Üdvözöljük a fotoakusztika oldalain

Introduction In various applications the measurement of gas permeation of materials is a crucially important. The rate at which molecules diffuses from a gaseous or liquid phase through a sheet of material, such as foils, membranes cloth, fabric etc., has a substantial importance in numerous practical applications, and consequently there exists a strong demand for instruments capable for providing quantitative information about this so called permeation process. The strong dependence of the permeation process on the experimental conditions, and the large range within which the permeation rate can vary, from sample to sample, poses a strong challenge on potential measurement methods. We have a good reason to believe that presently our photoacoustic system for gas permeation measurements has an unparalleled capacity of measuring these permeation rates. There are several areas where permeation of certain molecules through a material plays an important role. These applications include the food industry, the textile industry, the polymer industry etc. The shelf life of foodstuffs and medicines are strongly influenced by the diffusion of moisture through the packaging material. On the other hand, the taste of various foodstuff is influenced by the resistance of packaging to volatile organic compounds. In certain cases packaging is done with using modified atmosphere (such as high concentration of argon and/or carbon-dioxide), which should stay inside the package as long as possible. Special membranes are used in building construction in order to prevent gases to diffuse from the surrounding into the closed living space. Also important is the resistance of outdoor clothes to water droplets from outside to inside, while letting the moisture produced by sweating to leave the inside of the clothes. Yet, another application of membranes occurs in chemical industry where they are used for separating various components of a mixture (the so called pervaporation method). Most of the methods applied for measuring gas permeation are based on measuring the change in volume, mass or pressure caused by molecules either entering into a gas volume having a low concentration of the measured component or leaving a volume having a high concentration of the measured component. The applied measurement protocols include sorption-desorption tests and the time lag method. Generally speaking existing measurement methods are limited both in sensitivity and in selectivity. Some improvement can be achieved by introducing using an analytical method for the measurement of the permeated components such as: infrared spectroscopy, mass spectroscopy, gas chromatography or thermal conductivity. Photoacoustic spectroscopy can outperform these methods due to its high sensitivity, which is the consequence of the small sample volume and its inherent selectivity originating from the applied ultra narrow band laser radiation.