scholarly journals The role of contact angle and pore width on pore condensation and freezing

2020 ◽  
Vol 20 (15) ◽  
pp. 9419-9440 ◽  
Author(s):  
Robert O. David ◽  
Jonas Fahrni ◽  
Claudia Marcolli ◽  
Fabian Mahrt ◽  
Dominik Brühwiler ◽  
...  
Keyword(s):  
Contact Angle ◽  
Active Sites ◽  
Water Saturation ◽  
Sol Gel ◽  
Contact Angles ◽  
Ice Nucleation ◽  
Pore Width ◽  
Water Contact ◽  
Pore Condensation

Abstract. It has recently been shown that pore condensation and freezing (PCF) is a mechanism responsible for ice formation under cirrus cloud conditions. PCF is defined as the condensation of liquid water in narrow capillaries below water saturation due to the inverse Kelvin effect, followed by either heterogeneous or homogeneous nucleation depending on the temperature regime and presence of an ice-nucleating active site. By using sol–gel synthesized silica with well-defined pore diameters, morphology and distinct chemical surface-functionalization, the role of the water–silica contact angle and pore width on PCF is investigated. We find that for the pore diameters (2.2–9.2 nm) and water contact angles (15–78∘) covered in this study, our results reveal that the water contact angle plays an important role in predicting the humidity required for pore filling, while the pore diameter determines the ability of pore water to freeze. For T>235 K and below water saturation, pore diameters and water contact angles were not able to predict the freezing ability of the particles, suggesting an absence of active sites; thus ice nucleation did not proceed via a PCF mechanism. Rather, the ice-nucleating ability of the particles depended solely on chemical functionalization. Therefore, parameterizations for the ice-nucleating abilities of particles in cirrus conditions should differ from parameterizations at mixed-phase clouds conditions. Our results support PCF as the atmospherically relevant ice nucleation mechanism below water saturation when porous surfaces are encountered in the troposphere.

scholarly journals The Role of Contact Angle and Pore Width on Pore Condensation and Freezing

2019 ◽  
Author(s):  
Robert O. David ◽  
Jonas Fahrni ◽  
Claudia Marcolli ◽  
Fabian Mahrt ◽  
Dominik Brühwiler ◽  
...  
Keyword(s):  
Contact Angle ◽  
Active Sites ◽  
Water Saturation ◽  
Capillary Condensation ◽  
Contact Angles ◽  
Ice Nucleation ◽  
Pore Width ◽  
Kelvin Effect ◽  
Pore Condensation

Abstract. It has recently been shown that pore condensation and freezing (PCF) is a mechanism responsible for ice formation under cirrus cloud conditions. PCF is defined as the condensation of liquid water in narrow capillaries below water saturation due to the Kelvin effect, followed by either heterogeneous or homogeneous nucleation depending on the temperature regime and presence of an ice nucleating active site. By using sol-gel synthesized silica with well-defined pore diameters, morphology and distinct chemical surface-functionalization, the role of the water-silica contact angle and pore width on PCF is investigated. We find that contact angle and pore width play an important role in determining the relative humidity required for capillary condensation as predicted by the Kelvin effect and subsequent ice nucleation at cirrus temperatures. For the pore diameters and contact angles covered in this study, 2.2–9.2 nm and 15–78°, respectively, our results reveal that the contact angle plays an important role in predicting the humidity required for pore filling while the pore diameter determines the ability of pore water to freeze. For T > 235 K and below water saturation, pore diameters and contact angles were not able to predict the freezing ability of the particles suggesting an absence of active sites, thus ice nucleation did not proceed via a PCF mechanism. Rather, the ice nucleating ability of the particles depended solely on chemical functionalization. Therefore, parameterizations for the ice nucleating abilities of particles at cirrus conditions should differ from parameterizations at mixed-phase clouds conditions. Our results support PCF as the atmospherically relevant ice nucleation mechanism below water saturation when porous surfaces are encountered in the troposphere.

