Sophie Lakard

Effect of ultrasounds on the electrochemical synthesis of polypyrrole, application to the adhesion and growth of biological cells.

In this study, a new way to synthesize polypyrrole films is presented. This original way consists in the electropolymerization of polypyrrole under high frequency ultrasonic irradiation on conductive fluorine-doped tin oxide surfaces. The polypyrrole films obtained are then compared, in terms of chemical structure and morphology, to polypyrrole films synthesized by standard electrochemical methodology. Next, these polymer films are tested as an alternative to biomaterials that are commonly used as cell culture substrates. Thus, the adhesion and growth of osteoblastics cells and microbial cells on polymer-modified surfaces are investigated by using qualitative observation and quantitative tests. These studies proved the non-toxicity of the polymer films for osteoblastic and microbial cells but also a different behaviour of osteoblastic cells and microbial cells with polypyrrole films.

Ab initio study of the polymerization mechanism of poly(p-phenylenediamine)

The electrochemical oxidation of paraphenylenediamine (1,4-diaminobenzene, PPD) leads to the passivation of the electrode surface by a thin film as shown by using Cyclic Voltammetry technique. This film can be identified by InfraRed-Attenuated Total Reflectance as a polymeric film of poly(p-phenylenediamine), polyPPD. To establish the mechanism leading from PPD to polyPPD, we performed computations of energy and thermochemical values with the quantum-chemical Self-Consistent Field method at the Hartree–Fock level of theory. Then we compared this mechanism to the ones, previously established with similar ab initio calculations, leading to polyethyleneimine and polypropyleneimine in an attempt to generalize the mechanism of electropolymerization of diamines.

Charge properties of membranes modified by multilayer polyelectrolyte adsorption.

Alternate adsorption of polyanions and polycations on a polyethersulfone (PES) membrane was studied by the tangential streaming potential method using a parallel-plate channel to investigate the properties of the outer surface of the membrane. These streaming potential data were complemented by diffusion experiments and by membrane potential measurements in order to characterize the inner surface of the membrane. Tangential streaming potential measurements demonstrated that after completing a bilayer of poly(allylamine hydrochloride) (PAH) and poly(sodium 4-styrene sulfonate) (PSS), periodic variations in the zeta potential between positive and negative values appeared for multilayer films obtained from membrane dipped in polyelectrolyte (PE) solutions at 10 g/L. On the contrary, the zeta potential was always positive when multilayer films were obtained from 1 and 5 g/L polyelectrolyte concentration solutions. Diffusion experiments carried out with unmodified and modified membranes showed a decrease in the solute flux after functionalization of the membrane by several polyelectrolyte bilayers, indicating that the diffusional resistance of the PE layers contributes significantly to the overall resistance to diffusion of the modified membrane. By means of membrane potential measurements the pore walls of the membrane were functionalized since the charge of its pore walls was modified even if it is difficult to discriminate between the contribution of the membrane and that of the multilayer buildup.

Characterization of charge properties of an ultrafiltration membrane modified by surface grafting of poly(allylamine) hydrochloride

A polyethersulfone ultrafiltration membrane was functionalized by a cationic polyelectrolyte, the poly(allylamine) hydrochloride (PAH). The influence of the time of adsorption of PAH on the membrane charge properties was studied. Several characterization techniques were used to investigate the membrane modification. Tangential and transmembrane streaming potential measurements were conducted to characterize the outer and inner surfaces of the membrane, respectively. Both techniques indicated that the surface modification of the membrane was efficient. The charge of the outer surface was reversed (from negative values for the unmodified membrane to positive values for the modified membrane) and the charge of the inner surface was neutralized after adsorption of the cationic polyelectrolyte onto the pore walls. The modification of both the outer surface of the membrane and the pore walls was also put in evidence with membrane potential measurements. It was found that the charge of the PAH-modified membrane is affected by the time of immersion in PAH solution. Experimental data seem to show a fast modification of the membrane for the first 15 min; nevertheless, the modification was more pronounced after 24 h of PAH adsorption. Diffusion experiments carried out with unmodified and modified membranes for four salts (KCl, NaCl, MgCl, and CaCl(2)) showed a decrease in the salt permeability after functionalization of the membrane. The permeability decrease was greater for 2:1 salts than for 1:1 salts. This decrease was explained by electrostatic interactions.

Functionalization of organic membranes by polyelectrolyte multilayer assemblies: application to the removal of copper ions from aqueous solutions.

The functionalization of an organic polyethersulfone membrane (PES) was performed by alternating deposition of poly(allylamine hydrochloride) (PAH) and poly(sodium 4-styrene sulfonate) (PSS), leading to the formation of a polyelectrolyte multilayer film (PEM). The resulting assembly was characterized by tangential streaming potential measurements to determine the charge of the modified membranes as a function of the polyelectrolyte solution concentration and as a function of the immersion time of the membrane in the polyelectrolyte solutions. Then, the modified membranes were used to perform the ultrafiltration of aqueous solutions containing copper(II) ions. Different operating conditions were tested including: polyelectrolyte concentration, polyelectrolyte nature, thickness of the PEM film or pH of the Cu(2+) solutions. These filtration experiments demonstrated that it was possible to obtain a satisfactory retention of the copper ions (88%), thus proving that this type of assembly can be useful for the removal of copper ions from contaminated aqueous solutions.

Modeling of electrostatic forces induced by chemical surface functionalisation for microrobotics applications

Non-contact microrobotics is a promising way to avoid adhesion caused by the well-known scale effects. Nowadays, several non-contact micro-robots exist. Most of them are controlled by magnetic or dielectrophoresis phenomena. To complete this, we propose a method based on electrostatic force induced by chemical functionalisation of substrates. In this study, we show a model of this force supported by experimental results. We reached long range forces measuring an interaction force of several microNewtons and an interaction distance of tens micrometers. This paper shows the relevance of using chemical electrostatic forces for microrobotics applications.

Elaboration of Transparent Polymeric Films Trapping Copper Ions by Complexation

The aim of this work was to elaborate on a thin polymeric film for coating transparent fluorine-doped tin oxide (FTO) electrode supported on a glass substrate for trapping Cu 2+ ions. Possible applications are the easier detection of Cu 2+ ions due to complexation on the FTO surface or could be the making up of electrochromic devices using copper(I)-salt based electrolytes to avoid diffusion of Cu 2+ ions formed at the anode toward Cu(0) deposited on the cathode. These thin polymeric films proposed here as complexing material candidates toward copper ions belong to polyalkyleneimine polymers. They were obtained by anodic electropolymerization of aliphatic polyamines (with at least two primary amino groups) such as ethylenediamine, 1,3-diaminopropane, or diethylenetriamine on FTO electrode surfaces and characterized by IR attenuated total reflectance spectroscopy. Moreover, we have shown that polyalkyleneimine -type polymers used here present good chelating properties towards Cu 2+ ions due to the amino groups they contain.