Bulk Freezing Research Articles

Freezing Delay of a Drop Impacting on a Monolayer of Cold Grains.

We investigate a subfreezing droplet impact scenario in a low-humidity environment, where the target is a cold granular monolayer. When the undercooling degree of targets passes a threshold, such a granular layer effectively postpones the bulk freezing time of the droplet in comparison with the impact on the bare substrate underneath. In this case, the retraction of the droplet after impact reduces the contact area with the cold substrate, even though both the grains and the substrate are wettable to the liquid. We find that the significant changes in the dynamic behavior are triggered by freezing the liquid that wets the pores. Owing to the small dimension of the pores, the freezing process is rapid enough to match the dynamics over the droplet dimension. In certain circumstances, the rapid freezing may even stop liquid penetration and shed icing from the surface underneath.

Cold granular targets slow the bulk freezing of an impacting droplet.

When making contact with an undercooled target, a drop freezes. The colder the target is, the more rapid the freezing is supposed to be. In this research, we explore the impact of droplets on cold granular material. As the undercooling degree increases, the bulk freezing of the droplet is delayed by at least an order of magnitude. The postponement of the overall solidification is accompanied by substantial changes in dynamics, including the spreading-retraction process, satellite drop generation, and cratering in the target. The solidification of the wetted pores in the granular target primarily causes these effects. The freezing process over the pore dimension occurs rapidly enough to match the characteristic timescales of impact dynamics at moderate undercooling degrees. As a result, the hydrophilic impact appears "hydrophobic," and the dimension of the solidified droplet shrinks. A monolayer of cold grains on a surface can reproduce these consequences. Our research presents a potential approach to regulate solidified morphology for subfreezing drop impacts. It additionally sheds light on the impact scenario of strong coupling between the dynamics and solidification.

Photothermal Energy‐Storage Capsule with Sustainable Evaporation for Efficient Anti‐/Deicing

The inhibition of ice accumulation on surfaces is of great importance in various practical applications and extensive efforts have been made to address this daunting challenge. Among many others, the promising photothermal anti‐icing surfaces become ineffective under a nonillumination condition. Herein, a photothermal energy‐storage capsule (PESC) by leveraging both the solar‐to‐thermal conversion and energy‐storage capability is proposed for efficient anti‐/deicing. Under illumination, the surface temperature can rise to 55 °C, which endows fast droplet evaporation to prevent the subsequent bulk freezing, and the accumulated ice and frost in a low temperature quickly melts and fully evaporates. Importantly, sustainable droplet evaporation can be achieved without illumination which is attributed to the energy storage property of the PESC. This research provides a satisfactory paradigm for surface design in all‐weather anti‐/deicing applications.

Freeze-concentration of solutes during bulk freezing and its impact on protein stability

Storage of protein therapeutics in a frozen state provides operational flexibility for fill and finish of drug products and extends the shelf life of protein solutions. However, freezing of bulk protein solutions leads to progressive freeze-concentration of solutes which may result in protein instability. A novel method was designed to study the freeze-concentration of solutes in 1 L bottles. Lactate dehydrogenase (LDH) solutions in phosphate buffer, pH 7.0, with or without sucrose were studied and compared with the same solutions without LDH. These solutions were frozen at −30 °C and at different freezing rates. The contents of each frozen bottle were evenly sliced and forty-five representative samples were analyzed for solute concentrations and LDH quality attributes. A homogeneity score was devised to describe the overall homogeneity of the frozen bulk. In general, the solutes (i.e., LDH, phosphate, and sucrose) concentrated towards the center and bottom of the bottles during freezing. The homogeneity score was highly dependent upon the freezing rate with significant retention of LDH activity and tetrameric native structures observed at higher freezing rates. Lastly, multiple linear regression showed the significant impact of the freezing rate, sample location inside the bottle, and presence of sucrose on LDH stability, which provided insights into the stability of other proteins during bulk freezing.

