The polarization conductivity, σ'(ω) of a Ca-montmorillonite has been determined by complex impedance spectroscopy. The technique of thermally-stimulated currents (TSC) leads to the determination of the different relaxation parameters, such as the distribution function of the different relaxation processes. The results demonstrated the coherence of the two approaches, and confirmed that the conducting phenomenon is due to the hopping of charge carriers between localized sites. The energy corresponding to the hopping process is evaluated using two different methods of analysis of the TSC signal. The values obtained are compared to those observed on a Na-montmorillonite.

Montmorillonite-water-cation systems were characterized using high-frequency impedance spectroscopy by studying the influence of the solid concentration and the nature of the exchangeable cation (Na+, K+, Ca2+) on the dielectric characteristics of the dispersions. A new method is proposed to calculate the relaxation frequency (fr) and the dispersion factor (α) from a limited number of impedance measurements. By comparison with rheology, microscopy, X-ray diffraction and immersion calorimetry results, it is shown that impedance spectroscopy is a very powerful technique which yields structural information on a complex system. For Na-montmorillonite, two transitions are observed at 2.5% and 3.6% in solids. The cation mobility and the number of connections between particles are described by fr and α, respectively. The two transitions can then be attributed to the formation of the gel and to the reduction of the macroporosity within the gel, respectively. For Ca-montmorillonite, thick layer-stacks form at the lowest concentrations, and connections between these stacks are observed at 9% in solids, in good aggrement with rheological measurements. The K-montmorillonite displays progressive thickening of the tactoids, and no formation of a unique connected network, as revealed by the smooth evolution of fr and α.

This paper describes a study of the hydraulic reactions between metakaolin (MK) and air lime using electrochemical impedance spectroscopy (EIS) and nuclear magnetic resonance spectroscopy (NMR). Tests were carried out at 20, 25 and 30°C on lime-MK pastes with 10:1 w/w ratio. Tests over 28 days allowed identification of relevant changes in the EIS signals and characterization of pastes using thermal analysis (TGA/DSC), scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP) and uni-axial compressive tests. Tests over shorter periods of time (up to 42 h) allowed more detailed studies of the hydraulic phases formed at the very beginning of the reactions.

Results of thermal analyses demonstrate formation of hydraulic compounds such as CSH, C4AH13 and C3ASH6 and show their evolution over time. MIP analysis demonstrates changes in pore size distribution related to the formation and trasformation of hydraulic phases. Variations of impedance response with time are shown to be associated with reaction kinetics. Changes in the NMR signal within the first 42 h of reaction are shown to be associated with the dissolution of calcium hydroxide in the pore solution. Overall, this paper demonstrates the importance of NMR in the study of hydraulic reactions in lime based materials and the ability of EIS to detect the formation of hydraulic compounds and the end of the calcium hydroxide dissolution process.

Dispersions containing 1 mg/mL of several carbon nanomaterials were used to deposit films containing 1 to 20 layers. The electrical properties of the composite films were characterized via impedance spectroscopy along two directions: in-plane on the film topmost surface and also through the thickness. It was found that carbon black nanoparticles never achieved full in-plane interconnection while the multiwalled carbon nanotube (MWNT) and single-walled carbon nanotube were already percolated at one layer. Graphite flakes showed a complete percolation curve that allowed its resistance to change by 6–7 orders of magnitude. The differences in the microstructure, electrical response, and thermal decomposition behavior of these carbon nanomaterial–paper substrate films were explained by detailed equivalent circuit analysis of the impedance spectra. Interpretation was supplemented by scanning electron microscopy images and thermal analysis via Differential Scanning Calorimetry/Thermogravimetric Analysis (DSC/TGA). Thru-plane electrical properties were for the most part similar, although only films with short MWNT showed a clearly infiltrated network structure.

Atomic force microscopy (AFM) is one of the most sensitive tools for nanoscale imaging. As such, it is very sensitive to external noise sources that can affect the quality of collected data. The intensity of the disturbance depends on the noise source and the mode of operation. In some cases, the internal noise from commercial AFM controllers can be significant and difficult to remove. Thus, a new method based on spectrum analysis of the scanned images is proposed to reduce harmonic disturbances. The proposal is a post-processing method and can be applied at any time after measurements. This article includes a few methods of harmonic cancellation (e.g., median filtering, wavelet denoising, Savitzky-Golay smoothing) and compares their effectiveness. The proposed method, based on Fourier transform of the scanned images, was more productive than the other methods mentioned before. The presented data were achieved for images of conductive layers taken in a contact AFM mode.

The function of biologically important ion channels can be measured in supported lipid membranes by impedance spectroscopy. This approach offers substantial advantages over traditional electrophysiological measurements. In this article, we present an overview of the field, with a special emphasis on the reconstitution of ion channels in lipid bilayers tethered to gold electrodes and the modulation of their channel activity by specific ligand binding.