Freezing Temperature Of Water Research Articles

Redox Flow Batteries: Electrolyte Chemistries Unlock the Thermodynamic Limits.

Redox flow batteries (RFBs) represent a promising approach to enabling the widespread integration of intermittent renewable energy. Rapid developments in RFB materials and electrolyte chemistries are needed to meet the cost and performance targets. In this review, special emphasis is given to the recent advances how electrolyte design could circumvent the main thermodynamic restrictions of aqueous electrolytes. The recent success of aqueous electrolyte chemistries has been demonstrated by extending the electrochemical stability window of water beyond the thermodynamic limit, the operating temperature window beyond the thermodynamic freezing temperature of water and crystallization of redox-active materials, and the aqueous solubility beyond the thermodynamic solubility limit. They would open new avenues towards enhanced energy storage and all-climate adaptability. Depending on the constituent, concentration and condition of electrolytes, the performance gain has been correlated to the specific solvation environment, interactions among species and ion association at a molecular level.

A Thermodynamic Formulation of Water Potential in Soil

AbstractIn the mid‐20th century, harnessing of thermodynamics in describing water movement in soil, viz the concept of water potential, marks the emergence of modern soil physics, unsaturated soil mechanics, and vadose zone hydrology. Yet to date, a seamless linkage between thermodynamics and water potential is still missing, leading to several long‐lasting dilemmas regarding soil properties, for example, abnormal soil water density, peculiar film water viscosity and relative permittivity, pore water pressure, and water freezing temperature depression. Here, a thermodynamic framework is established by synthesizing recent advancements in soil‐water interaction. The classical thermodynamic concepts are revisited, highlighting the difference between macroscopic systems commonly treated in conventional theories and the intermolecular scale system subject to external fields. Soil water is conceived as an intermolecular scale open thermodynamic system subject to external fields of gravity, osmosis, and adsorption. The formulated thermodynamic framework is verified by reducing to the conventional definition of matric potential and a recently proposed unitary definition. The accuracy of the framework is further justified in terms of mechanical equilibrium criteria. The framework predicts the existence of spatially varied pore water pressure in soil pores and can serve as the theoretical basis for reconciling the physical origin of abnormal soil behavior such as water density, film water viscosity, relative permittivity, and negative or positive pore water pressure.

Hygroscopic hydrophobic coatings from cellulose: Manipulation of the aggregation morphology of water

Fogging and icing are common phenomena in nature, but they bring huge harm in the human life and production, such as the deterioration of optical devices, the detriment of vehicles operating, the destruction of power transmission lines. In this work, we designed and constructed a cationic cellulose derivative with both weak hygroscopicity and high hydrophobicity to achieve a spontaneous management of the aggregation morphology of interfacial water, via precisely controlling the chemical structure of cellulose derivatives. As a result, the resultant cationic cellulose derivative can be used as a transparent and water-resistant coating, which exhibits universal anti-fogging, excellent anti-icing and anti-bioadhesive properties. Under low humidity, the coating can effectively absorb water to form a pseudo-film due to the ionized structure and retained hydroxyl groups. Under high humidity, the coating can promote water droplets to roll off due to the high hydrophobicity. The coating with weak hygroscopic core and high hydrophobic surface thus has a universal anti-fogging performance. In addition, this ionized coating with weak hygroscopicity can adjust the interfacial water performance, so it can reduce the freezing temperature of water to −30 ℃, and the ice adhesion stress to 10 kPa at −30 ℃. The freezing time of water exceeds 2 h at −25 ℃. Furthermore, the bacterial killing percentage on this coating is more than 97 % for Staphylococcus aureus. Due to high hydrophobicity and low surface energy, this coating has outstanding water-resistance, self-cleaning property, anti-chlorella adhesion and anti-protein adhesion. Therefore, such a multifunctional coating prepared by a simple structure design from natural cellulose has a great potential in display devices, traffics, solar products, wind generator, agricultural greenhouse, and other fields.

Bioinspired Cryoprotectants of Glucose-Based Carbon Dots.