Protein aggregates nucleate ice: the example of apoferritin

Abstract. Biological material has gained increasing attention recently as a source of ice-nucleating particles that may account for cloud glaciation at moderate supercooling. While the ice-nucleation (IN) ability of some bacteria can be related to membrane-bound proteins with epitaxial fit to ice, little is known about the IN-active entities present in biological material in general. To elucidate the potential of proteins and viruses to contribute to the IN activity of biological material, we performed bulk freezing experiments with the newly developed drop freezing assay DRoplet Ice Nuclei Counter Zurich (DRINCZ), which allows the simultaneous cooling of 96 sample aliquots in a chilled ethanol bath. We performed a screening of common proteins, namely the iron storage protein ferritin and its iron-free counterpart apoferritin, the milk protein casein, the egg protein ovalbumin, two hydrophobins, and a yeast ice-binding protein, all of which revealed IN activity with active site densities > 0.1 mg−1 at −10 ∘C. The tobacco mosaic virus, a plant virus based on helically assembled proteins, also proved to be IN active with active site densities increasing from 100 mg−1 at −14 ∘C to 10 000 mg−1 at −20 ∘C. Among the screened proteins, the IN activity of horse spleen ferritin and apoferritin, which form cages of 24 co-assembled protein subunits, proved to be outstanding with active site densities > 10 mg−1 at −5 ∘C. Investigation of the pH dependence and heat resistance of the apoferritin sample confirmed the proteinaceous nature of its IN-active entities but excluded the correctly folded cage monomer as the IN-active species. A dilution series of apoferritin in water revealed two distinct freezing ranges, an upper one from −4 to −11 ∘C and a lower one from −11 to −21 ∘C. Dynamic light scattering measurements related the upper freezing range to ice-nucleating sites residing on aggregates and the lower freezing range to sites located on misfolded cage monomers or oligomers. The sites proved to persist during several freeze–thaw cycles performed with the same sample aliquots. Based on these results, IN activity seems to be a common feature of diverse proteins, irrespective of their function, but arising only rarely, most probably through defective folding or aggregation to structures that are IN active.

Effect of Type I Antifreeze Proteins on the Freezing and Melting Processes of Cryoprotective Solutions Studied by Site-Directed Spin Labeling Technique.

Antifreeze proteins (AFPs) protect organisms living in subzero environments from freezing injury, which render them potential applications for cryopreservation of living cells, organs, and tissues. Cryoprotective agents (CPAs), such as glycerol and propylene glycol, have been used as ingredients to treat cellular tissues and organs to prevent ice crystal’s formation at low temperatures. To assess AFP’s function in CPA solutions, we have the applied site-directed spin labeling technique to a Type I AFP. A two-step process to prevent bulk freezing of the CPA solutions was observed by the cryo-photo microscopy, i.e., (1) thermodynamic freezing point depression by the CPAs; and (2) inhibition to the growth of seed ice crystals by the AFP. Electron paramagnetic resonance (EPR) experiments were also carried out from room temperature to 97 K, and vice versa. The EPR results indicate that the spin labeled AFP bound to ice surfaces, and inhibit the growths of ice through the bulk freezing processes in the CPA solutions. The ice-surface bound AFP in the frozen matrices could also prevent the formation of large ice crystals during the melting processes of the solutions. Our study illustrates that AFPs can play an active role in CPA solutions for cryopreservation applications.

Thermodynamic and structural anomalies of water nanodroplets

Liquid water nanodroplets are important in earth’s climate, and are valuable for studying supercooled water because they resist crystallisation well below the bulk freezing temperature. Bulk liquid water has well-known thermodynamic anomalies, such as a density maximum, and when supercooled is hypothesised to exhibit a liquid–liquid phase transition (LLPT) at elevated pressure. However, it is not known how these bulk anomalies might manifest themselves in nanodroplets. Here we show, using simulations of the TIP4P/2005 water model, that bulk anomalies occur in nanodroplets as small as 360 molecules. We also show that the Laplace pressure inside small droplets reaches 220 MPa at 180 K, conditions close to the LLPT of TIP4P/2005. While the density and pressure inside nanodroplets coincide with bulk values at moderate supercooling, we show that deviations emerge at lower temperature, as well as significant radial density gradients, which arise from and signal the approach to the LLPT.

Leveraging single-pass tangential flow filtration to enable decoupling of upstream and downstream monoclonal antibody processing.

Decoupling upstream and downstream operations in biopharmaceutical production could enable more flexible manufacturing operations and could allow companies to leverage strategic or financial benefits that would be otherwise unattainable. A decoupling process was developed and scaled up utilizing single-pass tangential flow filtration for volume reduction, followed by bulk freezing in single-use bags prior to purification. Single-pass tangential flow filtration can be used to continuously concentrate harvested cell culture fluid, reducing the volume by 15-25× with a step yield of >96%. These concentration factors were reproduced with a second product, indicating that the process could be amenable to platform processes. Experimental data indicate that the product tested was stable for at least one year at -40 or -70°C. The concentration of the harvested cell culture fluid-either with or without a subsequent period of frozen storage-had no impact on the product quality attributes that were tested. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 34:405-411, 2018.

