Ice nucleation efficiency of AgI: review and new insights

Marcolli, Claudia; Nagare, Baban; Welti, André; Lohmann, Ulrike

doi:10.5194/acp-16-8915-2016

Cited by 116 publications

(136 citation statements)

References 93 publications

(172 reference statements)

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“…For AgI particles the freezing efficiency in CLINCH experiments was less than in IMCA-ZINC and the onset temperature was shifted to lower values. This is further investigated in Marcolli et al (2016). For ATD, freezing efficiencies in contact and immersion mode were similar.…”

Section: Kaolinitementioning

confidence: 95%

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Comparing contact and immersion freezing from continuous flow diffusion chambers

et al. 2016

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Abstract. Ice nucleating particles (INPs) in the atmosphere are responsible for glaciating cloud droplets between 237 and 273 K. Different mechanisms of heterogeneous ice nucleation can compete under mixed-phase cloud conditions. Contact freezing is considered relevant because higher ice nucleation temperatures than for immersion freezing for the same INPs were observed. It has limitations because its efficiency depends on the number of collisions between cloud droplets and INPs. To date, direct comparisons of contact and immersion freezing with the same INP, for similar residence times and concentrations, are lacking. This study compares immersion and contact freezing efficiencies of three different INPs. The contact freezing data were obtained with the ETH CoLlision Ice Nucleation CHamber (CLINCH) using 80 µm diameter droplets, which can interact with INPs for residence times of 2 and 4 s in the chamber. The contact freezing efficiency was calculated by estimating the number of collisions between droplets and particles. Theoretical formulations of collision efficiencies gave too high freezing efficiencies for all investigated INPs, namely AgI particles with 200 nm electrical mobility diameter, 400 and 800 nm diameter Arizona Test Dust (ATD) and kaolinite particles. Comparison of freezing efficiencies by contact and immersion freezing is therefore limited by the accuracy of collision efficiencies. The concentration of particles was 1000 cm −3 for ATD and kaolinite and 500, 1000, 2000 and 5000 cm −3 for AgI. For concentrations < 5000 cm −3 , the droplets collect only one particle on average during their time in the chamber. For ATD and kaolinite particles, contact freezing efficiencies at 2 s residence time were smaller than at 4 s, which is in disagreement with a collisional contact freezing process but in accordance with immersion freezing or adhesion freezing. With "adhesion freezing", we refer to a contact nucleation process that is enhanced compared to immersion freezing due to the position of the INP on the droplet, and we discriminate it from collisional contact freezing, which assumes an enhancement due to the collision of the particle with the droplet. For best comparison with contact freezing results, immersion freezing experiments of the same INPs were performed with the continuous flow diffusion chamber Immersion Mode Cooling chAmber-Zurich Ice Nucleation Chamber (IMCA-ZINC) for a 3 s residence time. In IMCA-ZINC, each INP is activated into a droplet in IMCA and provides its surface for ice nucleation in the ZINC chamber. The comparison of contact and immersion freezing results did not confirm a general enhancement of freezing efficiency for contact compared with immersion freezing experiments. For AgI particles the onset of heterogeneous freezing in CLINCH was even shifted to lower temperatures compared with IMCA-ZINC. For ATD, freezing efficiencies for contact and immersion freezing experiments were similar. For kaolinite particles, contact freezing became detectable at higher temperatures than imm...

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Section: Kaolinitementioning

confidence: 95%

“…Moreover, the freezing ability depends on the surface charge of AgI particles. A closer investigation of factors influencing the efficiency of AgI as an ice nucleus and reasons for the lower freezing efficiency in CLINCH compared with IMCA-ZINC are discussed in the companion paper by Marcolli et al (2016).…”

Section: Silver Iodidementioning

confidence: 99%

Comparing contact and immersion freezing from continuous flow diffusion chambers

et al. 2016

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“…As a contaminant, we selected AgI particles, which are a known ice nucleation promoter. 46 To control the degree of surface contamination, we used the following procedure. For low-level contamination, we cleaned glass microscopy coverslips by treating them for 7 min with a piranha solution (1:2 solution of hydrogen peroxide in hydrochloric acid), followed by bath sonication for 1 min in acetone and 1 min in isopropyl alcohol.…”

