A multi-transducer single-axis acoustic levitator for small-angle X-ray scattering experiments

We present a 40 kHz single-axis acoustic levitator for Small-Angle X-ray Scattering (SAXS) experiments. The levitator consists of 48 ultrasonic transducers of 9.8 mm in diameter and a small opposing plane reflector. The levitation stability is evaluated by using a high-speed camera for recording the position over time of a suspended drop. To demonstrate the capability of the levitator, it was assembled in a laboratory SAXS instrument (Xenocs Xeuss 2.0) for investigating the evaporation kinetics of liquid drops containing metallic silver nanoparticles. The spontaneous evaporation of the levitated water molecules decreases the droplet volume, leading to a systematic increase in the concentration of the particles in the system. As a result, the average distance between the particles decreases, giving rise to enhanced particle-particle interactions. For the evaluation of the droplet size and selection of correct scattering data for sample and blank scattering, a Python™ package was developed, allowing automatic video analysis and accurate subtraction of the background associated with the solvent in which the particles are suspended. Although the proposed levitator was used in SAXS experiments, it can also be used in many other research fields, such as pharmacy, biology, chemistry, and material sciences.