Particle Velocities near and along the Electrode during Electrophoretic Deposition: Influence of Surfactant Counter-Ions

Research into the micro-nanostructured coatings process has made a variety of new applications available. Electrophoretic deposition (EPD) is an efficient and attractive technique to produce coated materials. Therefore the understanding of the formation and growth mechanism of the coating process continues to be investigated. In this study, a home-made EPD laminar flow cell was used for in-situ investigation of the particle velocity and deposition of micronic particles on a cathode. Monodisperse polystyrene latex particles were functionalized with cationic surfactants: cetyltrimethyl ammonium bromide (CTAB) or cetyltrimethyl ammonium chloride (CTAC). The tangential velocity of the particles when they migrated to the electrode, the approach angle and the tangential velocity along the electrode were measured under a DC electric field. From the values of the velocities, the particle-electrode distance was evaluated in CTAB and CTAC solutions. The electrophoretic velocity was calculated from the electrophoretic mobility of the particles and the electric field applied to the particles. All these parameters depend on the type of surfactant counter-ions and influence the growth of the coating. Dense structures were obtained in CTAB solution while open structures were observed in CTAC solution

Electrical conductivity enhancement and wettability modification of (PDDA/PEDOT:PSS)n multilayer film

International audienceConductive polyelectrolyte multilayer films composed of conductive anionic poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) and insulating cationic polydiallyldimethylammonium chloride (PDDA) were successfully prepared by layer-by-layer method. The (PDDA/PEDOT:PSS)n multilayer thickness is affected by the PDDA concentration ranging from 0.25g.L−1 to 1g.L−1 as well as the number of deposited bilayers and the type of salts used as electrolyte (BaCl2 or NaCl). More precisely, film thickness measured by profilometry increases with PDDA concentration, number of adsorbed bilayers and with the presence of Ba2+ cations. From UV–Visible absorbance spectroscopy, we showed that the amount of adsorbed PEDOT:PSS is greater when PDDA concentration increases and that PEDOT is still incorporated into the multilayer film especially when divalent ions are employed to improve the film growth. Water contact angles were measured on (PDDA/PEDOT:PSS)n films with PEDOT:PSS as the outerlayer. Films are more hydrophobic in the presence of Ba2+ which is probably due to a modification of the PEDOT:PSS core/shell structure. A percolation threshold leading to electrical conduction was determined as a function of the number of adsorbed bilayers. The effect of several parameters such as PDDA concentration, type of salt and temperature on conductivity and activation energy was investigated

Electrodeposition and characterisation of polythiophene films on gold substrates

International audienceStar-shaped oligothiophenes are interesting to use in building super-structured materials. We have already used them to improve particle adhesion and assembly onto conductive substrates in an aqueous medium. In this study, electropolymerization of two different monomers, tris(2,2µ- dithienyl)methylcarbinol (TMC) and bithiophene (BT), was carried out on gold film, which was deposited by PVD on silicon wafers. The numbers of cycles and the scan rate have been changed to modify the morphology of the deposit. The polymer films were then characterised by cyclic voltammetry, classical microscopy, atomic force microscopy and scanning electronic microscopy. Polytris(2,2µ- dithienyl)methylcarbinol (PTMC) film was flatter, thicker and more uniform than polybithiophene (PBT) film. Finally electrophoretic deposition of composite particles has been carried out on PBT and PTMC films

Synthesis and characterization of polyaniline-silica composites: Raspberry vs core-shell structures. Where do we stand?

International audienc

The electrical and mechanical characteristics of conductive PVA/PEDOT:PSS hydrogel foams for soft strain sensors

Conductive hydrogels are of interest for highly flexible sensor elements. We compare conductive hydrogels and hydrogel foams in view of strain-sensing applications. Polyvinyl alcool (PVA) and poly(3,4-ethylenedioxythiophene (PEDOT:PSS) are used for the formulation of conductive hydrogels. For hydrogel foaming, we have investigated the influence of dodecylbenzenesulfonate (DBSA) as foaming agent, as well as the influence of air incorporation at various mixing speeds. We showed that DBSA acting as a surfactant, already at a concentration of 1.12wt%, efficiently stabilizes air bubbles, allowing for the formulation of conductive PVA and PVA/PEDOT:PSS hydrogel foams with low density ( 1500%). The resulting Young moduli depend on the air-bubble incorporation from mixing, and are affected by freeze-drying/rehydration. Using dielectric broadband spectroscopy under mechanical load, we demonstrate that PVA/PEDOT:PSS hydrogel foams exhibit a significant decrease in conductivity under mechanical compression, compared to dense hydrogels. The frequency-dependent conductivity of the hydrogels exhibits two plateaus, one in the low frequency range, and one in the high frequency range. We find that the conductivity of the PVA/PEDOT:PSS hydrogels decreases linearly as a function of pressure in each of the frequency regions, which makes the hydrogel foams highly interesting in view of compressive strain-sensing applications

