Cyclometallated phenyls with substituents para to the metal have a larger impact on the redox potentials and emission of complexes Ir(R-ppz)(2)(bipy)PF(6) than substituents at the meta position and ...hence enable tuning of emission wavelength over a wider range using the same substituent.
Electroactive films based on conducting polymers have numerous potential applications, but practical devices frequently require a combination of properties not met by a single component. This has ...prompted an extension to composite materials, notably those in which particulates are immobilised within a polymer film. Irrespective of the polymer and the intended application, film wetting is important: by various means, it facilitates transport processes - of electronic charge, charge-balancing counter ions ("dopant") and analyte/reactant molecules - and motion of polymer segments. While film solvent content and transfer have been widely studied for pristine polymer films exposed to molecular solvents, extension to non-conventional solvents (such as ionic liquids) or to composite films has been given much less attention. Here we consider such cases based on polyaniline films. We explore two factors, the nature of the electrolyte (solvent and film-permeating ions) and the effect of introducing particulate species into the film. In the first instance, we compare film behaviours when exposed to a conventional protic solvent (water) with an aprotic ionic liquid (Ethaline) and the intermediate case of a protic ionic liquid (Oxaline). Secondly, we explore the effect of inclusion of physically diverse particulates: multi-walled carbon nanotubes, graphite or molybdenum dioxide. We use electrochemistry to control and monitor the film redox state and change therein, and acoustic wave measurements to diagnose rheologically
vs.
gravimetrically determined response. The outcomes provide insights of relevance to future practical applications, including charge/discharge rates and cycle life for energy storage devices, "salt" transfer in water purification technologies, and the extent of film "memory" of previous environments when sequentially exposed to different media.
•The EQCM/PBD method has for the first time been applied to metal deposition/dissolution processes in deep eutectic solvents•The PBD responds to solution phase chemistry, while the E and QCM probes ...respond to interfacial processes only•The combination of electrochemical (E), gravimetric (QCM) and optical (PBD) responses provides diagnostic capability•EQCM/PBD data reveal the influence of Ag/Cl− complex speciation in the high chloride concentration ionic liquid•The PBD response reveals the intrusion of solubility limitations into Sn anodic stripping
The electrochemical quartz crystal microbalance (EQCM) and probe beam deflection (PBD) have been widely used to study interfacial processes in molecular solvent-based electrolytes. However, there has been limited use of the EQCM and none of PBD in room temperature ionic liquids, including deep eutectic solvents (DES). Here we explore the use of the combined EQCM/PBD technique to the study of Ag and Sn electrodeposition from a DES comprising a 1:2 mixture of choline chloride and ethylene glycol. While overcoming the effect of viscous loss in the acoustic wave (EQCM) part of the experiment is understood, the optical (PBD) technique fails to provide a meaningful response in slow scan rate voltammetric experiments; this contrasts sharply with the straightforward behaviour seen in aqueous media. Solution transport considerations reveal this to be a consequence of long surface-to-beam transit times in the viscous DES. The problem can be overcome by operating at scan rates 1-2 orders of magnitude slower, permitting application of this powerful technique to novel media of technological interest. The PBD responses reveal unanticipated chemical effects: multiple complexes in the Ag system and solubility limitations in the Sn system, neither of which is evident from the electrochemical or QCM responses.
The electrodeposition of metals from ionic solutions is intrinsically linked to the reactivity of the solute ions. When metal salts dissolve, the exchange of the anion with the molecular and ionic ...components from solution affects the speciation and therefore the characteristics of metal reduction. This study investigates the nucleation mechanism, deposition kinetics, metal speciation and diffusion coefficients of silver salts dissolved in Deep Eutectic Solvents. The electrochemical reduction of AgCl, AgNO
3
and Ag
2
O is studied in 1 : 2 choline chloride : ethylene glycol and 1 : 2 choline chloride : urea. Cyclic voltammetry is used to evaluate electrochemical kinetics. Detailed analysis of chronoamperometric data shows that silver deposits form
via
multiple 3D nucleation with mass transport controlled hemispherical growth. The nucleation mechanism was found to be potential dependent, varying from progressive to instantaneous as the reduction potential becomes more cathodic. Diffusion coefficients are determined using three different methods. Trends are rationalised in terms of solvent viscosity and silver speciation analysis with EXAFS. The morphology of electroreduced silver is investigated with scanning electron microscopy and shows that deposits from the urea based liquid form more dense morphologies than those from the ethylene glycol based liquid.
This study investigates the nucleation mechanisms and electrochemical kinetics of silver deposition in Deep Eutectic Solvents. The morphology of silver coatings is compared on the basis of deposition kinetics, solvent properties and solute speciation.
We have studied the anodic dissolution (electropolishing) of various stainless steel alloys in an ionic liquid comprising a 2 : 1 stoichiometric mix of ethylene glycol (EG) and choline chloride. We ...have used a combination of electrochemical and spectroscopic methods together with in situ liquid probe microscopy. We discuss the role and influence of the surface oxide passivation layer, characterized here by X-ray photoelectron spectroscopy (XPS) and linear sweep voltammetry, on the polishing process. We address the question of dealloying during the polish in order to contribute to our understanding of the viability of the ionic liquid as a replacement industrial electropolishing medium; the current commercial process uses a corrosive mixture of phosphoric and sulfuric acids. Also, we present data from ex situ and in situ liquid AFM studies giving both a qualitative and quantitative insight into the nature and scale of morphological changes at the steel surface during the polishing process.
