Georgia A. Arbuckle-Keil

Nickel ferrocyanide modified electrodes as active cation-exchange matrices : real time XRD evaluation of overlayer structure and electrochemical behavior

The dynamic variations in the structure of nickel ferrocyanide modified electrodes was determined using in situ diffractoelectrochemical techniques. X-ray powder diffraction peaks from the nickel ferrocyanide modified electrode were recorded during electrochemical oxidation/reduction of the surface overlayer and reversible changes in the unit cell lattice parameter observed. The electrochemical changes that occur during oxidation/reduction in various alkali cation electrolytes are correlated with changes in the lattice parameter. It is postulated that micro-domains form when two cations having markedly different radii such as cesium and potassium are intercalated into the nickel ferrocyanide structure so that distinct regions of the nickel ferrocyanide layer containing cesium exist separated from regions with the lighter alkali cations.

Changing resources: assessment of leaf litter carbohydrate resource change at a microbial scale of resolution

Abstract Studies of chemical changes in leaf litter resources during decomposition have relied upon bulk litter analysis using wet chemistry. We introduce, here, the use of microscopic Fourier transform infrared spectroscopy (FT–IR) to evaluate changes in the carbohydrate chemistry of leaf litters at the scale of resolution relevant to the study of microbes (μm) and the use of sequential, non-destructive sampling of the same point. We demonstrate some of the discriminatory power of the method and follow the effect of enzymatic degradation of leaf material which reflects changes in carbohydrate chemistry during natural decomposition and in the presence of a saprotrophic fungus.

Atomic force microscopy and micro-ATR-FT-IR imaging reveals fungal enzyme activity at the hyphal scale of resolution

We have combined the use of atomic force microscopy (AFM) and micro-attenuated total reflectance Fourier transform infrared (micro-ATR-FT-IR) imaging to show the extent of exoenzyme influence around individual hyphae of three fungal species growing on cellophane. AFM data show that surface roughness of the cellophane substrate is significantly lower adjacent to hyphae of Armillaria and Aspergillus, which produce cellulase enzyme, than for Mucor, which has lower cellulase activity. Additionally, the adhesive properties of the cellophane surface are significantly altered within the sphere of influence of the hyphae of Armillaria and Aspergillus. Micro-ATR-FT-IR imaging indicates that the cellophane substrate changes composition immediately adjacent to the hyphae of Armillaria and Aspergillus, but similar spectral changes do not occur in the presence of Mucor. This is consistent with the difference in cellulase enzyme activity in these fungal species. The appearance of new spectral peaks, consistent with those expected in the presence of enzymes and the minor decrease in peaks associated with cellophane adjacent to these hyphae are consistent with the hypothesis that the changes observed by AFM are due to local effects of enzyme action around individual hyphae.

An IR study of poly-1,4-phenylenevinylene (PPV), the 2,5-dimethoxy derivative [(MeO)2-PPV], and their corresponding xanthate precursor polymers and monomers

A detailed comparison of the infrared (IR) spectra of poly-1,4-phenylenevinylene (PPV), its xanthate precursor polymer, and its bis-xanthate precursor monomer along with the corresponding 2,5-dimethoxy derivatives has provided a clearer basis for characterizing these species with regard to both structure and purity. All the xanthate precursor monomers and polymers exhibit characteristic intense absorptions typical of the xanthate group near 1220, 1110, and 1050 cm(-1). Upon complete conversion of the precursor polymer to the vinylene linked final product, the intense IR peaks of the xanthate group have disappeared and new bands resulting from the vinylene linkages are found. The latter include a moderately strong band near 965 cm(-1) due to the out-of-plane -CHCH- deformation of the trans-vinylene conjugated with and linking the phenyl rings into an optoelectronic polymer. Unfortunately, the corresponding C-H stretching vibration of this same group of atoms expected to appear near 3020 cm(-1) falls in the same region of the spectrum as the aromatic C-H stretches of the phenyl rings. Similarly, for the 2,5-dimethoxy polymer derivative, [(MeO)(2)-PPV], the C-H stretching vibration near 3055 cm(-1) contains contributions from both aromatic and vinylene C-H. Density functional theory (DFT) calculations on the monomers were instrumental in assigning the infrared spectra of these materials. This study provides a systemic means for verifying that the precursor monomer has been polymerized into the precursor polymer and that thermal conversion to the conjugated polymer is complete.

