Nucleation Activity Research Articles

Accelerated nonisothermal crystallization and improved material properties of biobased poly(butylene 2,5-furandicarboxylate)/talc composites

Biobased poly(butylene 2,5-furandicarboxylate) (PBF) reflects the much poorer crystallizability than its petroleum-based counterpart poly(butylene terephthalate). By introducing talc platelets into PBF matrix to fabricate composites, the effects of low loadings’ layered filler upon nonisothermal melt crystallization and material properties of PBF/talc composites are investigated for the first time. Obviously accelerated crystallization of the composites relative to pure PBF is first evidenced by the simultaneous increase of crystallization temperature and decline of crystallization half-time, and further supported by both the crystallization rate coefficient and crystallization rate parameter. Nonisothermal crystallization kinetics are analyzed by both the Jeziorny model and Mo equations, and the intensifying effect of talc upon PBF's crystallization is attributed to the coupling of enlarging nucleation activity and lowering crystallization activation energy. Meanwhile, the incorporation of layered talc doesn't modify the crystal structure of PBF. Moreover, both the thermal and mechanical properties of PBF/talc composites are reinforced slightly.

Influence of smooth heater size on critical heat flux and heat transfer coefficient of saturated pool boiling heat transfer

In order to study the influence of smooth heater size on the performance of pool boiling heat transfer, saturated boiling experiments of FC-72 were conducted on eight sized smooth silicon chips (the test surfaces are denoted as S5 ∼ S30, and their dimensionless dimensions are in the range of Lh/Lc = 7 ∼ 42). The bubble dynamics during boiling were observed with a high-speed camera. The results indicated that in natural convection regime, the heat transfer coefficient decreases with increasing heater size at a given heat flux. Besides, the larger surfaces enter into the nucleate boiling regime earlier. In a fully developed nucleate boiling regime, S5 surface displays the optimal heat transfer performance. The reality is that no vapor columns are produced even in the high heat flux range due to its small bubble departure diameter and high bubble departure frequency. For S8 ∼ S15 surfaces, the wall temperatures increase continuously with the increase of heat flux, while S20 ∼ S30 surfaces present a trend of first keeping constant and then increasing. The active nucleation site densities on S15 ∼ S30 surfaces follow the law of Na = 0.45q2 in the whole nucleate boiling regime. By contrast, for S5 ∼ S12 surfaces, the nucleation site densities abide by this law only in a fully developed nucleate boiling regime. In addition, the departure diameter and departure frequency of bubbles increase with the increase of heat flux for all surfaces. It is observed that with the increase of smooth heater size, CHF presents a changing trend of first increasing (in range of Lh ≤ λD, λD is the most dangerous Taylor wavelength), then decreasing (in range of λD < Lh ≤ 3λD) and finally leveling off (in range of Lh > 3λD). Accordingly, the CHF value maximizes at the heater size Lh = λD. In the segment of decreased CHF, the decline rate of CHF in range of λD < Lh ≤ 2λD is larger than that in range of 2λD < Lh ≤ 3λD. Meanwhile, the influencing mechanisms of heater size on CHF were explained by consideration into bubble patterns and behavior.

Predicting Atmospheric Particle Phase State Using an Explainable Machine Learning Approach Based on Particle Rebound Measurements.

The particle phase state plays a vital role in the gas-particle partitioning, multiphase reactions, ice nucleation activity, and particle growth in the atmosphere. However, the characterization of the atmospheric phase state remains challenging. Herein, based on measured aerosol chemical composition and ambient relative humidity (RH), a machine learning (ML) model with high accuracy (R2 = 0.952) and robustness (RMSE = 0.078) was developed to predict the particle rebound fraction, f, which is an indicator of the particle phase state. Using this ML model, the f of particles in the urban atmosphere was predicted based on seasonal average aerosol chemical composition and RH. Regardless of seasons, aerosols remain in the liquid state of mid-high latitude cities in the northern hemisphere and in the semisolid state over semiarid regions. In the East Asian megacities, the particles remain in the liquid state in spring and summer and in the semisolid state in other seasons. The effects of nitrate, which is becoming dominant in fine particles in several urban areas, on the particle phase state were evaluated. More nitrate led the particles to remain in the liquid state at an even lower RH. This study proposed a new approach to predict the particle phase state in the atmosphere based on RH and aerosol chemical composition.