Evaluating the effect of grain size and salts on liquid water content in frozen soils of Antarctica by combining NMR, chemical equilibrium modeling, and scattered diffraction analysis

Recent studies point to the possible existence of liquid water on Mars surface. While many efforts have focused on experimental determination and modeling of liquid water content in inorganic-salt rich soils, additional factors that govern liquid water formation remain largely unexplored. The purpose of this study is to determine main soil properties that will affect unfrozen water content. We analyzed liquid water content and bulk freezing points using high field deuterium NMR measurements and compared the results to the amount of liquid water content at the same temperatures based on salt concentration and composition using an empirical chemical equilibrium model (FREZCHEM). We selected soils with a wide range of salt concentrations and composition collected from the McMurdo Dry Valleys, Antarctica. The comparison indicates that at 50% unfrozen water content the freezing temperatures deviate substantially from water content modeled based on salt composition. In particular, the NMR freezing points are lower than those calculated with FREZCHEM for all low to medium salt content samples. The results indicate that soil properties other than aqueous chemical composition add to liquid water content. Particle size does not necessarily correlate with the liquid water content, revealing that more detailed investigation including surface area and composition may be necessary to describe the dependence of unfrozen water content on soil properties. The study highlights the necessity of experimental measurements of water content due to effects of multiple factors that are difficult to take into account in simulations.

Two-Step Freezing in Alkane Monolayers on Colloidal Silica Nanoparticles: From a Stretched-Liquid to an Interface-Frozen State

The crystallization behavior of an archetypical soft/hard hybrid nanocomposite, that is, an n-octadecane C18/SiO2-nanoparticle composite, was investigated by a combination of differential scanning calorimetry (DSC) and variable-temperature solid-state (13)C nuclear magnetic resonance (VT solid-state (13)C NMR) as a function of silica nanoparticles loading. Two latent heat peaks prior to bulk freezing, observed for composites with high silica loading, indicate that a sizable fraction of C18 molecules involve two phase transitions unknown from the bulk C18. Combined with the NMR measurements as well as experiments on alkanes and alkanols at planar amorphous silica surfaces reported in the literature, this phase behavior can be attributed to a transition toward a 2D liquid-like monolayer and subsequently a disorder-to-order transition upon cooling. The second transition results in the formation of a interface-frozen monolayer of alkane molecules with their molecular long axis parallel to the nanoparticles' surface normal. Upon heating, the inverse phase sequence was observed, however, with a sizable thermal hysteresis in accord with the characteristics of the first-order phase transition. A thermodynamic model considering a balance of interfacial bonding, chain stretching elasticity, and entropic effects quantitatively accounts for the observed behavior. Complementary synchrotron-based wide-angle X-ray diffraction (WAXD) experiments allow us to document the strong influence of this peculiar interfacial freezing behavior on the surrounding alkane melts and in particular the nucleation of a rotator phase absent in the bulk C18.

Fluctuations and local ice structure in model supercooled water.

Large-scale simulations (up to 32,000 molecules) are used to analyze local structures and fluctuations for the TIP4P/2005 and TIP5P water models, under deeply supercooled conditions, near previously proposed liquid-liquid critical points. Bulk freezing does not occur in our simulations, but correlations between molecules with local ice-like structure (ice-like molecules) are strong and long ranged (∼4 nm), exceeding the shortest dimension of smaller simulation cells at the lowest temperatures considered. Correlations between ice-like molecules decay slowly at low temperature, on the order of a hundred nanoseconds. Local ice-like structure is strongly correlated with highly tetrahedral liquid structure at all times, both structures contribute to density fluctuations, and to the associated anomalous scattering. For the TIP4P/2005 and TIP5P models, we show that the apparent spontaneous liquid-liquid phase separations, recently reported [T. Yagasaki, M. Matsumoto, and H. Tanaka, Phys. Rev. E 89, 020301 (2014)] for small rectangular simulation cells below the proposed critical points, exhibit strong system size dependence and do not occur at all in the largest systems we consider. Furthermore, in the smaller rectangular systems where layers of different densities do occur, we find that the appearance of a region of low density is always accompanied simultaneously by an excess of local ice density, with no separation in time. Our results suggest that the density differences observed in direct simulations for the two models considered here are likely due to long-range correlations between ice-like molecules and do not provide strong evidence of liquid-liquid phase separation.

