Determination of Critical Micelle Concentration (CMC) of Surfactants by Contact Angle Measurement Method

By using a simple USB digital microscope equipped with a vertically adjustable stand and a physic concept of surface tension, a contact angle goniometer instrument was constructed with an aim of determining the critical micelle concentration (CMC) of the surfactants in everyday usage such as dishwashing solution and sodium dodecyl sulfate (SDS). The surfactants trap dirt and strains by micelles formation and removing dirt at concentration beyond the value at the CMC point. The CMC value can be extracted from the intersecting point between the two different linear fits of the contact angle as a function of the surfactant concentration, using image processing software and simple mathematic calculation. These CMC values of those cleaning agents are extremely helpful to reduce the use of excess chemicals and waste into an environment. In combination with the STEM concept, this instrument provides a simple design, easy to construct with high accuracy results. This interdisciplinary concept can be demonstrated as an excellent STEM tool for school or university students to explore the scientific phenomena at the surface which is no need for expensive equipment.