Section: Artificial Contaminationmentioning

confidence: 99%

Imparting Icephobicity with Substrate Flexibility

2017

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Ice accumulation hinders the performance of, and poses safety threats for, infrastructure both on the ground and in the air. Previously, rationally designed superhydrophobic surfaces have demonstrated some potential as a passive means to mitigate ice accretion; however, further studies on material solutions that reduce impalement and the contact time for impacting supercooled droplets (high viscosity) and can also repel droplets that freeze during surface contact are urgently needed. Here we demonstrate the collaborative effect of substrate flexibility and surface micro/nanotexture on enhancing both icephobicity and the repellency of viscous droplets (typical of supercooled water). We first investigate the influence of increased viscosity (spanning from 0.9 to 1078 mPa·s using water-glycerol mixtures) on impalement resistance and the droplet-substrate contact time after impact. Then we examine the effect of droplet partial solidification on recoil and simulate more challenging icing conditions by impacting supercooled water droplets (down to -15 °C) onto flexible and rigid surfaces containing ice nucleation promoters (AgI). We demonstrate a passive mechanism for shedding partially solidified (recalescent) droplets-under conditions where partial solidification occurs much faster than the natural droplet oscillation-which does not rely on converting droplet surface energy into kinetic energy (classic recoil mechanism). Using an energy-based model (kinetic-elastic-capillary), we identify a previously unexplored mechanism whereby the substrate oscillation and velocity govern the rebound process, with low areal density and moderately stiff substrates acting to efficiently absorb the incoming droplet kinetic energy and rectify it back, allowing droplets to overcome adhesion and gravitational forces, and recoil. This mechanism applies for a range of droplet viscosities, spanning from low- to high-viscosity fluids and even ice slurries, which do not rebound from rigid superhydrophobic substrates. For a low-viscosity fluid, i.e., water, if the substrate oscillates faster than the droplet spreading and retraction, the action of the substrate is decoupled from the droplet oscillation, resulting in a reduction in the droplet-substrate contact time.

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“…The subscripts V , L , and S take the place of parent phase (1) and daughter phase ( In order to investigate the heterogeneous condensation-desublimation nucleation transition, we examined condensation and desublimation behavior on silver iodide coated surfaces (AgI), a wellknown nucleation agent. 32 Figure 2a shows a plot of Figure 3e and f indicate the percent area fraction of the surface covered by concave pits of radius R (negative values) for our smooth and nanotextured silicon samples, respectively. Comparing the smooth and nanotextured silicon surfaces, we observed that the nanotextured surface has 18% of its area-a significant fraction-covered with nanopits with R < 10 * 12 r , while the smooth silicon has effectively none of its area covered with nanopits with R < 10 * 12 r .…”

Section: Resultsmentioning

confidence: 99%

Desublimation Frosting on Nanoengineered Surfaces

et al. 2018

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Ice nucleation from vapor presents a variety of challenges across a wide range of industries and applications including refrigeration, transportation, and energy generation. However, a rational comprehensive approach to fabricating intrinsically icephobic surfaces for frost formation-both from water condensation (followed by freezing) and in particular from desublimation (direct growth of ice crystals from vapor)-remains elusive. Here, guided by nucleation physics, we investigate the effect of material composition and surface texturing (atomically smooth to nanorough) on the nucleation and growth mechanism of frost for a range of conditions within the sublimation domain (0 °C to -55 °C; partial water vapor pressures 6 to 0.02 mbar). Surprisingly, we observe that on silicon at very cold temperatures-below the homogeneous ice solidification nucleation limit (<-46 °C)-desublimation does not become the favorable pathway to frosting. Furthermore, we show that surface nanoroughness makes frost formation on silicon more probable. We experimentally demonstrate at temperatures between -48 °C and -55 °C that nanotexture with radii of curvature within 1 order of magnitude of the critical radius of nucleation favors frost growth, facilitated by capillary condensation, consistent with Kelvin's equation. Our findings show that such nanoscale surface morphology imposed by design to impart desired functionalities-such as superhydrophobicity-or from defects can be highly detrimental for frost icephobicity at low temperatures and water vapor partial pressures (<0.05 mbar). Our work contributes to the fundamental understanding of phase transitions well within the equilibrium sublimation domain and has implications for applications such as travel, power generation, and refrigeration.

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Ice nucleation efficiency of AgI: review and new insights

Cited by 116 publications

References 93 publications

Comparing contact and immersion freezing from continuous flow diffusion chambers

Comparing contact and immersion freezing from continuous flow diffusion chambers

Imparting Icephobicity with Substrate Flexibility

Desublimation Frosting on Nanoengineered Surfaces

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