In nature, antifreeze proteins (AFPs) present in plants, fish, and insects living in cold regions exhibit unique abilities to decrease the freezing temperature of water, inhibiting ice growth and recrystallization. However, AFPs suffer from difficult extraction, low stability, and potential immunogenicity, which limit their wide applications in cryopreservation. Thus, AFP-inspired cryoprotectants with low cytotoxicity, simple design, and large-scale production are highly desired. Herein, carbon dots (CDs) from glucose (G-CDs) are synthesized by hydrothermal carbonization. The adsorption on ice crystals provides the G-CDs with an ice-shaping effect while inhibiting ice growth and recrystallization. The high inhibition of ice recrystallization activity and low cytotoxicity of the G-CDs make them promising cryoprotectant materials. Thus, G-CDs without any organic solvent can significantly improve sheep red blood cell recovery to ca. 60%. The use of glucose as a starting material provides these G-CDs with low-cost, biocompatibility, commercial availability, and mass-production characteristics, paving the way for the synthesis of both cryopreservation material CDs from sugars.

Liquid-Infused Micro-Nanostructured MOF Coatings (LIMNSMCs) with High Anti-Icing Performance.

In this article, a new kind of anti-icing material, liquid-infused micro-nanostructured MOF coating (LIMNSMC), was designed and prepared. The porous micro-nanostructures of metal-organic framework (MOF) coating were first utilized to immobilize the lubricating liquid. The anti-icing performance of LIMNSMC could be tuned by the viscosity, the amount of lubricating liquid, and the surface morphology. Under appropriate conditions, the LIMNSMC shows high anti-icing performance with the condensed water-freezing temperature of approximately -39 °C and the ice adhesion strength of approximately 10 kPa as the micro-nanostructures of MOF coating reduce the contact area and hinder the heat transfer between the surface and water droplets, and the lubricating layer effectively reduces the heterogeneous nucleation sites on the surface, as well as reduces the ice adhesion. LIMNSMCs exhibit good durability as the lubricating liquid can be effectively immobilized by the nanopores of MOFs. So, the high anti-icing performance of LIMNSMCs could be maintained throughout 10 freezing/melting cycles and six icing/de-icing cycles and slightly decreased after high-speed centrifugation and 50 abrasion cycles.

Facilely Fabricating Superhydrophobic Resin-based Coatings with Lower Water Freezing Temperature and Ice Adhesion for Anti-icing Application

This work is focused on the development of a facile strategy to fabricate superhydrophobic coatings, which are characterized with lower water freezing temperature and lower ice adhesion. First, a kind of polyacrylic acid (PAA) based resin material is synthesized as the coating-matrix. Then the functionally-modified SiO2 nanoparticles are added to regulate the surface morphology for obtaining the ideal superhydrophobicity. The as-synthesized resin coatings possess strong bonding strength with metal substrate, and the surface hierarchical morphologies (10 wt% SiO2 nanoparticles) induce the robust superhydrophobicity with a high water contact angle of 152°. Also, the superhydrophobic coatings are endowed with high icephobicity, and the freezing temperature of reference water droplet is reduced to −20.33°C comparing with that (−13.83°C) on the coatings without additive nanoparticles. Furthermore, the ice adhesion strength on the superhydrophobic coatings is only 250 kPa, exhibiting the great ability of ice repellence.

Mechanism of Proton Conduction in Perfluorinated Sulfonic Acid Polymers with High Ionic Exchange Capacity at Water-Freezing Temperature Region

