Andres Öpik

Corrosion behavior of polypyrrole coated mild steel

Abstract The effect of surface treatments such as polishing and immersion in acid on the corrosion behavior of polypyrrole coated mild steel was investigated. Polypyrrole films were polymerized electrochemically from the aqueous solution of pyrrole and sodium p-toluenesulphonate at a constant current density of 2 mA/cm2. Corrosion behavior of mild steel covered by these films was investigated by anodic potentiodynamic polarization technique. Remarkable shift of corrosion potential to the positive direction and strong decrease of reduction oxidation current were observed in all cases.

Ion transport investigations of polypyrroles doped with different anions by EQCM and CER techniques

The ion transfer in redox processes of conducting polypyrrole doped with various anions, such as 1-naphthalenesulfonate, 10-camphorsulfonate, p-toluenesulfonate, dodecylbenzenesulfonate was investigated by electrochemical quartz crystal microbalance (EQCM), contact electric resistance (CER), and cyclic voltamperometry in situ techniques. By using this setup, the doping levels of the synthesized PPy films and mobility of charge carries in these materials in KCl aqueous solution under linear potential scan were determined.

Environmental QCM sensors coated with polypyrrole

Abstract Polypyrrole (PPy) was investigated as an active material for relative humidity and SO 2 gas sensors. PPy films of different thickness were deposited on the both sides of quartz crystal microbalance (QCM) disks. The dependence of resonant frequency of those QCM-based sensors on relative humidity was investigated. Also, the dependence on SO 2 was measured in the atmosphere of nitrogen at room temperature in the concentration range from 0 to 100%. Very good sensitivity of PPy coated QCM disks to atmospheric humidity and concentration of SO 2 gives a possibility for the preparation of highly effective environmental and chemical gas sensors.

Molecularly imprinted polymer film interfaced with Surface Acoustic Wave technology as a sensing platform for label-free protein detection.

Molecularly imprinted polymer (MIP)-based synthetic receptors integrated with Surface Acoustic Wave (SAW) sensing platform were applied for the first time for label-free protein detection. The ultrathin polymeric films with surface imprints of immunoglobulin G (IgG-MIP) were fabricated onto the multiplexed SAW chips using an electrosynthesis approach. The films were characterized by analyzing the binding kinetics recorded by SAW system. It was revealed that the capability of IgG-MIP to specifically recognize the target protein was greatly influenced by the polymer film thickness that could be easily optimized by the amount of the electrical charge consumed during the electrodeposition. The thickness-optimized IgG-MIPs demonstrated imprinting factors towards IgG in the range of 2.8-4, while their recognition efficiencies were about 4 and 10 times lower toward the interfering proteins, IgA and HSA, respectively. Additionally, IgG-MIP preserved its capability to recognize selectively the template after up to four regeneration cycles. The presented approach of the facile integration of the protein-MIP sensing layer with SAW technology allowed observing the real-time binding events of the target protein at relevant sensitivity levels and can be potentially suitable for cost effective fabrication of a biosensor for analysis of biological samples in multiplexed manner.

Molecularly Imprinted Polymer Integrated with a Surface Acoustic Wave Technique for Detection of Sulfamethizole

The synergistic effect of combining molecular imprinting and surface acoustic wave (SAW) technologies for the selective and label-free detection of sulfamethizole as a model antibiotic in aqueous environment was demonstrated. A molecularly imprinted polymer (MIP) for sulfamethizole (SMZ) selective recognition was prepared in the form of a homogeneous thin film on the sensing surfaces of SAW chip by oxidative electropolymerization of m-phenylenediamine (mPD) in the presence of SMZ, acting as a template. Special attention was paid to the rational selection of the functional monomer using computational and spectroscopic approaches. SMZ template incorporation and its subsequent release from the polymer was supported by IR microscopic measurements. Precise control of the thicknesses of the SMZ-MIP and respective nonimprinted reference films (NIP) was achieved by correlating the electrical charge dosage during electrodeposition with spectroscopic ellipsometry measurements in order to ensure accurate interpretation of label-free responses originating from the MIP modified sensor. The fabricated SMZ-MIP films were characterized in terms of their binding affinity and selectivity toward the target by analyzing the binding kinetics recorded using the SAW system. The SMZ-MIPs had SMZ binding capacity approximately more than eight times higher than the respective NIP and were able to discriminate among structurally similar molecules, i.e., sulfanilamide and sulfadimethoxine. The presented approach for the facile integration of a sulfonamide antibiotic-sensing layer with SAW technology allowed observing the real-time binding events of the target molecule at nanomolar concentration levels and could be potentially suitable for cost-effective fabrication of a multianalyte chemosensor for analysis of hazardous pollutants in an aqueous environment.

A Mesoscale Simulation of the Morphology of the PEDT/PSS Complex in the Water Dispersion and Thin Film: the Use of the MesoDyn Simulation Code

intrinsically conducting polymer. Its complex with polystyrene sulfonic acid (PSS) attracts general interest ([1] and citations therein). The dispersion of the PEDT/PSS complex is usually prepared by an oxidative oligomerization of ethylenedioxythiophene (EDT) in the water solution in the presence of the soluble charge balancing and stabilizing polyanion of PSS. The oxidation (doping) process controls the number of the supposed ionic groups but the positions of the latter are random and not controlled (Fig. 1). The electrophoretic and viscosity characteristics of the swollen particles present in the dispersion are similar to those of nonstoichiometric polyelectrolyte complexes [2].

