STUDY OF COLLOIDAL AGGREGATION WITH STATIC AND DYNAMIC NEAR FIELD SCATTERING TECHNIQUES

Colloidal aggregation processes are widely studied both theoretically and experimentally especially in the 80s. Recently a new way of inducing aggregation had been observed. It is based on a transposition to a classical system of the quantum Casimir effect, in which two conducting, not charged plane plates in vacuum attract each other just because of the confinement of vacuum fluctuations. The classical case occurs in a solution close to a phase transition, with the fluctuations occurring in the order parameter. It has been recently demonstrated that colloidal particles confine these fluctuations, bringing them to stick. The advantage of this effect is that the interaction strength can be easily tuned with the temperature of the solutions, and it is completely reversible. The critical Casimir effect has been used to induce colloidal aggregation in the COLLOID project. The experiment has been realized aboard the International Space Station (ISS) to study colloidal aggregation in microgravity through the Near Field Scattering technique (NFS). In this work I show the data analysis of this experiment, especially on the side of dynamic near field scattering. The main information on the aggregates structure are obtained by combining both static and dynamic results, observing a more compact structure than what is usually expected. Similar analyses have also been performed on colloidal samples aggregating on ground, where the aggregation was induced by simply adding salt to the solution. Thanks to the technique of Single Particles Extinction and Scattering (SPES) we also measured the size distribution of the samples, obtaining a result which is different from the theoretical predictions. However, measured distributions are in good agreement with some standard scattering measurements on the same samples. A preliminary characterization of anisotropic particles has also been performed. They will be used for a new experiment aboard the ISS to study aggregation induced by Casimir effect, in which the anisotropic shape induces asymmetric interaction potentials.