American Association for Aerosol Research - Abstract Submission

AAAR 35th Annual Conference
October 17 - October 21, 2016
Oregon Convention Center
Portland, Oregon, USA

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Colloidal Probe Analysis of Cohesion Forces between Monodisperse, Monomorph Microparticles with Rough Surfaces

Alberto Baldelli, REINHARD VEHRING, University of Alberta, Canada

     Abstract Number: 136
     Working Group: Health Related Aerosols

Abstract
The effect of roughness, particle size, and crystal size on the cohesion forces between two microparticles of different size and shape was investigated. A piezoceramic dispenser was used to produce nearly identical solution droplets with an initial droplet diameter of about 70 μm. The aqueous droplets were dried under controlled conditions to create monodisperse and monomorph sodium nitrate microparticles in a diameter range of 0.7 to 17 μm. Initial conditions of the drying process differed in solution concentration, from 5 to 5∙10-4 mg/ml, and in drying gas temperature, from 50 to 150°C. By varying the process conditions, particles with different roughness were reproducibly produced. For instance, the mean squared roughness of the dried microparticles was controlled in a range from 2 to 6∙10-5 μm. Colloidal probe microscopy (CPM) was selected to analyze cohesion forces between pairs of particles of the same or different morphology. Because all microparticles produced for a given set of processing conditions had very similar morphology, cohesive interactions for a large set of fifteen morphology type combinations could be studied. For every case analyzed, the measured cohesion forces were compared with seven different theoretical models for the prediction of pull-off forces between two microparticles. Cohesion forces were found to vary by a factor of about 50 for particles of different roughness, with higher roughness leading to less cohesion. The best fit of the experimental results was achieved with cohesion models that accounted for surface roughness at different lengths scales. Cohesion models without roughness parameters, such as the Hamaker interaction model, yielded very poor correlation with the experimental results.