Collision of atoms with porous polymer surface: evidence of influence of bulk diffusion on anomalously long dwell time of Rb atoms
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We present the results of a systematic study of Knudsen’s flow of Rb atoms in cylindrical capillary cells coated with a polydimethylsiloxane (PDMS) compound. The purpose of the investigation is to measure the adsorption energy and dwell time of Rb atom on the two types of coating of high and median viscosities. We report the measurement of the adsorption energy which yields E = 0.026 eV. This parameter is the same for the two kinds of PDMS used. We find that at room temperature the dwell times for high viscosity and median viscosity PDMS are 22 ± 3 μs and 49 ± 6 μs, respectively. These dwell times are many orders of magnitude longer than the dwell time derived from the measured adsorption energy of Rb atom and temperature of the coating. A tentative explanation of this surprising result, based on the bulk diffusion of the atoms that collide with the surface and penetrate inside of the coating, is proposed.
KeywordsAtomic and Molecular Collisions
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