•Aniline electropolymerisation shown to not be solely controlled by pH in DESs.•Dynamic light scattering shows that the monomer is in a colloidal phase for all systems where electropolymerisation ...occurs.•Size of PANI particles similar to dimensions of colloidal dispersed phase.•Aniline emulsions tend to form when water is added to DESs.
The electropolymerisation of aniline is a well-studied and often used technology. While the mechanism has been investigated in a variety of media these have all concentrated on understanding the process on a molecular level. Anomalies in the electropolymerisation of aniline in four deep eutectic solvents, DESs, using urea, ethylene glycol, glycerol and oxalic acids as hydrogen bond donors with choline chloride led to an investigation of the aniline phase behaviour. It was only with oxalic acid that polymerisation was achieved and adjusting the pH of the other DESs using sulphuric acid did not enable polymer formation suggesting that pH was not the only factor enabling polymer growth. When 10 wt% water was added, polymers could be grown in all the DESs despite negligible change in solution pH. Dynamic light scattering showed that polymer only formed in systems where aniline formed an emulsion. Scanning electron microscopy, SEM and atomic force microscopy, AFM showed that the polyaniline films were formed of an agglomeration of small particles of the same dimensions as the dispersed monomer phase in solution. This suggests that the droplets of the monomer arrive at the electrode surface where they polymerise. This provides the first evidence that polyaniline grows by an emulsion polymerisation mechanism even in aqueous solutions.
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•Facile electro-deposition of bright Ni is possible from DES electrolytes at elevated temp. and high concentration.•Harder Ni deposits are obtained from DES than from aqueous ...electrolytes.•Similar deposition rates are measured despite the higher viscosity of the DES.•High temp. speciation of Ni2+ in DES determines morphology of deposit.•Ni deposition in DES shows a levelling effect when compared to Ni plating in aqueous electrolytes.
Metal electrodeposition using ionic liquid electrolytes and deep eutectic solvents is now well known but to our knowledge for electrolytic deposition of metals such as nickel no direct comparison has thus far been drawn between deposition using aqueous solutions and DES under otherwise identical conditions. In the current study it is shown that nickel deposition can be carried out with similar deposition rates in aqueous and ionic media despite the significant differences in viscosity and conductivity. It is, however, shown that in ionic media the morphology of the deposits is markedly different from that achieved using a Watts nickel bath and that one aspect of these differences manifests itself in significant increase in the coating hardness. It is proposed that the observed morphology differences occur due to the variations of nickel speciation in each electrolyte environment.
Eutectic mixtures of zinc chloride and donor molecules such as urea and acetamide are described and it is proposed that these constitute a new class of ionic liquids. FAB‐MS analysis shows that the ...liquids are made up of metal‐containing anions and cations in which the donor is coordinated to the cation. Data on the viscosity, conductivity, density, phase behaviour and surface tension are presented and these are shown to be significantly different to other related ionic liquids that incorporate quaternary ammonium salts. The conductivity and viscosity are comparable with other ionic liquids and the data fit well to the Hole theory model recently proposed.
Zinc chloride can disproportionate to give ZnCl3− (right‐hand side) and ZnCl+ when mixed with suitable donor molecules, for example, acetamide, urea or ethylene glycol. This gives rise to a new class of ionic liquids, such as depicted on the left‐hand side (ZnCl(urea)+).
The effects of nicotinic acid (NA), boric acid (BA) and benzoquinone (BQ) on the electrodeposition of Zn have been studied in a choline chloride (ChCl) ethylene glycol (EG) based deep eutectic ...solvent (DES), (1ChCl:2 EG), and for the first time a bright zinc coating has been achieved when NA was used.
In metal electroplating processes, small-molecule additives are often included in the plating bath to improve properties of coating such as brightness, roughness, thickness, hardness and resistance to corrosion. The effects of additives on the electrodeposition of Zn from aqueous solution have been extensively investigated. However, very few studies have considered the effects of additives on the electrodeposition of Zn from ionic liquids or deep eutectic solvents. The electrochemical properties of the plating liquid have been studied here using cyclic voltammetry, chronocoulometry, chronoamperometry and microgravimetry (EQCM). Redox peak currents decrease when additives were included in the Zn solution and total charge was also reduced in experiments where additives were present. The Zn deposition in the absence of additive is in good agreement with an instantaneous growth mechanism at short experimental time scales (being indeterminate over longer periods), however, this changes to one of a progressive growth mechanism when additives were included in the coating bath. The current efficiency of zinc deposition in the DES without additives was 95%, which was reduced when additives were included. The resultant surface morphologies, thickness, topography, roughness and crystal structure of the Zn coating were revealed by scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD), demonstrating that those additives serve as effective brighteners that can produce highly uniform and smooth zinc deposits.
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