Kinetic investigations at the cloud point of nonionic surfactants

Abstract

Kinetic relaxation measurements using the T-jump technique, electric birefringence, and light-scattering measurements were carried out with aqueous solutions of the neutral detergents C 10H 21-(OC 2H 4) 4OH, C 12H 25(OC 2H 4) 4OH, C 8H 17(OC 2H 4) 4OH, C 9H 19Ph(OC 2H 4) 5OH, C 9H 19Ph(OC 2H 4) 8OH, and Triton X-100 (Ph stands for the phenylen group) above and below the cloud point T c . Two relaxation processes could be detected in the clear solutions below T c . These processes could be associated with the change of the aggregation number and concentration of micelles according to the theory of Aniansson and Wall. The C 12E 4 system shows electric birefringence below T c from which it can be concluded that the micelles are nonspherical. In the turbid solutions above T c up to six relaxation times could be observed by recording the turbidity as a function of time. These processes could be associated with the normal micellar effects in clear solutions, with the transport of matter to the droplets of the dispersed new phase that is formed above T c and with the equilibration of the droplets, respectively. The aggregation number of the micelles and the dimensions of the droplets are calculated from the relaxation times. These values agree fairly well with the values obtained from light-scattering measurements.