The physical problem and the modelling of the sheath in collisional dusty plasma

The aim of this paper is to study the behaviour of sheath structure in plasma with collisions, and simulation of the effects of collisionality on the plasma sheath using the Runge-Kutta routine. We consider the near-wall region of an unmagnetized dusty plasma which consists of electrons, ions, micron-size dust particles and neutral particles. Since the dust particles are much heavier than electrons and ions, the latter are assumed to be out of thermal equilibrium with dust as a cold fluid. The neutrals are taken as immobile. Precise numerical solutions of the model are used to determine the collisional dependence of the sheath width and the impact energy at the wall

Tunable synthesis of Prussian Blue in exponentially growing polyelectrolyte multilayer films.

Polyelectrolyte multilayer (PEM) films have become very popular for surface functionalization and the design of functional architectures such as hollow polyelectrolyte capsules. It is known that properties such as permeability to small ionic solutes are strongly dependent on the buildup regime of the PEM films. This permeability can be modified by tuning the ionization degree of the polycations or polyanions, provided the film is made from weak polyelectrolytes. In most previous investigations, this was achieved by playing on the solution pH either during the film buildup or by a postbuildup pH modification. Herein we investigate the functionalization of poly(allylamine hydrochloride)/poly(glutamic acid) (PAH/PGA) multilayers by ferrocyanide and Prussian Blue (PB). We demonstrate that dynamic exchange processes between the film and polyelectrolyte solutions containing one of the component polyelectrolyte allow one to modify its Donnan potential and, as a consequence, the amount of ferrocyanide anions able to be retained in the PAH/PGA film. This ability of the film to be a tunable reservoir of ferrocyanide anions is then used to produce a composite film containing PB particles obtained by a single precipitation reaction with a solution containing Fe(3+) cations in contact with the film. The presence of PB in the PEM films then provides magnetic as well as electrochemical properties to the whole architecture.journal article2009 Dec 15importe

Effect of the supporting electrolyte anion on the thickness of PSS/PAH multilayer films and on their permeability to an electroactive probe.

Quartz crystal microbalance and cyclic voltammetry are used to investigate the influence of the supporting salt of polyelectrolyte solutions on the buildup and the structure of PSS/PAH polyelectrolyte multilayers (PSS: poly(4-styrene sulfonate); PAH: poly(allylamine hydrochloride)). This film constitutes a model polyelectrolyte multilayer system. The supporting electrolytes were sodium salts where the nature of the anion was changed by following the Hofmeister series from cosmotropic to chaotropic anions (F-, Cl-, NO3-, ClO4-). For all the investigated anions, the film thickness increases linearly with the number of deposition steps.Wefind that chaotropic anions lead to larger thickness increments per bilayer during the film buildup than cosmotropic ones, confirming results found on PSS/PDADMA multilayers (PDADMA:poly(diallyldimethylammonium)). Films constituted by more than nine PSS/PAH bilayers are still permeable to hexacyanoferrate(II) ions, Fe(CN)(6)4-, whatever the nature of the supporting salt anion. On the other hand, these films are impermeable to ruthenium(II) hexamine ions, Ru(NH3)(6)2+, after the third PAH layer in the presence of NaF, NaCl, or NaNO3. These results are explained by the presence of an excess of positive charges in the film, which leads to a positive Donnan potential. We find that this potential is more positive when more chaotropic anions are used during the film buildup. We also find that a film constructed in the presence of chaotropic anions swells and becomes more permeable to Fe(CN)(6)4- ions when the film is brought into contact with a solution containing more cosmotropic anions. All our experimental findings can be explained by a strong interaction between chaotropic anions with the NH3+groups of PAH that is equivalent, as far as the multilayer buildup and electrochemical response is concerned, to a deprotonation of PAH as it is observed when the film is constructed at a higher pH. We thus arrive to a coherent explanation of the effect of the nature of the anions of the supporting electrolyte on the polyelectrolyte multilayer. We also find that great care must be taken when investigating polyelectrolyte multilayer films by electrochemical probing because electrochemical reactions involving the probes can appreciably modify the multilayer structure.journal articleresearch support, non-u.s. gov't2009 Feb 17importe

Polymer multilayer films obtained by electrochemically catalyzed click chemistry.