Formation processes of paper-thin raft and coated bubble: Calcium carbonate deposition at gas–water interface

Travertines are hot spring carbonate deposits that exhibit characteristic fabrics, including a paper-thin raft and a coated bubble formed by the calcification of water and bubble surfaces, respectively. A previous study interpreted that compared with the water surface, the bubble surface displays more active CO2 degassing and resultant active CaCO3 precipitation. However, considering the CO2 partial pressure and the volumes of atmosphere and bubbles, it is possible that more active CO2 degassing occurs on the water surface. In addition, the surfaces of water and bubbles at the travertine-depositing sites are negatively charged, but it is still unclear whether the CaCO3 nucleation on these surfaces occurs via amorphous precursors, like the CaCO3 nucleation on negatively charged organic matter. This study provides a solution to these uncertainties by examining the aragonitic travertines formed in the Nagayu area of Japan. Through field observations, two types of paper-thin rafts were recognized: one with a smooth surface and formed in approximately 1 h, and the other with a rough surface and formed in approximately 3 h. In addition, the bubbles generated on the microbial mat during the daytime were covered with white minerals within an hour, and with ivory-colored minerals over 8 h after sunset, forming firm coated bubbles. Microelectrode measurements revealed that the active CO2 degassing on the water surface significantly increased the CaCO3 saturation state to cause active CaCO3 precipitation. In contrast, less active CO2 degassing on the bubble surface did not increase the saturation state, and moderate CaCO3 precipitation occurred due to the moderately high saturation state of the hot spring water. Various microscopic observations revealed that the smooth-surfaced paper-thin raft comprises a micritic layer of approximately 10–20 μm, which represents tightly arranged submicron-sized granular aragonite. At the lower surface of this layer, hemispherical aragonite partially grew toward the hot spring water. In addition, the rough-surfaced paper-thin raft and coated bubble comprise bundled and acicular aragonites arranged along the surfaces of water and bubble, from which hemispherical aragonite grew toward the hot spring water. Neither the paper-thin raft nor the coated bubble contains primary amorphous CaCO3. These results suggest that the smooth-surfaced paper-thin raft is formed by active CaCO3 nucleation on the water surface and subsequent crystal growth, and that the water surface is unfavorable for preserving the amorphous precursors potentially involved in the nucleation. The rough-surfaced paper-thin raft and the coated bubble could have been formed by the attachment of externally formed acicular aragonite to the water/bubble surface and subsequent crystal growth. The revealed formation processes of the paper-thin raft and coated bubble provide valuable information for interpreting their formation mechanism in other travertine deposits, including those in the geological past.

Mechanism underlying early hydration kinetics of carbonated recycled concrete fines-ordinary portland cement (CRCF-OPC) paste

Aiming to promote applications of carbonated recycled concrete fines (CRCF) as a low-carbon alternative to ordinary Portland cement (OPC), this study explored the effect of CRCF on the early hydration kinetics of OPC paste. The results show that CRCF is not only a highly active pozzolanic material but also an effective accelerator affecting the early hydration kinetics of OPC paste, thereby leading to an increased early compressive strength and a comparable 28-d compressive strength, even at a replacement ratio of 20%. Although the rheological properties and workability are negatively affected due to the high surface area and fine particle size of CRCF, the amorphous silica and silica-alumina gels and calcite present in CRCF facilitate initial ions dissolution and provide additional active nucleation sites for hydrates. As a result, the microstructure is densified due to the formation of additional C–S–H gels with high Si/Ca and Al/Ca ratios and carboaluminate phases, along with the inert filler effect of unreacted calcite particles. The incorporation of 20% CRCF to replace OPC can achieve a CO2 emissions reduction up to 25%. These indicate that the CRCF has a promising application scenario in transforming wasted concrete into high-value industrial products by CO2 activation.

