Evaluation of Elastic Properties and Conductivity of Chitosan Acetate Films in Ammonia and Water Vapors Using Acoustic Resonators

Abstract

Novel bio-materials, like chitosan and its derivatives, appeal to finding a new niche in room temperature gas sensors, demonstrating not only a chemoresistive response, but also changes in mechanical impedance due to vapor adsorption. We determined the coefficients of elasticity and viscosity of chitosan acetate films in air, ammonia, and water vapors by acoustic spectroscopy. The measurements were carried out while using a resonator with a longitudinal electric field at the different concentrations of ammonia (100–1600 ppm) and air humidity (20–60%). It was established that, in the presence of ammonia, the longitudinal and shear elastic modules significantly decreased, whereas, in water vapor, they changed slightly. At that, the viscosity of the films increased greatly upon exposure to both vapors. We found that the film’s conductivity increased by two and one orders of magnitude, respectively, in ammonia and water vapors. The effect of analyzed vapors on the resonance properties of a piezoelectric resonator with a lateral electric field that was loaded by a chitosan film on its free side was also experimentally studied. In these vapors, the parallel resonance frequency and maximum value of the real part of the electrical impedance decreased, especially in ammonia. The results of a theoretical analysis of the resonance properties of such a sensor in the presence of vapors turned out to be in a good agreement with the experimental data. It has been also found that with a growth in the concentration of the studied vapors, a decrease in the elastic constants, and an increase in the viscosity factor and conductivity lead to reducing the parallel resonance frequency and the maximum value of the real part of the electric impedance of the piezoelectric resonator with a lateral electric field that was loaded with a chitosan film. This leads to an increase in the sensitivity of such a sensor during exposure to these gas vapors.

Influence of Humidity on the Acoustic Properties of Mushroom Mycelium Films Used as Sensitive Layers for Acoustic Humidity Sensors

“…We have compared our data with the analogous data presented in [15]. The authors studied the influence of RH on the mechanical properties of the acetate chitosan film.…”

“…In the present work, the growth of the relative humidity in the range 17%-56% changed the elasticity and viscosity coefficients by 38% and 21.6% for the G. lucidum film and by 19% and 37.5% for the P. eryngii film, respectively. Such combinations led to a stronger effect of the humidity on the parameters of the resonator on quartz compared with the piezoceramic (Ba0.24Pb0.75Sr0.01(Ti0.47Zr0.53)O3) resonator described in [15].…”

“…These, in turn, affect the acoustic wave phase velocity and/or attenuation or resonant frequency. Both organic and inorganic materials have been used as sensitive films [ 4 , 5 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 ]. One of the opportunities that is poorly studied is the use of films of the mycelia from higher fungi.…”

The Effect of Glycerol-Based Suspensions on the Characteristics of Resonators Excited by a Longitudinal Electric Field

“…A similar need arises when monitoring the state of various reservoirs, wastewater, and groundwater, as well as in areas of science such as biology, medicine, food, pharmaceutical and in the gas- and oil-producing industry [ 8 , 9 , 10 , 11 ]. In this case, the choice of sensors is determined by factors such as the reliability, accuracy, commercial availability, and ease of use [ 12 , 13 , 14 , 15 ].…”

“…To study materials using BAW resonators, a good acoustic contact must be provided between the object under study and the surface of the piezoelectric plate [ 12 , 13 , 14 ]. This is automatically implemented if the object under study is a liquid.…”