A quartz-crystal microbalance apparatus for water sorption by polymers

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Abstract
A quartz-crystal microbalance (QCM) apparatus has been assembled for studying the water sorbed by polymeric materials from 0.1 to 100 μm thick. The apparatus consists of an UHV system with a turbomolecular pump, valves, low-pressure gauges, a capacitance manometer, a residual gas analyzer, and reservoirs for water vapor and other adsorbate gases. Up to five different polymer coated quartz crystals can be inserted into hangdown tubes using a 20-in.-long, water-cooled, sensor head with appropriate feedthroughs for the electrical connections and thermocouple leads. The QCM controller consists of a power supply, oscillators, frequency meter, and output for obtaining mass change data. The sensitivity of 14 ng/cm2 Hz corresponds to a mass change of about 0.1% for a 100-nm-thick polymer film. Sample temperatures are controlled to better than 0.1 °C by immersing the hangdown tubes in a liquid water bath. The controller is interfaced with computers for data acquisition, storage, manipulation, etc. to output data for sorption isotherms, the rate of sorption and desorption, and comparing the cyclic reproducibility of rate and capacity. Representative sorption data for three polymers are presented.

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