Optical deformation of single aerosol particles

Optical traps are used to isolate and manipulate small objects in air and liquids, enabling the thorough characterization of their properties in situ. However, no broadly applicable technique for mass measurements of optically trapped objects is currently available. Here we propose an optical balance for mass measurements of optically trapped aerosol particles. By analyzing light-induced harmonic oscillations of a particle, its mass is determined non-destructively and with high accuracy on a time scale of seconds. Its performance is demonstrated for aqueous salt droplets, where masses as low as 4 pg (4 × 10−15 kg) have been measured with an accuracy of ~100 fg. The balance is straightforward to implement and broadly applicable.

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“…Principle of mass measurement. Dual beam traps are widely used to trap particles 15,[44][45][46][47][48][49] . Fig.…”

Section: Resultsmentioning

confidence: 99%

Weighing picogram aerosol droplets with an optical balance

et al. 2020

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“…Such partitioning may fully or partially counteract the surface tension lowering effect of surfactants and must be considered when predicting particle activation (18)(19)(20)(21)(22). Accounting for this partitioning is challenging because few approaches directly measure aerosol particle surface tension (23)(24)(25)(26)(27) and so far none have investigated surfactant partitioning in detail. Most approaches infer surface tension from hygroscopic growth or critical supersaturation measurements (28).…”

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confidence: 99%

The surface tension of surfactant-containing, finite volume droplets

Bzdek

Reid

Malila

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

110

119

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Surface tension influences the fraction of atmospheric particles that become cloud droplets. Although surfactants are an important component of aerosol mass, the surface tension of activating aerosol particles is still unresolved, with most climate models assuming activating particles have a surface tension equal to that of water. By studying picoliter droplet coalescence, we demonstrate that surfactants can significantly reduce the surface tension of finite-sized droplets below the value for water, consistent with recent field measurements. Significantly, this surface tension reduction is droplet size-dependent and does not correspond exactly to the macroscopic solution value. A fully independent monolayer partitioning model confirms the observed finite-size-dependent surface tension arises from the high surface-to-volume ratio in finite-sized droplets and enables predictions of aerosol hygroscopic growth. This model, constrained by the laboratory measurements, is consistent with a reduction in critical supersaturation for activation, potentially substantially increasing cloud droplet number concentration and modifying radiative cooling relative to current estimates assuming a water surface tension. The results highlight the need for improved constraints on the identities, properties, and concentrations of atmospheric aerosol surfactants in multiple environments and are broadly applicable to any discipline where finite volume effects are operative, such as studies of the competition between reaction rates within the bulk and at the surface of confined volumes and explorations of the influence of surfactants on dried particle morphology from spray driers.

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“…To this end, we isolated single droplets directly in the e-cigarette aerosol by using an optical trap and recorded the temporal change in the droplet composition in situ by means of Raman scattering. Optical trapping allowed us to isolate single particles in air for an extended period of time [23][24][25][26] and thus monitor time-dependent processes affecting the particles, such as evaporation 25,27 , diffusion 28 , chemical reaction 29,30 , and phase transitions 31 or phase separations 32,33 . We report changes in chemical composition on the second timescale for droplets generated from four different e-liquids with the same ratio of PG and VG but with different nicotine concentrations and pHs.…”

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Tracing the composition of single e-cigarette aerosol droplets in situ by laser-trapping and Raman scattering

David

Parmentier

Taurino

et al. 2020

Sci Rep

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the partitioning of components between droplets and the gas phase in e-cigarette aerosols has a significant impact on deposition within the respiratory tract. However, exclusive detection of droplet composition has, so far, been elusive. consequently, the dynamics of partitioning between droplets and the gas phase remains unknown. Here, we combine optical trapping of single droplets with in situ Raman scattering for destruction-free monitoring of e-cigarette droplet composition with a time resolution of seconds. We find that the initial droplet composition is very close to the composition of the e-liquid. Upon dilution with air, the droplet composition changes exponentially on a time scale of seconds, mainly because of evaporation of propylene glycol. the nicotine content in the droplet is controlled by the pH. Nicotine evaporates from the droplets under basic conditions, but remains in the liquid under acidic conditions. these results are crucial for advancing e-liquid research and manufacturing. Electronic cigarettes (e-cigarettes) represent a multibillion dollar industry 1 and a fast growing market 2. The ongoing debates on e-cigarettes have made it very clear that more studies are needed 3,4 for better assessing their health effects and potential to reduce the risk of smoking-related diseases as compared to continued smoking 5-8 and, eventually, for designing products 4. E-cigarettes are devices designed to deliver nicotine to the user through aerosol droplets generated by heating up a liquid called "e-liquid". Most e-liquids are composed of propylene glycol (PG), vegetable glycerol (VG), nicotine, flavoring supplements, and water 9,10. Heating such an e-liquid evaporates all of its chemical compounds into the gas phase. When the gas phase cools down, liquid aerosol droplets are formed by condensation of the vapor. The different components of the e-liquid are then present both in the droplet and gas phases of the aerosol. Many studies have underlined the importance of and need for knowing which components remain in the droplet phase and which evaporate again into the gas phase 11-14. The partitioning of components between the droplet and gas phases, for example, affects their deposition in the respiratory tract 11-14. Yet, the dynamics of compound transfer between the droplet and gas phases remains largely unknown, mainly because of the lack of adequate in situ methods for exclusively probing the composition of the droplets in the aerosol with adequate time resolution. A few simulations have addressed this topic 11,13 , but, to the best of our knowledge, no corresponding experimental data are available. Many experimental methods measure the chemical composition of the whole e-cigarette aerosol, i. e. without distinction between the droplet and gas phases and without time resolution. Most measurements are off-line measurements that first sample the e-cigarette aerosol and then use ex situ analysis methods, typically chromatography and/or mass spectroscopy 1,14,15. These off-line measurements usually sample bot...

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Optical deformation of single aerosol particles

Cited by 42 publications

References 70 publications

Weighing picogram aerosol droplets with an optical balance

Weighing picogram aerosol droplets with an optical balance

The surface tension of surfactant-containing, finite volume droplets

Tracing the composition of single e-cigarette aerosol droplets in situ by laser-trapping and Raman scattering

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