| Abstract |
The phase behavior of a new system of layered organosilica nanoparticles suspended in organic solvents is presented in this work. In the first part of this study, the molecular characterization of the colloidal nanoparticles (LOS) suspended in toluene (good solvent) was carried out. The techniques that have been used were light scattering and x-ray small angle scattering. More specifically, the molecular weight of the particles, their hydrodynamic radius and the second Virial coefficient, A2 (which shows the quality of the solvent), were computed.
In the second part of this work, the dynamics of the nanoparticles dispersed in toluene were studied, at concentrations from the dilute to the non-dilute regime and at temperatures between 15– 45 oC. The experimental techniques that were used were light scattering and rheology. Additionally, in combination with turbidity measurements, the phase diagram of the system was constructed. Gelation was found to occur at intermediate concentrations (c ≥ 28.4 % wt), and at temperatures higher than the critical point for phase separation.
In the third part, the dynamics and the phase behavior of the nanoparticle suspensions in decane were studied. The phase diagram of the system was determined conducting turbidity measurements. On top of that, using scattering and rheological techniques, it was found that for concentrations c > 11 % wt and for temperatures below the critical point, the macroscopic phase separation is interrupted by a mechanism of dynamical arrest. The system finally is dynamically frozen due to the gelation that takes place. The experimental findings show the sensitivity of the stability and the phase behavior of these colloidal suspensions to the dispersion medium. Additionally, these suspensions provide the possibility to manipulate the thermodynamic interactions and the gelation transition in order to design new dispersions with desirable features.
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Μελέτη της θερμοδυναμικής και της φασικής συμπεριφοράς αιωρημάτων φυλλόμορφων οργανοπυριτικών νανοσωματιδίων
