Quantifying Critical Micelle Concentration and Nonidealities within Binary Mixed Micellar Systems: An Upper-Level Undergraduate Laboratory

TCE

The Chemical Educator

ISSN: 1430-4171 (electronic version)

Table of Contents

Abstract Volume 6 Issue 4 (2001) pp 223-226

Quantifying Critical Micelle Concentration and Nonidealities within Binary Mixed Micellar Systems: An Upper-Level Undergraduate Laboratory

Gary A. Baker,^‡ Frank V. Bright,^‡ and Siddharth Pandey^*,†

^†Department of Chemistry, New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801, pandey@nmt.edu, ^‡Department of Chemistry, Natural Sciences Complex, University at Buffalo, The State University of New York, Buffalo, New York 14260-3000, chefvb@acsu.buffalo.edu
Received April 11, 2001. Accepted May 8, 2001

Published online: 22 June 2001

Abstract. Micelle-based systems have a long history in many areas, for instance, membrane mimics, reaction media, and food additives. All prior educational laboratory experiments dealing with micelle-based systems that have been published and utilized deal with unary surfactant systems. Unfortunately, most practical applications that use surfactants and micelles involve mixtures because these often exhibit behavior unlike the individual components. That is, surfactant mixtures deviate significantly from a regular solution approximation (i.e., there is synergism) when the individual surfactant structures differ significantly. In this laboratory experiment, we describe a simple method that exploits the unique behavior of the fluorophore pyrene to rapidly determine the critical micelle concentration (CMC) of mixed micelle systems. We also determine the dimensionless interaction parameter, b, that describes the net pairwise interaction between surfactant species within a binary micellar system. The binary system we chose to study is sodium dodecyl sulfate (SDS) and dodecyl trimethylammonium bromide (DTAB) dissolved in water. The b value recovered by students using our method is statistically equivalent to the value reported in the literature using more sophisticated and protracted methods. This laboratory experiment opens the door for students to explore regular solution theory, non-ideal mixing, micelle formation, and fluorescence spectroscopy within a single experiment.

Key Words: Laboratories and Demonstrations; biochemistry; physical chemistry

(*) Corresponding author. (E-mail: pandey@nmt.edu)

Article in PDF format (163 KB) HTML format

Supporting Materials:

Student Handout and QBASIC program (10 KB PDF file) 10.1007/s00897010487b