Correlation of the Relations of Micellar Microstructure of Dilute CTAC/Counterion Systems with Counterion Chemical Structure, Counterion/CTAC Ratio, Drag Reduction and Rheological Behavior

W. Ge¹, E Kesselman², Y Talmon², and J. L. Zakin¹

¹Dept of Chemical & Biomolecular Engineering, Ohio State University Columbus, OH, USA

²Dept of Chemical Engineering, Technion-Israel Institute of Technology, Haifa, Israel

Counterion chemical structure  and counterion/cationic surfactant ratio control the micelle microstructures, drag reduction effectiveness and rheological  behavior of quaternary ammonium surfactant systems. Correlation of physical properties of dilute solutions of CTAC and their microstructures with the chemical structures of four para-halo-benzoate (F, Cl, Br, I) counterions and with different counterion/CTAC ratios will be shown. Microstructures  are determined by cryo-TEM imaging. Drag reduction effectiveness is measured over a range of temperatures and Reynolds numbers and, along with micelle microstructures, shear viscosities, dynamic viscosities and N1,   will be  related to the chemical structures of the four counterions and their molar ratios to CTAC.

Micelle microstructures of the four systems at low (0.6) and high (4.0) counterion to CTAC ratios will be shown. At 30 C  the para-F-benzoate system at ratio 0.6 shows only short threadlike micelle structures, is not drag reducing and has zero N1  At ratio 4.0, the Fluoro system is also not drag reducing  and has zero N1 while the  Chloro, Bromo and Iodo systems are all drag reducing and have appreciable N1.  The Fluoro system  also  showed only small zeta potential reductions at all ratios while the other three showed moderate to large decreases in zeta-potential with increase in counterion/CTAC ratio, crossing from positive to negative values at higher ratios. The ratios at the crossing points followed the order of the Hofmeister series: I, Br and Cl.  The effects of counterion chemical structure on relaxation times from dynamic viscosity measurements and estimates of counterion binding ratios obtained from NMR measurements will also be shown.