Thermodynamic properties of CTAB in aqueous solutions of neutral polymers at 25 degrees C

Interactions of polyethylene glycols (PEGs) and polypropylene glycols (PPOs ) in aqueous solutions of hexadecyltrimethylammonium bromide (CTAB) were in vestigated through thermodynamic properties at 25 degrees C. The densities and heat capacities of the solutions were measured with a vibrating tube de nsimeter and a Picker flow microcalorimeter, respectively. The variations i n the apparent molar volumes and heat capacities of both solutes, calculate d from the densities and heat capacities of the solutions, are unusually la rge in the vicinity of the CMC, reflecting the existence of very strong int eractions between CTAB and PPOs. With the more hydrophilic polymers, PEGs, the apparent properties of CTAB are less affected by the presence of the po lymer, indicating that PEGs interact only weakly with CTAB.