Real-Time Monitoring of Polyaniline Nanoparticle Formation on Surfaces

Abstract

The formation of polyaniline (PAni) nanoparticles on silica surfaces has been monitored in situ using evanescent wave cavity ring-down spectroscopy (EW-CRDS). Aniline hydrochloride in aqueous solution at different concentrations was oxidatively polymerized using sodium persulfate. The process was found to involve the nucleation and growth of polymer nanoparticles, whose size and coverages were measured using tapping mode atomic force microscopy (TM-AFM). The formation of PAni was confirmed by replacing the silica surface with indium doped tin oxide (ITO) electrodes and subsequently running cyclic voltammetry experiments on the material deposited, which yielded the characteristic electrochemical response. The number of active groups (monomers) per polymer particle was estimated using the peak current of the cyclic voltammograms, with knowledge of the nanoparticle surface coverage from TM-AFM analysis. The quantity of material in each particle was consistent with TM-AFM height data, assuming hemispherical particle morphology. The polymerization process was found to be governed by surface-controlled kinetics, from a fixed number of particle sites of 35 ((5) µm -2 . The reaction was first-order in aniline, with a rate constant for monomer addition of 0.7 ((0.4) × 10 -7 cm s -1 in the limit of large particle size. For smaller nanoparticles, however, at the early stage of polymerization, the polymerization rate constant appeared to be size-dependent and to increase with decreasing nanoparticle radius (assuming a hemispherical geometry). This could also be due to a change in the morphology of the nanoparticles at the very shortest times but may indicate size-dependent polymerization kinetics.

A semitransparent snake-like tactile and olfactory bionic sensor with reversibly stretchable properties

“…The active nucleation centers are isolated from each other in the early stage because of the hydrophobic nature of the PDMS substrate and the low concentration of aniline, which was previously proven by an in situ technique. 21 Homogeneous nucleation and growth in the solution occur simultaneously and cause precipitation onto the active sites on the thin film. With depleted reactive aniline cation radicals and oligomeric intermediates, the vertical growth of PANI nanofibers was achieved on the PANI polymerized solid PDMS substrates.…”

Probing Redox Reactions of Immobilized Cytochrome c Using Evanescent Wave Cavity Ring‐Down Spectroscopy in a Thin‐Layer Electrochemical Cell

“…The experimental setup for EW-CRDS was similar to that used previously [31][32][33][34][35] and is shown schematically in Figure 1 A. However, rather than using a diode laser, for the current studies, the second harmonic [generated using Type I b-barium borate (BBO) crystal] of a femtosecond Ti-Sapphire laser (SpectraPhysics XP Regenerative amplifier), which had been passed through a singlemode optical fibre (Nufern S405-HP), was employed as the light source.…”

“…[ [31][32][33][34][35] Electrochemistry: A platinum working electrode (disc diameter 2 mm) was positioned over the evanescent field at a distance of a 100 mm from the surface so as to form a thin-layer cell with the optical prism (see Figure 1 A). [36,37] Electrochemical measurements were performed in a three-electrode mode using a home-built potentiostat, with a AgCl-coated Ag wire in 0.1 m KCl as the reference electrode [38,39] and a platinum wire as the counter electrode.…”

“…The evanescent field typically extends only a few hundreds of nanometers beyond the interface and therefore can be used to investigate the absorbance properties of the liquid phase above the surface. The molecules of interest are typically deposited on a quartz prism [31] or modified quartz prism, [32][33][34] so allowing tailoring of the surface chemical environment and properties. Whilst EW-CRDS has mainly been used to study the adsorption of molecules to the prism surface, we have recently demonstrated the ability to extend the technique to study interactions of molecules with polymer films.…”

“…[33] Furthermore, by combining EW-CRDS or the related cavity enhanced absorption spectroscopy (CEAS) with electrochemical or hydrodynamic methods the capabilities have been extended to the study of surface processes in real time. [31][32][33][34][35][36] The studies herein report the ET kinetics for the reaction between immobilized cytochrome c and FeEDTA 2À . The kinetics are much slower than for the same reaction in solution and the reasons for this are considered.…”