Structure and solution properties of modified hydroxyethyl cellulose

We investigated the solution behavior and the macroscopic properties of samples of hydroxyethyl cellulose (HEC) which were modified by cationic groups (cat-HEC) and perfluoro chains (F-HMHEC). The systems were characterized with rheological, electric birefringence and scanning electron microscopic measurements. A solution of 1% HEC (MG 5·105) had a viscosity of about 100 mPas. The chemical modification caused an increase of the viscosity up to 1000 mPas. The solutions showed shear thinning behavior. With the addition of surfactant the viscosity of the cat-HEC and F-HMHEC solutions increased even more. Such solutions showed viscoelastic behavior and a yield stress value. The results are interpreted in terms of associations of the modified groups with the surfactant molecules by forming a three-dimensional network structure. These network structures could be made visible by freeze-fracture scanning electron microscopy (FFSEM).