Characterization of aggregates by the speed of sound waves and densitometry

Abstract
Scattering methods like X-ray or neutron small-angle scattering and dynamic light scattering are standard methods for the characterization of 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 new technique utilizes the dependence of the speed of sound waves on the number of dissolved particles at fixed concentration. Experimental results show the formation of micelles in a triblock copolymer (P-85) solution in the concentration range from 0.5% to 30% (W/W). Precision densitometry uses the mechanical oscillator method based on the measurement of the eigenfrequency of a U-shaped glass tube. By introduction of a phase shifted excitation it is possible to measure the ratio between the damping force and the spring force of the system where the damping force is related to the viscosity of the fluid. With this instrument it is possible to detect the formation and the dissolution of the gel phase of P-85. The data from ultra-sound velocimetry and densitometry can be used together with scattering data to establish a phase diagram of the P-85 solution.