Water unfrozen

Figure 6. Carbon Norit R 0.8 Extra PSD determined by nitrogen desorption data (N2), and PSDs of pores filled by water unfrozen in different environments at T < 273 K.

Figure 14. Characteristics of interfacial water in aqueous suspensions of A-300 sonicated (US) or treated in a ball-mill (MCA) at different concentration of silica (a) amounts of unfrozen water as a function of temperature at T < 273 K (b) relationship between the thickness of unfrozen water layer and temperature and changes in Gibbs free energy of interfacial water versus (c) pore radius, (d) pore volume, and (e) amounts of water unfrozen in these pores (f) interfacial Gibbs free energy as a function of silica concentration in suspensions differently treated.

Frequency sweeps (at a constant deformation, y = 4%) at different times and storage temperatures for the following samples (a) starch-sucrose-water (b) CSXW starch-sucrose-xanthan gum-water unfrozen quickly frozen without storage A quickly frozen and stored 91 days at — 18°C V quickly frozen and stored 91 days at — 80°C O slowly frozen without storage O slowly frozen and stored 91 days at — 18°C. 

The total volume of weakly (C ) and strongly (Cuw) bound waters (unfrozen at T < 273 K) at the silica interfaces (Table 38.5) is markedly larger than Vp (but significantly lower than Vemp) with one exception for SI-6 (Table 1). With increasing specific surface area of the first series samples, there is tendency of reduction of the free surface energy (Table 5, js) and the amount of weakly bound water Besides, the AG Cuw)y... 

Characteristics of Water Unfrozen at T<273 K and Bound to Initial and Wet-MCA-Treated Nanosilica Estimated by NMR Cryoporometry... 

All bound water unfrozen at F<273 K can be assigned to strongly associated water at 8h 5-5.5 ppm. WAW at 5h=1-2 ppm is not observed in any of the studied suspensions of the initial nanooxides. The total amounts of water bound by oxide nanoparticles in these suspensions (Table 2.8 Cuw = Cuw + C"w = lFp.5g/g at a major contribution of weakly bound water frozen at F>260 K Figure 2.40a) are much larger than that observed from the measurements of the water... 

Changes in the free energy of water unfrozen in carbon pores dependent on its concentration (on temperature) are shown for PS-t samples in different media (Figures 3.12 and 3.13 Table 3.5). 

Characteristics of Cell Structures in Contact with Bound Intracellular Water Unfrozen at T<273 K... 

Ice lollies are made from juice (water, sugar, citric acid, flavour and colour) and are frozen into shape using moulds immersed in a cold brine solution, in a similar manner to can ice making (see Section 12.4). The moulds are made from stainless steel or nickel, and pass in rows through a brine bath at - 45°C. Different layers of confection may be built up by allowing one outside layer to freeze, sucking out the unfrozen centre and refilling with another mix. The sticks are inserted before the centre freezes solid. The moulds finally pass... 

To survive freezing, a cell must be cooled in such a way that it contains little or no freezable water by the time it reaches the temperature at which internal ice formation becomes possible. Above that temperature, the plasma membrane is a barrier to the movement of ice crystals into the cytoplasm. The critical factor is the cooling rate. Even in the presence of external ice, most cells remain unfrozen, and hence, supercooled, 10 to 30 degrees below their actual freezing point (-0.5 °C in mammalian cells). Supercooled cell water has a higher chemical potential than that of the water and ice in the external medium, and as a consequence, it tends to flow out of the cells osmotically and freeze externally (Figure 1). 

Figure 11. A Survival of human red blood cells as a function of the molality of NaCi (m ) to which they are exposed after being frozen at 1.7 °C/min to various subzero temperatures while suspended in solutions of 0.5 ( ) or 1.0 (a) M glycerol in isotonic NaCI. Thawing was rapid. B Survival as a function of the fraction of water that remains unfrozen in the solutions. (From Mazur and Rigopoulos, 1983.)...

If we combine the data on survival of red cells vs. temperatiue in Figure 10 with the data in Figure 12 on the effect of temperature on the unfrozen fraction, we obtain the results shown in Figure 1 IB. The curves are mirror images of those in Figure 11A which relate survival to salt concentration. They show that survival drops from above 80% when the unfrozen water fraction is 0.14 or more, to below 20% when... 

Figure 12, Fractions of water in glycerol-NaCI-HjO solutions remaining unfrozen at various subzero temperatures. Glycerol molarities refer to the initial unfrozen solutions. The initial NaCI concentration in these solutions was 0.15 M. (From Mazur et al., 1981.)...

Mazur, P., Rail, W.F., Rigopoulos, N. (1981). Relative contributions of the fraction of unfrozen water and of salt concentration to the survival of slowly frozen human erythrocytes. Biophys. J. 36, 653-675. 

It is well known that the melting point of water confined to small pores is depressed [30, 31]. Therefore in concrete as the temperature decreases, the amount of frozen water will increase. Under normal temperature variation not all water in the pore structure will be frozen. The change from water in the liquid form to solid ice drastically reduces the Tfk of hydrogen (T2 ice <9 ps [32]). Ice will not be observed in an image, even with the SPRITE techniques, and our experimental images will be maps of unfrozen water distribution. 

As the temperature is lowered further, the viscosity of the unfrozen solution increases dramatically until molecular mobility effectively ceases. This unfrozen solution will contain the protein, as well as some excipients, and (at most) 50 per cent water. As molecular mobility has effectively stopped, chemical reactivity also all but ceases. The consistency of this solution is that of glass, and the temperature at which this is attained is called the glass transition temperature Tg-. For most protein solutions, Tg- values reside between -40 °C and -60 °C. The primary aim of the initial stages of the freeze-drying process is to decrease the product temperature below that of its Tg- value and as quickly as possible in order to minimize the potential negative effects described above. 

From DTA measurements phase diagrams can be constructed as shown for ethyleneglycol in Fig. 1.34. A solution of 40 % ethyleneglycol is only stabile in the glass phase below = -135 °C, at = -120 °C unfrozen water starts to crystallize, at = -65 °C a recrystallization is found, and at = —45 °C melting will start. As recrystallization is the growing of existing crystals, and not the nucleation of new ones, this event cannot be detected by DTA, but can be observed in a microscope when a transparent area becomes opaque. 

Hanafusa [1.36] showed with this method, how the amount of unfrozen water in a 0.57 % solution of ovalbumin reaches practically zero at -20 °C, if 0.01 M sucrose is added (Fig. 1.51). For globular proteins Hanafusa described the freezing process as follows between 0 °C and -20 °C, water molecules from the multilayer hydrate shell are decomposed. Be-... 

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