Studies on Behaviors of Critical Aggregation Concentration in Neutral Polymer/Sodium Dodecanoate Aqueous Solution System by means of Light Scattering Method

The critical aggregation concentration (cac) has been investigated by means of laser light scattering method in the tertiary aqueous solution systems of neutral polymer/anionic surfactant, where poly(vinyl pyrrolidone) or poly(ethyl oxazoline) are used as neutral polymers and sodium dodecanoate as an anionic surfactant. According to Nagarajan model and Andelman theory, it has been analyzed how experimental cac values depend on the polymer concentration, its molecular weight and chemical structure. Especially, for higher molecular weight (M-W) samples, the v-shape behavior of cac is observed as increasing polymer concentration. However, for much lower M-W samples, monotonically and very slowly decreasing trend of cac is observed. When cac data from the samples of only different M-W are replotted against the reduced concentration C[eta] instead of C, they are all overlapped. For the polymer samples of different chemical structures, the term of chain flexibility should be added to the reduced concentration. When such a new parameter of C[eta](M-W/R-o(2))(3/2) is used, final overlapping of all cac data has been obtained.