ISSN:
1089-7623
Source:
AIP Digital Archive
Topics:
Physics
,
Electrical Engineering, Measurement and Control Technology
Notes:
We have designed and constructed an easy to use, high performance Wilhelmy balance for the study of Langmuir monolayers. This balance is based on a leaf spring and a linear variable differential transformer and was built at a fraction of the cost of a commercial instrument. The balance calibration does not rely on any specific monolayer properties so that we could obtain an independent estimate of accuracy: approximately ±0.2 dyn/cm. In our calibration we follow the standard practice of ignoring the buoyancy of water; we show that this is fine to within the accuracy reported here, but to achieve a higher accuracy not only must the accuracy of the balance be improved, but also the buoyancy of water must be taken into account, which includes knowing and controlling the width and thickness of the Wilhelmy plate to a high degree. The relatively high precision of our Wilhelmy balance is consistently better than ±0.1 dyn/cm, obtained in part by designing an apparatus with very precise temperature regulation, typically ±0.02–0.03 °C. We discuss the conditions necessary to increase this performance. The balance was constructed to achieve good sensitivity while insuring that the Wilhelmy plate travels only a very small distance through the liquid subphase to minimize problems with nonzero contact angle. The control electronics are homemade and have been designed to allow electronic zeroing of the balance. In addition to low cost and good performance, this Wilhelmy balance can be easily adapted to work in many environments differing in available space, mechanical construction, and electronic and computer interfacing.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.1143353
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