Electrodeposited conducting polymer films derived from aromatic monomers are known to possess properties that depend significantly on the deposition protocol, particularly the electrochemical control ...function employed. This study explores the underlying reasons for this common observation for the specific case of polypyrrole films deposited from aqueous media onto gold electrodes under potentiostatic, potentiodynamic and galvanostatic control. Although the control functions impose different conditions, the control parameters (potential, potential range and scan rate, and current) were selected so as generate films at comparable rates; this avoids inappropriate attribution of structural and compositional variations to different thickness regimes, irrespective of how they were generated. In each case, film deposition was periodically interrupted and the film characterised by specular neutron reflectivity measurements. By using d4-pyrrole monomer in H2O solvent, the isotopic selectivity of neutron reflectivity was used to extract polymer and solvent concentration profiles as a function of distance from the electrode/film interface. Spatial integration of these profiles was used to quantify total film solvent populations; these are expressed as solvent volume fractions. Films grown under the three different control regimes have measurably distinct solvent volume fraction profiles and there is evolution of these profiles with increasing thickness. Ultimately, for the conditions employed, the order of increasing porosity (i.e. solvent content) by control function was potentiostatic < potentiodynamic < galvanostatic. At the end of the deposition process, the films were transferred to monomer-free electrolyte and redox cycled. This resulted in an overall increase in film solvation, but little difference in solvation with redox state (doping level). We conclude that film structure and associated solvation level do retain some memory of deposition protocol, but also respond to the medium of exposure.
Display omitted
•Polymer and solvent spatial profiles within polypyrrole films have been determined using in situ specular neutron reflectivity.•Growing polypyrrole films (under any given control regime) are spatially inhomogeneous composites of polymer and solvent.•Growing polypyrrole films have distinct solvation profiles dictated by electrochemical control function.•Subsequent redox cycling in monomer-free background electrolyte results in increased solvation.•Film solvation profiles respond to environment and potential cycling, but also retain some “memory” of deposition conditions
In this paper, we describe the first example of a sustained galvanic coating deposited on a surface from a non-aqueous liquid. We present the surface characterization of electroless silver deposits ...on copper substrates from a solution of Ag(+) ions in an ionic liquid based on a choline chloride (ChCl) eutectic. Through a study of these deposits and the mechanism of formation using acoustic impedance spectroscopy (QCM), probe microscopy (AFM) and electron microscopy (SEM/EDX), we demonstrate that sustained growth of the silver deposit is facilitated by the porous nature of the silver. This is in contrast to the dip-coating reaction of silver ions in aqueous media, where the reaction stops when surface coverage is reached. Electroless silver deposits of up to several microns have been obtained by dip coating in ionic liquids without the use of catalysts of strong inorganic acids.
This work demonstrates that a sustained galvanic coating of silver can be deposited onto copper substrates from a solution of Ag
+ ions in an ionic liquid (IL) based on a choline chloride (ChCl) ...eutectic. The sustained growth of the silver deposit was facilitated by the porous nature of the film and is proven using acoustic impedance spectroscopy on a quartz crystal microbalance (QCM). The silver and copper surfaces were characterised using atomic force microscopy (AFM) and scanning electron microscopy (SEM/EDX). In the commercial process of dip coating silver from ions in aqueous media, deposition does not continue once surface coverage has been achieved, without the use of catalysts. The process reported here using ionic liquids produces silver deposits of several microns by dip coating without the use of catalysts or strong inorganic acids.
The deposition of aluminium from a chloroaluminate based ionic liquid was studied to elucidate the effect of a diluent (toluene) and electrolyte (LiCl) on the deposit morphology. A wide variety of ...analytical techniques was applied to this system to determine the speciation and mechanism of material growth. These included:
27
Al NMR, FAB-MS, cyclic voltammetry, chronocoulometry, chronopotentiometry, scanning electron microscopy and atomic force microscopy. It was found that under-potential deposition (upd) causes a change in the way in which metal grows on the electrode surface. Metal grows in two regimes which are believed to be nano-material and bulk material. The addition of toluene causes a change in speciation and a decrease in upd which in turn changes the morphology of the deposit obtained and can lead to mirror finish aluminium. The addition of LiCl has the opposite effect encouraging upd and leading to larger crystallites and a dark grey deposit. It is also shown for the first time that under many conditions the rate of the anodic dissolution process is overall rate controlling and one effect of the addition of toluene is to increase the rate of anodic dissolution.
Analysis of the electrochemical deposition of metallic aluminium from imidazolium based ionic liquids: compositional, anode and double layer effects.
Salt modified starch: sustainable, recyclable plastics Abbott, Andrew P; Ballantyne, Andrew D; Conde, Jesus Palenzuela ...
Green chemistry : an international journal and green chemistry resource : GC,
01/2012, Letnik:
14, Številka:
5
Journal Article
Recenzirano
The ubiquitous nature of starch makes it a tantalising basis of sustainable plastic manufacture. Extensive hydrogen bonding between chains, however, makes the plasticisation of starch difficult but ...this work shows that the incorporation of a simple quaternary ammonium salt can lead to a flexible plastic with mechanical properties similar to oil derived plastics. Compression-moulding produces a transparent material with mechanical strength which is similar to some polyolefin plastics. It is shown that the material can be extruded and/or compression-moulded and these processes improve further the mechanical strength of the samples. Most importantly, it is shown that these plastics are recyclable and ultimately compostable.
Flexible, strong, transparent thermoplastic starch can be formed through compression-moulding using a simple quaternary ammonium salt as a plasticiser.
PDF