Effect of recrystallization on bainite transformation and mechanical properties of complex phase steel with high formability (CH steel)

Herein, the effect of recrystallization on the bainite transformation and mechanical properties of CH steel were investigated using SEM, TEM, EBSD, dilatometry, and tensile testing machine. First, precipitation was introduced to hinder recrystallization by batch annealing. Subsequently, the competitive relationship between austenite transformation and recrystallization was revealed using different annealing processes. Finally, the effect of recrystallization on bainite transformation was analyzed, mainly including bainite morphology, fraction, transformation rate, bainite nucleation rate of untransformed austenite and austenite-bainite orientation relationship, as well as the effect on the mechanical properties. After batch annealing, a large amount of cementite and nanoscale (Nb, Ti)C precipitated in the hot-rolled sheet, the austenite transformation start temperature (Ac1) and the pearlite to austenite transformation end temperature (Ac1f)of the cold-rolled sheet increased, and the austenite transformation end temperature (Ac3) of the cold-rolled sheet decreased, and the austenite transformation process accelerated. The microstructure of annealed sheets is consisted of ferrite, granular bainite, martensite, and a small fraction of retained austenite. Carbide hindered the recrystallization process during the annealing process, resulting in significant refining of the grains. The lower degree of recrystallization promoted bainite transformation, providing more nucleation sites, higher grain boundary and autocatalytic nucleation activation energy, improving bainite's fraction and transformation rate. The bainitic ferrite was mainly lathy in the recrystallized zone and polygonal in the non-recrystallized zone. Both a K-S and an N-W relationship between retained austenite and bainite, while the N-W relationship in the non-recrystallized zone was relatively higher. Without severe loss of plasticity, hindering recrystallization increased the dislocation, grain refinement, and precipitation strengthening values of the samples, and the strength significantly improved. However, with the increase of annealing temperature, recrystallization fraction increased gradually, and the increase in strength became less noticeable.

Numerical simulation of boiling behavior in vertical microchannels

High heat flux electronic devices put forward new requirements for heat dissipation, and boiling heat transfer technology is widely used because of its higher heat dissipation capacity. In this study, the volume of fluid method was employed, along with the incorporation of the Lee phase-change mass transfer model, to investigate two-phase flow and heat transfer in vertical upward rectangular microchannels. The heat flux was varied within the range of 10–40 kW/m2, while the mass flux was varied within the range of 200–600 kg/m2 s. With the increase in heat flux, bubble flow, slug flow, churn flow, and annular flow were found successively. A phase diagram was established to predict the flow pattern transition during the boiling process. When the flow pattern changes to the churn and the annular flow, the active nucleation site density increases obviously with the Boiling number (Bo). A new correlation was proposed for two-phase flow boiling heat transfer, suitable for vertical upward channels in microscale fluids. The friction factor obtained using the Darcy friction factor equation agrees well with the simulation results at a high-pressure drop. The instability in microchannels increases with the increase in heat flux, particularly in annular flow, resulting in more severe wall temperature fluctuations.

Accounting for Cloud Nucleation Activation Mechanism of Secondary Organic Matter from α-Pinene Oxidation Using Experimentally Retrieved Water Solubility Distributions.

Activation of cloud droplets of aerosol particles from biogenic precursors plays a critical role in Earth's climate system. However, the molecular-level understanding of the cloud condensation nuclei (CCN) activation process for secondary organic matter (SOM) is still lacking. Here, we reduced the gap by segregating SOM from α-pinene based on water solubility. The chemical composition and CCN activity of the solubility-segregated fractions of SOM were measured. The results demonstrated for the first time by laboratory experiment that highly oxygenated compounds such as hydroperoxides and highly oxygenated organic molecules are important contributors for the CCN activity of α-pinene SOM. Meanwhile, relatively less water-soluble species were also abundant. Analysis based on the Köhler theory demonstrated that less water-soluble compounds in SOM remain undissolved during the cloud activation process, suggesting that the traditional single-parameter parameterization for CCN activation would not be sufficient for representing the process. In combination with the recent developments in SOM formation chemistry, the present study helps in understanding the interactions between the biosphere and climate.

