A5047747771- Organic Electronics and Photovoltaics
- Organic Light-Emitting Diodes Research
- Conducting polymers and applications
- Force Microscopy Techniques and Applications
- Molecular Junctions and Nanostructures
- Porphyrin and Phthalocyanine Chemistry
- Polymer Surface Interaction Studies
- Thermochemical Biomass Conversion Processes
- Nonlinear Optical Materials Research
- Thin-Film Transistor Technologies
- Photochemistry and Electron Transfer Studies
- Luminescence and Fluorescent Materials
- Block Copolymer Self-Assembly
- Liquid Crystal Research Advancements
- Polymer crystallization and properties
- Ferroelectric and Piezoelectric Materials
- Hydrogels: synthesis, properties, applications
- Semiconductor materials and devices
- Polymer Nanocomposites and Properties
- Advanced Polymer Synthesis and Characterization
- Quantum and electron transport phenomena
- Graphene research and applications
- Electrochemical Analysis and Applications
- Ferroelectric and Negative Capacitance Devices
- Fluid Dynamics and Thin Films
University of Minnesota
2024
Loughborough University
2010-2023
University of California, San Diego
2023
Institut des Nanotechnologies de Lyon
2014-2019
Université Claude Bernard Lyon 1
2014-2019
Centre National de la Recherche Scientifique
2014-2019
Institut National des Sciences Appliquées de Lyon
2017-2019
University of Lausanne
2017
Instituto de Estructura de la Materia
2005-2012
University of Sheffield
2000-2011
We have studied the interplay between photophysics and film morphology of poly(9,9-dioctyl)fluorene (PFO) using a variety optical probes. Upon slowly warming spin-cast PFO from 80 to 300 K, fraction sample is transformed into different solid phase, $\ensuremath{\beta}$ phase. Absorption electroabsorption measurements show that phase has more extended conjugation than glassy As consequence, excited states are redshifted higher polarizability. The photoinduced absorption spectrum dominated by...
The π–π* absorption edge (Q band) of the soluble porphyrin polymer 1 lies in IR region and is unusually intense. Electroabsorption (Stark) spectra demonstrate that has an exceptionally large third-order nonlinear susceptibility.
Spin coating polymer blend thin films provides a method to produce multiphase functional layers of high uniformity covering large surface areas. Applications for such include photovoltaics and light-emitting diodes where performance relies upon the nanoscale phase separation morphology spun film. Furthermore, at micrometer scales, route self-organized structures templating applications. Understanding factors that determine final phase-separated in these systems is consequently an important...
The synthesis of a new soluble conjugated porphyrin polymer 4 is reported. MALDI TOF mass spectrum shows the presence oligomers with up to 13 repeat units and GPC gives Mn 53 kDa. electronic absorption spectra this exhibit an intense Q band at 800 nm in solution 853 solid state, demonstrating high degree conjugation. Electroabsorption spectroscopy that thin films have lower resonant third order NLO susceptibility than our previous 2, whereas closed z-scan measurements indicate off-resonance...
Organic electroluminescent devices (OEDs) emit light when an electric current is applied to a thin film section. They arise from two main technology branches—small molecules and emitting polymers. Apart the insight offered into fundamentals of their physics, which relevant topics such as electrical transport in biological systems molecular computers, understanding how mobilities these vary with morphology composition enables design improved materials for technological requirements, e.g. fast...
We have investigated a novel method of remotely switching the conformation weak polybase brush using an applied voltage. Surface-grafted polyelectrolyte brushes exhibit rich responsive behavior and show great promise as "smart surfaces", but existing methods involve physically or chemically changing solution in contact with brush. In this study, high grafting density poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) were grown from silicon surfaces atom transfer radical polymerization....
We have used absorption and electroabsorption spectroscopy to investigate the electronic structure of poly(para-phenylene vinylene) (PPV) poly (2-methoxy, 5-${(2}^{\ensuremath{'}}$-(ethyl)hexyloxy)-p-phenylene (MEH-PPV). In particular we examine often assumption that PPV its dialkoxy substituted derivatives are essentially same. The spectrum consists three peaks, while MEH-PPV has four peaks. discuss controversial origin extra peak as well evidence for Davydov splitting effects in PPV....