Molecular-level understanding of dynamic behaviors of complex mass transports, especially proton and water- in polymer electrolytes is essential to design better membrane materials used for polymer electrolyte fuel cells (PEFCs). NMR is one of the suitable experimental techniques for analyzing such molecular dynamics, since both complex static structures and dynamical motions of molecules can be tracked by high-resolution NMR spectra and a pulsed field gradient NMR (PFG-NMR). This technique is widely used to understand proton dynamics however, it cannot clearly distinguish vehicle and grotthuss mechanisms. Recently, we have developed a combination method of 2H, 17O MAS NMR and 1H PFG NMR measurement to overcome the drawback. We applied the technique to an organic-inorganic composite membrane, Zr-SPP-SPES, which forms controlled configuration of proton functional groups [1,2]. In the paper we proposed enhanced grottuss mechanism in a water-freezing temperature region called "packed acid mechanism”. [6]In the present study we prepared perfluorinated sulfonic acid membranes with different equivalent weight (EW) 500, 600, 700 and 900, to understand relationship between value of ion exchange capacity (IEC = 1000/EW) and proton conduction mechanism in water freezing region. 17O labeled water was used in order to distinguish signals from non-exchangeable protons in the membranes, thus natural abundance 17O (0.04%) NMR signals of water in membrane cannot be detected. 1H and 17O MAS NMR measurements were carried out on Agilent NMR systems 400WB at 9.4 T. A 4 mm diameter air tight rotor was used for sample spin at 12 kHz. 1H and 17O 1D-NMR spectra were obtained by using a single pulse sequence. Sample temperature was calibrated by measuring the 79Br signal of KBr powder under the same measurement condisions as described elsewhere. [3] 1H PFG NMR measurements were carried out on JNM LA-400 at 9.4 T. NMR spectrometer equipped with maximum gradient strength of 12 T/m. The diffusion coefficient (D) was measured by using a pulsed-field-gradient stimulated-echo pulse sequence. [4, 5] 17O NMR spectrum in all the membrane show a sharp peak around 0ppm, from temperature 6 to 42℃. With lowering temperature from -20 to -45 ℃, the width of the spectra of all the membranes is drastically increased then finally the spectrum is vanished at T = -45 ℃. The behavior of 17O NMR in all samples were almost similar. Since the width of the NMR spectrum is inversely proportional to the movement of the observed nucleus, it indicates that absorbed water molecules are completely freezing.In contrast to the 17O NMR, solid 1H NMR spectra show a sharp peak even at the low temperature range, from -25 to -45 ℃. This result indicates that proton conductivity is still remaining, even while absorbed water molecules are freezing. 1H PFG-NMR also revealed that proton conduction is present at low temperature as well as the results of 1H NMR. The sample with highest IEC value ( IEC ~ 2 ) shows highest proton conductivity D = 7 x 10-7 (m2/s) at T = -25 ℃ and D = 0.5 x 10-7 (m2/s) at T = -60 ℃.These three results indicate that protons in the membranes with high IEC move independently like a "packed acid mechanism” in freezing temperature region. This conduction mechanism would happen efficiently because sulfonic acid is tightly-packed, which is a noteworthy property of the high IEC membranes.

The use of cryoscopy method for determination of freezing temperature of waters having different content of deuterium

Using the method of cryoscopy we determined the freezing temperature of light water with D/H= 4.2 ppm, 18O/16O = 910 ppm. It was found that light water freezes at the above zero temperature (0.3 ± 0.1°C) irrespective of cooling rate. It is shown that light water begins to freeze only at an overcooled metastable state. Under conditions of experiment the nucleation and growth of dendrite crystals of ice depends on the cooling rate and starts at the temperature −5.3; −8.8; −9.8 ± 0.1°C at the average cooling rate respectively 0.2; 0.3; 0.5°C·min−1. It is shown than in usual water the growth of dendrite ice crystals starts at minus temperature (−6.4;−7.5; −8.8 ± 0.1°C) and increases with an increase of the average cooling rate respectively from 0.2 to 0.6°C·min−1. It was found that the initial freezing temperature of heavy water constituted −3.0− −4.0 ± 0.1° at the rate of its cooling 0.2−1.0°C·min−1. However in this case the freezing temperature of normal and heavy waters does not depend on the cooling rate and freezing of normal and heavy waters and according to reference data constitutes respectively 0.1 ± 0.1 and 3.9 ± 0.1°C.

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.

Differentiating Grotthuss proton conduction mechanisms by nuclear magnetic resonance spectroscopic analysis of frozen samples.

Available methods to analyze proton conduction mechanisms cannot distinguish between two proton-conduction processes derived from the Grotthuss mechanism. The two mechanistic variations involve structural diffusion, for which water movement is indispensable, and the recently proposed "packed-acid mechanism," which involves the conduction of protons without the movement of water and is typically observed in materials consisting of highly concentrated (packed) acids. The latter mechanism could improve proton conductivity under low humidity conditions, which is desirable for polymer electrolyte fuel cells. We proposed a method with which to confirm quantitatively the packed-acid mechanism by combining (2)H and (17)O solid-state magic-angle-spinning nuclear magnetic resonance (MAS-NMR) measurement and (1)H pulsed-field gradient (PFG)-NMR analysis. In particular, the measurements were performed below the water-freezing temperature to prevent water movement, as confirmed by the (17)O-MAS-NMR spectra. Even without water movement, the high mobility of protons through short- and long-range proton conduction was observed by using (2)H-MAS-NMR and (1)H-PFG-NMR techniques, respectively, in the composite of zirconium sulfophenylphosphonate and sulfonated poly(arylene ether sulfone) (ZrSPP-SPES), which is a material composed of highly concentrated acids. Such behavior contrasts with that of a material conducting protons through structural diffusion or vehicle mechanisms (SPES), in which the peaks in both (2)H and (17)O NMR spectra diminished below water-freezing temperature. The activation energies of short-range proton movement are calculated to be 2.1 and 5.1 kJ/mol for ZrSPP-SPES and SPES, respectively, which indicate that proton conduction in ZrSPP-SPES is facilitated by the packed-acid mechanism. Furthermore, on the basis of the mean-square displacement using the diffusivity coefficient below water-freezing temperature, it was demonstrated that long-range proton movement, of the order of 1.3 μm, can take place in the packed-acid mechanism in ZrSPP-SPES.

