CHARACTERIZATION OF AGGREGATES BY THE SPEED OF SOUND-WAVES AND DENSITOMETRY

Scattering methods like X-ray or neutron small-angle scattering and dy namic light scattering are standard methods for the characterization o f amphiphilic aggregates like micelles, vesicles and gels. Rheological experiments show the formation of gels indicated by a strong increase of the viscosity. Precision measurements of the speed of sound waves (pulse method) can be used to follow the micellization process. This n ew technique utilizes the dependence of the speed of sound waves on th e number of dissolved particles at fixed concentration. Experimental r esults show the formation of micelles in a triblock copolymer (P-85) s olution in the concentration range from 0.5% to 30% (W/W). Precision d ensitometry uses the mechanical Oscillator method based on the measure ment of the eigenfrequency of a U-shaped glass tube. By introduction o f a phase shifted excitation it is possible to measure the ratio betwe en the damping force and the spring force of the system where the damp ing force is related to the viscosity of the fluid. With this instrume nt it is possible to detect the formation and the dissolution of the g el phase of P-85. The data from ultra-sound velocimetry and densitomet ry can be used together with scattering data to establish a phase diag ram of the P-85 solution.