Elaboration of a structured hydrogel matrix with controlled dissolution

International audienc

Preparation of conductive PDDA/(PEDOT:PSS) multilayer thin film: Influence of polyelectrolyte solution composition

International audienceSelf-assembled multilayer films made of PEDOT:PSS poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)and PDDA poly(diallyldimethylammonium chloride) were prepared using layer-by-layer method.In order to modify the growth regime of the multilayer, to fabricate an electrical conductive film and tocontrol its thickness, the effects of pH, type of electrolyte, ionic strength and polyelectrolyte concentrationwere investigated. Optical reflectometry measurements show that the pH of the solutions has noeffect on the film growth while the adsorbed amount increases more rapidly when BaCl2 is used insteadof NaCl as electrolyte. An increase in the ionic strength (with NaCl) induces a change in the growth regimefrom a linear to an exponential one at low polyelectrolyte concentration. As UV–vis measurementsindicate, no decomplexation of PEDOT was recorded after film preparation. With polyelectrolyte concentrationbelow 1 g L1, no conductive films were obtained even if 50 bilayers were deposited. A conductivefilm was prepared with a polyelectrolyte concentration of 1 g L1 and the measured conductivity was0.3 S m1. A slight increase in conductivity was recorded when BaCl2 was used probably due to amodification of the film structure

Polyelectrolyte modification of ultrafiltration membrane for removal of copper ions

International audienc

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

International audienc

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

Use of hydrogen bonded layer-by-layer assemblies for particle manipulation

International audienceWith the constant progress in miniaturization of systems and devices, the manipulation of µ-objects is becoming increasingly important. Chemical functionalization is a promising way to improve this manipulation, in particular multilayer polymer films based on hydrogen bonds can allow to achieve reversible adhesion of µ-objects. To prepare such hydrogen-bonded Layer-by-Layer (LbL) films, poly(ethylene glycol) (PEG), poly(acrylic acid) (PAA), Tannic acid (TA) and Poly(N-isopropylacrylamide) carboxylic acid-terminated (PNIPAM) were selected due to their hydrogen donor or acceptor properties. The growth of these films was originally confirmed by in situ optical reflectometry. Their erasability was also investigated by exposure to an aqueous solution with a pH gradient. Depending on the polymer couple, the pH of disintegration was adjusted from an acidic to a basic medium. The surface roughness was also affected by the building block of the LbL architecture since a rougher surface was recorded for PEG/TA than for PEG/PAA. To mimic the manipulation of an object, adsorption and desorption of a model object (silica particles) was carried out onto a LbL film. Two approaches were employed: optical reflectometry as an indirect method and optical microscopy for direct visualization. For both analyses, particles of different sizes could be adsorbed onto a PEG/PAA or PAA/PNIPAM film. Finally, a complete desorption of the particles was recorded due to the disintegration of the LbL film when the pH was increased

Predictive tools for selection of appropriate polyelectrolyte multilayer film for the functionalization of organic membranes

International audienceLayer-by-layer adsorption of oppositely charged polyelectrolytes is a suitable method to improve the filtration properties of polyethersulfone (PES) membrane. Therefore, a weak polycation (poly(allylamine hydrochloride, PAH) was combined with either a weak polyanion (polyacrylic acid, PAA) or a strong polyanion (polystyrene sulfonate, PSS) to create a polyelectrolyte multilayer film (PEM) of 11 layers. Adsorption of the polyelectrolytes was performed using saline solutions at native pH or pH 6. The growth of (PAH-PAA)n or (PAH-PSS)n multilayer film was monitored in situ by optical reflectometry (OR) and quartz crystal microbalance (QCM-D). At the end of the build-up, a rinsing step at pH 2 was done to test the stability of the film at the filtration conditions. The rinsing step did not lead to desorption of the (PAH-PSS)n multilayer. On the contrary, films made of PAH and PAA were strongly affected, but did not entirely disassemble by changing the pH. Filtration efficiency of PEM-modified membrane was finally investigated by filtrating copper ions solution. These membranes were alternately immersed into polyelectrolyte solutions during 10 min to achieve the functionalization. As predicted by the OR and QCM-D results, a good retention of copper cations was recorded for (PAH-PAA)n modified membrane. On the contrary, a poor retention was observed for membrane modified by (PAH-PSS)n multilayer despite their good behavior during the filtration step. This could be attributed to a different wall pores modification

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