Selective Analysis of Grotthuss Proton Diffusion in Polymer Electrolyte Membranes at a Freezing Temperature Region: A 2H and 17O Solid-State NMR Investigation

Molecular-level understanding of dynamic behaviors of complex mass transports –especially proton and water- in polymer electrolytes is essential to design better membrane materials used for polymer electrolyte fuel cells (PEFCs). NMR is one of the suitable experimental techniques for analyzing such molecular dynamics, since both complex static structures and dynamical motions of molecules can be tracked by high-resolution NMR spectra and a pulsed field gradient NMR (PFG-NMR). Widely used a pulsed field gradient NMR method, however, cannot clearly distinguish vehicle and grotthuss mechanisms. To overcome this drawback, we applied a combination method of 2H, 17O MAS NMR and 1H PFG NMR measurement. We selectively observed grotthuss mechanism in the absence of a vehicle mechanism in a water-freezing temperature region.In order to demonstrate advantage of this method, we applied this to sulphonated poly (arylene ether sulphone) (SPES) and a composite of zirconium sulphophenylphosphonate (ZrSPP) and SPES using nano capping technique (Capping-ZrSPP-SPES), in which enhanced grottuss mechanism is expected by controlled configuration of proton functional groups. [1, 2] 2H and 17O labeled water was used in order to distinguish signals from non-exchangeable protons in SPES, and because natural abundance 17O (0.04%) NMR signals of water in membrane cannot be detected. Incubating the composites in 2H labeled water at 100% RH for three days resulted in the exchange of the protons of sulfonic acid and adsorbed water, and thus the 2H MAS NMR spectrum included only the signal of the mobile proton. Similarly, for 17O MAS NMR analysis, the composite was incubated in 17O labeled water at 100% RH for three days. After reaching equilibrium, air tight sample tubes were sealed to avoid change of the water content during NMR measurements. 2H and 17O MAS NMR measurements were carried out on Agilent NMR systems 400WB at 9.4 T. A 4 mm diameter air tight rotor was used for sample spin at 12 kHz. 2H and 17O 1D-NMR spectra were obtained by using a single pulse sequence. Sample temperature was calibrated by measuring the 79Br signal of KBr powder under the same measurement condisions as described elsewhere. [3] 1H PFG NMR measurements were carried out on JNM LA-400 at 9.4 T. NMR spectrometer equipped with maximum gradient strength of 12 T/m. The diffusion coefficient (D) was measured by using a pulsed-field-gradient stimulated-echo pulse sequence. [4, 5]Fig. 1 shows the temperature variations of 2H and 17O NMR spectra of SPES, respectively, at 47, -15 and -39 °C. 2H and 17O NMR singnals of SPES are broadened as temperature decrease. At -39 °C, 2H and 17O NMR signals are significantly broadened. This indicates that water is freezing at -39 °C and proton in SPES cannot move.On the other hand, the temperature variation of 2H NMR signal from Capping-ZrSPP-SPES showed different behaviors. As shown in Fig. 2 (b), 2H resonance peak is still sharp in the water-freezing temperature, suggesting that the protons in the Capping-ZrSPP–SPES retained their mobility even at -39 °C. These results indicate that protons in the Capping-ZrSPP–SPES move independently like a grotthuss mechamisum in freezing temperature region. More detailed and 1H PFG NMR results will be presented at the Meeting.

Low-density liquid water is the mother of ice: on the relation between mesostructure, thermodynamics and ice crystallization in solutions

