Counteranion-controlled properties of polyelectrolyte multilayers

Polyelectrolyte multilayers consisting of poly(diallyldimethylammonium chloride) (PDADMA) and poly(sodium 4-styrenesulfonate) (PSS) were studied on a quartz crystal microbalance (QCM) utilizing a novel method to determine the elastic properties of the films. Since the multilayer was found to consist of a hard core and soft outer layer, as can be realized on the basis of the multilayer zone model, the multilayer films were made thick enough to reveal the elastic properties of the bulk material of the film. Several hundreds of layers were deposited using a fully automated multilayer deposition machine. We found out that, in addition to the increase in the bilayer mass, a remarkable increase of stiffness of the polyelectrolyte multilayer was observed while changing the counteranion used in the deposition process. The increase of stiffness was found to be comparable to the glass transition of common polymers. The increase is attributed to the counteranions that take part in polyelectrolyte charge compensation. The correlation of storage shear modulus and mass density to the hydration entropy of the anion could be clearly observed

Preparation of multilayers containing conjugated thiophene-based polyelectrolytes. Layer-by-layer assembly and viscoelastic properties

We study the layer-by-layer assembly and properties of polyelectrolyte multilayers containing anionic and cationic poly(alkoxythiophene) derivatives, poly(3-(3'-thienyloxy)propanesulfonate) (P3TOPS) and poly(3-(3'-thienyloxy)propyltriethylammonium) (P3TOPA), together with poly(diallyldimethylammonum chloride) (PDADMA) or poly(styrenesulfonate) (PSS). These polythiophenes are rigid-rod-type polyelectrolytes which tend to aggregate in aqueous medium. Three types of multilayers have been prepared: (P3TOPS/P3TOPA)(n) (all-thiophene films), (P3TOPS/PDADMA)(n), and (PSS/P3TOPA)(n). The layer-by-layer adsorption of polythiophenes was followed by UV-vis spectroscopy and surface plasmon resonance (SPR). Adsorption of P3TOPS and P3TOPA took place within 10 min from dilute aqueous solution (1 mM with respect to monomers). The adsorption of anew polyion layer on top of polythiophene was always accompanied by a partial loss of the polythiophene layer. As the result, the amount of polythiophene in the film oscillated as a function of the number of layers. This behavior was attributed to the adsorption and partial desorption of aggregated polythiophene, supported by atomic force microscope (AFM) images of dry films. Per bilayer, the amount of polythiophene remaining in the film increased linearly and corresponded approximately to the formation of a thiophene monolayer. The viscoelastic properties of the film; also exhibited a marked terminal layer effect in cases where the length and hydrophobicity of the polyions were different. This effect was studied with (PSS/PDADMA) multilayers and was attributed to the formation of loops and tails, All multilayers studied appeared very soft, comparable to protein layers. This softness was attributed mainly to the film/solution interface with a hydrogel-like outer part of the films (zone III)

New insights on the interaction between thiophene derivatives and Au surfaces: the case of 3,4-ethylenedioxythiophene and the relevant polymer.

The nature of the interface between electrogenerated poly(3,4-ethylenedioxythiophene) and the Au substrate is studied in detail. In particular, the adsorption of the relevant monomer, namely, 3,4-ethylenedioxythiophene, is investigated and compared with that of other thiophene derivatives. Different deposition procedures have been adopted: very thin films of the thiophene derivatives have been obtained through chemisorption processes from vapor and liquid phases, on Au polycrystalline substrates, Au nano particles possessing different size, and a Au(111) single crystal. Different techniques, operating both in situ and ex situ, have been employed for the characterization of these deposits, that is, X-ray photoemission and surface enhanced Raman spectroscopy. The results show that the poly(3,4-ethylenedioxythiophene)/metal interface is far from being simply constituted by unreacted molecules in contact with the substrate; rather, the formation of oligothiophene species and sulfur atoms at the interface has been ascertained

New Insights on the Interaction between Thiophene Derivatives and Au Surfaces. The Case of 3,4-Ethylenedioxythiophene and the Relevant Polymer

The nature of the interface between electrogen-erated poly(3,4-ethylenedioxythiophene) and the Au substrateis studied in detail. In particular, the adsorption of the relevantmonomer, namely, 3,4-ethylenedioxythiophene, is investigatedand compared with that of other thiophene derivatives. Di!er-ent deposition procedures have been adopted: very thin "lms ofthe thiophene derivatives have been obtained through chemi-sorption processes from vapor and liquid phases, on Au poly-crystalline substrates, Au nanoparticles possessing di!erent size,and a Au(111) single crystal. Di!erent techniques, operatingboth in situ and ex situ, have been employed for the characterization of these deposits, that is, X-ray photoemission and surface- enhanced Raman spectroscopy. The results show that the poly(3,4-ethylenedioxythiophene)/metal interface is far from being simply constituted by unreacted molecules in contact with the substrate; rather, the formation of oligothiophene species and sulfur atoms at the interface has been ascertained