Ice Growth Research Articles

Retrievals of ice microphysical properties using dual-wavelength polarimetric radar observations during stratiform precipitation events

Abstract. Ice growth processes within clouds affect the type and amount of precipitation. Hence, the importance of an accurate representation of ice microphysics in numerical weather and numerical climate models has been confirmed by several studies. To better constrain ice processes in models, we need to study ice cloud regions before and during monitored precipitation events. For this purpose, two radar instruments facing each other were used to collect complementary measurements. The C-band POLDIRAD weather radar from the German Aerospace Center (DLR) in Oberpfaffenhofen and the Ka-band MIRA-35 cloud radar from the Ludwig Maximilians University of Munich (LMU) were used to monitor stratiform precipitation in the vertical cross-sectional area between the two instruments. The logarithmic difference of radar reflectivities at two different wavelengths (54.5 and 8.5 mm), known as the dual-wavelength ratio, was exploited to provide information about the size of the detected ice hydrometeors, taking advantage of the different scattering behavior in the Rayleigh and Mie regime. Along with the dual-wavelength ratio, differential radar reflectivity measurements from POLDIRAD provided information about the apparent shape of the detected ice hydrometeors. Scattering simulations using the T-matrix method were performed for oblate and horizontally aligned prolate ice spheroids of varying shape and size using a realistic particle size distribution and a well-established mass–size relationship. The combination of dual-wavelength ratio, radar reflectivity, and differential radar reflectivity measurements as well as scattering simulations was used for the development of a novel retrieval for ice cloud microphysics. The development of the retrieval scheme also comprised a method to estimate the hydrometeor attenuation in both radar bands. To demonstrate this approach, a feasibility study was conducted on three stratiform snow events which were monitored over Munich in January 2019. The ice retrieval can provide ice particle shape, size, and mass information which is in line with differential radar reflectivity, dual-wavelength ratio, and radar reflectivity observations, respectively, when the ice spheroids are assumed to be oblates and to follow the mass–size relation of aggregates. When combining two spatially separated radars to retrieve ice microphysics, the beam width mismatch can locally lead to significant uncertainties. However, the calibration uncertainty is found to cause the largest bias for the averaged retrieved size and mass. Moreover, the shape assumption is found to be equally important to the calibration uncertainty for the retrieved size, while it is less important than the calibration uncertainty for the retrieval of ice mass. A further finding is the importance of the differential radar reflectivity for the particle size retrieval directly above the MIRA-35 cloud radar. Especially for that observation geometry, the simultaneous slantwise observation from the polarimetric weather radar POLDIRAD can reduce ambiguities in retrieval of the ice particle size by constraining the ice particle shape.

X-ray microtomography of ice crystal formation and growth in a sponge cake during its freezing and storage

X-ray tomography has been used to characterize microstructural changes taking place into sponge cake upon freezing and subsequent storage at fluctuating temperatures. The CellDyM cooling cell, initially developed for snow, was used to subject a sponge cake sample to freezing and thermal cycling directly inside the X-ray tomograph. 3D images of the same sample have been scanned at different times during 6 days. An original image processing based on Digital Volumetric Correlation (DVC) has been implemented in order to segment the images and then to quantify porosity changes and ice crystal formation and growth. Overall, the obtained results have shown that (i) all the ice crystals are located at the pore surface and no crystal was found inside the sponge cake crumb matrix and (ii) during the thermal cycling, the size of the ice crystals linearly increases while the number of ice crystals tends towards a plateau. These tendencies can be related to a recrystallization phenomenon occurring due to thermal cycling. More generally, the proposed methodology could be applied to other frozen porous products during freezing and frozen storage. • First study of ice crystal formation and growth in a sponge cake during freezing and storage. • In-situ freezing and thermal cycling were performed inside a laboratory X-ray μCT apparatus. • Dynamic X-ray μCT and Digital Volumetric Correlation were implemented to quantify ice crystals. • Ice crystals were located at the pore surface and their size increased by recrystallization due to the thermal cycling.

