Enhancement and maximum in the isobaric specific-heat capacity measurements of deeply supercooled water using ultrafast calorimetry

Knowledge of the temperature dependence of the isobaric specific heat (Cp) upon deep supercooling can give insights regarding the anomalous properties of water. If a maximum in Cp exists at a specific temperature, as in the isothermal compressibility, it would further validate the liquid–liquid critical point model that can explain the anomalous increase in thermodynamic response functions. The challenge is that the relevant temperature range falls in the region where ice crystallization becomes rapid, which has previously excluded experiments. Here, we have utilized a methodology of ultrafast calorimetry by determining the temperature jump from femtosecond X-ray pulses after heating with an infrared laser pulse and with a sufficiently long time delay between the pulses to allow measurements at constant pressure. Evaporative cooling of ∼15-µm diameter droplets in vacuum enabled us to reach a temperature down to ∼228 K with a small fraction of the droplets remaining unfrozen. We observed a sharp increase in Cp, from 88 J/mol/K at 244 K to about 218 J/mol/K at 229 K where a maximum is seen. The Cp maximum is at a similar temperature as the maxima of the isothermal compressibility and correlation length. From the Cp measurement, we estimated the excess entropy and self-diffusion coefficient of water and these properties decrease rapidly below 235 K.

Molecular Dynamics Simulations of Crystal Nucleation near Interfaces in Incompatible Polymer Blends

We apply molecular dynamics (MD) simulations to investigate crystal nucleation in incompatible polymer blends under deep supercooling conditions. Simulations of isothermal nucleation are performed for phase-separated blends with different degrees of incompatibility. In weakly segregated blends, slow and incompatible chains in crystallizable polymer domains can significantly hinder the crystal nucleation and growth. When a crystallizable polymer is blended with a more mobile species in interfacial regions, enhanced molecular mobility leads to the fast growth of crystalline order. However, the incubation time remains the same as that in pure samples. By inducing anisotropic alignment near the interfaces of strongly segregated blends, phase separation also promotes crystalline order to grow near interfaces between different polymer domains.

Sn – Zn – Ga alloys for leadfree soldering obtained by rapid quenching

The paper presents the results of a study of the structural-phase state of the foil of eutectic near eutectic Sn – Zn alloys doped by Ga obtained by rapid melt quenching at a melt cooling rate of 105 K/s. Using the methods of X-ray diffraction analysis, scanning electron microscopy, and X-ray spectrometry, it was established that the foil solidifies with the formation of tin-based supersaturated solid solution and its microstructure is formed as a result of the decomposition of the solid solution by discontinuous mechanism at room temperature. The homogeneity of the composition and distribution of gallium and zinc inclusions over the volume of the foil was established. Using the electron backscatter diffraction technique, it was shown that the foils have a microcrystalline structure due to the deep supercooling of the melt, which leads to a high crystal nucleation rate. The grain size decreases depending on the distance to the mold. The increase in grain size is associated with a change in the solidification conditions over the thickness of the foil: deterioration of heat removal and a decrease in supercooling. There is no pronounced grain texture in the foils.

X-ray phase contrast imaging of Vitis spp. buds shows freezing pattern and correlation between volume and cold hardiness

Grapevine (Vitis spp.) buds must survive winter temperatures in order to resume growth when suitable conditions return in spring. They do so by developing cold hardiness through deep supercooling, but the mechanistic process of supercooling in buds remains largely unknown. Here we use synchrotron X-ray phase contrast imaging to study cold hardiness-related characteristics of V. amurensis, V. riparia, and V. vinifera buds: time-resolved 2D imaging was used to visualize freezing; and microtomography was used to evaluate morphological changes during deacclimation. Bud cold hardiness was determined (low temperature exotherms; LTEs) using needle thermocouples during 2D imaging as buds were cooled with a N2 gas cryostream. Resolution in 2D imaging did not allow for ice crystal identification, but freezing was assessed by movement of tissues coinciding with LTE values. Freezing was observed to propagate from the center of the bud toward the outer bud scales. The freezing events observed lasted several minutes. Additionally, loss of supercooling ability appears to be correlated with increases in bud tissue volume during the process of deacclimation, but major increases in volume occur after most of the supercooling ability is lost, suggesting growth resumption processes are limited by deacclimation state.

Comparison of various models of supercooled water loss factor with experimental data at microwaves

An improved formula for the supercooled water loss factor at frequencies 10…180 GHz in the temperature range 0 ... –70 °C is presented. The formula based on the experimental data obtained by the authors on measurements of attenuation in the pore water of silicate materials. The formula contains two terms connected the Debye dependence of the loss factor on frequency and temperature, and non-Debye, determined by the influence of the second critical point of water. Comparison of the proposed formula and the model formulas of other authors is carried out. A significant discrepancy between the calculation results (at several times) of the loss factor at frequencies above 100 GHz and temperatures below –30 °C has been founded. The model based on the measurements provides the most adequate representation of the behavior of the loss factor with an error of ~ 30% in the area of deep supercooling of water and in the upper part of the studied frequency band.

X-ray phase contrast imaging of Vitis spp. buds shows freezing pattern and correlation between volume and cold hardiness

Grapevine (Vitis spp.) buds must survive winter temperatures in order to resume growth when suitable conditions return in spring. They do so by developing cold hardiness through deep supercooling, but the mechanistic process of supercooling in buds remains largely unknown. Here we use synchrotron X-ray phase contrast imaging to study cold hardiness-related characteristics of V. amurensis, V. riparia, and V. vinifera buds: time-resolved 2D imaging was used to visualize freezing; and microtomography was used to evaluate morphological changes during deacclimation. Bud cold hardiness was determined (low temperature exotherms; LTEs) using needle thermocouples during 2D imaging as buds were cooled with a N2 gas cryostream. Resolution in 2D imaging did not allow for ice crystal identification, but freezing was assessed due to movement of tissues coinciding with LTE values. Freezing was observed to propagate from the center of the bud toward the outer bud scales. The freezing events observed lasted several minutes. Additionally, loss of supercooling ability appears to be correlated with increases in bud tissue volume during the process of deacclimation, but major increases in volume occur after most of the supercooling ability is lost, suggesting growth resumption processes are limited by deacclimation state.HighlightX-ray phase contrast imaging shows freezing occurs over several minutes and propagates from center toward tip of Vitis spp. buds. Incremental increase in bud volume correlates with cold deacclimation