EQCM and XPS investigations on the redox switching of conducting poly(o-aminophenol) films electrosynthesized onto Pt substrates

Electrochemically addressed FET-like nanofluidic channels with dynamic ion-transport regimes

Nanofluidic channels in which the ionic transport can be modulated by the application of an external voltage to the nanochannel walls have been described as nanofluidic field effect transistors (nFETs) because of their analogy with electrolyte-gated field effect transistors. The creation of nFETs is attracting increasing attention due to the possibility of controlling ion transport by using an external voltage as a non-invasive stimulus. In this work, we show that it is possible to extend the actuation range of nFETs by using the supporting electrolyte as a "chemical effector". For this aim, a gold-coated poly(ethylene terephthalate) (PET) membrane was modified with electroactive poly-o-aminophenol. By exploiting the interaction between the electroactive poly-o-aminophenol and the ions in the electrolyte solution, the magnitude and surface charge of the nanochannels were fine-tuned. In this way, by setting the electrolyte nature it has been possible to set different ion transport regimes, i.e.: cation-selective or anion-selective ion transport, whereas the rectification efficiency of the ionic transport was controlled by the gate voltage applied to the electroactive polymer layer. Remarkably, under both regimes, the platform displays a reversible and rapid response. We believe that this strategy to preset the actuation range of nFETs by using the supporting electrolyte as a chemical effector can be extended to other devices, thus offering new opportunities for the development of stimulus-responsive solid-state nanochannels.

Electrochemically addressable nanofluidic devices based on PET nanochannels modified with electropolymerized poly-o-aminophenol films

Nanofluidic field-effect transistors (nFETs) have attracted attention from the scientific community due to their remarkable level of control over ionic transport. Particularly, the combination of nanofluidic systems and electroactive polymers has demonstrated to be an interesting approach to achieve an electrochemically addressable device. In this work, the development of nFETs based on the integration of electropolymerized poly-o-aminophenol (POAP) films into track-etched nanochannels is proposed. The electropolymerization of POAP on the tip side of Au-sputtered asymmetric PET nanochannels not only allowed having a programmable tip diameter but also offered a precise and very rapid control of ionic transport by switching an external bias voltage. Moreover, the system exhibited a reversible behaviour between non-selective and anion-selective states. We believe that this work provides new tools and concepts to design and build high-performance nanofluidic field-effect transistors working under electrochemically controlled conditions.

Composite nanofiltration membrane with asymmetric selective separation layer for enhanced separation efficiency to anionic dye aqueous solution

The development of high performance membrane is crucial for enhanced separation efficiency of nanofiltration process in treating wastewaters from dye and textile industries. In this work, a novel thin-film composite nanofiltration membrane with an asymmetric separation layer composed of relatively compact skin and loose body was designed and fabricated for improved perm-selectivity and antifouling property. Nascent composite membrane with loose poly(piperazine amide) (PA) separation layer was interfacially synthesized and performed with secondary surface reaction using an aqueous tannic acid (TA) solution. Membrane characterizations verified the formation of compact TA skin on top of the loose PA layer through forming covalent bonds via esterification reaction. Compared with the composite nanofiltration membrane with PA symmetric separation layer having the same glucose rejection of about 82.0%, the permeability to pure water of the composite membrane with PA/TA asymmetric separation layer was higher by 28.0%, the water fluxes to aqueous solutions dissolved with model anionic dyes of alizarin yellow R, sunset yellow and Congo red under steady state were higher by 50.3, 43.9 and 36.1%, and the steady-state flux declines were lowered by 27.8, 43.4 and 23.5%, respectively. Furthermore, the PA/TA-based membrane also exhibited better antifouling property and rejection ability to alizarin yellow R.

In Situ Electrochemical-AFM and Cluster-Ion-Profiled XPS Characterization of an Insulating Polymeric Membrane as a Substrate for Immobilizing Biomolecules

The electrochemical oxidation of ortho-aminophenol (oAP) by cyclic voltammetry (CV), on platinum substrates in neutral solution, produces a polymeric film (PoAP) that grows to a limiting thickness of about 10 nm. The insulating film has potential use as a bioimmobilizing substrate, with its specificity depending on the orientation of its molecular chains. Prior investigations suggest that the film consists of alternating quinoneimine and oAP units, progressively filling all the platinum sites during the electrosynthesis. This work concerns the evaluation of the growth orientation of PoAP chains, which until now was deduced only from indirect evidence. Atomic force microscopy (AFM) has been used in situ with an electrochemical cell so that PoAP deposition on a specific area can be observed, thus avoiding any surface reorganization during ex situ transport. In parallel with microscopy, XPS experiments have been performed using cluster ion beams to profile this film, which is exceptionally thin, without damage while retaining molecular information.

Self-patterning porous films of giant vesicles of {Mo72Fe30}(DODMA)3 complexes as frameworks

This work describes the preparation and properties of self-patterning porous films consisting of giant vesicles formed by a 2.5-nm-diameter, polyoxometalate (POM) cluster {Mo72Fe30} macroanion, and a double-tailed cationic surfactant dimethyldistearylammonium bromide (DODMABr) in CHCl3-CH3OH mixture solvent (VCHCl3: VCH3OH=3:1). These inverse vesicles with the diameter in the range of 0.45~1.3μm in organic solution and the porous films consisting of the giant vesicles of the {Mo72Fe30}(DODMA)3 complexes were characterized by SEM, TEM, XPS and AFM observations. Self-patterning of these giant vesicles into porous films that are highly ordered honeycomb films on solid surfaces can survive drying as the frameworks are firstly studied in detail. Water contact angle measurements proved that the porous films of {Mo72Fe30}(DODMA)3 vesicles were endowed hydrophobic property from the hydrophilic surface. This porous film materials consisting of giant vesicles may be promising new options in many fields like photoelectrochemistry, sterilization, template, catalysis, in-situ synthesis.

Electro-chemo-biomimetics from conducting polymers: fundamentals, materials, properties and devices

Conjugated conducting polymers, intrinsic conducting polymers or conducting polymers are complex and mixed materials; their electroactive fractions follow reversible oxidation/reduction reactions giving reversible volume variations to lodge or expel charge-balance counterions and osmotic-balance solvent molecules. The material content (reactive macromolecules, ions and water) mimics the dense intracellular matrix gel of living cells. Here the electropolymerization mechanism is reviewed highlighting the presence of parallel reactions resulting in electroactive and non-electroactive fractions of the final material. Conducting polymers are classified into nine different material families. Each of those families follows a prevalent reaction-driven exchange of anions or cations during oxidation/reduction (p-doping/p-dedoping or n-doping/n-dedoping). Polyaniline families also follow reaction-driven exchange of protons. The polymer/counterion composition changes for several orders of magnitude in a reversible way with the reversible reaction. The value of each of the different composition-dependent properties of the material also shifts in a reversible way driven by the reaction. Each property mimics another change in functional biological organs. A family of biomimetic devices is being developed based on each biomimetic property. Those electrochemical devices work driven by reactions of the constitutive material, as biological organs do. The simultaneous variation of several composition-dependent properties during the reaction announces an unparalleled technological world of multifunctional devices: several tools working simultaneously in one device. Such properties and devices are driven by electrochemical reactions: they are Faradaic devices and must be characterized by using electrochemical cells and electro-chemical methodologies.