Enhanced mortar strength and resistance to seawater degradation in the presence of calcined coal-series kaolin

The hydration process of blended mortars and its resistance to seawater degradation in the presence of calcined coal-series kaolin (CCK) was investigated in this study. The TG tests were used to quantify the effect of calcination temperature on the chemical-bound water content of the blended pastes while the XRD tests were applied to analyze the main crystalline hydration phases of the blended pastes, which were further quantified using the Rietveld-XRD refinement. In addition, microcalorimetric tests were used to characterize the degree of hydration. The hydration process of the blended mortars was further investigated in detail via combining SEM and pozzolanic activity tests. Based on this, the resistance to seawater degradation of the blended mortars with added CCK were verified via the expansion and strength loss tests, and the mechanism was analyzed via the electric flux and the total Cl− content tests. The optimal percentage of CCK (12%) was determined via a linear weighted sum method. The CCK obtained at 800 °C had the highest pozzolanic activity, promoting hydration reactions to form new gels (C-S-H, C-A-H and C-A-S-H) at active nucleation sites in mortars. These further enhanced both the flexural and compressive strengths (the compressive strength reached ∼53.7 MPa) of the blended mortars. However, CCK reduced the generation of Mg(OH)2, AFt and Friedel’s salt, decreasing seawater degradation to the mortars. Therefore, this study provides a new strategy to prepare high-strength mortar with high resistance to seawater degradation.

Development and characterization of the Portable Ice Nucleation Chamber 2 (PINCii)

Abstract. The Portable Ice Nucleation Chamber 2 (PINCii) is a newly developed continuous flow diffusion chamber (CFDC) for measuring ice nucleating particles (INPs). PINCii is a vertically oriented parallel-plate CFDC that has been engineered to improve upon the limitations of previous generations of CFDCs. This work presents a detailed description of the PINCii instrument and the upgrades that make it unique compared with other operational CFDCs. The PINCii design offers several possibilities for improved INP measurements. Notably, a specific icing procedure results in low background particle counts, which demonstrates the potential for PINCii to measure INPs at low concentrations (&lt;10 L−1). High-spatial-resolution wall-temperature mapping enables the identification of temperature inhomogeneities on the chamber walls. This feature is used to introduce and discuss a new method for analyzing CFDC data based on the most extreme lamina conditions present within the chamber, which represent conditions most likely to trigger ice nucleation. A temperature gradient can be maintained throughout the evaporation section in addition to the main chamber, which enables PINCii to be used to study droplet activation processes or to extend ice crystal growth. A series of both liquid droplet activation and ice nucleation experiments were conducted at temperature and saturation conditions that span the spectrum of PINCii's operational conditions (-50≤ temperature ≤-15 ∘C and 100 ≤ relative humidity with respect to ice ≤160 %) to demonstrate the instrument's capabilities. In addition, typical sources of uncertainty in CFDCs, including particle background, particle loss, and variations in aerosol lamina temperature and relative humidity, are quantified and discussed for PINCii.

Comparison of the Grain-Refining Efficiencies of Ti and LaB6 Inoculants in Additively Manufactured 2024 Aluminum Alloy: The Important Role of Solutes

