Aerial wetting contact angle measurement using confocal microscopy

Chesna, Jacob W.; Wiedmaier, Bob F.; Wang, Jinlin; Samara, Ayman; Leach, Richard; Her, Tsing-Hua; Smith, Susan L.

doi:10.1088/0957-0233/27/12/125202

Cited by 9 publications

(4 citation statements)

References 19 publications

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“…The contact angle θ between the particles and the hydrophobic glass slides was measured using a scanning confocal microscope (Zeiss, Axio Observer 510 MP, objective lens MAG x63k Plan-Apochromat, 1.4 aperture), following a method described elsewhere . The measurements were made at approximately 40% RH.…”

Section: Methodsmentioning

confidence: 99%

Gas-Particle Uptake and Hygroscopic Growth by Organosulfate Particles

Ohno

Wang

Mahrt

et al. 2022

ACS Earth Space Chem.

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Organosulfate compounds make up a substantial fraction of the particle mass concentration in some regions of the Earth's atmosphere, and organosulfate particles can have sufficiently high viscosity to limit rates of gas-particle interactions. Viscosity varies with relative humidity (RH). Herein, organosulfate particles were exposed to the gas-phase products of αpinene photooxidation. The gas-particle partitioning of these species was studied from 15 to 70% RH and <1 to 16 ppb NO at 299 K. The uptake of the α-pinene oxidation products increased with the increase in RH, and higher gas-phase NO concentrations resulted in increased particle-phase concentrations of nitrogen compounds. Particle hygroscopicity was examined by optical microscopy. Hygroscopic growth at elevated RH was sufficient to explain the RH-dependent uptake measurements, and kinetic limitations tied to particle viscosity were not observed. The lack of kinetic limitations combined with the Stokes−Einstein equation implied a viscosity much less than 1 × 10 6 Pa s. This value is consistent with estimated viscosities based on literature parameterizations for water mass fractions in the particles of at least 0.05 at 15% RH. Overall, these results suggest that organosulfate hygroscopicity plays a key role in their viscosity and hence in regulating gas-particle partitioning, thereby simplifying the treatment of atmospheric chemistry and transport of pollutants in models of the Earth's atmosphere. The role of organosulfates is expected to take on increasing importance for projected future emission trends.

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Section: Methodsmentioning

confidence: 99%

Gas-Particle Uptake and Hygroscopic Growth by Organosulfate Particles

Ohno

Wang

Mahrt

et al. 2022

ACS Earth Space Chem.

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“…Several studies have reported the use of laser scanning confocal microscopy (LSCM) technique to evaluate the wetting properties . Chesna et al exploited the confocal microscopy to determine the radius and height of small droplets (<1 mm), based on which the CA is computed using a spherical approximation of the droplet shape

θ = \cos^{- 1} (1 - \frac{h_{d}}{r_{d}})

…”

Section: Definition Of Surface Wettability: Beyond General Classifica...mentioning

confidence: 99%

Assessment and Interpretation of Surface Wettability Based on Sessile Droplet Contact Angle Measurement: Challenges and Opportunities

Kung

Sow

Zahiri

et al. 2019

Adv Materials Inter

132

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www.advmatinterfaces.de the sessile CA remains the favored method for quantifying wettability, mostly due to its conceptual and measurement simplicity. [9,31] However, the classification on the basis of the cut-off CA of 90° has attracted criticism. [32,33] The simplistic evaluation criteria of relative wettability are becoming inadequate in satisfying the needs of superwettability studies to classify different wetting phenomena. [34] Several works have questioned the accuracy of the sessile-droplet measurement as the CA value approaches the limits of 0° or 180°. [35,36] Yet, evaluation of surfaces in the superhydrophobic (CA > 150°) and superhydrophilic (CA < 10°) regimes is central in the development of enhanced wettabilities. Moreover, the interpretation of the CA results is often complicated by several factors, including surface smoothness, heterogeneity and cleanliness. [37] The Chun Haow Kung obtained his B.A.Sc. and M.A.Sc. in Chemical Engineering at the University of British Columbia (UBC). His graduate work with Prof. Mérida's group at UBC focused on the development and application of novel wetting characterization techniques, smart stimuli-responsive materials as well as electrochemical and hydrogen energy systems. He is currently a Research Scientist at Ballard Power Systems Inc. where he continues to pursue his interest in the polymer electrolyte membrane (PEM) fuel cell technology. Beniamin Zahiri is currently a researcher in the University of Illinois at Urbana-Champaign

