Optical Trapping–Polarized Raman Microspectroscopy of Single Ethanol Aerosol Microdroplets: Droplet Size Effects on Rotational Relaxation Time and Viscosity

Nakajima, Ryosuke; Miura, Atsushi; Abe, Sayaka; Kitamura, Noboru

doi:10.1021/acs.analchem.0c05406

Cited by 9 publications

(4 citation statements)

References 56 publications

(108 reference statements)

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“…On the other hand, ethanol molecules partition to the spherical droplet surface in a Langmuir-type trend. This discrepancy in interfacial partitioning may be caused by a large pressure gradient across the radius of the droplet produced by its highly curved surface. − Thus, the mobility of ethanol molecules in nanodroplets may be much lower than that of the planar analogue, resulting in a decreased interfacial partitioning. It is possible that this increased pressure along with the lessened availability of analyte molecules inhibits formation of a cancelling secondary monolayer.…”

Section: Resultsmentioning

confidence: 99%

In Situ Detection of Chemical Compositions at Nanodroplet Surfaces and In-Nanodroplet Phases

et al. 2022

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Small-volume nanodroplets play an increasingly common role in chemistry and biology. Such nanodroplets are believed to have unique chemical and physical properties at the interface between a droplet and its surrounding medium, however, they are underexamined. In this study, we present the novel technique of vibrational sum frequency scattering (VSFS) spectroscopy as an interface-specific, high-performance method for the in situ investigation of nanodroplets with sub-micron radii; as well as the droplet bulk through simultaneous hyper-Raman scattering (HRS) spectroscopy. We use laboratory-generated nanodroplets from aqueous alcohol solutions to demonstrate this technique's ability to separate the vibrational phenomena which take place at droplet surfaces from the underlying bulk phase. In addition, we systemically examine interfacial spectra of nanodroplets containing methanol, ethanol, 1propanol, and 1-butanol through VSFS. Furthermore, we demonstrate interfacial differences between such nanodroplets and their analogous planar surfaces. The sensitivity of this technique to probe droplet surfaces with few-particle density at standard conditions validates VSFS as an analytical technique for the in situ investigation of small nanodroplets, providing breakthrough information about these species of ever-increasing relevance.

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Section: Resultsmentioning

confidence: 99%

In Situ Detection of Chemical Compositions at Nanodroplet Surfaces and In-Nanodroplet Phases

et al. 2022

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“…The chemical pathways of aerosols have a complicated interplay with the physicochemical properties of aerosols, which could be affected by the chemical composition of aerosols. Atmospheric aerosols usually contain both inorganic and organic species, , which determine the ionic strength and viscosity of aerosols, respectively. − These two physicochemical properties have been recognized to play key roles in the reaction kinetics of aerosols. ,, A high ionic strength in aerosols can enhance the reactive uptakes of gaseous reactants, the reaction rate coefficients in aerosol bulks, and the rates of aqueous photolysis. − Several recent studies also found that high ionic strengths can enhance the reactive uptakes of SO 2 by peroxides and the sulfate formations from the subsequent SO 2 oxidation in deliquesced aerosol particles. , Conversely, a high viscosity in organic aerosols can lead to slow diffusion times of molecular species and thus the prolonged time scales of dynamic processes in aerosols, while the relationship between viscosity and diffusivity could also highly depend on phase states of aerosols and molecular interactions. ,− …”

Section: Introductionmentioning

confidence: 99%

Accelerated Sulfur Oxidation by Ozone on Surfaces of Single Optically Trapped Aerosol Particles