Multifunctional nanocomposite transparent UV-blocking films sythesized by sol-gel process for optical, automotive and aeronautic applications

2005 ◽  
Vol 901 ◽  
Author(s):  
Phani Ratna Ayalasomayajula ◽  
S. Santucci
Keyword(s):  
Thin Films ◽  
Contact Angle ◽  
Morphological Changes ◽  
Sol Gel ◽  
Chemical Properties ◽  
Contact Angles ◽  
Nanocomposite Films ◽  
Energy Materials ◽  
Water Contact ◽  
Uv Blocking

AbstractDevelopment of UV blocking thin films with effective cut-off features with steep edges and high transmission in the visible and IR region have been developed. The unique optical, mechanical and chemical properties of silica and ceria nanocomposites with surface functional groups making them most promising candidate for applications in opto-electronic, automotive, and aeronautic industries. On the other hand, highly hydro and oleophobic films are being actively considered in optical, automotive and aeronautic industries to increase adhesion and scratch, abrasion resistance properties. In order to fill the gap, and fulfill the requirements to meet both ends, it could be proved that morphological changes in the nanometer range influences the water contact angles and their hystersis of low energy materials. Nanocomposite films of SiO2 and CeO2 with surface functionalisation with decafluorooctly-triethoxy silane itself forms nano-hemispheres (similar to lotus leaf) at and above 100°C favoring an increase in water contact angle from 122° (25°C) to 145°(400°C). The structural, optical, and hydrophobic properties have been examined by employing X-ray diffraction, UV-visible spectroscopy, contact angle techniques, respectively. The cut-off behavior of the deposited and annealed nanocomposite thin films have been tuned by varying different amounts of CeO2 in SiO2.

Optical Transparent and Hydrophobic Properties of TEOS/OTES Hybrid Materials by Sol-Gel Processing

2019 ◽  
Vol 798 ◽  
pp. 134-139
Author(s):  
Usanee Pantulap ◽  
Benjamon Petchareanmongkol ◽  
Waraporn Kaewdang ◽  
Kanit Tapasa
Keyword(s):  
Contact Angle ◽  
Sol Gel ◽  
Contact Angles ◽  
Light Transmittance ◽  
Film Properties ◽  
Water Contact ◽  
Atomic Force ◽  
Commercial Glass ◽  
Gel Processing ◽  
Hydrolysis Of

The objective of this project was to develop the hydrophobic film for self-cleaning glasses. The effects of octyltriethoxysilane (OTES) additions to hydrolysis of tetraethylorthosilicate (TEOS) on hydrophobic and optically transparent properties were studied. The film was prepared by sol-gel method from the precursors namely, TESO, OTES, isopropanol alcohol (IPA), and deionized water (DI). The sols for coating were obtained with TEOS/OTES ratio of 50:50 to 99:1. The sols were deposited on a commercial glass and dried at 60oC for an hour. After drying, the film properties were characterized by fourier transform infrared spectroscopy (FTIR), UV-VIS Spectrophotometer, x-Ray Diffractometer (XRD), atomic force microscope (AFM), optical microscopy and contact angle meter. It was found that contact angles of the hybrid films increased with the OTES addition, reaching a maximum at 10 wt.%, and the contact angle values were the same as for further addition. The light transmittance was rather stable with increasing amounts of OTES. For the optimized condition, the water contact angle of 108o and light transmittance of 91%, was obtained with TEOS/OTES ratio of 90:10.

Effects of Air Exposure Time and Annealing Temperature on Superhydrophobic Surface of Titanium Dioxide Films

2017 ◽  
Vol 751 ◽  
pp. 137-142
Author(s):  
S.Tipawan Khlayboonme ◽  
Warawoot Thowladda
Keyword(s):  
Contact Angle ◽  
Surface Morphology ◽  
Exposure Time ◽  
Annealing Temperature ◽  
Sol Gel ◽  
Contact Angles ◽  
Angle Measurement ◽  
Elemental Distribution ◽  
Water Contact ◽  
Air Exposure

TiO2 thin films coated on glass substrates for self-cleaning applications were prepared by sol-gel dip-coating technique. The influence of annealing temperature and air exposure time on wettability was investigated by a water contact-angle measurement. Thermal annealing at temperatures of 100, 200 and 300 °C in air were conducted to the films. Surface morphology of the films was observed by FE-SEM. Elemental distribution and optical properties were examined by EDX mapping and UV-Vis transmission spectroscopy, respectively. Atomic bonding was confirmed by FTIR. The contact angle reached a maximum when the films were annealed at 200 °C. The contact angles of the as-synthesized films were 61.4±2.7°. During storage in air for 20 days, the contact angles increased to 143.1±2.1°. The films were further reannealed with 100 °C for 20 min, the contact angles were enhanced to 153.1±1.3°. The association of contact angle among the surface morphology, elemental distribution and atomic bonding of the films will be discussed.

