HYDROPHOBICALLY AND CATIONICALLY MODIFIED HYDROXYETHYL CELLULOSE AND THEIR INTERACTIONS WITH SURFACTANTS

We investigated the solution behavior and the macroscopic properties of samples of hydroxyethyl cellulose (HEC) which are modified by perfluoroalkyl chains (F-HMHEC) and by cationic groups (cat-HEC). The systems were characterized by rheological, electric birefringence and scanning electron microscopic measurements. A solution of 1% HEC (molecular weight, 5 x 10(5) g mol-1) has a viscosity of about 100 mPa s. The chemical modification causes an increase in viscosity up to 1000 mPa s. The solutions of the modified systems show shear thinning behavior. On the addition of surfactant the viscosity of the F-HMHEC and cat-HEC solutions increases even more. Such solutions show viscoelastic behavior and a yield stress value. The rheological properties were characterized by oscillatory measurements. The results are interpreted in terms of associations of the side chains of the polymer with the surfactant molecules. The surfactants and the modified HEC form a three-dimensional network structure. It is shown for the first time that the three-dimensional network structure can be made visible by freeze-fracture scanning electron microscopy. The influence of the cooling rate on the microscopic structures was shown by using melting nitrogen and liquid propane as cryogens.