In this thesis, acoustical and other physical properties of soft submicron suspensions were investigated in order to provide invaluable clues for their adaptation in theragnostic applications. Two types of dispersions were studied: fluorocarbon droplets stabilised with a polymeric (PLGA, PLGA-PEG) shell or a semifluorinated surfactant (called FTAC) shell. Since preparation of polymeric particles had been already developed, we first studied factors affecting mean diameter, size distribution, and coarsening of emulsions made of FTAC stabilising droplets of various fluorocarbons. Mechanical parameters used for emulsion synthesis and surfactants length were optimised to get the smallest droplets (~200 nm in diameter) that stay mainly submicrometric for several weeks. In addition, a full characterisation of surfactant properties was conducted. Next, for ultrasonic theragnostic purpose, it was necessary to improve our understanding in the mechanisms underlying interactions between ultrasonic waves and particles of a suspension. To do so, ultrasound propagation studies through dilute suspensions were carried out in a large frequency range (3-90 MHz) with subsequent modelling. The model could fit with a good accuracy our experimental data on polymeric particles and reveals information about unknown parameters of the shell: the geometrical parameters (shell thickness) and the viscoelastic parameters of the shell (speed of sound, shear moduli at infinite and zero frequencies, and the relaxation frequency). Therefore, such a model provides the required feedback for tuning the physicochemical parameters of nanoparticles in order to optimize their design.