scholarly journals Technical note: Fundamental aspects of ice nucleation via pore condensation and freezing including Laplace pressure and growth into macroscopic ice

2020 ◽  
Vol 20 (5) ◽  
pp. 3209-3230 ◽  
Author(s):  
Claudia Marcolli
Keyword(s):  
Negative Pressure ◽  
Active Sites ◽  
Water Saturation ◽  
Particle Surface ◽  
Ice Nucleation ◽  
Nucleation Theory ◽  
Ice Crystal ◽  
Spherical Cap ◽  
Pore Opening ◽  
Pore Condensation

Abstract. Pore condensation and freezing (PCF) is an ice nucleation mechanism that explains ice formation at low ice supersaturation. It assumes that liquid water condenses in pores of solid aerosol particles below water saturation, as described by the Kelvin equation, followed by homogeneous ice nucleation when temperatures are below about 235 K or immersion freezing at higher temperatures, in case the pores contain active sites that induce ice nucleation. Porewater is under tension (negative pressure) below water saturation as described by the Young–Laplace equation. This negative pressure affects the ice nucleation rates and the stability of the pore ice. Here, pressure-dependent parameterizations of classical nucleation theory are developed to quantify the increase in homogeneous ice nucleation rates as a function of tension and to assess the critical diameter of pores that is required to accommodate ice at negative pressures. Growth of ice out of the pore into a macroscopic ice crystal requires ice supersaturation. This supersaturation as a function of the pore opening width is derived, assuming that the ice phase first grows as a spherical cap on top of the pore opening before it starts to expand laterally on the particle surface into a macroscopic ice crystal.

scholarly journals Technical note: Fundamental aspects of ice nucleation via pore condensation and freezing including Laplace pressure and growth into macroscopic ice

2019 ◽  
Author(s):  
Claudia Marcolli
Keyword(s):  
Negative Pressure ◽  
Active Sites ◽  
Water Saturation ◽  
Particle Surface ◽  
Ice Nucleation ◽  
Nucleation Theory ◽  
Ice Crystal ◽  
Spherical Cap ◽  
Pore Opening ◽  
Pore Condensation

Abstract. Pore condensation and freezing (PCF) is an ice nucleation mechanism that explains ice formation at low ice supersaturation. It assumes that liquid water condenses in pores of solid aerosol particles below water saturation, as described by the Kelvin equation, followed by homogeneous ice nucleation when temperatures are below about 235 K or immersion freezing at higher temperatures, in case the pores contain active sites that induce ice nucleation. Pore water is under tension (negative pressure) below water saturation as described by the Young-Laplace equation. This negative pressure affects the ice nucleation rates and the stability of the pore ice. Here, pressure dependent parameterizations of classical nucleation theory are developed to quantify the increase of homogeneous ice nucleation rates as a function of tension and to assess the critical diameter of pores that is required to accommodate ice at negative pressures. For growth out of the pore into a macroscopic ice crystal, ice supersaturation is required. The required supersaturation as a function of the pore opening width is derived, assuming that the ice phase first grows as a spherical cap on top of the pore opening before it starts to expand laterally on the particle surface into a macroscopic ice crystal.

scholarly journals Influence of moisture content on the contact angle and surface tension measured on birch wood surfaces

2021 ◽  
Author(s):  
Rami Benkreif ◽  
Fatima Zohra Brahmia ◽  
Csilla Csiha
Keyword(s):  
Surface Tension ◽  
Contact Angle ◽  
Moisture Content ◽  
Solid Wood ◽  
Contact Angles ◽  
Surface Moisture ◽  
Wood Coatings ◽  
The Relationship ◽  
Wood Surfaces

AbstractSurface tension of solid wood surfaces affects the wettability and thus the adhesion of various adhesives and wood coatings. By measuring the contact angle of the wood, the surface tension can be calculated based on the Young-Dupré equation. Several publications have reported on contact angle measured with different test liquids, under different conditions. Results can only be compared if the test conditions are similar. While the roles of the drop volume, image shooting time etc., are widely recognized, the role of the wood surface moisture content (MC) is not evaluated in detail. In this study, the effect of wood moisture content on contact angle values, measured with distilled water and diiodomethane, on sanded birch (Betula pendula) surfaces was investigated, in order to find the relationship between them. With increasing MC from approximately 6% to 30%, increasing contact angle (decreasing surface tension) values were measured according to a logarithmic function. The function makes possible the calculation of contact angles that correspond to different MCs.

