Tom Lindfors

pH sensitivity of polyaniline and its substituted derivatives

Abstract The pH sensitivity of electrically conducting polyaniline (PANI) and its derivatives poly( o -methylaniline) (P o MeANI), poly( o -ethylaniline) (P o EtANI), poly( o -propylaniline) (P o PrANI) and poly( N -methylaniline) (PNMeANI) have been studied with potentiometry and UV–vis spectroscopy. The electropolymerisation of PANI was carried out either in hydrochloric acid (HCl), methanesulphonic acid (MSA), benzenesulphonic acid (BSA) or dodecylbenzenesulphonic acid (DBSA). It is shown that the pH sensitivity of PANI and its derivatives depend on the substituent and the size of the acid anion that is used in the electropolymerisation. PANI membranes prepared in HCl show a selective and slightly super-Nernstian potentiometric pH response (62.4±0.9 mV per pH; pH 2–9), while PNMeANI, P o PrANI and PANI prepared with DBSA have a strongly suppressed pH response. The hysteresis effect observed in the UV–vis measurements for all membrane types studied restrict the use of PANI-based optical pH sensors to the pH range of only 5–8.

Potentiometric and UV–vis characterisation of N-substituted polyanilines

Poly(N -methylaniline) (PNMeANI), poly(N -ethylaniline) (PNEtANI), poly(N- propylaniline) (PNPrANI) and poly(N -butylaniline) (PNBuANI) films were polymerised on glassy carbon and tin oxide (TO) substrates in 1.0 M HClO4. The pH sensitivity of the polymer films was investigated with potentiometry and UV/vis measurements in aqueous buffer solutions with pH 2/9. The results of these measurements were compared with polyaniline (PANI) prepared in 1.0 M HCl. In this study, the potential and the UV/vis spectrum of the different polymer films deposited on TO were measured simultaneously. These optopotentiometric measurements give information about the surface and bulk processes in the N-substituted polyaniline films when they are in contact with the buffer solutions of different pH. It was shown that the N-substituted polyaniline films were not pH sensitive. The suppressed potentiometric pH sensitivity of the N-substituted polyanilines, which were observed when changing pH, are caused by reduction of the polymer films from their emeraldine to leucoemeraldine oxidation state. Polymerisation of PNMeANI in 0.1 M dodecylbenzenesulphonic acid (DBSA) solution is also reported in this paper. # 2002 Elsevier Science B.V. All rights reserved.

Biocomposites of Nanofibrillated Cellulose, Polypyrrole, and Silver Nanoparticles with Electroconductive and Antimicrobial Properties

In this work, flexible and free-standing composite films of nanofibrillated cellulose/polypyrrole (NFC/PPy) and NFC/PPy-silver nanoparticles (NFC/PPy-Ag) have been synthesized for the first time via in situ one-step chemical polymerization and applied in potential biomedical applications. Incorporation of NFC into PPy significantly improved its film formation ability resulting in composite materials with good mechanical and electrical properties. It is shown that the NFC/PPy-Ag composite films have strong inhibition effect against the growth of Gram-positive bacteria, e.g., Staphylococcus aureus. The electrical conductivity and strong antimicrobial activity makes it possible to use the silver composites in various applications aimed at biomedical treatments and diagnostics. Additionally, we report here the structural and morphological characterization of the composite materials with Fourier-transform infrared spectroscopy, atomic force microscopy, and scanning and transmission electron microscopy techniques.

Raman and UV–vis spectroscopic study of polyaniline membranes containing a bulky cationic additive

Abstract Electrically conducting soluble polyaniline (PANI), containing different amounts of a bulky lipophilic cationic additive, tridodecylmethylammonium chloride (TDMACl), was studied by Raman (λexc=780 nm) and UV–vis spectroscopy. PANI was made simultaneously electrically conducting and soluble with bis[4-(1,1,3,3-tetramethylbutyl)phenyl]phosphoric acid in dichloromethane. The PANI membranes were prepared by drop casting on glassy carbon or ITO substrates. Raman and UV–vis measurements were carried out in a 0.1 M CaCl2 solution at potentials between 400 and −600 mV (vs. SCE) at pH 6, or alternatively at the open circuit potential at pH 10. The results of Raman, UV–vis and cyclic voltammetric measurements confirm that the incorporation of TDMACl into the PANI membrane facilitates the oxidation and reduction of PANI.