Tuning Ice Nucleation by Mussel-Adhesive Inspired Polyelectrolytes: The Role of Hydrogen Bonding

Tuning Ice Nucleation by Mussel-Adhesive Inspired Polyelectrolytes: The Role of Hydrogen Bonding

Probability forecasts of ice accretion on wind turbines derived from multiphysics and neighbourhood ensembles

AbstractThis study explores the potential of a multiphysics regional ensemble prediction system to improve forecasts of wind turbine icing, examining several error‐representation schemes to capture the forecasting uncertainties of the icing process. An 11‐member multiphysics ensemble based on the Weather Research and Forecasting (WRF) model is run for two winter periods over Europe. Regional verification of surface variables shows that parametrization diversity makes the multiphysics ensemble less underdispersive compared with the European Centre for Medium‐Range Weather Forecasts (ECMWF) global ensemble, without deteriorating the overall forecast accuracy significantly, in particular at forecast ranges below 36 hr. Probability forecasts of active ice growth in the day‐ahead time range (12–36 hr) are derived for two wind farms on hilly terrain in Central Europe and their skill is assessed in terms of relative operating characteristics, reliability, and potential economic value (PEV). Probability forecasts enhance the maximum PEV significantly, but the improvement of the multiphysics ensemble seems modest compared with a simple neighbourhood ensemble approach. Icing forecasts are affected by a considerable degree of overconfidence, meaning that forecast probabilities cannot be used at face value, but require calibration for users to draw benefit from them. The multiphysics ensemble fares slightly better in this regard; however, results point to persistent ensemble underdispersiveness and yet underrepresented forecast uncertainty. Overall, findings show that a large portion of the gain in skill through the use of probabilistic icing forecasts is obtained with a computationally cheap neighbourhood method, a technique easily accessible to forecast users without complex ensemble prediction systems.

Global existence and large‐time behavior of a parabolic phase‐field model with Neumann boundary conditions

In this paper, we continue to study an initial boundary value problems to a model describing the evolution in time of diffusive phase interfaces in sea ice growth. In a previous paper, the global existence and the large‐time behavior of weak solutions in one space was studied under Dirichlet boundary conditions. Here, we show that the global existence of weak solutions and the large‐time behavior are also studied under Neumann boundary condition. In this paper, we study in space dimension lower than or equal to 3.

Annual cycle observations of aerosols capable of ice formation in central Arctic clouds

The Arctic is warming faster than anywhere else on Earth, prompting glacial melt, permafrost thaw, and sea ice decline. These severe consequences induce feedbacks that contribute to amplified warming, affecting weather and climate globally. Aerosols and clouds play a critical role in regulating radiation reaching the Arctic surface. However, the magnitude of their effects is not adequately quantified, especially in the central Arctic where they impact the energy balance over the sea ice. Specifically, aerosols called ice nucleating particles (INPs) remain understudied yet are necessary for cloud ice production and subsequent changes in cloud lifetime, radiative effects, and precipitation. Here, we report observations of INPs in the central Arctic over a full year, spanning the entire sea ice growth and decline cycle. Further, these observations are size-resolved, affording valuable information on INP sources. Our results reveal a strong seasonality of INPs, with lower concentrations in the winter and spring controlled by transport from lower latitudes, to enhanced concentrations of INPs during the summer melt, likely from marine biological production in local open waters. This comprehensive characterization of INPs will ultimately help inform cloud parameterizations in models of all scales.

Freezing‐induced stiffness and strength anisotropy in freezing clayey soil: Theory, numerical modeling, and experimental validation

AbstractThis paper presents a combined experimental‐modeling effort to interpret the coupled thermo‐hydro‐mechanical behaviors of the freezing soil, where an unconfined, fully saturated clay is frozen due to a temperature gradient. By leveraging the rich experimental data from the microCT images and the measurements taken during the freezing process, we examine not only how the growth of ice induces volumetric changes of the soil in the fully saturated specimen but also how the presence and propagation of the freezing fringe front may evolve the anisotropy of the effective media of the soil–ice mixture that cannot be otherwise captured phenomenologically in the isotropic saturation‐dependent critical state models for plasticity. The resultant model is not only helpful for providing a qualitative description of how freezing affects the volumetric responses of the clayey material, but also provide a mean to generate more precise predictions for the heaving due to the freezing of the ground.

Preparation of Poly(vinyl Alcohol) Microparticles for Freeze Protection of Sensitive Fruit Crops.

