An optical method for determining size distributions of water droplets

Gatherer, Robert D. B.; Sayer, Robert M.; Reid, Jonathan P.

doi:10.1016/s0009-2614(02)01531-2

Cited by 16 publications

(21 citation statements)

References 16 publications

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“…As mentioned above, it is known for large droplets, and WGM measurements by standard CCD spectrometers, that there are limits to fitting the dispersion corrected refractive index terms and the radius as all unconstrained parameters. 41 Nevertheless, the fitted radii are in good accord with optical images that are also acquired (where the droplet diameter can be roughly measured in image "pixels").…”

Section: Voltage-pulse Waveform and Droplet Sizesupporting

confidence: 64%

Drop-on-demand microdroplet generation: a very stable platform for single-droplet experimentation

2016

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. (2016). Drop-on-demand microdroplet generation: a very stable platform for single-droplet experimentation. RSC Advances: an international journal to further the chemical sciences, 6 (65), 60215-60222. Drop-on-demand microdroplet generation: a very stable platform for single-droplet experimentation AbstractThis paper reports the performance of drop-on-demand piezo-activated microdroplet generation investigated using microdroplet cavity enhanced fluorescence spectroscopy. Aqueous microdroplets, doped with a fluorescent dye, exhibit fluorescence spectra that are dominated by cavity resonances (termed whispering gallery modes) that, when analysed using Mie theory, allow for the determination of the radius of each microdroplet. The effect of controlled changes in the square-wave droplet generator voltage waveform on droplet size is investigated as well as the size reproducibility of successive microdroplets. Furthermore, using custom square-wave waveforms, microdroplet radii spanning ∼10 to 30 μm are produced from the same droplet dispenser. These non-standard waveforms do not sacrifice the reproducibility of microdroplet generation with <1% size variation. Tuning the single square-wave pulsewidths induces predictable changes in the microdroplet radius and steps on the order of tens of nanometers are detectable. With finer voltage adjustments the microdroplet size is essentially tunable. These results confirm the extremely high stability and reproducibility of on-demand microdroplet generation and that precise size control is possible, rendering them suitable platforms for many applications in fundamental and applied research in areas including mass spectrometry, aerosol investigations and liquid-phase chemistry Aqueous microdroplets, doped with a fluorescent dye, exhibit fluorescence spectra that are dominated by cavity resonances (termed whispering gallery modes) that, when analysed using Mie theory, allow for the determination of the radius of each microdroplet. The effect of controlled changes in the square-wave droplet generator voltage waveform on droplet size is investigated as well as the size reproducibility of successive microdroplets. Furthermore, using custom square-wave waveforms, microdroplet radii spanning ~10 to 30 μm are produced from the same droplet dispenser. These non-standard waveforms do not sacrifice the reproducibility of microdroplet generation with <1% size variation. Tuning the single squarewave pulsewidths induces predictable changes in the microdroplet radius with steps on the order of tens of nanometers are detectable. With finer voltage adjustments the microdroplet size is essentially tunable. These results confirm the extremely high stability and reproducibility of on-demand microdroplet generation and that precise size control is possible, rendering them suitable platforms for many applications in fundamental and applied research in areas including mass spectrometry, aerosol investigations and liquid-phase chemistry.3

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Section: Voltage-pulse Waveform and Droplet Sizesupporting

confidence: 64%

Drop-on-demand microdroplet generation: a very stable platform for single-droplet experimentation

2016

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“…4 demonstrates such a peak). Morphological Raman resonances (or cavity-enhanced Raman scattering) 30,[45][46][47] were not used to size the particles as they were observed in some spectra but not all.…”

