Optical manipulation and characterisation of aerosol particles using a single-beam gradient force optical trap

Mitchem, Laura; Reid, Jonathan P.

doi:10.1039/b609713h

Cited by 146 publications

(150 citation statements)

References 47 publications

Supporting

Mentioning

149

Contrasting

Order By: Relevance

“…The experimental setup has been described in depth previously (34). To summarize, an aqueous aerosol droplet 3-4 μm in radius is trapped in optical tweezers.…”

Section: Methodsmentioning

confidence: 99%

Comparing the mechanism of water condensation and evaporation in glassy aerosol

Bones

Reid

Lienhard

et al. 2012

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

Self Cite

190

255

View full text Add to dashboard Cite

Atmospheric models generally assume that aerosol particles are in equilibrium with the surrounding gas phase. However, recent observations that secondary organic aerosols can exist in a glassy state have highlighted the need to more fully understand the kinetic limitations that may control water partitioning in ambient particles. Here, we explore the influence of slow water diffusion in the condensed aerosol phase on the rates of both condensation and evaporation, demonstrating that significant inhibition in mass transfer occurs for ultraviscous aerosol, not just for glassy aerosol. Using coarse mode (3-4 um radius) ternary sucrose/sodium chloride/aqueous droplets as a proxy for multicomponent ambient aerosol, we demonstrate that the timescale for particle equilibration correlates with bulk viscosity and can be ≫10 3 s. Extrapolation of these timescales to particle sizes in the accumulation mode (e.g., approximately 100 nm) by applying the Stokes-Einstein equation suggests that the kinetic limitations imposed on mass transfer of water by slow bulk phase diffusion must be more fully investigated for atmospheric aerosol. Measurements have been made on particles covering a range in dynamic viscosity from <0.1 to >10 13 Pa s. We also retrieve the radial inhomogeneities apparent in particle composition during condensation and evaporation and contrast the dynamics of slow dissolution of a viscous core into a labile shell during condensation with the slow percolation of water during evaporation through a more homogeneous viscous particle bulk.water uptake | whispering gallery modes | Raman spectroscopy | optical tweezers | viscous aerosol A tmospheric aerosol particles are typically complex mixtures of organic and inorganic species with correspondingly complex equilibria and temporal responses to changes in humidity. Secondary organic aerosols (SOA) continue to receive a great deal of attention due to their impact on radiative forcing, mainly through the indirect effect (1). Ambient aerosol typically contains a significant organic fraction, arising from the oxidation of volatile organic compounds (2). SOA has been largely thought of as existing as a liquid phase, or as a combination of a solid phase within a liquid droplet, but the reality is likely to be far more nuanced. Recently, Virtanen et al. demonstrated that ambient SOA particles can have similar mechanical properties to crystalline ðNH 4 Þ 2 SO 4 particles at 10-20% RH but exist as amorphous glasses to low relative humidity (RH) rather than forming crystalline phases (3). This picture is consistent with the conclusions of Mikhailov et al. (4) and Zobrist et al. (5), who suggested that the existence of glassy states may have profound consequences for the properties of atmospheric aerosol particles, particularly at low temperatures.The term glassy refers to an amorphous, highly viscous state with a dynamic viscosity (η) of greater than 1 × 10 12 Pa s and the mechanical properties of a solid (6). In thermodynamic terms, a glass is in a nonergodic metastable state...

show abstract

“…The experimental setup has been described in depth previously (34). To summarize, an aqueous aerosol droplet 3-4 μm in radius is trapped in optical tweezers.…”

Section: Methodsmentioning

confidence: 99%

Comparing the mechanism of water condensation and evaporation in glassy aerosol

Bones

Reid

Lienhard

et al. 2012

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

Self Cite

190

255

View full text Add to dashboard Cite

show abstract

“…A major advantage of the aerosol optical tweezers (AOT) technique, as well as the electrodynamic balance (EDB), is that there are no surface contact points because the droplets are suspended in air (Mitchem and Reid 2008;Verdeny et al 2011;Bzdek et al 2016). This contactless aspect of the AOT, combined with the surface resonant whispering gallery modes (WGMs) retrieved in the cavity enhanced Raman spectrum, provides a unique direct and real-time assessment of the droplet's morphology, size, and refractive index Reid 2013, 2015).…”

