No abstract

The effects of composition, size, and phase state on ultrafine seed particle growth by α-pinene ozonolysis were determined from diameter growth measurements after a fixed reaction time in a flow tube reactor. Modeling time-dependent particle growth under a given set of conditions allowed the reaction growth factor (GF) to be determined, which is defined as the fraction of α-pinene molecules that react to give a product that grows the particles. Growth factors were compared for initial seed particle diameters of 40, 60, and 80 nm that were composed of freshly formed α-pinene secondary organic aerosol (SOA), effloresced ammonium sulfate, and deliquesced ammonium sulfate. Overall, SOA seed particles gave the lowest growth factors. Effloresced ammonium sulfate particles gave somewhat higher growth factors and showed a slight dependence on relative humidity. Deliquesced ammonium sulfate particles gave the highest growth factors. Seed particle-size dependencies suggested that both surface-and volume-limited reactions may contribute to growth. Overall, the growth factors were found to vary by more than 4x across the reaction conditions studied. The results highlight the crucial role that seed particle characteristics play in determining particle growth rates in a size range relevant to formation of cloud condensation nuclei.

Online analysis of ultrafine (<100 nm diameter) particles was performed by sending the aerosol through a condensation growth chamber (CGC) to create micrometer-size aqueous droplets that were subsequently analyzed by mass spectrometry with droplet-assisted ionization (DAI). Three experiments are reported which illustrate key performance characteristics of the method and give insight into the ion formation process: size-selected cortisone particles, size-selected secondary organic aerosol (SOA) particles, and freshly nucleated SOA under atmospherically relevant conditions. In each case, SOA was produced by α-pinene ozonolysis. For size-selected cortisone particles between 30 and 90 nm diameter and SOA particles between 30 and 70 nm, the ion signal intensity was found to be approximately independent of particle size. This observation is attributed to the formation of aqueous droplets in the CGC whose size distribution is independent of the original particle size. A consequence of this behavior is that the sensitivity of molecular detection increases as the particle size decreases, and the method is particularly well suited for new particle formation studies under atmospherically relevant conditions. This aspect of the CGC−DAI method was illustrated by the online analysis of freshly nucleated SOA samples with median diameters, number concentrations, and mass concentrations on the order of 25 nm, 10 4 cm −3 , 0.2 μg m −3 , respectively. Mass spectra of freshly nucleated SOA could be explained by condensation of highly oxidized molecules (HOMs) that subsequently reacted in the particle phase. Size-selected SOA showed increasing oligomerization with increasing particle size, which is consistent with established particle growth mechanisms.

We explored the potential of biomimetic thin films fabricated by means of matrix-assisted pulsed laser evaporation (MAPLE) for releasing combinations of active substances represented by flavonoids (quercetin dihydrate and resveratrol) and antifungal compounds (amphotericin B and voriconazole) embedded in a polyvinylpyrrolidone biopolymer; the antifungal activity of the film components was evaluated using in vitro microbiological assays. Thin films were deposited using a pulsed KrF* excimer laser source which were structurally characterized using atomic force microscopy (AFM) and Fourier transform infrared spectroscopy (FTIR). High-quality thin films with chemical structures similar to dropcast ones were created using an optimum laser fluence of ~80 mJ/cm2. Bioactive substances were included within the polymer thin films using the MAPLE technique. The results of the in vitro microbiology assay, which utilized a modified disk diffusion approach and were performed using two fungal strains (Candida albicans American Type Culture Collection (ATCC) 90028 and Candida parapsilosis American Type Culture Collection (ATCC) 22019), revealed that voriconazole was released in an active form from the polyvinylpyrrolidone matrix. The results of this study show that the MAPLE-deposited bioactive thin films have a promising potential for use in designing combination devices, such as drug delivery devices, and medical device surfaces with antifungal activity.

Field desorption ‐ mass spectrometry (FD‐MS) was evaluated as a tool for characterisation of the complex mixtures of compounds typical of synthetic lubricants. The lubricants were initially screened using field ionisation, then tested samples were subjected to field desorption. Results are presented for various formulations for an ester, an ester‐synthetic oil mixture, polyisobutylenes, PAO additives, and a fully formulated oil.