This paper was originally accepted as a Topical Review but published, in error, regular article.
Progress in the development of generic molecular devices based on responsive polymers is discussed. Characterisation specially synthesised polyelectrolyte gels, "grafted from" brushes and triblock copolymers reported. A Landolt pH-oscillator, bromate/ sulfite/ferrocyanide, with a room temperature period 20 min range 3.1 < pH 7.0, has been used to drive periodic oscillations volume hydrogel. The gel coupled reaction changes by factor at least 6. continuously stirred, constant volume, tank...
Iridescence is an optical phenomenon whereby colour changes with the illumination and viewing angle. It can be produced by thin film interference or diffraction. Iridescent structures are fairly common in nature, but relatively little known about their production evolution. Here we describe responsible for producing blue-green iridescent Heliconius butterflies. Overall wing scale of non-iridescent species very similar, both having longitudinal ridges joined cross-ribs. However, scales have...
Abstract Cyphochilus beetle scales are amongst the brightest structural whites in nature, being highly opacifying whilst extremely thin. However, formation mechanism for voided intra-scale structure is unknown. Here we report 3D x-ray nanotomography data chitin networks of intact white and Lepidiota stigma . Chitin-filling fractions found to be 31 ± 2% 34 1% , indicating previous measurements overestimated their density. Optical simulations using finite-difference time domain morphologies...
Herein, the cytotoxicity of a novel zwitterionic sulfobetaine hydrogel system with nano-clay crosslinker has been investigated. We demonstrate that careful selection composition (monomer to Laponite content) allows material be formed into controlled shapes using an extrusion based additive manufacturing technique ability tune mechanical properties product. Moreover, printed structures can support their own weight without requiring curing during printing which enables use printing-then-curing...
We have investigated the performance of conjugated polymer light emitting diodes (LEDs) as their active areas are reduced to dimensions typical for pixellated displays. find that by reducing diameter device from our standard size (1.5×3 mm) 50 μm, current density can be sustained before LED failure increases a factor 9. This increase in is mirrored similar maximum brightness. propose such effects occur due improved thermal management small area devices. Using pulsed driving schemes, devices...
We have used helium-3 nuclear reaction analysis to study the morphology of spin-cast blends poly(9,-dioctylfluorene) (F8) and poly(9,-dioctylfluorene-alt-benzothiadiazole) as a function composition, casting solvent, initial solvent concentration. In cast from toluene, surface segregated layer is observed for broad range F8 compositions. The excess has maximum nm at an volume fraction ϕ = 0.5, dropping down –2 0.2 0.8. existence such layers could play important role in charge transport...
In this paper, we propose a new procedure which aims at measuring the polarisation switching current nanoscale on ferroelectric thin films with atomic force microscope tip used as top electrode. Our technique is an adaptation of so-called positive up negative down method commonly operated large electrodes. The main obstacle that must be overcome to implement such measurement enhancement signal noise ratio, in context where stray capacitance sample/tip/lever/lever holder system generates...
We have used neutron reflectometry to characterize the swelling behaviour of brushes poly[2-(diethyl amino)ethyl methacrylate], a polybase, as function pH. The brushes, synthesized by "grafting from" method atom transfer radical polymerization, were observed approximately double their thickness in low pH solutions, although pKa is shifted lower than dilute solution. composition–depth profile obtained from experiments for swollen reveals region depleted polymer between substrate and extended...
Poly(3,4 ethylene dioxythiophene)/poly(styrene sulfonate) (PEDT/PSS) blends are widely used in organic light‐emitting diodes (OLEDs) to enhance their performance. Using neutron reflectometry study such blends, it is shown that substantial segregation of the blend components occurs at surface (see Figure), a result will have implications both for performance and stability optoelectronic devices using PEDT/PSS.
The reversible height change dynamics of a poly(methacrylic acid) brush, weak polyelectrolyte in response to pH changes, were observed using atomic force microscopy. brush thickness could be repeatably and reversibly switched between 40 nm at 3 120 10.5. swelling collapse transitions took 6 s the AFM measurements, but high resolution spectroscopy measurements showed that can made happen less than second. We conclude time these switches is limited practise by physical taken exchange solvents...