Rheological behavior of two kinds of quaternary ammonium gemini surfactants in aqueous solution

Different flow behaviors influenced by shear rate were observed in two concentration regions (3similar to9 mmol.kg(-1) and 10similar to40 mmol.kg(-1)) of quaternary ammonium Gemini surfactant C-12-s-C-12.2Br(s=2) in aqueous solution. The solution in the former concentration region kept Newtonian flow through out the range of shear rate gamma examined from 0 to 1875 s(-1). But in the latter concentration region, the flow transformed from Newtonian to dilatant flow after gamma reached a value of critical shear rate gamma* which depended on temperature and concentration. And a sharp increase of the zero-shear viscosity eta(0) along with the raise of c appeared in this region. It was suggested that the tangle of thread-like micelles of C-12-s-C-12.2Br(s=2) existed in the solution led to the phenomenon mentioned above. The surfactants C-12-s-C-12.2Br(s=2) turns to C-12-s-E-n-C-12.2Br (s=2, n=1, 2, 3) by insertion of one, two or three oxyethyl groups into the spacer of it. By the reason of the evident variation in geometric shape of unit molecule, this kind of Gemini surfactant in aqueous solution only aggregated into sphere micelles so that it retained Newtonian behavior over the range of c=0similar to120 mmol.kg(-1) and gamma=0similar to1875 s(-1) with slight increase of eta(0). In addition, reducing temperature favors shear induced structure transform but gives small effect on those systems keeping Newtonian behaviors over the tempretures range sutdied.