Characterization of an Optoelectronic Polymer, Poly(2-phenoxy p -phenylene vinylene), and its Precursor Polymer by Dynamic Infrared Spectroscopy

Numerous applications of dynamic infrared spectroscopy to study a variety of polymer systems have been described in the literature. Typically, dynamic spectral changes are used to determine the molecular and submolecular reorientations that give rise to a materials observable mechanical properties. In the present study, the normal modes are characterized by their time-dependent response to an applied perturbation as an aid to assignment of the observed vibrational bands. Characterization of a newly synthesized optoelectronic polymer, poly(2-phenoxy p-phenylene vinylene), and its precursor polymer, is described. Vibrational modes along the backbone and side chain are expected to exhibit significantly different responses to mechanical perturbation due to delayed phase response of the phenoxy substituent. In-phase spectra, quadrature spectra, and two-dimensional infrared correlation maps are included in this characterization. This study has demonstrated that dynamic infrared spectroscopy can be used to distinguish backbone phenylene ring stretches from ring stretches associated with the phenoxy substituent. Density functional theory calculations are applied to confirm infrared spectral assignments. The mechanical properties are briefly discussed in light of the dynamic response.

Comparison of methodologies for separation of fungal isolates using Fourier transform infrared (FTIR) spectroscopy and Fourier transform infrared-attenuated total reflectance (FTIR-ATR) microspectroscopy.

Twenty distinct fungal isolates were analysed using three methods of sample preparation for FTIR spectroscopy and FTIR-ATR microspectroscopy to test for differences in surface chemical composition between living and dried fungal samples, as well as differences between surface chemistry and overall chemistry of homogenized dried samples. Results indicated that visually the FTIR spectra of different fungi are remarkably similar with subtle discernable differences, which statistical analysis of the spectra supported. Within each data set, different fungal isolates were responsible for statistical differences. Lack of congruence between each of the methods used suggests that determination of chemical composition is highly dependent upon the method of sample preparation and analysis (surface vs. whole) applied.

Vapor-Phase Fuming Sulfuric Acid-Doped Poly(p-phenylene vinylene) as a Potential Humidity Sensor

Vapor-phase doping of poly(p-phenylene vinylene) (PPV) with fuming sulfuric acid has been investigated using the quartz crystal microbalance. Thin films of PPV were obtained on quartz crystal substrates by spin casting a precursor polymer, which is thermally converted to give the PPV product. Dopant mass uptake and the resistance of the film were recorded in situ during doping. A decrease in the resistance and therefore an increase in the conductivity of the film from the insulating to the metallic regime was observed. Mass uptake information was used to determine the dopant concentration at the maximum conductivity, the doping rate, and the diffusion coefficient of the polymer. The dopant concentration results were verified by Rutherford backscattering spectrometry and elemental analysis. The observation that the doped material tends to lose its metallic properties upon exposure to moisture in the atmospheric air has been used to investigate its potential as a humidity-sensing device. The golden metallic appearance of the film changes as well. The conductivity can be returned by application of a dynamic vacuum. Fuming sulfuric acid-doped films were exposed to a range of relative humidities, from 4 to 75%. A rapid and significant linear response (over four orders of magnitude) to all percent humidities was observed. Fuming sulfuric acid-doped PPV may have the potential for applications as a humidity sensor or as a disposable shut-off switch in moisture-sensitive devices.

In Situ Analysis of the Thermal Elimination Reaction in the Synthesis of Poly(p-phenylene vinylene)(PPV) and PPV Derivatives

In situ spectroscopy is an important tool to characterize polymers synthesized via a precursor route. Highly conjugated polymers such as poly(p-phenylene vinylene) (PPV) and PPV derivatives are commonly prepared from a precursor polymer because the final polymers are very insoluble and intractable. Preparation in the precursor form enables the polymer materials to be cast as films. The PPV polymers are obtained from the precursor forms using a thermal elimination reaction. The exact conditions of the reaction are important as they influence the properties of the resultant polymer. The details of this thermal elimination reaction have been analyzed using thermal gravimetric analysis (TGA) coupled with infrared analysis of the evolved gas products. In situ infrared spectroscopy of the precursor films during thermal conversion to the polymers has provided further details about the elimination reaction. We have characterized PPV synthesized from a tetrahydrothiophenium monomer (sulfonium precursor route) nd via the xanthate precursor route. PPV derivatives under study include poly (2,5- dimethoxy-p-phenylene vinylene) and poly(phenoxy phenylene vinylene).