Mogens Hinge

Nitrophenyl Groups in Diazonium-Generated Multilayered Films: Which are Electrochemically Responsive?

Various nitrophenyl-containing organic layers have been electrografted to glassy carbon surfaces using diazonium chemistry to elucidate the extent by which the layer structure influences the solvent (i.e., acetonitrile) accessibility, electroactivity, and chemical reactivity of the films. For most of these films, cyclic voltammetric and impedance spectroscopy measurements show that the electron-transfer process at the electrode is facile and independent of film thickness and structure. This is consistent with the occurrence of self-mediated electron transfers throughout the film with nitrophenyl groups serving as redox stations. Importantly, this behavior is seen only after the first potential sweep, the effect of which is to increase the porosity of the layer by inducing an irreversible desorption of nonchemisorbed material along with a reorganization of the film structure. From a kinetic point of view, the radical anions of surface-attached nitrophenyl groups are reactive toward the residual water present in acetonitrile. Thin layers (thickness of 1 to 2 nm) containing redox-active groups only in the outer part of the layer are protonated two to three times as fast as groups located in a more hydrophobic but still solvent-accessible inner layer. Hence, kinetic measurements can detect small differences in the layer environment. Finally, a deconvolution of the cyclic voltammetric response of an electrode grafted from 4-nitrobenzenediazonium discloses that roughly 25% of the overall signal can be attributed to the presence of 4-azonitrophenyl moieties introduced during the electrografting process.

On Surface-Initiated Atom Transfer Radical Polymerization Using Diazonium Chemistry To Introduce the Initiator Layer

This work features the controllability of surface-initiated atom transfer radical polymerization (SI-ATRP) of methyl methacrylate, initiated by a multilayered 2-bromoisobutyryl moiety formed via diazonium chemistry. The thickness as a function of polymerization time has been studied by varying different parameters such as the bromine content of the initiator layer, polarity of reaction medium, ligand type (L), and the ratio of activator (Cu(I)) to deactivator (Cu(II)) in order to ascertain the controllability of the SI-ATRP process. The variation of thickness versus surface concentration of bromine shows a gradual transition from mushroom to brush-type conformation of the surface anchored chains in both polar and nonpolar reaction medium. Interestingly, it is revealed that very thick polymer brushes, on the order of 1 μm, can be obtained at high bromine content of the initiator layer in toluene. The initial polymerization rate and the overall final thickness are higher in the case of nonpolar solvent (toluene) compared to polar medium (acetonitrile or N,N-dimethylformamide). The ligand affects the initial rate of polymerization, which correlates with the redox potentials of the pertinent Cu(II)/Cu(I) complexes (L = Me(6)TREN, PMDETA, and BIPY). It is also observed that the ability of polymer brushes to reinitiate depends on the initial thickness and the solvent used for generating it.

Redox grafting of diazotated anthraquinone as a means of forming thick conducting organic films.

Thick conductive layers containing anthraquinone moieties are covalently immobilized on gold using redox grafting of the diazonium salt of anthraquinone (i.e., 9,10-dioxo-9,10-dihydroanthracene-1-diazonium tetrafluoroborate). This grafting procedure is based on using consecutive voltammetric sweeping and through this exploiting fast electron transfer reactions that are mediated by the anthraquinone redox moieties in the film. The fast film growth, which is followed by infrared reflection absorption spectroscopy, atomic force microscopy, X-ray photoelectron spectroscopy, ellipsometry, and coverage calculation, results in a mushroom-like structure. In addition to varying the number of sweeps, layer thickness control can easily be exerted through appropriate choice of the switching potential and sweep rate. It is shown that the grafting of the diazonium salt is essentially a diffusion-controlled process but also that desorption of physisorbed material during the sweeping process is essentially for avoiding blocking of the film due to clogging of the electrolyte channels in the film. In general, sweep rates higher than 0.5 V s(-1) are required if thick, porous, and conducting films should be formed.

Synthesis and photovoltaic properties from inverted geometry cells and roll-to-roll coated large area cells from dithienopyrrole-based donor–acceptor polymers

A series of donor–acceptor low band gap polymers composed of alternating dithienopyrrole or its derivative as donors and phthalimide or thieno[3,4-c]pyrrole-4,6-dione as acceptors (P1–P4) are synthesized by Stille coupling polymerization. All polymers show strong absorption in the visible region, for P2 and P4 possessing thieno[3,4-c]pyrrole-4,6-dione as an acceptor, their film absorption covers the region of 500–800 nm and 500–750 nm respectively, which makes them attractive as low band gap polymer solar cell (PSC) materials. With the incorporation of thiophene bridges, P3 and P4 have 0.24 and 0.21 eV higher HOMO energy levels than P1 and P2, respectively. A bandgap as low as 1.66 eV is obtained for P2. An up-scaling experiment is performed on bulk-heterojunction PSCs with an inverted device geometry fabricated on a small scale by spin coating and on a large scale using roll-to-roll (R2R) slot-die coating and screen printing. In both cases the best performing polymer is P2 with a Voc of 0.56 V, a Jsc of −12.6 mA cm−2, a FF of 40.3%, and a PCE of 2.84% for small spin coated devices, and a Voc of 0.56 V, a Jsc of −8.18 mA cm−2, a FF of 30.7%, and a PCE of 1.40% are obtained for R2R-fabricated devices with a significantly better performance than a standard P3HT/PCBM driven device.