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“…Based on previous measurements, the reactive uptake coefficient of O 3 on oleic acid, squalene, triolein, and canola oil is approximately 8.0 × 10 –4 , 4.0 × 10 –4 , 1.5 × 10 –5 , and 5 × 10 –4 , respectively (see Table S2). ,,,,,− ,,− Most previous studies have also reported the uptake coefficients of O 3 on unsaturated lipids to be independent of RH. ,,, Based on eq and the approximate reactive uptake coefficients mentioned above, the fraction of oleic acid, squalene, triolein, and canola oil reacted by the time the new phase was first observed was approximately 2–44% at low RH (Table ). At medium RH conditions, the fraction of unsaturated lipids reacted when the new phase was first observed was comparable to that at low RH conditions, except for squalene.…”

Section: Discussionmentioning

confidence: 99%

Possible Effects of Ozone Chemistry on the Phase Behavior of Skin Oil and Cooking Oil Films and Particles Indoors

Mahrt

Gregson

et al. 2022

ACS Earth Space Chem.

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Heterogeneous reactions occurring between ozone and films or particles containing skin oil or cooking oil can be a sink of ozone and a source of organic compounds indoors with negative health effects. To predict this heterogeneous chemistry, information on the phase behavior (number and types of phases) within these films and particles, and its evolution during ozone exposure, is needed. In this work, we used optical microscopy to directly observe the phase behavior of proxies for skin oil and cooking oil particles (diameters of 110–220 μm) during exposure to O3. As a proxy for skin oil, we used a multicomponent mixture of unsaturated lipids. For cooking oil, we used a commercially available canola oil. We also studied single-component unsaturated lipids (squalene, triolein, and oleic acid) and jojoba oil (mostly unsaturated monoesters) as simpler proxies for skin oil and cooking oil. Prior to reactions with ozone, the particles were all liquid. Exposure to ozone led to the formation of a new phase within the particles. For oleic acid, the new phase was most likely a high-molecular-weight liquid formed by liquid–liquid phase separation. For all other systems, the new phase was likely solid or semi-solid. Our results, together with the resistor model and the reaction extent, were then used to predict the time it takes for a new phase to form in skin oil and cooking oil films indoors. Based on our results, we predict that a new phase will form in skin oil films with a thickness of 0.1–1 μm after a timescale of 3 h to 7 days under typical indoor ozone concentrations (6 ppb) and relative humidity (RH) conditions ranging from 5 to 65%. In cooking oil films, we predict that a new phase will form after 1.5–16 h for films of 0.1–1 μm thickness under ozone concentrations of 6 ppb and RH conditions ranging from 5 to 65%. A new phase will likely impact diffusion rates and partitioning coefficients within the films and hence ozone loss rates indoors, production rates of respiratory irritants, and partitioning of these irritants between films, particles, and the gas phase.

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Aerial wetting contact angle measurement using confocal microscopy

Cited by 9 publications

References 19 publications

Gas-Particle Uptake and Hygroscopic Growth by Organosulfate Particles

Gas-Particle Uptake and Hygroscopic Growth by Organosulfate Particles

Assessment and Interpretation of Surface Wettability Based on Sessile Droplet Contact Angle Measurement: Challenges and Opportunities

Possible Effects of Ozone Chemistry on the Phase Behavior of Skin Oil and Cooking Oil Films and Particles Indoors

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