CuInS 2 /PEDOT Photovoltaic Structure

Structures based on combination of electrically conductive polymers with inorganic semiconductors are currently intensively investigated with the aim to prepare low-cost, largearea and flexible photovoltaic devices. In this study, multilayer structures consisting of CuInS 2 (CIS) and poly(3,4-ethylenedioxythiophene) (PEDOT) doped with polystyrenesulfonate (PSS) thin films were prepared and investigated for photovoltaic applications. Polycrystalline CIS absorber layers were synthesized on top of a layered structure on Cu tape substrate using socalled non-vacuum CISCuT technique. Thin PEDOT buffer layers doped with PSS were deposited onto KCN etched and vacuum annealed CIS films. The deposition was performed using the spin-casting technique from an aqueous dispersion of PEDOT/PSS mixed with Nmethylpyrrolidone, isopropanol, glycerin and epoxysilane additives. Optimal deposition parameters for stable PEDOT films with a good adherence to the surface of CIS were selected experimentally. The morphology and thickness of prepared films and structures was determined using SEM technique. Average film thickness was about of 1.5 μm for CIS and 50 nm for PEDOT films. Current-voltage and impedance characteristics were measured. Significant photovoltage and photocurrent of the photovoltaic structures were observed under standard illumination intensity. The best structure showed an open-circuit voltage of 510 mV and a shortcircuit current density of 20.2 mA/cm 2 .

A computational approach to study functional monomer-protein molecular interactions to optimize protein molecular imprinting

Molecular imprinting has become a promising approach for synthesis of polymeric materials having binding sites with a predetermined selectivity for a given analyte, the so‐called molecularly imprinted polymers (MIPs), which can be used as artificial receptors in various application fields. Realization of binding sites in a MIP involves the formation of prepolymerization complexes between a template molecule and monomers, their subsequent polymerization, and the removal of the template. It is believed that the strength of the monomer‐template interactions in the prepolymerization mixture influences directly on the quality of the binding sites in a MIP and consequently on its performance. In this study, a computational approach allowing the rational selection of an appropriate monomer for building a MIP capable of selectively rebinding macromolecular analytes has been developed. Molecular docking combined with quantum chemical calculations was used for modeling and comparing molecular interactions among a model macromolecular template, immunoglobulin G (IgG), and 1 of 3 electropolymerizable functional monomers: m‐phenylenediamine (mPD), dopamine, and 3,4‐ethylenedioxythiophene, as well as to predict the probable arrangement of multiple monomers around the protein. It was revealed that mPD was arranged more uniformly around IgG participating in multiple H‐bond interactions with its polar residues and, therefore, could be considered as more advantageous for synthesis of a MIP for IgG recognition (IgG‐MIP). These theoretical predictions were verified by the experimental results and found to be in good agreement showing higher binding affinity of the mPD‐based IgG‐MIP toward IgG as compared with the IgG‐MIPs generated from the other 2 monomers.

Correlation of the morphology and electrical conductivity in thin films of PEDT/PSS complex: an integrated meso-scale simulation study

Using an integrated meso-scale simulation methodology, the morphology and electrical conductivity relationship of the poly(ethylene-dioxy)thiophene/poly-styrenesulphonate (PEDT/PSS) complex in the range of PSS/PEDT mass ratios 1.4–20 has been established. The morphology presented as a density field has been generated by dynamic density field theory-based MesoDyn simulation code for all systems taking into account the substrate surface effect. Generated anisotropic morphologies have been characterised by the modified anisotropy parameter Q i and Q Di values indicating the anisotropy along the system diagonals and coordinates, respectively. Based on the hopping mechanism of the conductivity, the values of the percolation-related critical parameter are identified and correlated with the macroscopic in-plane (∥) and out-of-plane ( ⊥ ) electrical conductivities, relative to the substrate surface. These macroscopic conductivities are also calculated accurately by applying the Kirchoff laws to the respective random resistor networks. The results are in a reasonable agreement with the available experimental data.

On the Percolation Behavior of the Thin Films of the PEDT/PSS Complex: a Mesoscale Simulation Study

The broad range of the electrical conductivities is the characteristic feature of the electronically conducting polymers [1]. Thus, the conductivity of poly(ethylenedioxythiophene)/poly(styrene sulfonate) (PEDT/PSS, Fig. 1) film varies ca over 5 orders of magnitude, depending on the PEDT/PSS mass ratio in the range of 1:2.5 to 1:20 [2,3].The conductivity is attributed to the presence of a conducting, i.e. percolating network, and the film is imagined as a percolating conductor-insulator composite [4–7]. Due to the polaronic nature of the charge carriers in the film [8], this is a rough approximation. However, as shown below, it serves well as a reasonable starting point for the numerical modeling.