Surface Tension Properties of Aqueous Surfactant Solutions

1 Surface Tension Properties of Aqueous Surfactant Solutions 

The surface tension of water increases from 72 to 73 mN/m when 1 M NaCl is added. On the other hand, the magnitude of surface tension decreases from 72 to 39 mN/m when only 0.008 M (0.008 M X 288 = 2.3 g/L) SDS (molecular weight of SDS = 288) is dissolved. It thus becomes 

The magnitude of y changes slowly in the case of methanol as compared to detergent solutions. The methanol-water mixtures gave following y data (20°C)  

In the case of proteins, the amphiphilic property arises from the different kinds of amino acids (25 different amino acids) (Chattoraj and Birdi, 1984 Tanford, 1980). Some amino acids have lipophilic groups (such as phenylalanine, valine, leucine, etc.), while others have hydrophilic groups (such as glycine, aspartic acid, etc.). 

In fact, one finds from surface tension measurements that some proteins are considerably more hydrophobic (such as hemoglobin) than others (such as bovine serum albumin, ovalbumin). These properties of proteins have been extensively investigated, and these data have been found to be related to biological functions (Birdi, 1999 Chattoraj and Birdi, 1984 Tanford, 1980). 

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