Flame-Formed Carbon Nanoparticles: Morphology, Interaction Forces, and Hamaker Constant from AFM

Abstract

Interaction forces acting between combustion-generated carbon particles were studied by using atomic force microscopy (AFM). To this aim, carbon nanoparticles were produced in fuelrich ethylene/air laminar premixed flames with different equivalent ratios F, and analyzed at a fixed residence time in the flame. Particles were collected on mica substrates by means of a thermophoretic sampling system and then analyzed by AFM. A characterization of particle dimension and morphology were performed operating AFM in semicontact mode, showing that the shape of the particles collected on a sampling plate is never spherical. Increasing the flame-equivalent ratio, particle shape moves from an almost atomically thick object to thicker compounds, indicating the transformation from particles made of small, defective graphene-like sheets to particles containing stacked aromatic layers. Attractive and adhesive forces between a titanium nitride probe and sampled particles were calculated from force-distance curves acquired in AFM force spectroscopy mode. Assuming that van der Walls forces are the main contribution to attractive forces, the measurement of attractive forces allowed the evaluation of the Hamaker constant for the carbon particles as a function of the flame-equivalent ratio. The comparison of the measured Hamaker constants with the values for benzene and HOPG, suggests a continuous increase of the aromatic domains and the three-dimensional order within the particles when the flame-equivalent ratio increases.

Human peripheral blood mononuclear cells (PBMCs) from smokers release higher levels of IL-1-like cytokines after exposure to combustion-generated ultrafine particles

“…Elemental analysis confirmed the low presence of H atoms in the soot particles, as the amount of C was approximately 96%, in mass, of the total material, and H was approximately 2.5–2.8%, with the rest being trace compounds. Atomic force microscopy of the material deposited directly from the flame on mica disks and before any further sample treatment showed that the soot particles were made up of spherical particles with sizes on the order of 20–30 nm and larger, chain-like, soot agglomerates with sizes up to a few hundred nanometers 39 40 .…”

Molecular dynamics simulations of incipient carbonaceous nanoparticle formation at flame conditions

“…The transition from gas-phase molecules to particles is not well understood although the use of new and sophisticated diagnostic techniques in recent years has increased our knowledge of particle inception and growth as well as of particle morphology [1][2][3][4][5][6][7]. The presence of stacked PAH molecules was revealed by HR-TEM [5,[8][9][10] and AFM [11] in nascent soot particles. These particles are characterised by the concurrent presence of well-organised and amorphous regions.…”

Direct Measurement of Adhesion Force of Individual Aerosol Particles by Atomic Force Microscopy

“…Therefore, care must be taken when comparing the adhesion forces among different particles types, especially when the measurements were conducted under different experimental setups. The adhesion force collected by De Falco [21] on flame-formed carbon nanoparticles by a similar method is shown in Figure 6 for comparison. The intention here was not to directly compare the absolute adhesion forces with various micrometer-sized particles measured in this study.…”

“…Despite the potential and compatibility of AFM for aerosol research, studies characterizing the physical properties of individual aerosol particles using AFM are still limited. For example, De-Falco et al (2015) performed a measurement of flame-formed carbon nanoparticles and evaluated the adhesion force between the tip and the particle [21]. Tan et al [22] and Moutinho et al [23] fixed a dust particle onto an AFM cantilever tip and measured the adhesion force between the dust particle and the substrates.…”

“…Comparison of adhesion force of aerosol particles measured in this study. A range of adhesion force values for flame-formed carbon soot particles[21] are also shown for comparison. Hollow shapes indicate the adhesion force values of individual particles, whereas solid shapes and whiskers indicate the mean and standard deviation, respectively.…”