Atmospherically relevant core–shell aerosol studied using optical trapping and Mie scattering

Abstract

Solid core-liquid shell aerosols have been trapped in a counter-propagating optical trap confirming potential core-shell morphology in the atmosphere. Mie spectroscopy can be used to measure the core radius and film thickness to 0.5 and 1 nm precision respectively and to measure the wavelength dependent refractive indices of silica (core) and oleic acid (shell).

Core-Shell Modeling of Light Scattering by Vesicles: Effect of Size, Contents, and Lamellarity

“…We find that the extruded samples scatter as expected from the calculated scattering of a sample of 100-nm-diameter unilamellar vesicles, as shown in Fig. 5 (using the wavelength-dependent refractive index of oleic acid from Jones et al (47) for n membrane and wavelength-dependent refractive index of water from Engen et al (48)). The calculated turbidity for the largest unilamellar vesicles that can occupy the volume (r ¼ 5 mm) is still much smaller than the experimentally measured turbidity for unextruded vesicles, suggesting that the size of vesicles alone can not completely account for the excess scattering.…”

“…We measure the membrane thickness of oleic acid vesicles by fitting a model containing information about all of the parameters p except the thickness t to measured sample turbidity. We use the wavelength-dependent refractive index of oleic acid from Jones et al (47) for n membrane and wavelength-dependent refractive index of water from Engen et al (48). To control for size and lamellarity, we extrude vesicles through 50-nm-diameter pores to achieve an almost completely unilamellar sample (46).…”

Measurement of the Raman spectra and hygroscopicity of four pharmaceutical aerosols as they travel from pressurised metered dose inhalers (pMDI) to a model lung

“…The optical trap uses a counter propagating dual beam (CPDB) trap 33 configuration first described by Rkiouak et al (Rkiouak, et al, 2014) and deployed in several 34 subsequent experiments (Tang, et al, 2014) (Jones, et al, 2015) (Hunt, et al, 2015). This trapping 35 setup is remarkable because it is capable of stably trapping micron-sized solid particles of non-36 spherical geometry for periods of time up to several hours.…”

Interpreting turbidity measurements for vesicle studies

“…We measure the membrane thickness of oleic acid vesicles by fitting a model containing information about all of the parameters p except the thickness t to measured sample turbidity. We use the wavelength-dependent refractive index of oleic acid from Jones et al 34 for n membrane , and wavelength-dependent refractive index of water from Engen et al 35 . To control for size and lamellarity, we extrude vesicles through 50-nm-diameter pores to achieve an almost completely unilamellar sample 33 , and use the size distribution determined with dynamic light scattering DLS (Malvern Zetasizer Nano C).…”

“…We have measured the turbidities of extruded and unextruded vesicle samples, and also calculated the corresponding turbidities of unilamellar vesicles with our model using the wavelength-dependent refractive index of oleic acid from Jones et al 34 for n membrane , and wavelength-dependent refractive index of water from Engen et al 35 . Our results ( Fig.…”