The present work aims to boost our understanding of factors governing the grain-refining efficiency of inoculation treatments by comparing the grain-refining efficiencies of two inoculators: Ti nanoparticles and LaB6 nanoparticles, in a 2024 Al alloy during additive manufacturing (AM). Experimental results obtained by scanning electron microscopy show that the LaB6 nanoparticle possessed almost no refining effect on the alloy, with the addition content ranging from 0.5 wt.% to 2 wt.%. Conversely, the Ti nanoparticle resulted in a more pronounced refinement and a fine, fully equiaxed microstructure at 1 wt.% Ti addition. Based on transmission electron microscopy analysis, the higher refining efficiency of Ti inoculation was ascribed to the incorporation of both Ti solute and the in situ-formed L12-Al3Ti nucleation particles. The former significantly increased the overall undercooling ahead of the growing Al grain, which ensured the activation of heterogeneous nucleation on the L12-Al3Ti nanoparticles, leading to grain refinement. This work highlights that despite the addition of nucleation particles, the incorporation of appropriate solutes to generate sufficient undercooling is the prerequisite for the activation of heterogenous nucleation in AM.

Advanced nanocellulose hybrid fillers for sustainable polypropylene biomaterials with enhanced oxygen barrier properties

Research was undertaken on the design and preparation of advanced polymer biomaterials containing innovative nanocellulose hybrid fillers with functional physicochemical properties, characterized by high mechanical strength, enhanced thermal resistance, and improved gas barrier properties, which are important in the packaging industry. Such innovative polymer composite nanomaterials with renewable fillers, which will reduce the consumption of petroleum raw materials, which is also directly related to the reduction of energy consumption. Novel TiO2-ZnO/nanocellulose hybrid systems were prepared by a solvothermal method, and their structural, textural, morphological, chemical composition, and thermal properties were evaluated. Polymer composites with nanocellulose synthesized using enzymatic hydrolysis and with hybrid fillers, were obtained by two-step extrusion. Various techniques were used to determine the supermolecular structure and nucleation activity of the biomaterials, barrier tests and mechanical properties were also carried out. It was found that the composites containing hybrid fillers exhibited increased nucleation activity, which favored the formation of a pseudohexagonal polymorphic variety of the polymer matrix, providing high tensile strength while maintaining high flexibility. In addition, the use of novel hybrid fillers made it possible to achieve higher barrier properties against oxygen and water vapor in composite films. A significant achievement is the finding of a previously unrecorded relationship between the shaping of supermolecular structure (polymorphism, nucleation) and physicochemical properties (mechanical, barrier), which is of great significance for the design of modern packaging.

Deep learning-based approach to R-134a bubble detection and analysis for geothermal applications

This study utilized deep learning to analyse bubble images of R134a fluid produced on bare and novel oleophilic coated stainless steel heat exchanger plates to compare the heat transfer performance in terms of bubble parameters. This work was carried out as a part of the GeoHex project. The vapour bubbles of the boiling R134a fluid, produced on two types of heat exchanger plates, were captured with a high-speed camera during a boiling experiment. A deep learning algorithm based on the Mask R–CNN model was trained for bubble detection in the experimental videos. The algorithm achieved a bubble detection accuracy of 61.22% and 78.6% for the coated and uncoated plates, respectively. The lower accuracy for the coated plate could be attributed to the challenge of distinguishing bubbles from the complex coating pattern. The algorithm determined the number of detected bubbles, bubble sizes, and centroids per frame, tracking each bubble frame by frame. The tracking results were used to calculate the bubble parameters such as departure frequency, departure diameter, and active nucleation site density. The calculated departure diameter for both plates exhibited a difference of 3%, which corresponded closely to the experimental results showing a 4% variation in heat transfer coefficient, which was measured under identical experimental conditions utilizing the GeoHex rig. However, the calculated departure frequency and active nucleation site density exhibited a 17% disparity between the coated and uncoated plates, primarily stemming from the lower detection accuracy for the coated plate. Some limitations of the trained model were identified in accurately detecting very small, out of focus, and mutually occluded bubbles. Future research should focus on improving experimental rig designs to capture better side-view images and develop advanced machine learning or other techniques to address these limitations.

