The spectroscopy and chemical dynamics of microparticles explored using an ultrasonic trap

Abstract

Microsized particles play an important role in many diverse areas of science and technology, for example, surface reactions of micron-sized particles play a key role in astrochemistry, plasma reactors and atmospheric chemistry. To date much of our knowledge of such surface chemistry is derived from 'traditional' surface science-based research. However, the large surface area and morphology of surface material commonly used in such surface science techniques may not necessarily mimic that on the surface of micron/nano scale particles. Hence, a new generation of experiments in which the spectroscopy (e.g., albedo) and chemical reactivity of micron-sized particles can be studied directly must be developed. One, as yet underexploited, non-invasive technique is the use of ultrasonic levitation. In this article, we describe the operation of an 'ultrasonic trap' to store and study the physical and chemical properties of microparticles.

Mass Spectrometry of Levitated Droplets by Thermally Unconfined Infrared-Laser Desorption

“…[1][2][3][4][5] In most applications the levitated liquid samples either serve as model systems for natural or anthropogenic aerosols 6 or as wall-less reactors for e.g. cell biology or chemical and physical transitions.…”

Novel high-temperature and pressure-compatible ultrasonic levitator apparatus coupled to Raman and Fourier transform infrared spectrometers

“…The cooling system will help us explore the condensation of volatile gases of planetary relevance such as water and ammonia onto mineral surfaces. 5,40,41 Thus, the new apparatus will permit future experiments relevant to astrochemistry, planetary chemistry, biochemistry, material science, atmospheric chemistry, and combustion processing.…”

“…Furthermore, a levitator can be used to probe the differences between the physical and chemical processes on the bulk samples typically used in surface science and the surfaces of micrometersized levitated particles. 5,6 Finally, owing to their small total heat capacity, the levitated particle can be heated to a high temperature (see Sec. II C) over very short time scales and be cooled more rapidly (see Subsection 3 of the Appendix) thus allowing precise control of the sample temperature.…”

Reply to Ref #2

“…For example, Schenk et al (2012) used an acoustic levitator to measure hygroscopicity of imidazolium-based ionic liquids, and low temperature acoustic levitation was developed to study homogeneous and heterogeneous freezing of aqueous droplets (Ettner et al, 2004;Diehl et al, 2009Diehl et al, , 2014. Particles which can be acoustically levitated are typically > 20 µm (Mason et al, 2008;Krieger et al, 2012), while most of atmospheric aerosol particles are significantly smaller (Seinfeld and Pandis, 2016). Therefore, compared to the other two levitation techniques (i.e., EDB and optical levitation), acoustic levitation is much less widely utilized in atmospheric chemistry (Krieger et al, 2012).…”