Structure analysis using acoustically levitated droplets.

Synchrotron diffraction with a micrometer-sized X-ray beam permits the efficient characterization of micrometer-sized samples, even in time-resolved experiments, which is important because often the amount of sample available is small and/or the sample is expensive. In this context, we will present acoustic levitation as a useful sample handling method for small solid and liquid samples, which are suspended in a gaseous environment (air) by means of a stationary ultrasonic field. A study of agglomeration and crystallization processes in situ was performed by continuously increasing the concentration of the samples by evaporating the solvent. Absorption and contamination processes on the sample container walls were suppressed strongly by this procedure, and parasitic scattering such as that observed when using glass capillaries was also absent. The samples investigated were either dissolved or dispersed in water droplets with diameters in the range of 1 micrometer to 2 millimeters. Initial results from time-resolved synchrotron small- and wide-angle X-ray scattering measurements of ascorbic acid, acetylsalicylic acid, apoferritin, and colloidal gold are presented.