Poly(vinyl alcohol) (PVA) displays ice recrystallization inhibition (IRI) properties as many antifreeze proteins found in cold tolerant organisms. The molecular architecture and composition (molecular weight and distribution of pendant OH and acetate groups) have been studied to improve the antifreezing properties of PVA, suggesting that the molecular architecture of PVA plays an important role in IRI activity. The present work deals with the preparation of PVA microparticles using an alkaline treatment. The effect of PVA molecular weight on the morphology and antifreezeing properties of PVA microparticles was investigated. The antifreezeing property of PVA microparticles on the susceptibility of flower bud tissues to freeze damage was also evaluated. The alkaline treatment of an aqueous PVA solution produced stable polymer chain aggregates with spherical shapes. The average size of the PVA microparticles increased significantly with the increasing molecular weight of the PVA macromolecule precursor. The PVA microparticles inhibited the growth of ice crystals and blocked ice growth at concentrations as low as 0.01 % w/v. The effect of impeding ice crystal growth by preventing the joining of adjacent ice crystals is attributed to the larger size of the PVA particles adsorbed on the ice surface compared to the aggregated PVA macromolecules in saline solution. The thermal hysteresis activity of PVA macromolecules and microparticles was not detected by differential scanning calorimetry analysis. The PVA microparticles reduced the incidence of freeze injuries in flower bud tissues by 55% and their application, considering the low toxicity of PVA, has a high potential for freeze protection in fruit crops.

Inhibition Effect of Ti3C2Tx MXene on Ice Crystals Combined with Laser-Mediated Heating Facilitates High-Performance Cryopreservation

The phenomena of ice formation and growth are of great importance for climate science, regenerative medicine, cryobiology, and food science. Hence, how to control ice formation and growth remains a challenge in these fields and attracts great interest from widespread researchers. Herein, the ice regulation ability of the two-dimensional MXene Ti3C2Tx in both the cooling and thawing processes is explored. Molecularly speaking, the ice growth inhibition mechanism of Ti3C2Tx MXene is ascribed to the formation of hydrogen bonds between functional groups of -O-, -OH, and -F distributed on the surface of Ti3C2Tx and ice/water molecules, which was elucidated by the molecular dynamics simulation method. In the cooling process, Ti3C2Tx can decrease the supercooling degree and inhibit the sharp edge morphology of ice crystals. Moreover, taking advantage of the outstanding photothermal conversion property of Ti3C2Tx, rapid ice melting can be achieved, thus reducing the phenomena of devitrification and ice recrystallization. Based on the ice restriction performance of Ti3C2Tx mentioned above, Ti3C2Tx is applied for cryopreservation of stem-cell-laden hydrogel constructs. The results show that Ti3C2Tx can reduce cryodamage to stem cells induced by ice injury in both the cooling and thawing processes and finally increase the cell viability from 38.4% to 80.9%. In addition, Ti3C2Tx also shows synergetic antibacterial activity under laser irradiation, thus realizing sterile cryopreservation of stem cells. Overall, this work explores the ice inhibition performance of Ti3C2Tx, elucidates the physical mechanism, and further achieves application of Ti3C2Tx in the field of cell cryopreservation.

In situ measurements of tetrahydrofuran hydrate and ice growth in the presence of copper surface with fringe projection: Growth kinetics and interfacial morphology

In recent years, study on the gas hydrate in the presence of solid surfaces has attracted much interest due to the importance of hydrate deposition on the pipe wall and shutdown of these pipelines. The present work examined the in situ and online monitoring of tetrahydrofuran (THF) hydrate and ice growth on a solid surface using a high-resolution interferometry method. Michelson interferometer was applied to directly measure the thickness of ice and hydrate films using the fringe-shifting technique. Furthermore, the change in the interface morphology during hydrate growth was developed as a function of distortion in the fringe intensity distribution in terms of universal scaling laws. Universal exponent β for the growing interface of THF hydrate was experimentally studied and reported for the first time. Dynamic exponent β was derived as 0.2042, which is in general agreement with other experimental studies of local growth processes. Further, the value of the growth exponent β for the ice growth was obtained by 0.2971, which is close to the value predicted by ballistic deposition and Eden models. Based on the measured dynamic exponents, we suggest that THF hydrate and ice growth can lead to self-similar morphologies and be classified according to their dynamical behavior.