scholarly journals Efficiency of immersion mode ice nucleation on surrogates of mineral dust

2007 ◽  
Vol 7 (19) ◽  
pp. 5081-5091 ◽  
Author(s):  
C. Marcolli ◽  
S. Gedamke ◽  
T. Peter ◽  
B. Zobrist
Keyword(s):  
Contact Angle ◽  
Active Sites ◽  
Quantitative Agreement ◽  
Ice Nucleation ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Aqueous Suspensions ◽  
Freezing Temperatures ◽  
Good Agreement ◽  
Heterogeneous Ice Nucleation

Abstract. A differential scanning calorimeter (DSC) was used to explore heterogeneous ice nucleation of emulsified aqueous suspensions of two Arizona test dust (ATD) samples with particle diameters of nominally 0–3 and 0–7 μm, respectively. Aqueous suspensions with ATD concentrations of 0.01–20 wt% have been investigated. The DSC thermograms exhibit a homogeneous and a heterogeneous freezing peak whose intensity ratios vary with the ATD concentration in the aqueous suspensions. Homogeneous freezing temperatures are in good agreement with recent measurements by other techniques. Depending on ATD concentration, heterogeneous ice nucleation occurred at temperatures as high as 256 K or down to the onset of homogeneous ice nucleation (237 K). For ATD-induced ice formation Classical Nucleation Theory (CNT) offers a suitable framework to parameterize nucleation rates as a function of temperature, experimentally determined ATD size, and emulsion droplet volume distributions. The latter two quantities serve to estimate the total heterogeneous surface area present in a droplet, whereas the suitability of an individual heterogeneous site to trigger nucleation is described by the compatibility function (or contact angle) in CNT. The intensity ratio of homogeneous to heterogeneous freezing peaks is in good agreement with the assumption that the ATD particles are randomly distributed amongst the emulsion droplets. The observed dependence of the heterogeneous freezing temperatures on ATD concentrations cannot be described by assuming a constant contact angle for all ATD particles, but requires the ice nucleation efficiency of ATD particles to be (log)normally distributed amongst the particles. Best quantitative agreement is reached when explicitly assuming that high-compatibility sites are rare and that therefore larger particles have on average more and better active sites than smaller ones. This analysis suggests that a particle has to have a diameter of at least 0.1 μm to exhibit on average one active site.

scholarly journals Ice nucleation abilities of soot particles determined with the Horizontal Ice Nucleation Chamber

2018 ◽  
Vol 18 (18) ◽  
pp. 13363-13392 ◽  
Author(s):  
Fabian Mahrt ◽  
Claudia Marcolli ◽  
Robert O. David ◽  
Philippe Grönquist ◽  
Eszter J. Barthazy Meier ◽  
...  
Keyword(s):  
Particle Size ◽  
Water Saturation ◽  
Particle Surface ◽  
Water Vapor Sorption ◽  
Contact Angles ◽  
Ice Nucleation ◽  
Particle Surface Area ◽  
Soot Particles ◽  
Microphysical Properties ◽  
Homogeneous Freezing

Abstract. Ice nucleation by different types of soot particles is systematically investigated over the temperature range from 218 to 253 K relevant for both mixed-phase (MPCs) and cirrus clouds. Soot types were selected to represent a range of physicochemical properties associated with combustion particles. Their ice nucleation ability was determined as a function of particle size using relative humidity (RH) scans in the Horizontal Ice Nucleation Chamber (HINC). We complement our ice nucleation results by a suite of particle characterization measurements, including determination of particle surface area, fractal dimension, temperature-dependent mass loss (ML), water vapor sorption and inferred porosity measurements. Independent of particle size, all soot types reveal absence of ice nucleation below and at water saturation in the MPC regime (T>235 K). In the cirrus regime (T≤235 K), soot types show different freezing behavior depending on particle size and soot type, but the freezing is closely linked to the soot particle properties. Specifically, our results suggest that if soot aggregates contain mesopores (pore diameters of 2–50 nm) and have sufficiently low water–soot contact angles, they show ice nucleation activity and can contribute to ice formation in the cirrus regime at RH well below homogeneous freezing of solution droplets. We attribute the observed ice nucleation to a pore condensation and freezing (PCF) mechanism. Nevertheless, soot particles without cavities of the right size and/or too-high contact angles nucleate ice only at or well above the RH required for homogeneous freezing conditions of solution droplets. Thus, our results imply that soot particles able to nucleate ice via PCF could impact the microphysical properties of ice clouds.

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