COUPLING A IONIC SURFACTANT AND A DRUG SALT: EQUILIBRIUM CHARACTERISTIC PARAMETERS & STRAIN HARDENING IN START-UP FLOW

摘要: Surfactant solutions containing Cetylpyridinium Chloride (CPyCl), a classical ionic surfactant, and Sodium Diclofenac (Diclo), a non-steroidal anti-inflammatory drug, were investigated in a wide range of compositions using rheology and Cryo-EM. Solutions were made at three different concentrations of CPyCl, ie 5.0, 16.7 and 33.0 mM. The ratio between the salt and the surfactant concentrations, R= CPyCl/Diclo, was within the range 0.4< R< 1.4. Linear viscoelastic rheology was performed at 25 C using a stress controlled DHR-2 Rheometer (TA instruments), equipped with sandblasted 40 mm diameter parallel plates, a Peltier system to control the temperature, and a solvent trap to avoid evaporation. The use of dilute solutions allowed to examine their microstructure via cryo-EM imaging, eg avoiding high density of micelles. High-resolution images of vitrified specimens were recorded with a Glacios FEG electron microscope (Thermo Fisher) at 200 kV. Nonlinear rheological experiments were performed at 25 C with a strain-controlled ARES rheometer (TA instruments, USA), using a 50 mm–0.017 rad cone-plate geometry.