In-situ comparison of interface instability of basal and edge planes during unidirectional growth of sea ice

The evolutions of water/ice interface with distinct ice orientations are one of the central problems in sea ice growth. Some misunderstandings prevailed in previous hypothesis on morphological evolution of sea ice, which need the validation with carefully designed experiments. Up to now, there is no in-situ comparison of unidirectional freezing behavior between distinct ice orientations, which makes the previous hypothesis on sea ice growth skeptical about its physical basis. The aim of this paper is to provide an in-situ comparison of unidirectional growth behavior of lamellar sea ice between basal and edge planes. Our experiment is realized by a delicate design of parallel freezing samples with two specified ice orientations in a modeled sea water under an imposed thermal gradient. The planar instability as well as the unidirectional cellular/dendritic growth patterns of water/ice interfaces of basal and edge plane ice are compared. It is found that the instability grows faster for edge plane ice, which is addressed by an incubation time coupled with the surface tension anisotropy. In addition, two types of tilted growth patterns of sea ice after planar instability are observed simultaneously, which are suggested to stem from distinct physical origins and provide a new insight into the tilted growth of cellular/dendritic ice. Collectively, these experimental results are suggested to promote our understanding of morphological evolution of unidirectional growth of sea ice, as well as its diverse relevance to many other areas involving ice growth.

Tilt grain boundary energy in 〈0001〉/φ bicrystals of pure ice

This work presents measurements of the relative energy ( γgb/ γs) of the tilt grain boundary (GB) in pure ice bicrystals with crystalline misorientation 〈0001〉/ φ. The GBs had different inclinations and were annealed at −5 °C and −18 °C. A GB structure model called the facet model (FM) was applied. The FM assumes that the GB is composed of facets. The facets are oriented with the principal faces of the cell primitive of the coincident site lattice (CSL). The CSL is associated with the bicrystalline misorientation. In general, ( γgb/ γs) varies by more than one order of magnitude between temperatures −5 °C ( γgb/ γs ~ 0.03) and −18 °C ( γgb/ γs ~ 0.35), so GB structural changes are very noticeable with temperature. The GB energy does not depend on the inclination at temperatures near 0 °C, while the dependence on inclination presents a slight significance at −18 °C. Finally, it was observed that the GB relative energy ( γgb/ γs) for bicrystalline 〈0001〉/ φ samples is lower than the relative energy at other crystalline misorientations. These experimental data are unique and could explain the slow GB migration in 〈0001〉/ φ bicrystals and they could help to understand grain growth in polar ice where the most frequent crystalline misorientation is 〈0001〉/ φ.

Submolecular Insights into Interfacial Water by Hydrogen-Sensitive Scanning Probe Microscopy.

ConspectusWater-solid interfaces have attracted extensive attention because of their crucial roles in a wide range of chemical and physical processes, such as ice nucleation and growth, dissolution, corrosion, heterogeneous catalysis, and electrochemistry. To understand these processes, enormous efforts have been made to obtain a molecular-level understanding of the structure and dynamics of water on various solid surfaces. By the use of scanning probe microscopy (SPM), many remarkable structures of H-bonding networks have been directly visualized, significantly advancing our understanding of the delicate competition between water-water and water-solid interactions. Moreover, the detailed dynamics of water molecules, such as diffusion, clustering, dissociation, and intermolecular and intramolecular proton transfer, have been investigated in a well-controlled manner by tip manipulation. However, resolving the submolecular structure of surface water has remained a great challenge for a long time because of the small size and light mass of protons. Discerning the position of hydrogen in water is not only crucial for the accurate determination of the structure of H-bonding networks but also indispensable in probing the proton transfer dynamics and the quantum nature of protons.In this Account, we focus on the recent advances in the H-sensitive SPM technique and its applications in probing the structures, dynamics, and nuclear quantum effects (NQEs) of surface water and ion hydrates at the submolecular level. First, we introduce the development of high-resolution scanning tunneling microscopy/spectroscopy (STM/S) and qPlus-based atomic force microscopy (qPlus-AFM), which allow access to the degrees of freedom of protons in both real and energy space. qPlus-AFM even allows imaging of interfacial water in a weakly perturbative manner by measuring the high-order electrostatic force between the CO-terminated tip and the polar water molecule, which enables the subtle difference of OH directionality to be discerned. Next we showcase the applications of H-sensitive STM/AFM in addressing several key issues related to water-solid interfaces. The surface wetting behavior and the H-bonding structure of low-dimensional ice on various hydrophilic and hydrophobic solid surfaces are characterized at the atomic scale. Then we discuss the quantitative assessment of NQEs of surface water, including proton tunneling and quantum delocalization. Moreover, the weakly perturbative and H-sensitive SPM technique can be also extended to investigations of water-ion interactions on solid surfaces, revealing the effect of hydration structure on the interfacial ion transport. Finally, we provide an outlook on the further directions and challenges for SPM studies of water-solid interfaces.