Predicting the temperature and extent of ice freezing in aqueous solutions is crucial for areas as diverse as cryobiology and materials design. It has long been recognized that the thermodynamics of liquid water controls the temperature and kinetics of ice crystallization. Parameterizations of the freezing temperatures in terms of the water activity of the solution have been successfully established, but the fundamental origin of the thermodynamic control of the non-equilibrium crystallization of ice has remained elusive. Here we use large-scale molecular simulations to elucidate the relationship between the structure, thermodynamics, and ice crystallization temperatures for solutions of mW water and a strongly hydrophilic solute that mimics LiCI ions. Fast cooling of solutions with up to 20 mol% ions results in the formation of nanosegregated glasses with domains of low-density amorphous ice and an ion-rich vitrified solution. Slow cooling of the mixtures results in nucleation and growth of ice within the domains of four-coordinated liquid water. The temperature of crystallization Tx coincides with the temperature of appearance of nanoscopic domains of four-coordinated liquid water in the mixture, T(L). We use the insight provided by the simulations to derive a thermodynamic expression for the crystallization temperature as a function of the water activity, T(X)(a(W)), analogous to the dependence of the melting temperature, T(m)(a(W)). The simple expression derived in this work provides a good account of the experimental freezing temperatures of water and the well-known steepest dependence of Tx on solute concentration compared to that of T(m).

The Physical, Chemical and Biological Effects by Room Temperature Ceramic Far‐infrared Ray Emitting Material Irradiated Water: A Pilot Study

AbstractFar infrared ray (FIR) is non‐ionizing electromagnetic radiation with wavelengths of 4‐16 μm. Ceramic far infrared ray emitting materials (cFIR) are sources of FIR that exhibit only non‐thermal effects at room temperature. Certain physical, chemical and biological effects of cFIR irradiation were investigated in this study that heretofore has not been well characterized. We demonstrated that cFIR irradiation reduced the size of water clusters, and significantly increased the freezing temperature of water. We also observed an increase in the volatility of a complex mixture of alcohol, water and solutes and recorded elevated total phenol in green tea infusions prepared using cFIR irradiated water. The effects of cFIR irradiated water on living cells were also investigated. The MC3T3‐E1 murine osteoblast cells grown in the presence of cFIR irradiated water exhibited anti‐oxidative effects on H2O2‐mediated toxicity, as evidenced by late stage increase in intracellular alkaline phosphatase. The presence of cFIR irradiated water also resulted in significant decrease in COX‐2 production in the chondrosarcoma cell line, SW1353, in response to lipopolysaccharide induction. Based on our findings, the possible anti‐inflammatory effects of cFIR irradiated water and implications of our study with regard to bone and joint health were discussed.

Bound water freezing in AntarcticUmbilicaria aprinafrom Schirmacher Oasis

AbstractThe effect of low temperature onUmbilicaria aprinacollected from Schirmacher Oasis, East Antarctica, was determined over a wide range of hydration using proton free induction decays, proton nuclear magnetic resonance (NMR) spectra and differential scanning calorimetry methods. The proton NMR line is a superposition of the broad component from the solid matrix of the thallus and a narrower component from the averaged bound water pool. Proton free induction decays may be resolved into three components: a solid component well described by the Abragam function and two exponentially decaying components from water loosely bound and water tightly bound in the thallus. With decreased temperature the loosely bound water pool (freezing water) is transferred to the tightly bound water pool (non-freezing water), and vanishes below -40°C. Bound water freezing and melting temperatures decrease with the decrease of hydration level, suggesting that heterogeneous ice nucleation is responsible for water freezing. The onset of bound water freezing temperature isc.10°C lower than the melting temperature. TheU. aprinathalli do not reveal the ability to stimulated ice nucleation at higher temperature. Freeze-thaw cycles showed that forn> 5 cycles no substantial change occurs in the difference between melting and freezing temperatures.

Freezing Point Depression of Water in Phospholipid Membranes: A Solid-State NMR Study

Lipid-water interaction plays an important role in the properties of lipid bilayers, cryoprotectants, and membrane-associated peptides and proteins. The temperature at which water bound to lipid bilayers freezes is lower than that of free water. Here, we report a solid-state NMR investigation on the freezing point depression of water in phospholipid bilayers in the presence and absence of cholesterol. Deuterium NMR spectra at different temperatures ranging from -75 to + 10 degrees C were obtained from fully (2)H2O-hydrated POPC (1-palmitoyl-2-oleoylphosphatidylcholine) multilamellar vesicles (MLVs), prepared with and without cholesterol, to determine the freezing temperature of water and the effect of cholesterol on the freezing temperature of water in POPC bilayers. Our 2H NMR experiments reveal the motional behavior of unfrozen water molecules in POPC bilayers even at temperatures significantly below 0 degrees C and show that the presence of cholesterol further lowered the freezing temperature of water in POPC bilayers. These results suggest that in the presence of cholesterol the fluidity and dynamics of lipid bilayers can be retained even at very low temperatures as exist in the liquid crystalline phase of the lipid. Therefore, bilayer samples prepared with a cryoprotectant like cholesterol should enable the performance of multidimensional solid-state NMR experiments to investigate the structure, dynamics, and topology of membrane proteins at a very low temperature with enhanced sample stability and possibly a better sensitivity. Phosphorus-31 NMR data suggest that lipid bilayers can be aligned at low temperatures, while 15N NMR experiments demonstrate that such aligned samples can be used to enhance the signal-to-noise ratio of is 15N chemical shift spectra of a 37-residue human antimicrobial peptide, LL-37.