Electrochemical modification of chromium surfaces using 4-nitro- and 4-fluorobenzenediazonium salts

Chromium surfaces can be electrografted with organic surface films using 4-nitro- or 4-fluorobenzenediazonium salts, despite the fact that the surfaces are covered with a protective chromium oxide layer.

Tailoring Membrane Nanostructure and Charge Density for High Electrokinetic Energy Conversion Efficiency

The electrokinetic energy conversion (EKEC) of hydraulic work directly into electrical energy has been investigated in charged polymeric membranes with different pore charge densities and characteristic diameters of the nanoporous network. The membranes were synthesized from blends of nitrocellulose and sulfonated polystyrene (SPS) and were comprehensively characterized with respect to structure, composition, and transport properties. It is shown that the SPS can be used as a sacrificial pore generation medium to tune the pore size and membrane porosity, which in turn highly affects the transport properties of the membranes. Furthermore, it is shown that very high EKEC efficiencies (>35%) are encountered in a rather narrow window of the properties of the nanoporous membrane network, that is, with pore diameters of ca. 10 nm and pore charge densities of 4.6 × 10(2) to 1.5 × 10(3) mol SO3(-) m(-3) for dilute solutions (0.03 M LiCl). The high absolute value of the efficiency combined with the determination of the optimal membrane morphology makes membrane-based EKEC devices a step closer to practical applications and high-performance membrane design less empirical.

An isoindigo containing donor-acceptor polymer: synthesis and photovoltaic properties of all-solution-processed ITO- and vacuum-free large area roll-coated single junction and tandem solar cells

In this work, the design, synthesis, and characterization of a donor–acceptor polymer from dithieno[3,2-b:2′,3′-d]pyrrole and isoindigo (i-ID) are presented. The synthesized polymer has been applied in the fabrication of large area ITO-free organic photovoltaic devices, both by spin coating and roll coating; the latter was used to construct both single junction and multi-junction organic photovoltaic (OPV) architectures.

Synthesis of β-cyclodextrin diazonium salts and electrochemical immobilization onto glassy carbon and gold surfaces

This study shows that diazotized β-cyclodextrin (β-CD) can be produced, isolated, and immobilized onto glassy carbon and gold surfaces. 4-(1,2,3-Triazol-4-yl)benzenediazonium-β-CD tetrafluoroborate (pDz-β-CD) and 3-(1,2,3-triazol-4-yl)benzenediazonium-β-CD tetrafluoroborate (mDz-β-CD) were successfully prepared by Cu((I))-catalyzed azide alkyne coupling (CuAAC) of 6-monodeoxy-6-monoazido-β-cyclodextrin (N(3)-β-CD) and 4-ethynylaniline and 3-ethynylaniline, respectively, followed by diazotization. The products were isolated and stored successfully for several months at -18 °C. The intermediates and products were verified by Attenuated Total Reflectance Fourier Transform Infrared, Nuclear Magnetic Resonance, and Heteronuclear Single Quantum Coherence. pDz-β-CD and mDz-β-CD were immobilized onto glassy carbon and gold surfaces facilitated by electrochemical reduction of the diazonium group. The thus generated aryl radical reacted with the surface. The modified gold surfaces were investigated by Polarization Modulation Infrared Reflection Absorption Spectroscopy and cyclic voltammetry employing the redox probe K(3)Fe(CN)(6) to analyze the extent of blocking of the surfaces. Finally, the availability of the cavity of surface-immobilized β-CD was shown by complexation of ferrocene followed by cyclic voltametric analysis.

Improved Adhesion Between PMMA and Stainless Steel Modified with PMMA Brushes

In this work, various lengths and densities of poly(methyl methacrylate) (PMMA) brushes were synthesized on stainless steel (SS) surfaces via surface initiated atom transfer radical polymerization. Subsequently, the joints between the bulk PMMA and the PMMA brushed stainless steel were obtained by injection molding, and for these the degree of adhesion was assessed by tensile testing. Several conditions are required to facilitate the mixing between the brushes and the bulk polymer and to reduce the residual stress at the interface: preheating of the SS samples before the injection molding; a long packing time; and a mold temperature above the glass transition temperature (Tg) of PMMA during the injection molding. This treatment leads to a cohesive failure in the bulk PMMA. It was observed that the stress concentrated at the rim, due to contraction of bulk PMMA during cooling, results in a weak adhesion at the rim of the joint. A combination of high density and long brush length of PMMA film provides better adhesion. The large number of PMMA brush chains apparently promotes good penetration into the bulk PMMA chains and ultimately results in high adhesion strength.

The use of dielectric spectroscopy in the investigation of the effect of polymer choice on the flocculation of polystyrene particles.

The flocculation of colloidal suspensions using synthetic polymeric flocculants is an important operation in separation processes. Optimizing flocculant use requires insight into the underlying mechanisms governing flocculation. As most existing methods for the online characterization of flocculation processes can only be used on dilute suspensions, new methods applicable at high solid content levels are of interest. This study used dielectric spectroscopy to investigate the mechanisms involved in the flocculation of polystyrene particles with three different cationic polymers. We observed that the relaxation time of the dielectric dispersion increased as particle flocculation was initiated. Reduction of particle charge due to polymer addition was found to reduce the magnitude of the dielectric dispersion, whereas the formation of aggregates increased it. This resulted in decreasing magnitude when charge reduction was the primary cause of flocculation, whereas the magnitude increased when the particles were flocculated by bridging.