The study of the new particle formation is crucial because the composition and dynamics of the mentioned nuclei determines whether the aerosol will be formed or not.
Nucleation is currently a hot issue in the aerosol science field and much attention has been devoted to the problem as can be seen in the literature [Kulmala et al. Science, 318, 2007] and in the appearance of a special issue in one of the most relevant publications on aerosols, the Journal of Aerosol Science and Technology in April, 2011 [Aerosol Sci and Tech, 45 (4), 2011].
One of the most important difficulties for the study of aerosol nucleation is the lack of instrumentation with good performance and enough sensitivity for size-classifying the sub-3nm nanoparticles.
Typical aerosol instrument’s performances decay from 5nm to 3nm, being impossible to measure any particle below that size. However, the nucleation phenomena occur below 3nm, in which size range molecules, molecular clusters, and particle nuclei coexist.
Therefore, there is a real need for the development of an aerosol analyzer for very small nanoparticles.
Parallel Plate DMA
The differential mobility analyzer (DMA) is a powerful instrument that continuously separates aerosol particles according to their migration velocities in an electric field. Because of the low fields employed, the mobility can be related to particle size or ion cross section.
The development of an ion-DMA, specifically designed for sub 2nm ions is very innovative. A DMA classification region can be seen as a channel where ions with different electrical mobilities (ie, sizes) are separated through the superposition of two perpendicular forces, one given by a high sheath flow rate and the other by an electric field. The combination of both forces is responsible of the Resolving Power (RP) achievable by the instrument.
DMAs normally used in aerosol studies for bigger particles reach RP around 10, which is good enough for particles because the distributions are normally broad. However, when dealing with sub-3nm nano-particles, the Brownian motion is not negligible anymore, and the RP becomes of capital importance for the adequate performance of the instrument. Sheath flow rates of hundreds of L/min with the lowest possible turbulence are needed.
To minimize the dwelling time in the classification zone and therefore minimize the diffusion effect, Computational Fluid Dynamics simulations (CFD) are necessary to successfully design the volume of the classification region of the DMA. In addition to the increasing Brownian motion, the high reactivity of molecular ions forces the sheath gas to be as clean and stable as possible making Filters and stable temperatures are extremly important for small ions DMAs.
The last technology in machining will be used in the manufacturing of the classification region, additive manufacturing by laser. The appearance of this technology has made possible the fabrication of very complicated geometries needed for an optimal performance of the instrument.
GANS Nucleation Spectrometer
The proposed instrument for this goal is based on the coupling of a high resolution Differential Mobility Analyser (DMA) able to size-classify particles smaller than 2nm with a modified Condensation Particle Counter also able to detect particles smaller than 3 nm.
The instrument can be operated remotely and will be conceived and designed to give a complete solution to the study of the nucleation problem, avoiding any sample preparation step, and able to remotely send data to any web-server using internet 3G or Ethenet connection.
Projects and publications
- GANS project
- Talanta 130 (2014) 400-407
- EAC 2013 Prague
- IAC 2014 Korea
- EAC 2015 Milan