Conductive multilayer film based on composite materials made of conjugated polyelectrolytes and inorganic particles

International audiencePoly(3,4-ethylenedioxythiophene)–polystyrene sulfonate (PEDOT:PSS) conjugated polymer blend and a cationic poly(3-hexylthiophene) (P3HT)-based conjugated polyelectrolyte incorporating imidazolium ionic side groups were first adsorbed as monolayer on inorganic colloidal particles. At the plateau of adsorption isotherm, adsorbed amount of PEDOT:PSS on alumina particles appears lower than the adsorbed amount of P3HT on silica particles. Both polyelectrolytes strongly modify the surface charge of particles as reveals by zeta potential variation. Functionalized particles were then assembled using Layer-by-Layer method in order to prepare (PDDA/Al2O3-PEDOT:PSS)n and (SiO2-P3HT/PEDOT:PSS)n conductive multilayer film. Thicker PDDA/Al2O3-PEDOT:PSS films were elaborated when a drying step was added during the LbL build-up. The same effect was observed when composite particle concentration was increased from 1 to 10 g.L−1. Electrical behavior of film was completely modified in comparison with PDDA/PEDOT:PSS assembly. After heating at 150 °C, no conductivity was detected due to microcracks visible on SEM images. For SiO2-P3HT/PEDOT:PSS assembly, thickness is higher than for PDDA/Al2O3-PEDOT:PSS assembly using the same experimental procedure. However, even if two conductive polyelectrolytes were embedded into the film, conductivity was too low at 30 °C to be measured by van der Pauw technique probably due to the cracking of the film induced by incorporation of silica particles

Nanoarchitectonics of eco-friendly nickel oxide nanoplatelets for energy storage

[EN] Nanostructured nickel hydroxide coatings were prepared directly by aqueous electrophoretic deposition (EPD) method without binder or organic solvent. β-Ni(OH) nanoplatelets were first synthetized by chemical precipitation from nickel nitrate in ammonia under ultrasound. These particles, stabilized at pH ≈ 8, present an equivalent diameter of 250 nm and an electrophoretic mobility of ≈ + 2.5 × 10 m V s. Cathodic EPD was performed at room temperature for different values of particles concentration, deposition time and applied electric field. An optimal coating was achieved using a 1 g L of β-Ni(OH) particles suspension during 30 min deposition time at an electric field of 75 V m. In this work, the suspension conductivity was studied showing that a very narrow range of conductivity can leads to efficient deposition in aqueous EPD. The β-Ni(OH) coatings were heated at 325 °C in air for 1, 2 and 3 h to form NiO films. The electrochemical properties of the NiO films were evaluated by cyclic voltammetry (CV) and galvanostatic charge/discharge (GCD). Significant differences were observed in term of specific capacitance values as a function of annealing time and film thickness. Finally, the film microstructure was determined by the calculation of the electrochemically active surface area (ECSA) using Randles–Ševčík equation.Funding was provided by Ministère de l'Enseignement supérieur, de la Recherche et de l'Innovation.Peer reviewe

Flexible and conductive multilayer films based on the assembly of PEDOT:PSS and water soluble polythiophenes

International audienceFlexible conductive polyelectrolyte multilayer films built upon anionic poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) and cationic poly(3-hexylthiophene)-based conjugated polyelectrolytes (P3HT-R) containing imidazolium, pyridinium and phosphonium ionic groups were prepared using electrostatic layer-by-layer assembly. Adsorbed amount of each polyelectrolyte strongly increases when divalent cations (Ba2+) are employed as electrolyte and when the rinsing step is avoided during the build-up. The electrical properties of these (P3HT-R/PEDOT:PSS)n multilayer films were then investigated using the van der Pauw method leading to an average conductivity of ∼2 S m−1. Semiconducting behavior of these organic coatings was demonstrated by the direct relationship between the conductivity and the temperature. (P3HT-R/PEDOT:PSS)n multilayer films exhibited p-type semiconducting behavior as showed by Seebeck measurements. Finally, these films were successfully deposited onto flexible polymer sheets and their conductivity was found to be not affected by applying a bending stress