Recent
studies have shown the potential of the photosensitizer
chemistry of humic acid, as a proxy for humic-like substances in atmospheric
aerosols, to contribute to secondary organic aerosol mass. The mechanism
requires particle-phase humic acid to absorb solar radiation and become
photoexcited, then directly or indirectly oxidize a volatile organic
compound (VOC), resulting in a lower volatility product in the particle
phase. We performed experiments in a photochemical chamber, with aerosol-phase
humic acid as the photosensitizer and limonene as the VOC. In the
presence of 26 ppb limonene and under atmospherically relevant UV–visible
irradiation levels, there is no significant change in particle diameter.
Calculations show that SOA production via this pathway is highly sensitive
to VOC precursor concentrations. Under the assumption that HULIS is
equally or less reactive than the humic acid used in these experiments,
the results suggest that the photosensitizer chemistry of HULIS in
ambient atmospheric aerosols is unlikely to be a significant source
of secondary organic aerosol mass.
Fingering is a hydrodynamic instability that occurs when a more mobile fluid displaces a fluid of lower mobility. When the primary source of the mobility difference is viscosity, the instability is termed viscous fingering. Viscous fingering is often, though not always, undesirable in industrial processes, particularly secondary petroleum recovery. Linear stability analysis by Hejazi et al. has indicated that the production of a non-monotonic viscosity profile can stabilize the interface. Herein, we use step-growth polymerization at the interface between two miscible monomers as a model system. In particular a dithiol monomer displaced a diacrylate that reacted to form a linear polymer that behaves as a Newtonian fluid. Viscous fingering was imaged in a horizontal Hele-Shaw cell via Schlieren, which is sensitive to changes in index of refraction and therefore polymer conversion. By varying reaction rate via initiator concentration along with flow rate via a syringe pump, we were able to demonstrate increasing stabilization of the flow with increasing Damköhler number.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.