FTIR-ATR Study of Water Uptake and Diffusion through Ion-Selective Membranes Based on Poly(acrylates) and Silicone Rubber

For the first time, FTIR-ATR spectroscopy was used to study the water uptake and its diffusion in ion-selective membranes (ISMs) based on poly(acrylates) (PAs) and silicone rubber (SR), which are emerging materials for the fabrication of ISMs for ultratrace analysis. Three different types of PA membranes were studied, consisting of copolymers of methyl methacrylate with n-butyl acrylate, decyl methacrylate, or isodecyl acrylate. Numerical simulations with the finite difference method showed that in most cases the water uptake of the PA and SR membranes could be described with a model consisting of two diffusion coefficients. The diffusion coefficients of the PA membranes were approximately 1 order of magnitude lower than those of plasticized poly(vinyl chloride) (PVC)-based ISMs and only slightly influenced by the membrane matrix composition. However, the simulations indicated that during longer contact times, the water uptake of PA membranes was considerably higher than that for plasticized PVC membranes. Although the diffusion coefficients of the SR and plasticized PVC membranes were similar, the SR membranes had the lowest water uptake of all membranes. This can be beneficial in preventing the formation of detrimental water layers in all-solid-state ion-selective electrodes. With FTIR-ATR, one can monitor the accumulation of different forms of water, i.e., monomeric, dimeric, clustered, and bulk water.

Impedance spectroscopic study on single-piece all-solid-state calcium-selective electrode based on polyaniline

Single-piece all-solid-state calcium-selective electrodes (CaSPEs) have been studied with impedance spectroscopy. The molar ratio (y) of the protonic acid, bis(2-ethylhexyl)hydrogenphosphate, to a repeat unit of polyaniline (PANI) was y= 0.50. The protonation was performed both at 25 and 110 °C. Impedance measurements were used to study the electronic and ionic processes in the CaSPE membranes. The results were compared with a calcium coated-wire ion-selective electrode (CaCWE). The bulk resistance of the CaSPEs decreases with PANI concentrations up to 10%(m/m), owing to improved ionic mobility in the CaSPE membranes. The charge transfer at the substrate/membrane interface was found to be facilitated by incorporation of PANI in the electrode matrix. PANI also stabilizes the bulk resistance of the CaSPEs compared to the CaCWE. Two types of membranes were studied: (i)‘wet’ membranes that had been in contact with an aqueous 0.1 mol dm–3 CaCl2 solution and (ii)‘dry’ membranes. The obtained impedance spectra were fitted to equivalent circuits describing the CaSPE system.

Electrochemical synthesis of poly(3,4-ethylenedioxythiophene) in aqueous dispersion of high porosity reduced graphene oxide

We report here the one-step electrochemical synthesis of poly(3,4-ethylenedioxythiophene) (PEDOT) in an aqueous dispersion of reduced graphene oxide (rGO). The electrochemical polymerization is carried out at 1.05 V in aqueous media in the presence of 10−2 M 3,4-ethylenedioxythiophene and 1 g L−1 rGO. Unlike composites of PEDOT and graphene oxide or poly(styrene sulfonate) which have rather smooth and non-porous surface morphologies, the scanning electron microscopy images reveal that the PEDOT composite films obtained in this work have uniformly porous and open surface morphology. X-ray photoelectron spectroscopy (XPS) showed that rGO had initially a low concentration of oxygen-containing surface groups (C : O ratio = 6.5), but both FTIR spectroscopy and XPS showed that the electropolymerization resulted in the formation of OH groups in the composite film. Characterization with cyclic voltammetry and electrochemical impedance spectroscopy demonstrates that the composite films behave almost like ideal capacitors having an areal capacitance of 12.2 mF cm−2. The composite films had a very good potential cycling stability in 0.1 M KCl with only 12.4% degradation of the capacitance in a three-electrode cell after 3000 cycles between −0.5 and 0.5 V. The degradation was higher (32.8%) in the broader potential range of −0.8 and 0.7 V.

