Two bis (quaternary ammonium bromide) surfactants, hexanediyl-1,6-bis(dimethyldodecylammonium bromide) (12-6-12) and dimethylparaphenyl-a,w-bis(dimethyldodecylammonium bromide) (12-fi-12), were synthesised and their degree of solubility in water and melting point were compared. Hydrophobically modified HEC was synthesised from HEC and bromo tetradecane in an homogeneous reaction. The degree of hydrophobically modification of the synthesised HMHEC 2 was compared with a commercially HMHEC by capillary viscosimetry measurements.
The interactions in aqueous solutions of hydrophobically modified HEC (HMHEC) with the dimeric surfactant hexanediyl-1,6 bis (dimethyldodecyl ammonium bromide) and the single chained analogue dodecyltrimethylammonium bromide (DoTAB), were investigated by shear viscosimetry and capillary viscosimetry. From the measurements in capillary viscosimetry, intrinsic viscosity [eta] and Huggins constant kH were estimated and plotted against concentration of surfactant. The measurements were performed on solution in the dilute regime of HMHEC, where the polymer exist as individual, or partially overlapping coils, due to interassociation between the hydrophobes on HMHEC. [eta] showed a strong decrease and kH showed a strong increase below CMC and the opposite behaviour above CMC as a function of surfactant concentration. Both systems of HMHEC with surfactant revealed phase-separation in a region around CMC, due to very strong intermolecular interactions. High values of kH revealed strong interactions in both systems of HMHEC with DoTAB and 12-6-12. The highest values and a more co-operative pattern of [eta] and kH in surfactant concentration were found in the HMHEC/12-6-12 system.
The measurements in rheology on semidilute aqueous solutions of HMHEC with surfactant showed shear thinning behaviour for both DoTAB and 12-6-12. The value of zero-shear viscosity at maximum, occurring around CMC for both HMHEC/12-6-12 and HMHEC/DoTAB, was the highest for HMHEC/DoTAB. The shear thinning started at the highest shear rate for the HMHEC/12-6-12 system.