Zg. Lin et al., Experimental studies on drag reduction and rheology of mixed cationic surfactants with different alkyl chain lengths, RHEOL ACT, 39(4), 2000, pp. 354-359
Experimental studies of the effects of mixtures of cationic surfactants on
their drag reduction and rheological behaviors are reported. Cationic alkyl
trimethyl quaternary ammonium surfactants with alkyl chain lengths of C-12
and C-22 were mixed at different molar ratios (total surfactant concentrat
ions were kept at 5 mM with 12.5 mM sodium salicylate (NaSal) as counterion
). Drag reduction tests showed that by adding 10% (mol) of C-12, the effect
ive drag reduction range expanded to 4-120 degrees C, compared with 89-130
degrees C with only the C-22 surfactant. Thus mixing cationic surfactants w
ith different alkyl chain lengths is an effective way of tuning the drag re
duction temperature range. Cryo-TEM micrographs revealed thread-like micell
ar networks for surfactant solutions in the drag reducing temperature range
while vesicles were the dominant microstructures at non-drag reducing temp
eratures. High extensional viscosity was the main rheological feature for a
ll solutions except 50% C-12 (mol) solution, which also does not show stron
g viscoelasticity. It is not clear why this low extensional viscosity solut
ion with relatively weak viscoelasticity is a good drag reducer.