This
paper reports on the anomalous diffusion of C1–C6 alcohol vapors in the high-free-volume, amorphous glassy
perfluoropolymer Teflon AF 2400. In this material, during time lag
measurements, the transient in the pressure increase curve of aliphatic
alcohols exhibits a quite unusual behavior, different from the previously
reported diffusion of permanent gases and that of other vapors (such
as hydrocarbons, acetone, dichloromethane, etc.). Such unusual behavior
can be explained by the simultaneous diffusion of dynamic molecular
aggregates: clusters, made of at least two or three molecules with
different diffusion coefficients, differing in orders of magnitude
from those of single molecules. The probability of cluster formation
increases at higher C1–C6 alcohol vapor
activities. Moreover, the average cluster size decreases from methanol
to pentanol with increasing molecular size, because of the longer
hydrocarbon chain and, consequently, the lower polarity. Weak (butanol,
pentanol) and almost zero (hexanol) clustering ability in Teflon AF
2400 was confirmed independently by the ENSIC model and through evaluation
of diffusion from gravimetric sorption experiments in the vapor activity
range (0.15–0.95). In addition, we present a novel method for
the treatment of raw sorption kinetic data recorded by a gravimetric
sorption apparatus equipped with a calibrated quartz (McBain’s)
spiral balance. The mentioned treatment allows one to eliminate overlapping
mechanical oscillations of the spiral balance (caused by the initial
charging of the sample gas/vapor into the evacuated measuring chamber)
and successfully reconstruct the real elongation of the spiral caused
by gas/vapor sorption into a polymer material. This allows to calculate
accurate values of the gas/vapor diffusion coefficients, even from
highly noisy sorption data.
Electrical impedance spectroscopy (EIS) is a non-destructive, rapid and real-time measurement method which does not require special high-tech measurement devices and can be applied to food quality assessment. This method is rapid, effective and affords low-cost investigation of the product. The conventional EIS method requires a set of metal electrodes in direct contact with the medium to be measured. The complicated electrochemical processes on the electrodes-electrolyte interface could substantially affect the value of the impedance measured. The present study sought to explore the possibilities of using the impedance method for quality control in orange juices, to introduce the electrodeless method of electrolyte impedance measurement and to compare this with the conventional impedance methods. The electrical properties of the orange juices were described with the help of an equivalent circuit. An equivalent circuit was designed with constant phase element approximation. The values of the equivalent circuit components were fitted using a non-standard algorithm inspired by the behaviour of actual ant colonies. Implementing the electrodeless method obviated the electrodes phenomena effects and the behaviour of the electrolyte is similar to inductance. The proposed electrodeless method is generally applicable to measuring the electrochemical properties of electrolytes.
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