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The first part of this work presents the construction of an inexpensive and easy to handle contact angle goniometer. The instrument provides contact angles that are within ±2° of the values obtained by a commercial apparatus and are in good agreement with values reported in the literature. In the second part of this work, the contact angle method is used to measure the critical micelle concentration (cmc) of two common surfactants in aqueous solutions: SDS (sodium dodecylsulfate) and Triton X-100 (polyoxyethyleneglycol 9-10 p - tert -octyl phenol). The cmc values obtained by the contact angle method are consistent with those reported in literature and also with those obtained by surface tension measurements using a simplified Du Nüoy tensiometer.
Dionı́sio et al. (2000) studied this question.