10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Characterization of a Dimer Preparation Method for Nanoscale Aerosol
NICHOLAS ROTHFUSS, Sarah Suda Petters, Markus Petters, North Carolina State University
Abstract Number: 876 Working Group: Instrumentation
Abstract The synthesis of nanoscale aerosol dimers by charge-assisted particle coagulation is a technique suited for a variety of applications that are just beginning to be explored. Here we build upon the approach of Rothfuss and M. Petters (Aerosol Sci. Technol. 50(12), 2016), which has been implemented for the measurement of particle phase state. Dimer particle morphologies are prepared by coagulation of mobility selected particles carrying opposite charges. Coagulated charge-neutral dimers can subsequently be isolated by electrostatic filtration and used in studies that exploit the unique particle morphology to study aerosol properties. The nanoscale dimers are differentiated by their electrical mobility and detected using a condensation particle counter. This technique allows for the detection of changes in particle morphology in response to conditioning. However, application of the technique requires a high concentration of analyte monomers prior to coagulation and may result in complex and non-intuitive signals in the mobility spectra of the output aerosol. A more detailed understanding of the dimer preparation and isolation method is necessary for the design and interpretation of experiments that use this technique. This work presents a detailed set of characterization experiments for the output of this system. The minimum monomer number concentration and minimum monomer diameter for application of this technique are presented. Physical contributions to observed mobility spectra under typical experimental configurations are identified, and conditions where dimer morphologies can unambiguously be detected and isolated are reported. Possible methodological approaches for experiments where dimer signal magnitude and/or the difference between fully uncoalesced and fully coalesced dimer mobility diameters are near noise levels are discussed, including the use of probe monomers as compensation for weak analyte monomer number concentration, potential modifications to instrument topology, and processing strategies for mobility spectra.