Droplet freezing and ice adhesion strength measurement on super-cooled hydrophobic surfaces

ABSTRACTThis report investigates the freezing of water droplets on hydrophobic surfaces and reports a means to quantitatively measure the ice-adhesion strength at micro-patterned hydrophobic surfaces. Water droplets were placed on a super-cooled surface where they froze following the heterogeneous nucleation phase-transition. The freezing occurred with two distinct transitions: (a) an initial snapping transition freezing of the external shell of the droplet, and (b) a subsequent bulk freezing of the droplet with a characteristic formation of peaked apex protruding upwardly. To measure the ice-adhesion strength, frozen droplets were sheared from the surface using a Universal Materials Tester (UMT) measuring the resulting knock-off forces. Ice formation and adhesion was investigated on three variations of hydrophobic polydimethylsiloxane (PDMS) surfaces: regularly patterned with high and low surface densities of micro-pillar arrays and non-patterned flat surfaces. Patterning the surfaces was found to accelerate freezing transitions but decrease the measured ice-adhesion strength in correlation with a reduction of total interfacial contact area. However, a more concentrated local stress was observed for the less dense surface structures, indicating a potential area of concern for more fragile systems.

Structures of simple liquids in contact with nanosculptured surfaces.

We present a density functional study of Lennard-Jones liquids in contact with a nanocorrugated wall. The corresponding substrate potential is taken to exhibit a repulsive hard core and a Van der Waals attraction. The corrugation is modeled by a periodic array of square nanopits. We have used the modified Rosenfeld density functional in order to study the interfacial structure of these liquids which with respect to their thermodynamic bulk state are considered to be deep inside their liquid phase. We find that already considerably below the packing fraction of bulk freezing of these liquids, inside the nanopits a three-dimensional-like density localization sets in. If the sizes of the pits are commensurate with the packing requirements, we observe high-density spots separated from each other in all spatial directions by liquid of comparatively very low density. The number, shape, size, and density of these high-density spots depend sensitively on the depth and width of the pits. Outside the pits, only layering is observed; above the pit openings these layers are distorted with the distortion reaching up to a few molecular diameters. We discuss quantitatively how this density localization is affected by the geometrical features of the pits and how it evolves upon increasing the bulk packing fraction. Our results are transferable to colloidal systems and pit dimensions corresponding to several diameters of the colloidal particles. For such systems the predicted unfolding of these structural changes can be studied experimentally on much larger length scales and more directly (e.g., optically) than for molecular fluids which typically call for sophisticated x-ray scattering.

PH-responsive poly(N,N-dimethylaminoethyl methacrylate-co-2-acrylamido-2-methyl-propanosulfonic acid) cryogels: swelling, elasticity and diffusive properties

Tough and fast responsive ionic P(DMAEMA-co-AMPS) cryogels were prepared below the bulk freezing temperature of water.

Surfactant-induced phases in water-supported alkane monolayers: I. Thermodynamics.

Alkanes longer than n = 6 carbons do not spread on the water surface, but condense in a macroscopic lens. However, adding trimethylammonium-based surfactants, C(m)TAB, in submillimolar concentrations causes the alkanes to spread and form a single Langmuir-Gibbs (LG) monolayer of mixed alkanes and surfactant tails, which coexists with the alkane lenses. Upon cooling, this LG film surface-freezes at a temperature T(s) above the bulk freezing temperature T(b). The thermodynamics of surface freezing (SF) of these LG films is studied by surface tension measurements for a range of alkanes (n = 12-21) and surfactant alkyl lengths (m = 14, 16, 18), at several concentrations c. The surface freezing range T(s)-T(b) observed is up to 25 °C, an order of magnitude larger than the temperature range of SF monolayers on the surface of pure alkane melts. The measured (n,T) surface phase diagram is accounted for well by a model based on mixtures' theory, which includes an interchange energy term ω. ω is found to be negative, implying attraction between unlike species, rather than the repulsion found for SF of binary alkane mixtures. Thus, the surfactant/alkane mixing is a necessary condition for the occurrence of SF in these LG films. The X-ray derived structure of the films is presented in an accompanying paper.