Determination of Water Uptake of Polymeric Ion-Selective Membranes with the Coulometric Karl Fischer and FT-IR-Attenuated Total Reflection Techniques

The water uptake of plasticized poly(vinyl chloride) (PVC) and silicone rubber (SR) based calcium-selective membranes which are commonly used in solid-contact and coated-wire ion-selective electrodes (SC-ISEs and CWEs) was quantified with the oven based coulometric Karl Fischer (KF) technique. Two different membrane types were studied: (1) the plasticized PVC or SR (RTV 3140) membrane matrix without other added membrane components and (2) the full Ca(2+)-selective membrane formulation consisting of the membrane matrixes, potassium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate and calcium ionophore IV (ETH 5234) or calcium ionophore I (ETH 1001). The membranes were contacted for 24 h either asymmetrically from one side or symmetrically from both sides with deionized water (DIW) or 0.1 M solutions of CaCl(2), KCl, or NaCl. It was found that the water uptake was higher for symmetrically contacted membranes. The highest water uptake (0.15-0.17 wt %) was obtained for the plasticized PVC based Ca(2+)-selective membranes in DIW, whereas the water uptake was lower in 0.1 M electrolyte solutions. Symmetrically contacted Ca(2+)-selective SR membranes had much lower water uptake in 0.1 M CaCl(2) (0.03 wt %) than their plasticized PVC counterparts (0.1 wt %). However, the (noncontacted) SR membranes contained initially much more water (0.09-0.15 wt %) than the PVC membranes (0.04-0.07 wt %). Furthermore, in good accordance with the KF measurements, it was verified with FT-IR-attenuated total reflection (ATR) spectroscopy that the water content at the substrate/membrane interface and consequently in the whole membrane was influenced by the electrolyte solution.

A Jet Ring Cell with a Renewable Solid Support for Amperometric Detection of Glucose in a Sequential Injection Analysis System

Abstract A new amperometric method for the detection of glucose has been developed. A jet ring cell with a renewable solid support (JRR) is connected to a sequential injection analysis (SIA) system. The solid support, consisting of small spherical particles of agarose gel, with a mean bead size of 90 μm, is coupled with the enzyme glucose oxidase (GOD). The suspension is injected through a multiport valve in the SIA-system and is trapped in the JRR cell by a gap of 10 μm between the glassy carbon (GC) working electrode and a stainless steel counter electrode. The subsequent injection of glucose results in formation of hydrogen peroxide, which is detected by oxidation at 1.0 V (vs. Ag/AgCl/KCl (3 M)). Thereafter the suspension is removed by reversing the pump flow and subsequently replaced with fresh suspension for the next determination of glucose. The linear working range for the JRR-sensor, at this stage of the work, is 100 μM - 5 mM.

Dispersible composites of exfoliated graphite and polyaniline with improved electrochemical behaviour for solid-state chemical sensor applications

We report here the in situ polymerization of aniline in the presence of exfoliated graphite of two different grades (graphene and graphite) resulting in composite materials which are readily dispersible in N-methylpyrrolidone. Compared to polyaniline (PANI) prepared without graphene/graphite which becomes electrically non-conducting at pH > 3, the PANI–graphene/graphite composites showed significantly improved pH stability and electrochemical behaviour in aqueous electrolyte solutions at pH ≤ 8, without any further need of surface functionalization of the graphene/graphite flakes to stabilize the conducting form of polyaniline (PANI). The improved electroactivity is ascribed to the synergistic effect of graphene/graphite and PANI, and the network formation of the electrically conducting exfoliated graphites in the PANI matrix, which was electrochemically confirmed by simple cyclic voltammetric measurements at pH = 9.5 in the presence of the Ru(NH3)62+/3+ and Fe(CN)63−/4− redox couples. Due to the dispersibility of the composites, thin films possessing stability in water can easily be prepared by solution casting for different types of solid-state chemical sensor and ion-selective electrode applications operating at neutral pH. By using sodium ascorbate as a model substance, we show that its amperometric detection at pH = 7.3 with the PANI–graphite films results in a current amplification of 1.3–10.2 times in the concentration range of 10−4–10−2 M, compared to conventional PANI, which clearly demonstrates the advantage of incorporating exfoliated graphites in the PANI films. The materials reported in this paper were systematically characterized with cyclic voltammetry, FTIR, Raman and X-ray photoelectron spectroscopy, scanning electron microscopy, X-ray diffraction and electrical conductivity measurements.