Characterization of hydroxypropylmethyl- cellulose-stabilized emulsions

Abstract

 Emulsions stabilized with hydroxypropylmethylcellulose were characterized with respect to their particle size and their flow behavior. This part of the study focuses on the latter.

During shear experiments an increase in viscosity was detected with increasing phase volume fraction. After a critical phase volume fraction, φ, of 0.6 had been exceeded, yield stresses of between 7 and 17 Pa were exhibited. In the emulsions without yield stress the relative emulsion viscosities were examined against the relevant theories, which resulted in good agreement being found with the predictions of Krieger and Dougherty. Using the extrapolated maximum phase volume fraction, it was thus possible to calculate the thickness of the adsorbate layer as approximately 60 nm.

In the dynamic measurements, a maximum was determined for the material functions. This was attributed to shear-induced restructuring processes in the emulsions. The dynamic measurements in the linear viscoelastic range showed that, in spite of increasing phase volume fraction, the critical relaxation time decreased, whereas the values of the moduli rose at small oscillation frequencies.

Time-dependent measurements showed that thixotropy was detected for emulsions with a phase volume fraction of φ≥0.7.

Creep tests showed that the compliance fell with increasing phase volume fraction. The zero shear modulus and the relative elastic compliance were calculated for the emulsions that exhibited yield stresses. Good agreement was found between the zero shear modulus and the values for the storage modulus determined in dynamic measurements.