We report the covalent layer-by-layer construction of polyelectrolyte multilayer (PEM) films by using an efficient electrochemically triggered Sharpless click reaction. The click reaction is catalyzed by Cu(I) which is generated in situ from Cu(II) (originating from the dissolution of CuSO(4)) at the electrode constituting the substrate of the film. The film buildup can be controlled by the application of a mild potential inducing the reduction of Cu(II) to Cu(I) in the absence of any reducing agent or any ligand. The experiments were carried out in an electrochemical quartz crystal microbalance cell which allows both to apply a controlled potential on a gold electrode and to follow the mass deposited on the electrode through the quartz crystal microbalance. Poly(acrylic acid) (PAA) modified with either alkyne (PAA(Alk)) or azide (PAA(Az)) functions grafted onto the PAA backbone through ethylene glycol arms were used to build the PEM films. Construction takes place on gold electrodes whose potentials are more negative than a critical value, which lies between -70 and -150 mV vs Ag/AgCl (KCl sat.) reference electrode. The film thickness increment per bilayer appears independent of the applied voltage as long as it is more negative than the critical potential, but it depends upon Cu(II) and polyelectrolyte concentrations in solution and upon the reduction time of Cu(II) during each deposition step. An increase of any of these latter parameters leads to an increase of the mass deposited per layer. For given buildup conditions, the construction levels off after a given number of deposition steps which increases with the Cu(II) concentration and/or the Cu(II) reduction time. A model based on the diffusion of Cu(II) and Cu(I) ions through the film and the dynamics of the polyelectrolyte anchoring on the film, during the reduction period of Cu(II), is proposed to explain the major buildup features.journal articleresearch support, non-u.s. gov't2010 Feb 16importe

Physico-chemical characterization of polymer multilayer films obtained by electrostatic interactions and covalent bonds

Les films multicouches de polymères étudiés dans ce travail ont été obtenus soit par interactions électrostatiques soit par liaisons covalentes par chimie "click". La construction a été réalisée par dépôt couche par couche. Dans le cas des films électrostatiques, les produits de construction étaient des polycations et des polyanions. Dans le cas des films covalents, les produits de construction étaient des polymères portant soit des azides soit des alcynes. En présence du Cu(I), une cycloaddition est réalisée entre l'azide et l'alcyne pour former le triazole assurant la liaison covalente. Tout d'abord, nous avons étudié l'effet de la série de Hofmeister des anions sur la construction d'un film multicouche PSS/PAH et sur sa perméabilité à des ions sondes électrochimiques. Nous avons observé que les films PSS/PAH construits en présence d'anions chaotropes étaient plus épais et plus perméables aux ions Fe(CN)64- que ceux construits en présence d'anions cosmotropes. Dans une seconde étude, nous avons élaboré des films multicouches à cohésion covalente composés de PAA et d'éthylène glycol (EGq). Nous avons observé que les films construits à partir de EGq de 13 monomères étaient plus épais et plus rugueux que ceux construits à partir de EGq de 3 monomères. De plus, lorsque ces chaînes étaient dialcyne, les films étaient plus épais et plus rugueux que ceux dont les chaînes étaient diazide. La dernière étude portait sur la perméabilité ionique d'un film hybride composé d'une partie covalente et d'une partie électrostatique. Nous avons observé qu une modulation de la perméabilité anionique/cationique du film était possible lorsque le pH extérieur était modifié.The polymer multilayer films studied in this work were obtained either by electrostatic interactions or by covalent bonds in "click-chemistry". The buildup of these films was carried out according to the Layer-by-Layer method. In the case of electrostatic films, the reagents were polycations and polyanions. In the case of covalent films, the reagents were polymers modified by either azide or alkyne groups. In the presence of Cu(I), a cycloaddition occurs between azide and alkyne groups to form the triazole group which ensures the covalent bond. First, we studied the effect of the Hofmeister series of the monovalent anions on the buildup of a PSS/PAH multilayer film and on its permeability to redox probes. We observed that PSS/PAH films built in the presence of chaotropic anions were thicker and more permeable to Fe(CN)64- ions than those built in the presence of cosmotropic anions. Then, in a second study, we investigated multilayer films built by "click-chemistry" using PAA and ethylene glycol chains (EGq). We observed that films built with 13-monomer EGq chains were thicker and rougher than those built with 3-monomer EGq chains. Moreover, when these chains were homobifonctionalized by alkyne groups, the films were thicker and rougher than those whose EG chains were homobifonctionalized by azide groups. The last study was about ionic permeability of a hybrid film composed of a covalent part and a electrostatic part. We observed that a modulation of the hybrid film permeability to anionic and cationic probes was possible when the external pH was changed