et al. 2023

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The sulfur oxidation in mixed sodium thiosulfate/sucrose/aqueous microdroplets by gaseous ozone is studied in this work via aerosol optical tweezers coupled with Raman spectroscopy, which can simultaneously determine various physicochemical properties and the heterogeneous reaction kinetics of single optically trapped microdroplets, allowing for elucidating their complicated interplay. According to the kinetics measurement results at different relative humidities, ozone concentrations, and stoichiometries of inorganic and organic solutes, this work finds that a high aerosol ionic strength can accelerate the ozone oxidation of thiosulfate at air−water interfaces, while a high aerosol viscosity prolongs the reaction time scales due to diffusion-limited kinetics. The kinetic multilayer model of aerosol surface and bulk chemistry (KM-SUB) is utilized to investigate the observed heterogeneous kinetics results and to retrieve the surface reaction rate coefficients. The KM-SUB model fit results indicate that the observed kinetics of sulfur oxidation in binary sodium thiosulfate aqueous microdroplets with high ionic strengths is dominated by interfacial reactions, and the fitted surface reaction rate coefficients increase 1 order of magnitude when the droplet ionic strength increases around 40 M. This work further utilizes the kinetics measurements of ozone dependence to discuss the coupling among properties of ozone gas-interface-bulk partitioning and surface reaction rate in the kinetics model. Finally, this work also exploits the surface reaction of thiosulfate with ozone to retrieve the aerosol viscosity of microdroplets containing ternary aqueous sodium thiosulfate and sucrose mixtures, demonstrating the feasibility of pinning down aerosol viscosities via reaction kinetics.

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“…24,25 Conversely, a high viscosity in organic aerosols can lead to slow diffusion times of molecular species and thus the prolonged timescales of dynamic processes in aerosols, while the relationship between viscosity and diffusivity could also highly depend on phase states of aerosols and molecular interactions. 19,[26][27][28][29][30] The roles of chemical composition in the heterogeneous reaction kinetics of aerosols are often rationalized in terms of the effects of ionic strength and diffusivity to reactions in aerosol bulks. However, for the reactions at aerosol surfaces or interfaces, it still requires more advanced investigations to clarify the potential role of chemical composition.…”

Section: Introductionmentioning

confidence: 99%

Accelerated Sulfur Oxidation by Ozone on Surfaces of Single Optically Trapped Aerosol Particles

Hsu

Lin

Huang

et al. 2023

Preprint

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The sulfur oxidation in mixed sodium thiosulfate/sucrose/aqueous micro-droplets by gaseous ozone is studied in this work via aerosol optical tweezers coupled with Raman spectroscopy, which can simultaneously determine various physicochemical proper- ties and the heterogeneous reaction kinetics of single optically trapped micro-droplets, allowing for elucidating their complicate interplay. According to the kinetics measurement results at different relative humidities, ozone concentrations and stoichiometries of inorganic and organic solutes, this work finds that a high aerosol ionic strength can accelerate the ozone oxidation of thiosulfate at air-water interfaces, while a high aerosol viscosity prolongs the reaction timescales due to diffusion-limited kinetics. The kinetic multilayer model of aerosol surface and bulk chemistry (KM-SUB) is utilized to investigate the observed heterogeneous kinetics results and to retrieve the surface reaction rate coefficients. The KM-SUB simulations results indicate that the observed kinetics of sulfur oxidation in binary sodium thiosulfate aqueous micro-droplets with high ionic strengths is dominated by interfacial reactions, and the fitted surface reaction rate coefficients increase one order of magnitude when the droplet ionic strength increases around 40 M. Furthermore, this work demonstrated that including the effects of inter- facial ion depletion in the kinetics simulations can lead to an excellent agreement with the experimental results, implying its potential role in the interfacial kinetics.

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Optical Trapping–Polarized Raman Microspectroscopy of Single Ethanol Aerosol Microdroplets: Droplet Size Effects on Rotational Relaxation Time and Viscosity

Cited by 9 publications

References 56 publications

In Situ Detection of Chemical Compositions at Nanodroplet Surfaces and In-Nanodroplet Phases

In Situ Detection of Chemical Compositions at Nanodroplet Surfaces and In-Nanodroplet Phases

Accelerated Sulfur Oxidation by Ozone on Surfaces of Single Optically Trapped Aerosol Particles

Accelerated Sulfur Oxidation by Ozone on Surfaces of Single Optically Trapped Aerosol Particles

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