CLOUDING AND DIFFUSION OF NONIONIC SURFACTANTS IN AGAROSE GELS AND SOLUTIONS

Light transmittance and NMR self-diffusion measurements were carried o ut on nonionic micellar systems of hexaethylene (C12E6) and octaethyle ne (C12E8) glycol mono-n-dodecyl ether in gels and solutions of agaros e with and without NaSCN. The influence of agarose on the clouding beh avior and the diffusion of C12E8 and C12E6 micelles as well as the eff ect of C12E8 and C12E6 on the gelation behavior of agarose was studied . The light transmittance measurements show that on increasing the aga rose or surfactant concentration, the cloud-point of the surfactant on cooling is decreased, indicating an incompatibility between dissolved agarose chains and surfactant (segregative phase behavior) as also de monstrated directly, whereas the gelation temperature of agarose remai ns practically unchanged. The cloud-point of the surfactant on heating in agarose gels is much less affected, indicating a less repulsive in teraction between agarose in the gel state and surfactant. This hyster esis in clouding of the surfactant becomes more apparent at higher con centrations. The observed self-diffusion Of C12E8 and C12E6 in agarose /1.0 M NaSCN systems is faster in the gel (more open structure) than i n the solution state. The self-diffusion of surfactant in the presence of agarose is lowered compared to the polymer-free case due to the ob struction effect. The presence of NaSCN (1.0 M) does not affect the se lf-diffusion Of C12E8 but causes an increase of the self-diffusion coe fficient Of C12E6, compared to the salt-free case. In salt-free soluti ons of C12E6 the micelles display an increase in size at increasing te mperatures, whereas on addition of NaSCN (1.0 M) no significant micell ar growth is observed.