Controlled Chemistry via Contactless Manipulation and Merging of Droplets in an Acoustic Levitator

Abstract

A unique, versatile, and material-independent approach to manipulate contactlessly and merge two chemically distinct droplets suspended in an acoustic levitator is reported. Large-amplitude axial oscillations are induced in the top droplet by low-frequency amplitude modulation of the ultrasonic carrier wave, which causes the top sample to merge with the sample in the pressure minimum below. The levitator is enclosed within a pressure-compatible process chamber to enable control of the environmental conditions. The merging technique permits precise control of the substances affecting the chemical reactions, the sample temperature, the volumes of the liquid reactants down to the picoliter range, and the mixing locations in space and time. The performance of this approach is demonstrated by merging droplets of water (H2O) and ethanol (C2H5OH), conducting an acid–base reaction between aqueous droplets of sodium hydroxycarbonate (NaHCO3) and acetic acid (CH3COOH), the hypergolic explosion produced via merging a droplet of an ionic liquid with nitric acid (HNO3), and the coalescence of a solid particle (CuSO4·5H2O) and a water droplet followed by dehydration using a carbon dioxide laser. The physical and chemical changes produced by the merging are traced in real time via complementary Raman, Fourier-transform infrared, and ultraviolet–visible spectroscopies. The concept of the contactless manipulation of liquid droplets and solid particles may fundamentally change how scientists control and study chemical reactions relevant to, for example, combustion systems, material sciences, medicinal chemistry, planetary sciences, and biochemistry.

Combining Mass Spectrometry of Picoliter Samples with a Multicompartment Electrodynamic Trap for Probing the Chemistry of Droplet Arrays

“…Reactive transformations in levitated droplets have largely been investigated with nondestructive optical probes 15,[17][18][19][20][21][22][23] . While functional group information is available from Raman spectroscopy, it cannot always provide specific information on the composition of a droplet undergoing chemical transformations.…”

“…Reactive transformations in levitated droplets have largely been investigated with nondestructive optical probes. ,− While functional group information is available from Raman spectroscopy, it cannot always provide specific information on the composition of a droplet undergoing chemical transformations. Coupling measures of droplet microphysical and optical properties with chemically specific characterization by mass spectrometry (MS) will provide a more complete mechanistic understanding of droplet reactions.…”

Effects of Nitrogen Dioxide on the Oxidation of Levitated exo-Tetrahydrodicyclopentadiene (JP-10) Droplets Doped with Aluminum Nanoparticles

“…The levitator experimental apparatus has been reviewed in detail previously , and employed in various experiments. ,,,− A schematic top view of the levitator apparatus illustrating its key components is presented in Figure . In the acoustic levitator, ultrasonic sound waves with a frequency of 58 kHz are produced by a piezoelectric transducer and reflect from a concave plate to generate a standing wave (see Figures –).…”

Design and Performance of an Acoustic Levitator System Coupled with a Tunable Monochromatic Light Source and a Raman Spectrometer for In Situ Reaction Monitoring

“…In recent years, acoustic levitation − has been utilized in a range of scientific disciplines including but not limited to analytical chemistry, astrochemistry, materials science, and pharmaceuticals. ,− Acoustic levitation has also been used in contactless mixing of two droplets to initiate a chemical reaction , and to transport protein crystal samples in crystallography experiments . In acoustic levitation, a liquid droplet, a solid particle, or a suspension is levitated slightly below the pressure nodes of the ultrasonic standing wave.…”