Physico-chemical characterization of polymer multilayer films obtained by electrostatic interactions and covalent bonds

Les films multicouches de polymères étudiés dans ce travail ont été obtenus soit par interactions électrostatiques soit par liaisons covalentes par chimie "click". La construction a été réalisée par dépôt couche par couche. Dans le cas des films électrostatiques, les produits de construction étaient des polycations et des polyanions. Dans le cas des films covalents, les produits de construction étaient des polymères portant soit des azides soit des alcynes. En présence du Cu(I), une cycloaddition est réalisée entre l’azide et l’alcyne pour former le triazole assurant la liaison covalente. Tout d’abord, nous avons étudié l’effet de la série de Hofmeister des anions sur la construction d’un film multicouche PSS/PAH et sur sa perméabilité à des ions sondes électrochimiques. Nous avons observé que les films PSS/PAH construits en présence d’anions chaotropes étaient plus épais et plus perméables aux ions Fe(CN)64- que ceux construits en présence d’anions cosmotropes. Dans une seconde étude, nous avons élaboré des films multicouches à cohésion covalente composés de PAA et d’éthylène glycol (EGq). Nous avons observé que les films construits à partir de EGq de 13 monomères étaient plus épais et plus rugueux que ceux construits à partir de EGq de 3 monomères. De plus, lorsque ces chaînes étaient dialcyne, les films étaient plus épais et plus rugueux que ceux dont les chaînes étaient diazide. La dernière étude portait sur la perméabilité ionique d’un film hybride composé d’une partie covalente et d’une partie électrostatique. Nous avons observé qu’une modulation de la perméabilité anionique/cationique du film était possible lorsque le pH extérieur était modifié.The polymer multilayer films studied in this work were obtained either by electrostatic interactions or by covalent bonds in "click-chemistry". The buildup of these films was carried out according to the Layer-by-Layer method. In the case of electrostatic films, the reagents were polycations and polyanions. In the case of covalent films, the reagents were polymers modified by either azide or alkyne groups. In the presence of Cu(I), a cycloaddition occurs between azide and alkyne groups to form the triazole group which ensures the covalent bond. First, we studied the effect of the Hofmeister series of the monovalent anions on the buildup of a PSS/PAH multilayer film and on its permeability to redox probes. We observed that PSS/PAH films built in the presence of chaotropic anions were thicker and more permeable to Fe(CN)64- ions than those built in the presence of cosmotropic anions. Then, in a second study, we investigated multilayer films built by "click-chemistry" using PAA and ethylene glycol chains (EGq). We observed that films built with 13-monomer EGq chains were thicker and rougher than those built with 3-monomer EGq chains. Moreover, when these chains were homobifonctionalized by alkyne groups, the films were thicker and rougher than those whose EG chains were homobifonctionalized by azide groups. The last study was about ionic permeability of a hybrid film composed of a covalent part and a electrostatic part. We observed that a modulation of the hybrid film permeability to anionic and cationic probes was possible when the external pH was changed

Caractérisation physico-chimique de films multicouches de polymères obtenus par interactions électrostatiques et par liaisons covalentes