Section: Aerosol Generation and Reactionmentioning

confidence: 99%

Oxidation of biogenic and water-soluble compounds in aqueous and organic aerosol droplets by ozone: a kinetic and product analysis approach using laser Raman tweezers

et al. 2008

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The results of an experimental study into the oxidative degradation of proxies for atmospheric aerosol are presented. We demonstrate that the laser Raman tweezers method can be used successfully to obtain uptake coefficients for gaseous oxidants on individual aqueous and organic droplets, whilst the size and composition of the droplets is simultaneously followed. A laser tweezers system was used to trap individual droplets containing an unsaturated organic compound in either an aqueous or organic (alkane) solvent. The droplet was exposed to gas-phase ozone and the reaction kinetics and products followed using Raman spectroscopy. The reactions of three different organic compounds with ozone were studied: fumarate anions, benzoate anions and alpha-pinene. The fumarate and benzoate anions in aqueous solution were used to represent components of humic-like substances, HULIS; alpha-pinene in an alkane solvent was studied as a proxy for biogenic aerosol. The kinetic analysis shows that for these systems the diffusive transport and mass accommodation of ozone is relatively fast, and that liquid-phase diffusion and reaction are the rate determining steps. Uptake coefficients, gamma, were found to be (1.1 +/- 0.7) x 10(-5), (1.5 +/- 0.7) x 10(-5) and (3.0-7.5) x 10(-3) for the reactions of ozone with the fumarate, benzoate and alpha-pinene containing droplets, respectively. Liquid-phase bimolecular rate coefficients for reactions of dissolved ozone molecules with fumarate, benzoate and alpha-pinene were also obtained: kfumarate = (2.7 +/- 2) x 10(5), kbenzoate = (3.5 +/- 3) x 10(5) and kalpha-pinene = (1-3) x 10(7) dm3 mol(-1) s(-1). The droplet size was found to remain stable over the course of the oxidation process for the HULIS-proxies and for the oxidation of alpha-pinene in pentadecane. The study of the alpha-pinene/ozone system is the first using organic seed particles to show that the hygroscopicity of the particle does not increase dramatically over the course of the oxidation. No products were detected by Raman spectroscopy for the reaction of benzoate ions with ozone. One product peak, consistent with aqueous carbonate anions, was observed when following the oxidation of fumarate ions by ozone. Product peaks observed in the reaction of ozone with alpha-pinene suggest the formation of new species containing carbonyl groups.

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“…The phase function was dependent on the refractive index, the incident wavelength, and the particle size. Accordingly, the phase function could be utilized to calculate the particle diameter (Chang and Biswas, 1992;Gatherer et al, 2002;Hopkins et al, 2003;Mitchem et al, 2006;Symes et al, 2006;Davies et al, 2012;Haddrell et al, 2013). In addition, the chemical composition or mixing state of particle could influence the refractive index, size, and density, which in sequence directly affect their optical properties (Liu and Mishchenko, 2007;Gangl et al, 2008).…”

Section: Introductionmentioning

confidence: 99%

Measurement and Evaluation of Elastic Light Scattering from a Single Levitated Irregular Particle

Kao

Huang

Chen

et al. 2017

Aerosol Air Qual. Res.

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This study introduced a convenient experimental method to measure and to evaluate the elastic light scattering from a single irregular particle. The particle levitation system was used to trap a particle and to maintain the particle at null position by utilizing electrodynamic balance. Moreover, the Raman spectroscopy was applied to observe the light scattering of a single particle. The influences of relative humidity on optical properties of particle were also discussed. For comparison with experimental results, the classical Lorenz-Mie theory was employed to compute the phase function of a single particle. The experimental results demonstrated that the measurements of light scattering were in approximate trend with the model. In particular, numerical simulation results showed that the scattering intensity was underestimated in backward scattering directions. Consequently, the effect of surface roughness and irregular morphology of particle might be resulted in deviations of backward scattering. Besides, the experiments suggested that while using the weighted average method to estimate the refractive index might cause some significant deviations of light scattering between measuring and modeling.

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An optical method for determining size distributions of water droplets

Cited by 16 publications

References 16 publications

Drop-on-demand microdroplet generation: a very stable platform for single-droplet experimentation

Drop-on-demand microdroplet generation: a very stable platform for single-droplet experimentation

Oxidation of biogenic and water-soluble compounds in aqueous and organic aerosol droplets by ozone: a kinetic and product analysis approach using laser Raman tweezers

Measurement and Evaluation of Elastic Light Scattering from a Single Levitated Irregular Particle

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