Effect of viscosity on electrical conductivity in liquid foods

The electrical conductivities of foods affect their heating with ohmic heating and microwaves, and are required for electrical tomography studies. A range of model foods consisting of solutions of sodium carboxymethyl cellulose (NaCMC), NaCMC + sugars, concentrated skim milk, whey protein and viscous sugar solutions, with various amounts of electrolytes were prepared. The electrical conductivity was measured using a parallel plate sensor connected to an RCL meter using an a.c. voltage. The conductivity was found to increase with concentration, but was reduced by the effects of viscosity on ion mobility. The conductivity was closely related to bulk viscosity for sugar solutions following the modified Walden equation, but was unrelated to the viscosity of NaCMC solutions. Instead an “ion-diffusion” viscosity was defined and calculated from the electrical conductivity data, and this was found to relate well to the expected viscosity of the solution to which ions are exposed at a molecular scale.

Investigation and Modeling of the Electrical Conductivity of Graphene Nanoplatelets-Loaded Doped-Polypyrrole

In this study, a hybrid of graphene nanoplatelets with a polypyrrole having 20 wt.% loading of carbon-black (HGPPy.CB20%), has been fabricated. The thermal stability, structural changes, morphology, and the electrical conductivity of the hybrids were investigated using thermogravimetric analyzer, differential scanning calorimeter, X-ray diffraction analyzer, scanning electron microscope, and laboratory electrical conductivity device. The morphology of the hybrid shows well dispersion of graphene nanoplatelets on the surface of the PPy.CB20% and the transformation of the gravel-like PPy.CB20% shape to compact spherical shape. Moreover, the hybrid’s electrical conductivity measurements showed percolation threshold at 0.15 wt.% of the graphene nanoplatelets content and the curve is non-linear. The electrical conductivity data were analyzed by comparing different existing models (Weber, Clingerman and Taherian). The results show that Taherian and Clingerman models, which consider the aspect ratio, roundness, wettability, filler electrical conductivity, surface interaction, and volume fractions, closely described the experimental data. From these results, it is evident that Taherian and Clingerman models can be modified for better prediction of the hybrids electrical conductivity measurements. In addition, this study shows that graphene nanoplatelets are essential and have a significant influence on the modification of PPy.CB20% for energy storage applications.

Matching Rheology, Conductivity and Joule Effect in PU/CNT Nanocomposites

We investigated polyurethane (PU)–carbon nanotube (CNT) nanocomposites (PU/CNT) in a range of concentrations from 1 to 8 wt% CNT as hot melt adhesives. We studied the thermal properties of the nanocomposites, which is relevant from an applied point of view. The phase angle plots versus complex modulus results revealed the existence of a maximum above a given CNT concentration. The intensity of the peak and associated relaxation time was analyzed with percolation theory, leading to a new method to determine the rheological percolation threshold. A lower threshold value was obtained from the electrical conductivity data, which was justified recalling that the hopping/tunnelling effect takes place in the nanocomposite, as stated by previous studies in the literature. Joule effect studies indicated that the heating effect was very significant, reaching temperature increases, ΔT, of 60 °C for low voltages. For the first time, the percolation equation was applied to the ΔT to obtain the corresponding threshold. Stimulus-responsive systems were conceived considering the correlation between the ΔT and the conductivity. The case of PU/CNT nanocomposites acting as hot melt adhesives that are welded/unglued by applying/removing an electrical voltage is presented.

Coastal groundwater systems: mapping chloride distribution from borehole and geophysical data

Information on chloride (Cl) distribution in aquifers is essential for planning and management of coastal zone groundwater resources as well as for simulation and validation of density-driven groundwater models. We developed a method to derive chloride concentrations from borehole information and helicopter-borne electromagnetic (HEM) data for the coastal aquifer in the Elbe-Weser region where observed chloride and electrical conductivity data reveal that the horizontal distribution of salinity is not uniform and does not correlate with the coastline. The integrated approach uses HEM resistivity data, borehole petrography information, grain size analysis of borehole samples as well as observed chloride and electrical conductivity to estimate Cl distribution. The approch is not straightforward due to the complex nature of the geology where clay and silt are present. Possible errors and uncertainties involved at different steps of the method are discussed.

THE EFFECT OF REACTANTS' INITIAL TEMPERATURES ON THE RATE CONSTANT AND CONVERSION OF SAPONIFICATION REACTION TAKING PLACE IN A NON-ISOTHERMAL AND NON-ADIABATIC BATCH REACTOR

This experimental research studied the saponification reaction of ethyl acetate with sodium hydroxide, which was carried out in a well-agitated non-isothermal and non-adiabatic batch reactor. As no isolation system was provided in this experiment, this study investigated other routes for boosting the reactants conversion. Subsequently, the effect of initial feed temperatures on the reaction rate constant and reaction conversion was assessed. For this purposes, the reaction rates of equimolar reactants were measured when they were heated from 20°C (ambient temperature) to 30°C, 40°C and 50°C. The decrease in the reactants concentrations throughout the reaction durationwas determined at equal time intervals by recording the electrical conductivity data of the reaction mixture. The results were represented graphically for time-conversion, temperature-conversion and temperature-rate constants profiles. They had shown that the reaction rate constant increased with rising of the initial feed temperatures. Even though, the conversion was boosted when the reactants were initially heated above 20°C, no significant change in conversion was achieved between 30, 40, and 50°C. The resulted value of activation energy was about 50 % less than the most accurate published values.