Les films multicouches de polymères étudiés dans ce travail ont été obtenus soit par interactions électrostatiques soit par liaisons covalentes par chimie "click". La construction a été réalisée par dépôt couche par couche. Dans le cas des films électrostatiques, les produits de construction étaient des polycations et des polyanions. Dans le cas des films covalents, les produits de construction étaient des polymères portant soit des azides soit des alcynes. En présence du Cu(I), une cycloaddition est réalisée entre l azide et l alcyne pour former le triazole assurant la liaison covalente. Tout d abord, nous avons étudié l effet de la série de Hofmeister des anions sur la construction d un film multicouche PSS/PAH et sur sa perméabilité à des ions sondes électrochimiques. Nous avons observé que les films PSS/PAH construits en présence d anions chaotropes étaient plus épais et plus perméables aux ions Fe(CN)64- que ceux construits en présence d anions cosmotropes. Dans une seconde étude, nous avons élaboré des films multicouches à cohésion covalente composés de PAA et d éthylène glycol (EGq). Nous avons observé que les films construits à partir de EGq de 13 monomères étaient plus épais et plus rugueux que ceux construits à partir de EGq de 3 monomères. De plus, lorsque ces chaînes étaient dialcyne, les films étaient plus épais et plus rugueux que ceux dont les chaînes étaient diazide. La dernière étude portait sur la perméabilité ionique d un film hybride composé d une partie covalente et d une partie électrostatique. Nous avons observé qu une modulation de la perméabilité anionique/cationique du film était possible lorsque le pH extérieur était modifié.The polymer multilayer films studied in this work were obtained either by electrostatic interactions or by covalent bonds in "click-chemistry". The buildup of these films was carried out according to the Layer-by-Layer method. In the case of electrostatic films, the reagents were polycations and polyanions. In the case of covalent films, the reagents were polymers modified by either azide or alkyne groups. In the presence of Cu(I), a cycloaddition occurs between azide and alkyne groups to form the triazole group which ensures the covalent bond. First, we studied the effect of the Hofmeister series of the monovalent anions on the buildup of a PSS/PAH multilayer film and on its permeability to redox probes. We observed that PSS/PAH films built in the presence of chaotropic anions were thicker and more permeable to Fe(CN)64- ions than those built in the presence of cosmotropic anions. Then, in a second study, we investigated multilayer films built by "click-chemistry" using PAA and ethylene glycol chains (EGq). We observed that films built with 13-monomer EGq chains were thicker and rougher than those built with 3-monomer EGq chains. Moreover, when these chains were homobifonctionalized by alkyne groups, the films were thicker and rougher than those whose EG chains were homobifonctionalized by azide groups. The last study was about ionic permeability of a hybrid film composed of a covalent part and a electrostatic part. We observed that a modulation of the hybrid film permeability to anionic and cationic probes was possible when the external pH was changed.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

Synthesis at the Air-Water Interface of a Two-Dimensional Semi-Interpenetrating Network Based on Poly(dimethylsiloxane) and Cellulose Acetate Butyrate

International audienceThe UV-induced cross-linking of methacryloxypropyl-terminated poly(dimethylsiloxane) oligomers was studied at the air–water interface either in pure PDMS Langmuir monolayers or in mixed films containing cellulose acetate butyrate. Surface pressure–area isotherms, area measurement at constant surface pressure, Brewster angle microscopy observations, and infrared–visible sum frequency generation (SFG) spectroscopy were combined to follow the evolution of the monolayers upon in situ UV photoirradiation. For both systems, the mean area per repeat unit decreases with irradiation time reflecting the monolayer contraction. In addition, SFG measurements evidence the conversion of the methacrylate groups into unconjugated poly(methacrylate) ones. These results demonstrate PDMS cross-linking, leading to the formation of either a single PDMS network or a PDMS network entrapped in a CAB matrix. The network formation is accompanied by morphology changes as shown by atomic force microscopy on the transferred monolayer. Indeed, filamentous structures appear on both pure and mixed preirradiated monolayers