Electrochemical co-deposition of carbon nanotube/Ni composite layer

The type and content of particles in the plating solution greatly affect the electrodeposition process, making it important to study the effect of carbon nanotubes (CNTs) on the electrodeposition of nickel during the preparation of CNTs/Ni composites. In this paper, cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometric analysis (CA), and electrochemical impedance spectroscopy (EIS) were adopted to study the nucleation mechanism in the early stage of electrocrystallization. Field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) were used to reveal the electrocrystallization properties. The results showed that Ni was electrodeposited by 3D nucleation/growth and was controlled by diffusion and electrochemical kinetics. Increasing the CNTs concentration shortened the time required for 3D growth. Additionally, the polarizability of the electrodeposited nickel increased upon increasing the CNTs content, which helped increase the electro-crystallization probability of Ni. As the concentration of CNTs increased, the charge transfer resistance decreased, the Ni nucleation activation energy decreased, and the Ni nucleation became easier. The introduction of CNTs changed the preferred growth orientation of pure nickel, and the surface growth morphology was mainly a spiral in a stepwise pyramid.

Advances in the use of carbonaceous scaffolds for constructing stable composite Li metal anodes

Compositing lithium metal anodes (LMAs) with carbon-based materials has been given much attention because of the latter's low density, high mechanical strength, stable electrochemical properties, and large specific surface area. Such a composite LMA stands out because of its ability to reduce the volume expansion, lower the local current density, and provide active nucleation sites for uniform Li+ plating. Recent research advances in carbon-based materials as scaffolds to make composite anodes are reviewed, including composites with pure metals and their alloys, and compositing strategies to improve anode stability.

Enhancement in pool boiling performance of GNP/Cu-Al2O3 nano-composite coated copper microporous surface

An experimental analysis of pool boiling is conducted on the GNP/Cu-Al2O3 (GNP-graphene nano particle) nanocomposite coated copper surfaces at atmospheric pressure using DI (distilled water) as boiling fluid. A two-step electro-deposition technique is used for fabrication of these micro/nano porous coated surfaces. A modified surface structure is formed due to this deposition and various surface morphology parameters such as surface structure, roughness, wettability are analysed. Results show the enhancement in BHTC (boiling heat transfer coefficient) and CHF (Critical heat flux) in nano composite coated surfaces compare to the bare copper surface. The maximum CHF of 2415 (kW/m2) and BHTC of 171.28 (kW/m2K) is found in the NCCS (nano-composite coated superhydrophilic) surfaces which are 122% and 239% more than the bare copper surfaces. The boiling performance is augmented mainly because of the improvement in roughness, wettability and also for the high thermal conductivity of the GNP/Cu- Al2O3 nano coating. Quantitative study of the bubble dynamics like active nucleation site density, bubble emission frequency, departure diameter of bubbleand their impact on heat transfer performance in the case of NCCS surfaces is performed with high-speed visualization.

High-pressure drop rates in solid-state batch one-step scCO2 foaming of acrylic polymers: A way to stabilize the structure of micro-nano foams

One-step solid-state batch scCO2 foaming is used with the target of achieving acrylic polymer micro-nano foams. Foaming is triggered by an average pressure drop (APDR), covering two decades, from 0.3 to 30 MPa.s−1. This study principally addresses the combined beneficial effects of block copolymer addition (BCP, here denoted as MAM) and high APDR. Numerous subtle kinetic parameters actually interplay and compete in the production of the final foams. In particular, the material effective temperature, the effective glass transition temperature of the plasticized system and the instantaneous PDR are physical quantities each having their own kinetics during foaming. The resulting foam morphologies are quantified by SEM microscopy and image analysis. A high APDR and the presence of BCP are shown to play a key role in the final structure of the foams. Over the scrutinized range of saturation temperature (40 °C to 60 °C i.e. rather ‘low’ temperatures in the CO2 supercritical state), the APDR is the main factor for significantly reducing cell size and increasing nuclei density in foams from neat PMMA. In the block copolymer approach, increasing the APDR is of secondary importance as the targeted reduction of the porosity dimensions and augmentation of nuclei density are mostly the consequence of MAM presence. In this latter case, increasing the APDR still promotes the ‘efficiency’ of the BCP nucleants. A real efficient nucleation activity of MAM additive is observed at a very high APDR (30 MPa.s−1), leading to monomodal homogeneous distribution of tiny pores in nearly nanosized foams. At lower APDR, an interesting reproducible double porosity (foams containing intra-wall and inter-wall pores) is detected in PMMA/MAM systems. In such double porosity foams, benefits from the Knudsen effect achieved within well expanded local domains (showing micron-sized pores) may remain meaningful thanks to a locally poorly expanded nanoporous thick solid skeleton encapsulating these local domains. Thereby, the radiative thermal conduction can be minimized and does not override the conductive component at the sample scale. This work provides further insight on acrylic polymer BCP foams influenced by different kinetics.

