (MELLF) on the ferrofluid surface solves the problem of low reflectivity of pure ferrofluids. This combination provides a liquid optical surface that can be precisely shaped in a magnetic field. We present experimental results obtained with a prototype deformable liquid mirror based on this combination.

Ribbon-like and spontaneously folded structures of tungsten oxide nanofibers fabricated via electrospinning

Tungsten oxide (WO3) nanofibers with shapes ranging from cylindrical to ribbon-like were prepared by annealing electrospun polyvinylpyrrolidone/ammonium metatungstate (PVP/AMT) fibers. Formation of periodically folded “zigzag” patterns in PVP/AMT and WO3 ribbon-like fibers was observed for the first time at the initial stage of the electrospinning process on the surface of a stationary substrate. Among methods tested (capillary needle, needleless dc- and ac-electrospinning), only the capillary needle dc-electrospinning process was effective in producing ribbon-like fiber structures. Annealing of such PVP/AMT fibers at 500 °C in air led to the formation of 80 ± 10 nm thick WO3 ribbons with a width-to-thickness ratio of up to 50 : 1. Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), and Raman spectroscopy were used to analyze the material. Analyses revealed that regardless the fibers shape, the annealed oxide fibers were polycrystalline with a grain size of 60 ± 30 nm and consisted of the monoclinic phase of WO3. When compared to cylindrical fibers, the ribbon-like WO3 nanofibers exhibited higher porosity but lower mechanical strength with increased width of the ribbon-like structure.

Assembly of polystyrene-coated gold nanoparticles at the air–water interface

Gold nanoparticles (NPs) coated with thiol-terminated polystyrene chains of varying molar mass were added to polystyrene-b-polymethylmethacrylate (PS-b-PMMA) block copolymer monolayers at the air-water interface. Composite films were transferred to solid substrates by the Langmuir-Blodgett technique. For most of the investigated systems, TEM micrographs and AFM images reveal the formation of 2D island-like aggregates of particles organized on a close-packed hexagonal lattice. This characteristic aggregate formation is lost when PS ligands are within the same length regime as the PS block from the copolymer. The results are compared with those obtained for analogous systems containing no copolymer where NPs are deposited on either a bare water surface or bare glass. Interparticle distance between NPs is found to depend on the surface on which they are deposited, the presence or not of the copolymer monolayer, and ligand length.

Applications of magnetically shaped liquid optical surfaces

In this paper we present preliminary results on a new type of optical material. By combining a thin reflective colloidal film with a superparamagnetic liquid known as a ferrofluid, it is possible to produce an optical quality surface that can be shaped by the application of a magnetic field. Ferrofluids are colloidal suspensions of nanometer-sized magnetic particles and are considered a well established, low-risk technology. We have demonstrated deformations of several microns at frequencies exceeding 100 Hz, making the material useful as a deformable mirror for adaptive optics and also of potential interest in numerous other optical devices. Liquid optics are relatively inexpensive when compared to conventional glass surfaces of similar quality and are free of mechanical constraints such as resonance and limits on the displacement of adjacent actuators. We present results to date and discuss some of the potential applications of liquid optics as well as the challenges remaining in realising practical devices based on this technology.

Carbon Nanospheres for Biomedical Applications

Carbon nanostructures, e.g., nanotubes, fullerenes, carbon blacks, etc., are being extensively explored for numerous biomedical applications. The most of such studies, however, deal with carbon nanotubes, and comparatively less is known on the biomedical potential of other nanosize carbon particles. In the present work, carbon and metal/carbon core/shell spherical nanoparticles have been prepared using the decomposition of monosaccharide-based compositions under hydrothermal conditions with or without the presence of metal seed particles. The effects of different process conditions on the particle size, structure, and composition have been examined using TEM, XRD, UV-Vis, FTIR and Raman spectroscopies. The nearly perfect spherical particles with the dimensions in the range of 20 – 100 nm have been obtained depending on the process parameters such as precursor concentration, presence of seed particles and polymeric additives, process temperature and time. The particles prepared with 5 – 20 nm gold seeds clearly showed the core/shell structure with the thickness of carbon shell in the range of 10 – 50 nm. The FTIR experiments have indicated a strong effect of the processing conditions on the chemical activity of nanoparticle surfaces in the attachment of the additional surface functional groups and organic molecules. It has been found that the both hydrothermally prepared carbon and metal/carbon core/shell nanoparticles possess very good dispersibility and stability in the both water and simulated body fluids in the most of experiments. The particles have been successfully functionalized with several molecules such as polyethyleneglucol and biotin. Selected samples of well-dispersed carbon nanospheres with different concentrations have been tested for their interaction with several cultured cell lines including epidermal keratinocytes, fibroblasts, and dog macrophages.