Deeply-cooled water under strong confinement: neutron scattering investigations and the liquid–liquid critical point hypothesis

We present an overview of recent experimental investigations into the properties of strongly-confined water below the bulk freezing temperature. Under strong confinement, the crystallization of water is completely suppressed and the behavior of the confined liquid state can be measured at temperatures and pressures that are inaccessible to the bulk liquid. We focus on two phenomena that have recently been discovered in strongly confined water: the density minimum and the fragile-to-strong dynamic crossover. All experimental results seem to indicate that confined water undergoes a unique kind of transition below the bulk homogeneous nucleation limit. Much of the recent work on deeply-cooled water under strong confinement has been motivated by the liquid-liquid critical point (LLCP) hypothesis. We discuss this hypothesis in the context of the various experimental findings.

Phase Transition of Water Confined in Saponites Using Positron Annihilation Spectroscopy

The temperature dependent Positron lifetime and Doppler broadening spectroscopy have been carried out to study the phase transition of water confined in interlamellar spaces of saponite clay in the temperature range 300K-200K. The change in slope/discontinuity in S-parameter and Ps lifetime as a function of temperature is an indication of phase transition. Two phase transition temperatures viz. above and below the bulk freezing temperature have been observed for water confined in saponite clay. This indicates the presence of two regimes of water confined in interlamellar spaces. The freezing-melting cycle is also marked by significant hysteresis.

Ice nucleation efficiency of clay minerals in the immersion mode

Abstract. Emulsion and bulk freezing experiments were performed to investigate immersion ice nucleation on clay minerals in pure water, using various kaolinites, montmorillonites, illites as well as natural dust from the Hoggar Mountains in the Saharan region. Differential scanning calorimeter measurements were performed on three different kaolinites (KGa-1b, KGa-2 and K-SA), two illites (Illite NX and Illite SE) and four natural and acid-treated montmorillonites (SWy-2, STx-1b, KSF and K-10). The emulsion experiments provide information on the average freezing behaviour characterized by the average nucleation sites. These experiments revealed one to sometimes two distinct heterogeneous freezing peaks, which suggest the presence of a low number of qualitatively distinct average nucleation site classes. We refer to the peak at the lowest temperature as "standard peak" and to the one occurring in only some clay mineral types at higher temperatures as "special peak". Conversely, freezing in bulk samples is not initiated by the average nucleation sites, but by a very low number of "best sites". The kaolinites and montmorillonites showed quite narrow standard peaks with onset temperatures 238 K

Conditioning of wastewater sludge using freezing and thawing: Role of curing

Freeze/thaw (F/T) treatment is an efficient pre-treatment process for biological sludges. When bulk sludge was frozen, tiny unfrozen regimes in the ice matrix were continuously dehydrated by surrounding ice fronts, termed as the “curing stage”. This work demonstrated that the F/T treatment could not only enhance sludge dewaterability, but also solubilize organic matters from sludge matrix. Most enhancement of sludge dewaterability was achieved during bulk freezing stage, with the waste activated sludge more readily dewatered than the mixed sludges after treatment. Conversely, the freezing stage released only limited quantities of organic matters to liquid. Conversely, the curing contributed mostly on chemical oxygen demand (COD) solubilization and NH 3–N release. The crystallization of intra-aggregate moisture was claimed to damage cell membranes so to release intracellular substances to surroundings. The F/T treatment with sufficient curing is advised to effectively condition biological sludge as the feedstock of the following anaerobic digestion process.

Freezing behavior of argon layers confined in mesopores

Adsorbed layers of argon in mesoporous Vycor glass exhibit a peculiar phase behavior. We have studied their liquid-solid transition in pores with a mean pore diameter of 8 nm via ultrasonic measurements. An effective medium analysis reveals that during isothermal filling at low temperatures ($T<{T}_{\mathrm{fr},\mathrm{bulk}}$) frozen layers form on top of liquidlike surface layers. These frozen layers are bulklike (i.e., ${G}_{\mathrm{Ar},\mathrm{SL}}\ensuremath{\approx}{G}_{\mathrm{Ar},\mathrm{bulk}}$ holds for their intrinsic shear modulus). We detect that both the first and the second layer undergo a continuous phase transition in a broad temperature range of at least 40 K. A complete freezing is only achieved at very low temperatures of approximately 20 K (i.e., far below the bulk freezing temperature). Whereas those two adsorbed layers remain stable during cooling, the third one becomes unstable around 66 K, rearranges, and solid capillary condensate is formed (delayering transition).