Franz-Hubert Haegel

An overview of the spectral induced polarization method for near-surface applications

Over the last 15 years significant advancements in induced polarization (IP) research have taken place, particularly with respect to spectral IP (SIP), concerning the understanding of the mechanisms of the IP phenomenon, the conduction of accurate and broadband laboratory measurements, the modelling and inversion of IP data for imaging purposes and the increasing application of the method in near-surface investigations. We summarize here the current state of the science of the SIP method for near-surface applications and describe which aspects still represent open issues and should be the focus of future research efforts. Significant progress has been made over the last decade in the understanding of the microscopic mechanisms of IP; however, integrated mechanistic models involving different possible polarization processes at the grain/pore scale are still lacking. A prerequisite for the advances in the mechanistic understanding of IP was the development of improved laboratory instrumentation, which has led to a continuously growing data base of SIP measurements on various soil and rock samples. We summarize the experience of numerous experimental studies by formulating key recommendations for reliable SIP laboratory measurements. To make use of the established theoretical and empirical relationships between SIP characteristics and target petrophysical properties at the field scale, sophisticated forward modelling and inversion algorithms are needed. Considerable progress has also been made in this field, in particular with the development of complex resistivity algorithms allowing the modelling and inversion of IP data in the frequency domain. The ultimate goal for the future are algorithms and codes for the integral inversion of 3D, time-lapse and multi-frequency IP data, which defines a 5D inversion problem involving the dimensions space (for imaging), time (for monitoring) and frequency (for spectroscopy). We also offer guidelines for reliable and accurate measurements of IP spectra, which are essential for improved understanding of IP mechanisms and their links to physical, chemical and biological properties of interest. We believe that the SIP method offers potential for subsurface structure and process characterization, in particular in hydrogeophysical and biogeophysical studies.

Anodic polymerization of thiophene derivatives from microemulsions and liquid crystals

Abstract Intrinsically conducting polymers (ICPs) of substituted thiophenes were obtained by anodic polymerization from microemulsions of the heterocyclic aromatic oils 3,4-ethylenedioxythiophene (EDOT) and 3-methoxythiophene (MOT) with high oil and nonionic surfactant content. A liquid crystal was polymerized for the first time allowing the formation of a free membrane in a platinum loop. Polymerization takes place under all conditions, but current transients and cyclovoltammograms yield a clear dependence of ICP properties on the composition of the microemulsion. Optimum conditions obtained for the polymerization current do not coincide with optimum redox properties. To understand these results, the multicomponent systems were characterized by phase behavior, conductivity, viscosity and dynamic light scattering. For microemulsions of EDOT, 0.5 M aqueous LiClO 4 solution and a commercial alkyl polyethoxylate, a transition from the oil-in-water to the bicontinuous microemulsion was found at an oil content of about 45%. Continuous water domains exist up to a very high monomer content of more than 60% by weight.

Improved analysis of polycyclic aromatic hydrocarbons in aqueous solutions by gas chromatography

The analysis of organics in aqueous solutions by gas chromatography needs sample pretreatment in order to avoid contact of water with the stationary phase of the column. A new method based on dehydration by boron trifluoride and its use for the analysis of polycyclic aromatic hydrocarbons in microemulsions is described.

In situ measurements on surfactant–mineral interactions by polarographic adsorption kinetics

Adsorption of surfactants at the mercury/electrolyte interface causes changes in electrode capacity. This phenomenon can be used for surfactant analysis in low and ultra-low concentration ranges. Tensammetry is carried out by alternating current or potential pulse techniques. Time-dependent concentration changes can be determined by adsorption kinetics at the mercury/electrolyte interface. As the interaction of surfactants with the mercury/electrolyte interface strongly depends on the potential of the electrode, repeated potential jumps can be used to generate adsorption–desorption cycles. This permits rapid determination of constant or time-dependent concentration. The adsorption kinetics of cationic and non-ionic surfactants on clay minerals were determined by Kalousek polarography. These two types of surfactant exhibit different behaviour. Many other adsorption phenomena might also be investigated by using the method described here.