Multi‐phase‐field microporomechanics model for simulating ice‐lens growth in frozen soil

AbstractThis article presents a multi‐phase‐field poromechanics model that simulates the growth and thaw of ice lenses and the resultant frozen heave and thaw settlement in multi‐constituent frozen soils. The growth of segregated ice inside the freezing‐induced fracture is implicitly represented by the evolution of two‐phase fields that indicate the locations of segregated ice and the damaged zone, respectively. The evolution of two‐phase fields is induced by their own driving forces that capture the physical mechanisms of ice and crack growths, respectively, while the phase‐field governing equations are coupled with the balance laws such that the coupling among heat transfer, solid deformation, fluid diffusion, crack growth, and phase transition can be replicated numerically. Unlike phenomenological approaches that indirectly capture the freezing influence on the shear strength, the multiphase‐field model introduces an immersed approach where both the homogeneous freezing and the ice‐lens growth are distinctively captured by the freezing characteristic function and the driving force accordingly. Verification and validation examples are provided to demonstrate the capacities of the proposed models.

Design of Capacitance and Impedance Dual-Parameters Planar Electrode Sensor for Thin Ice Detection of Aircraft Wings

An ice types recognition and ice thickness detection system was designed based on capacitance and impedance double parameters. By studying the influence of electrode structure on sensor performance based on finite element simulation, the finger electrode was selected with better performance, and a planar electrode sensor was designed suitable for wing thin ice detection. After the thin ice (2.5 mm) making experiment, the capacitance and impedance spectra of three ice types (glaze ice, rime ice and mixed ice) were obtained. Among them, capacitance can reflect the growth of ice well, and the impedance spectra of different ice types are significantly different. Therefore, a capacitance-based regression model and an impedance-based classification model were built. The results of regression model show that about 90% of the calculation error of thin ice thickness is concentrated in the range of [−0.2 mm, 0.2 mm]. Finally, a field test was conducted in the ice wind tunnel to preliminarily determine the system effectiveness.

Numerical analysis of blade icing influence on the dynamic response of an integrated offshore wind turbine

When a wind turbine is working in a cold and humid environment, icing may occur which lead to its performance reduction or even blades fracture. In this paper, a CFD-WTIA (Wind Turbine Integrated Analysis) coupled method is established to analyze the blade icing process and its influence on the overall dynamic performance of an integrated jacket-support offshore wind turbine. Firstly, motions of the blades are calculated by the WTIA method and used as input into CFD. Then, dispersed multi-phase model and melting-solidification model are used to simulate the icing growth phenomenon of three-dimensional blades. The k-ε turbulence model is used to calculate the aerodynamic performance before and after icing. Finally, the aerodynamic results after blade icing are returned to WTIA for integrated dynamic response acquisition. At the same time, the dynamic response of the wind turbine under the combined influence of ice and sea ice is analyzed. Results show that the blade ice-accretion increases linearly along the blade span-wise direction and is mainly concentrated on the leading edge of the blade. Lift and drag coefficients are seen deceased and increased respectively after icing. Power production, generator torque, rotor speed, as well as blade vibration are quantitatively studied. The methodology and findings of this paper can provide a good reference for the safety performance evaluation of an icing offshore wind turbine.

The importance of Canadian Arctic Archipelago gateways for glacial expansion in Scandinavia

The last glacial cycle began around 116,000 years before present during a period with low incoming solar radiation in Northern Hemisphere summer. Following the glacial inception in North America, the marine sediment record depicts a weakening of the high-latitude ocean overturning circulation and a multi-millennial eastward progression of glaciation across the North Atlantic basin. Modelling studies have shown that reduced solar radiation can initiate inception in North America and Siberia; however, the proximity to the temperate North Atlantic typically precludes ice growth in Scandinavia. Using a coupled Earth-system–ice-sheet model, we show that ice forming in North America may help facilitate glacial expansion in Scandinavia. As large coherent ice masses form and start filling the ocean gateways in the Canadian Archipelago, the transport of comparatively fresh North Pacific and Arctic water through the archipelago is diverted east of Greenland, resulting in a freshening of North Atlantic deep convection regions, sea-ice expansion and a substantial cooling that is sufficient to trigger glacial inception in Scandinavia. This mechanism may also help explain the Younger Dryas cold reversal and the rapid regrowth of the Scandinavian Ice Sheet following several warm events in the last glacial period.

