Micelle formation and adsorption at air/water interface were investigated as function of temperature for aqueous solutions of the nonionic surfactant, n-nonyl-β-D-thiomaltoside (NTM), used as a membrane-protein solubilizer by surface tension measurements (drop volume method). For comparison with NTM, such surface tension measurements were performed even for aqueous solutions of decanoyl-N-methylglucamide (MEGA-10). Examination was also made of the effect of adding alcohols (methanol, ethanol and 1-butanol) on critical micellization concentration (cmc) and on surface activity. As for the behavior of surface activity as well as cmc, NTM was found more similar to ionic surfactants than typical nonionic surfactants such as poly oxy ethylene alkyl ethers ; NTM exhibited no cloud point at least up to 100°C, but showed a minimum cmc at 28.3°C in the curve of temperature vs. cmc. Light scattering measurement at 25°C (the Debye plot) gave a comparatively small aggregation number of 16.4, indicating that the present thermodynamic analysis based on the phase separation model (PSM) may involve a rough approximation. However, a thermodynamical feature of NTM may be understood from PSM and facilitates comparison with MEGA-10 and alkyl glucosides.
In addition, the hydrophilic-lipophilic balance (H.L.B.) value not indicated by Davies was determined for sulfur in amphiphilic organic compounds (-S-) as 1.5.