Section: Introductionmentioning

confidence: 99%

Advanced aerosol optical tweezers chamber design to facilitate phase-separation and equilibration timescale experiments on complex droplets

Gorkowski

Beydoun

Aboff

et al. 2016

Aerosol Science and Technology

Self Cite

View full text Add to dashboard Cite

The phase-separation of mixed aerosol particles and the resulting morphology plays an important role in determining the interactions of liquid aerosols with their gas-phase environment. We present the application of a new aerosol optical tweezers chamber for delivering a uniformly mixed aerosol flow to the trapped droplet's position for performing experiments that determine the phaseseparation and resulting properties of complex mixed droplets. This facilitates stable trapping when adding additional phases through aerosol coagulation, and reproducible measurements of the droplet's equilibration timescale. We demonstrate the trapping of pure organic carbon droplets, which allows us to study the morphology of droplets containing pure hydrocarbon phases to which a second phase is added by coagulation. A series of experiments using simple compounds are presented to establish our ability to use the cavity enhanced Raman spectra to distinguish between homogeneous single-phase, and phase-separated core-shell or partially engulfed morphologies. The core-shell morphology is distinguished by the pattern of the whispering gallery modes (WGMs) in the Raman spectra where the WGMs are influenced by refraction through both phases. A coreshell optimization algorithm was developed to provide a more accurate and detailed analysis of the WGMs than is possible using the homogeneous Mie scattering solution. The unique analytical capabilities of the aerosol optical tweezers provide a new approach for advancing our understanding of the chemical and physical evolution of complex atmospheric particulate matter, and the important environmental impacts of aerosols on atmospheric chemistry, air quality, human health, and climate change. EDITORThomas Kirchstetter

show abstract

“…Therefore, laser trapping and Raman spectroscopy is the powerful means to study the chemical and physical properties of single droplets in air. 12,13 As demonstrated in a previous publication, the ammonium sulfate concentrations in individual aerosol water droplets (0.07 -0.11 mol dm -3 ) generated by an ultrasonic nebulizer are independent of those in mother solutions (0.05 -1.00 mol dm -3 ) under constant relative humidity conditions. 8 This phenomenon is one of the characteristic features of the aerosol water droplets, and will not be observed in colloidal particles such as water-in-oil emulsions.…”

Section: Introductionmentioning

confidence: 80%

Reversible Control of the Equilibrium Size of a Single Aerosol Droplet by Change in Relative Humidity

2014

View full text Add to dashboard Cite

Noncontact levitation of single micrometer-sized water droplets in air can be achieved by a laser trapping technique. The equilibrium size of a water droplet is quite sensitive to relative humidity in the surrounding gas phase. In order to investigate the physical and chemical properties of single water droplets in air as a function of the droplet size or solute concentration, laser trapping experiments were conducted under controlled humidity conditions. In this study, we developed a trapping chamber equipped with a relative humidity controller and demonstrated the reversible control of the equilibrium size of a single droplet levitated in air through a change in relative humidity. Furthermore, relative humidity was successfully evaluated by means of cavity enhanced Raman spectroscopy of a trapped water droplet.

show abstract

Optical manipulation and characterisation of aerosol particles using a single-beam gradient force optical trap

Cited by 146 publications

References 47 publications

Comparing the mechanism of water condensation and evaporation in glassy aerosol

Comparing the mechanism of water condensation and evaporation in glassy aerosol

Advanced aerosol optical tweezers chamber design to facilitate phase-separation and equilibration timescale experiments on complex droplets

Reversible Control of the Equilibrium Size of a Single Aerosol Droplet by Change in Relative Humidity

Contact Info

Product

Resources

About