An Inexpensive Glass Capillary ‘Tensiometer’ for Determining the Critical Micelle Concentration of Surfactants

TCE

The Chemical Educator

ISSN: 1430-4171 (electronic version)

Table of Contents

Abstract Volume 14 Issue 6 (2009) pp 239-242

An Inexpensive Glass Capillary ‘Tensiometer’ for Determining the Critical Micelle Concentration of Surfactants

Gregory D. Smith* and Violet G. Pena

Indianapolis Museum of Art, 4000 Michigan Road, Indianapolis, IN 46208-3326, gdsmith@imamuseum.org
Received January 18, 2009. Accepted September 2, 2009.

Published online: 31 December 2009

Abstract. A simple tensiometer costing pennies per unit is described for measuring the critical micelle concentration (CMC) of surfactants in student laboratory exercises. The instrument is based on a glass melting point capillary. The CMC is determined by the diminishing capillary rise in the thin tube due to a loss of surface tension with increasingly concentrated surfactant solutions. At the critical micelle concentration, the rapid change in capillary rise ceases and the calculated surface tension remains relatively constant. The equipment is proven by measuring reasonably accurate CMC values for an ionic (sodium dodecyl sulfate, 6.04 ± 0.21 mM) and nonionic (Surfonic JL-80X, 0.22 ± 0.02 mM) surfactant.

Key Words: Laboratories and Demonstrations; general chemistry; quantitative analysis

(*) Corresponding author. (E-mail: gdsmith@imamuseum.org)

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