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2016/12/20 14:00 Assistant Prof. Ta-Chih Hsiao（Graduate Institute of Environmental Engineering, NCU）
Seminar
Poster： ╱ Post date：2016-12-14NCU IHOS Seminar Announcement
Speaker：Assistant Prof. Ta-Chih Hsiao
Place：S-325, Science Building 1
Abstract：
Title：Aqueous Film Formation on Irregularly Shaped Inorganic Nanoparticles before Deliquescence
Speaker：Assistant Prof. Ta-Chih Hsiao
Graduate Institute of Environmental Engineering, NCU
Time：12/20（Tue.）14：00
Place：S-325, Science Building 1
Abstract：
A hygroscopic tandem differential mobility analyzer (H-TDMA) and a hygroscopic coupled DMA and aerosol particle mass (H-DMA-APM) were coupled to examine water film formation and the deliquescence behavior of inorganic nanoparticles. The two systems complement each other because H-DMA-APM measures mass change, while H-TDMA measures diameter (volume) change of nanoparticles upon water uptake. The former mass change was in particular more capable to discern minute particle phase changes than the latter size change at moderate RHs. The mass and diameter changes were used to derive the particle effective density for evaluation of water film formation on the nanoparticle surface before and after deliquescence transition. The measurements further showed that approximately 3–5 and 12–20 monolayers of water molecules formed on the respective surface of 50- and 100-nm sodium chloride and ammonium sulfate aerosols before deliquescence relative humidity (DRH). These findings support the physical basis of the coated-surface model by Russell and Ming (2002), and suggest that the phase transition of inorganic nanoparticles near deliquescence is a gradual process instead of an abrupt change. This phenomenon changed the surface tension ratio and surface energy values, thus confirming the explanation by (Biskos et al. 2006a; Biskos et al. 2006c) that the DRH of nanoparticles increases as the particle size decreases. This is the first direct observation of nanoparticle deliquescence phase transition using the H-DMA–APM system, and the detailed characterization of water film formation on inorganic nanoparticles is feasible with the presented measurement systems.
Last modification time：2016-12-14 PM 5:19
