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)

Water-soluble full-length single-wall carbon nanotube polyelectrolytes: Preparation and characterization

HiPco single-wall carbon nanotubes (SWNTs) have been noncovalently modified with ionic pyrene and naphthalene derivatives to prepare water-soluble SWNT polyelectrolytes (SWNT-PEs), which are analogous to polyanions and polycations. The modified nanotubes have been characterized with UV-vis-NIR, fluorescence, Raman and X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The nanotube-adsorbate interactions consist of π-π stacking interactions between the aromatic core of the adsorbate and the nanotube surface and specific contributions because of the substituents. The interaction between nanotubes and adsorbates also involves charge transfer from adsorbates to SWNTs, and with naphthalene sulfonates the role of a free amino group was important. The ionic surface charge density of the modified SWNTs is constant and probably controlled by electrostatic repulsion between like charges. The linear ionic charge density of the modified SWNTs is similar to that of common highly charged polyelectrolytes

Layer-by-layer deposition of a polythiophene/Au nanoparticles multilayer with effective electrochemical properties

Multilayers consisting of a water soluble polythiophene derivative and Au nanoparticles have been deposited onto different electrode substrates by means of layer-by-layer deposition technique. The assembly of the films has been performed by taking advantage of the electrostatic interactions between the positively charged imidazolic moiety of the polythiophene chain and the negative charges of citrate ions surrounding Au nanoparticles, as well of the affinity of S to Au. The nanoparticles result stably grafted to the organic matrix. The resulting modified electrodes have been characterised through electrochemical, spectroelectrochemical and microscopic techniques. The results evidenced that a high number of individual nanoparticles is present inside the multilayer. The presence of nanoparticles is of chief importance for most effective charge percolation through the multilayer, as suggested by the responses to electroactive probe species in solution. The electrocatalytic performances of the modified electrodes have been tested with respect to the oxidation of ascorbic acid. © Springer-Verlag 2011

Preparation and Characterization of a RedoxMultilayer Film Containing Au Nanoparticles

Gold nanoparticles encapsulated by negatively charged molecules have been stably anchored at a Au substratethrough layer-by-layer deposition technique, employing a redox polyviologen derivative as the cationiccounterpart. UV-vis spectroscopy, quartz crystal microbalance, transmission electron microscopy, scanningelectron microscopy, atomic force microscopy, and voltammetric measurements have been performed in orderto characterize the systems and to give a rationale to the effect of the deposition conditions on the propertiesof the resulting multilayers. The behavior of two benchmark electroactive species ([Fe(CN)6]4- and[Ru(NH3)6]3+) has been studied on nanoparticle-terminated multilayers. The nanoparticles provide chargepercolation through the multilayer and charge transfer with redox species in solution. The results imply thatthe electrochemical behavior of nanoparticle-containing films is partly dependent on the charge compensationmode within polyelectrolyte multilayers

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