Mechanical Properties of Bare and Coated Soot Aggregates
ALEXEI KHALIZOV, Ali Hasani,
New Jersey Institute of Technology Abstract Number: 330
Working Group: Carbonaceous Aerosol
AbstractSoot, a product of incomplete combustion of fossil fuels, is a global warming agent and an air pollutant. The environmental effects of soot particles depend on their morphology. Freshly released soot particles are fractal aggregates made of spheroidal monomers, but in atmospheric samples collected away from emission sources they often appear collapsed. A body of work has concluded that the collapse is caused by liquid menisci forming by vapor condensation on soot aggregates. The menisci create forces that result in breakage of the connections between the soot monomers, leading to rearrangement of the monomers to a more compact configuration.
To gain better understanding of the mechanistic details of soot aggregate restructuring, we used atomic force microscopy (AFM) to perform force-displacement measurements on bare, coated, and coated-denuded soot aggregates to determine their mechanical properties. The force curve was determined by measuring the deflection of the cantilever as it approached the particle and was retracted from the particle. Peaks observed in the distributions of forces for soot aggregates can be related to the processes that occur during aggregate stretching and mechanical failure, such as the unfolding of the monomer chain and the cleavage of the weakest connection between monomers. We found that these forces were significantly affected in the presence of a condensate or after a condensation-denuding cycle. We will discuss how these results will be used for the parameterization of a physical model for soot restructuring.