Diagnosing Discrepancies between Observations and Models of Surface Energy Fluxes in a Midlatitude Lake

Abstract The physical processes of heat exchange between lakes and the surrounding atmosphere are important in simulating and predicting terrestrial surface energy balance. Latent and sensible heat fluxes are the dominant physical process controlling ice growth and decay on the lake surface, as well as having influence on regional climate. While one-dimensional lake models have been used in simulating environmental changes in ice dynamics and water temperature, understanding the seasonal to daily cycles of lake surface energy balance and its relationship to lake thermal properties, atmospheric conditions, and how those are represented in models is still an open area of research. We evaluated a pair of one-dimensional lake models, Freshwater Lake (FLake) and the General Lake Model (GLM), to compare modeled latent and sensible heat fluxes against observed data collected by an eddy covariance tower during a 1-yr period in 2017, using Lake Mendota in Madison, Wisconsin, as our study site. We hypothesized transitional periods of ice cover as a leading source of model uncertainty, and we instead found that the models failed to simulate accurate values for large positive heat fluxes that occurred from late August into late December. Our results ultimately showed that one-dimensional models are effective in simulating sensible heat fluxes but are considerably less sensitive to latent heat fluxes than the observed relationships of latent heat flux to environmental drivers. These results can be used to focus future improvement of these lake models especially if they are to be used for surface boundary conditions in regional numerical weather models. Significance Statement While lakes consist of a small amount of Earth’s surface, they have a large impact on local climate and weather. A large amount of energy is stored in lakes during the spring and summer, and then removed from lakes before winter. The effect is particularly noticeable in high latitudes, when the seasonal temperature difference is larger. Modeling this lake energy exchange is important for weather models and measuring this energy exchange is challenging. Here we compare modeled and observed energy exchange, and we show there are large amounts of energy exchange happening in the fall, which models struggle to capture well. During periods of partial ice coverage in early winter, lake behavior can change rapidly.

The Spruce Budworm Genome: Reconstructing the Evolutionary History of Antifreeze Proteins.

Insects have developed various adaptations to survive harsh winter conditions. Among freeze-intolerant species, some produce “antifreeze proteins” (AFPs) that bind to nascent ice crystals and inhibit further ice growth. Such is the case of the spruce budworm, Choristoneura fumiferana (Lepidoptera: Tortricidae), a destructive North American conifer pest that can withstand temperatures below −30°C. Despite the potential importance of AFPs in the adaptive diversification of Choristoneura, genomic tools to explore their origins have until now been limited. Here, we present a chromosome-scale genome assembly for C. fumiferana, which we used to conduct comparative genomic analyses aimed at reconstructing the evolutionary history of tortricid AFPs. The budworm genome features 16 genes homologous to previously reported C. fumiferana AFPs (CfAFPs), 15 of which map to a single region on chromosome 18. Fourteen of these were also detected in five congeneric species, indicating Choristoneura AFP diversification occurred before the speciation event that led to C. fumiferana. Although budworm AFPs were previously considered unique to the genus Choristoneura, a search for homologs targeting recently sequenced tortricid genomes identified seven CfAFP-like genes in the distantly related Notocelia uddmanniana. High structural similarity between Notocelia and Choristoneura AFPs suggests a common origin, despite the absence of homologs in three related tortricids. Interestingly, one Notocelia AFP formed the C-terminus of a “zonadhesin-like” protein, possibly representing the ancestral condition from which tortricid AFPs evolved. Future work should clarify the evolutionary path of AFPs between Notocelia and Choristoneura and assess the role of the “zonadhesin-like” protein as precursor of tortricid AFPs.

A Stiff, Tough, and Thermally Insulating Air- and Ice-Templated Plant-Based Foam.

By forming and directionally freezing an aqueous foam containing cellulose nanofibrils, methylcellulose, and tannic acid, we produced a stiff and tough anisotropic solid foam with low radial thermal conductivity. Along the ice-templating direction, the foam was as stiff as nanocellulose–clay composites, despite being primarily methylcellulose by mass. The foam was also stiff perpendicular to the direction of ice growth, while maintaining λr < 25 mW m–1 K–1 for a relative humidity (RH) up to 65% and <30 mW m–1 K–1 at 80% RH. This work introduces the tandem use of two practical techniques, foam formation and directional freezing, to generate a low-density anisotropic material, and this strategy could be applied to other aqueous systems where foam formation is possible.