Is Carbon Black a Suitable Model Colloidal Substrate for Diesel Soot?

Abstract

Soot formation in diesel engines is known to cause premature engine wear. Unfortunately, genuine diesel soot is expensive to generate, so carbon blacks are often used as diesel soot mimics. Herein, the suitability of a commercial carbon black (Regal 250R) as a surrogate for diesel soot dispersed in engine base oil is examined in the presence of two commonly used polymeric lubricant additives. The particle size, morphology, and surface composition of both substrates are assessed using BET surface area analysis, TEM, and XPS. The extent of adsorption of a poly(ethylene-co-propylene) (dOCP) statistical copolymer or a polystyrene-block-poly(ethylene-co-propylene) (PS-PEP) diblock copolymer onto carbon black or diesel soot from n-dodecane is compared indirectly using a supernatant depletion assay technique via UV spectroscopy. Thermogravimetric analysis is also used to directly determine the extent of copolymer adsorption. Degrees of dispersion are examined using optical microscopy, TEM, and analytical centrifugation. SAXS studies reveal some structural differences between carbon black and diesel soot particles. The mean radius of gyration determined for the latter is significantly smaller than that calculated for the former, and in the absence of any copolymer, diesel soot suspended in n-dodecane forms relatively loose mass fractals compared to carbon black. SAXS provides evidence for copolymer adsorption and indicates that addition of either copolymer transforms the initially compact agglomerates into relatively loose aggregates. Addition of dOCP or PS-PEP does not significantly affect the structure of the carbon black primary particles, with similar results being observed for diesel soot. In favorable cases, remarkably similar data can be obtained for carbon black and diesel soot when using dOCP and PS-PEP as copolymer dispersants. However, it is not difficult to identify simple copolymer-particle-solvent combinations for which substantial differences can be observed. Such observations are most likely the result of dissimilar surface chemistries, which can profoundly affect the colloidal stability.

Comparative nanostructure analysis of gasoline turbocharged direct injection and diesel soot-in-oil with carbon black

“…Band deconvolution using the fiveband model as proposed by Sadezky et al [43], comprising four Lorenzian and one Gaussian peak profiles, was attempted. However, the D2 mode peak consistently relaxed to zero intensity and was thus not included, consistent with previous reports [37]. Numerous fitting models were explored, yet the only fit that resulted in convergence across all three samples, normalised to fitting parameters and analysis conditions, was obtained using mixed symmetric Gaussian-Lorentzian functions for the G and D1 modes and mixed asymmetric Gaussian-Lorentzian functions to fit the D3 and D4 modes.…”

“…Studies by Mabuchi et al [36] used an analogous approach to investigate the wear of hydrogen-free diamond-like carbon coatings for engine applications. However, Growney et al [37] found that the capability of carbon black to substitute engine soot is highly dependent on the lubricating oil formulation. Practical investigations by Antusch et al [17] showed distinctive differences in the direct comparison of engine soot and carbon black in engine wear tests.…”

The internal structure of poly(methyl methacrylate) latexes in nonpolar solvents

“…However, the approach has predominantly been employed in water, due to application in the study of biomolecules [93,94]. Growney et alrecen tlyusedthetec hniqueto study polymer-stabilized carbon black particles in n-alkanes, which shows its versatility in nonpolar solvents as well [95][96][97]. To enable more precise determination of colloidal properties, sedimentation measurements can be performed in isotopically-labeled solvents, which are chemically identical but differ in fluid properties.…”

Material‐Dependent Antagonistic Effects between Soot and ZDDP

“…The layer structure of individual CB particles can be seen in the high magnification transmission electron microscopy (TEM) images. Detailed comparisons between real engine soot and soot surrogate R250R can be found in Armes et al Figure S1 in the Supporting Information shows the solubility of the soot with and without PIBSI (polyisobutylene succinimide) dispersant. The PIBSI dispersant (1.0 wt%) was used to suspend the CB in the oil and for fair comparison, dispersant was added to all test lubricants as noted in the experimental section.…”