Antifreeze Protein Produced Endogenously in Winter Rye Leaves

After cold acclimation, winter rye (Secale cereale L.) is able to withstand the formation of extracellular ice at freezing temperatures. We now show, for the first time, that cold-acclimated winter rye plants contain endogenously produced antifreeze protein. The protein was extracted from the apoplast of winter rye leaves, where ice forms during freezing. After partial purification, the protein was identified as antifreeze protein because it modified the normal growth pattern of ice crystals and depressed the freezing temperature of water noncolligatively.

Freezing temperatures of water, alkanoic acids and their mixtures

Freezing temperatures of water, methanoic acid, ethanoic acid, propanoic acid, butanoic acid, 2-methylpropanoic acid, their binary mixtures and some multicomponent mixtures have been determined using a kinetic technique. The liquid phase activity coefficients for the binary mixtures have been derived from the results and fitted to the equation of Renon and Prausnitz. The resulting parameters have been used to predict the freezing temperatures of the multicomponent mixtures. Good agreement with the experimental results is found.

A kinetic description of antifreeze glycoprotein activity.

The antifreeze glycoproteins (AFGP) of polar fish have the ability to depress the freezing temperature of water approximately 500 times the amount expected based on the number of AFGP molecules in solution; yet AFGP solutions have a purely colligative melting point depression. The difference of solution melting and freezing temperatures is the antifreeze activity of AFGP. One characteristic of AFGP activity that requires further examination is the effect of concentration on antifreeze activity, especially whether the activity saturates at high concentrations or the measured activity increases ad infinitum. This study first surveys the activity of the various antifreeze components from both Pagothenia borchgrevinki and the Arg-containing antifreeze glycoprotein from Eleginus gracilis (EgAF). It was found that all AFGP components examined have a plateau in activity at high concentration, but the actual value of the plateau activity differs between the different length AFGP components and between AFGP and EgAF. While the low molecular weight components of both AFGP and EgAF lose activity at deep supercooling, at high concentration activity is restored. The activity data is then shown to fit a reversible kinetic model of AFGP activity, and the coefficients obtained are used to compare the activity differences between AFGP components and between AFGP and EgAF. The model is also shown to describe the activity of the antifreeze protein of the fish Pseudopleuronectes americanus and the thermal hysteresis protein of the insect, Tenebrio molitor.

Antifreeze glycoproteins: influence of polymer length and ice crystal habit on activity.

AbstractThe effect of the ice crystalline habit and the length of the polymer on the ability of the antifreeze glycoproteins (AFGP) from polar fish to depress the freezing temperature of water was investigated. The low‐molecular‐weight components of the glycoproteins, AFGP‐ 6–8, are inactive when a solution of such a sample is nucleated at −6°C. A solution of large AFGP (1–4) is fully functional under the same conditions. The low‐molecular‐weight components differ from the height‐molecular‐weight components in that they contain some proline replacing the alanine in the Ala‐Ala‐Thr · disaccharide polymer unit. In the present experiments, antifreeze activity was examined in the presence of two different forms of ice crystal growth habits, and homodimders of AFGP 6 and 8 were prepared to investigate the function of polymer length and the on antifreeze activity at different degrees of supercooling. The results indicate that the ice crystal growth habit and the introduction of proline into the polymer unit may be responsible for the loss of activity at deep supercooling (−6°C) of AFGP 6–8. The loss in the ability of AFGP to depress the freezing temperature of water at deep supercooling is not solely due to polymer length, as carbodiimide‐linked dimers of AFGP 6 do not function under these freezing conditions. A Model of antifreezing action based on Langmuirian adsorption of AFGP on the ice surface and direct competition between water and AFGP molecules for the incorporation sites in the ice crystal lattice is presented.

A Technique for Measuring Relative Threshold Nucleation Temperatures for Active Nucleation Catalysts

Abstract A technique is described for using dilatometers to measure and compare the freezing temperature of water in the presence of various nucleation catalysts. Nucleation is indicated by the increase in volume that water undergone upon freezing.