Heterogeneous Ice Nucleation in Model Crystalline Porous Organic Polymers: Influence of Pore Size on Immersion Freezing.

Heterogeneous ice nucleation activity is affected by aerosol particle composition, crystallinity, pore size, and surface area. However, these surface properties are not well understood, regarding how they act to promote ice nucleation and growth to form ice clouds. Therefore, synthesized materials for which surface properties can be tuned were examined in immersion freezing mode in this study. To establish the relationship between particle surface properties and efficiency of ice nucleation, materials, here, covalent organic frameworks (COFs), with different pore diameters and degrees of crystallinity (ordering), were characterized. Results showed that out of all the highly crystalline COFs, the sample with a pore diameter between 2 and 3 nm exhibited the most efficient ice nucleation activity. We posit that the highly crystalline structures with ordered pores have an optimal pore diameter where the ice nucleation activity is maximized and that the not highly crystalline structures with nonordered pores have more sites for ice nucleation. The results were compared and discussed in the context of other synthesized porous particle systems. Such studies give insight into how material features impact ice nucleation activity.

Determining Roles of Potassium-Feldspar Surface Characters in Affecting Ice Nucleation.

The roles of surface characteristics of the feldspar surface on ice nucleation have remained elusive. Here, simple strategies arereported to quantitatively analyze the effects of the surface morphology and molecular composition of the potassium-feldspar surface on ice nucleation. The steps are found to be responsible to the high ice nucleation efficacy according to the fact that water drop freezing temperature increases by about 4.5°C atop the freshly cleavage feldspar surface being rich of steps comparing to the flattened ones. After the molecular component and atomic structure are destroyed by the fluorination, a tremendous decrease of the ice nucleation temperatures by around 9.0°C isobserved on both cleavage and flattened surfaces, and the steps still improve the ice nucleation activity of the hydrophobic cleavage surfaces. The influence of the surface composition also implies the importance of the molecular component and structure specificity on K-feldspar in facilitating ice nucleation.

Lichen species across Alaska produce highly active and stable ice nucleators.

Forty years ago, lichens were identified as extraordinary biological ice nucleators (INs) that enable ice formation at temperatures close to 0°C. By employing INs, lichens thrive in freezing environments that surpass the physiological limits of other vegetation, thus making them the majority of vegetative biomass in northern ecosystems. Aerosolized lichen INs might further impact cloud glaciation and have the potential to alter atmospheric processes in a warming Arctic. Despite the ecological importance and formidable ice nucleation activities, the abundance, diversity, sources, and role of ice nucleation in lichens remain poorly understood. Here, we investigate the ice nucleation capabilities of lichens collected from various ecosystems across Alaska. We find ice-nucleating activity in lichen to be widespread, particularly in the coastal rainforest of Southeast Alaska. Across 29 investigated lichen, all species show ice nucleation temperatures above -15 °C and ~30% initiate freezing at temperatures above -6 °C. Concentration series of lichen ice nucleation assays in combination with statistical analysis reveal that the lichens contain two subpopulations of INs, similar to previous observations in bacteria. However, unlike the bacterial INs, the lichen INs appear as independent subpopulations resistant to freeze-thaw cycles and against temperature treatment. The ubiquity and high stability of the lichen INs suggest that they can impact local atmospheric processes and that ice nucleation activity is an essential trait for their survival in cold environments.