Freezing of ice

Ice-cream. Crystallization of lactose in ice-cream causes a sandy texture. In freshly hardened ice-cream, the equilibrium mixture of a- and /1-lactose is in the glass state and is stable as long as the temperature remains low and constant. During the freezing of ice-cream, the lactose solution passes through the labile zone so rapidly and at such a low temperature that limited lactose crystallization occurs. 

Cooling solutions to below their freezing point results in the formation of ice. If solutions of sugars are cooled rapidly, non-equilibrium ice formation occurs. This is the most common form of ice in frozen dairy products (e.g. ice-cream). Rapid freezing of ice-cream mixes results in the freeze concentration of lactose and other sugars, resulting in supersaturated solutions if the temperature is too low to permit crystallization. The rapid cooling of lactose results in the formation of a supersaturated, freeze-concentrated amorphous matrix. 

Given that interstellar ices are the building blocks of comets and comets are thought to be an important source of the species that fell on primitive Earth, the structures of molecules in comets may be related to the origin of life. It is possible that organic materials formed in the solid ice phase of interstellar materials provided raw materials used for life originating solely on Earth. If so, the deep freeze of ice in the Oort cloud would have been an excellent place to store these, especially the unstable ones, awaiting delivery to a planet. 

Several authorshave conceptually related the transition from planar to cellular freezing of ice to the condition of constitutional supercooling Here the theoretical framework of morphological stability theory for a planar interface is combined with simple models of diffusion and free convection to derive the transition salinity in dependence on growth conditions. 

The oxygen isotopic composition of seawater (5 0 ) is controlled by fractionation effects due to evaporation and precipitation at the sea surface, freezing of ice in polar regions, the admixing... 

The first indication of the complexity that one may encounter in understanding the freezing of ice came from a set of experiments reported in 1970s by Speedy and Angell [3]. These scientists studied the freezing of micro-droplets of ultra-pure water - the droplets were of a few micrometer (pm) diameter. The reason for choosing such a small size was to avoid the presence of impurities in the sample. Impurities act as seed for crystal nucleation and growth, and have to be avoided if we want to understand the crystallization of pure water. Since it is practically... 

We have aheady discussed in Chapter 2 that water exhibits a large number of anomalies at low temperature, below its freezing temperature. The properties of liquid water at low temperature may be explained qualitatively in terms of the existence of two disordered forms - the high-density liquid (HDL) and the low-density liquid (LDL). Our common water consists mostly of HDL. The freezing of ice seems to be intimately connected with these two forms. However, scientists are... 

We now discuss the first successful simulation of the freezing of ice, which revealed a wealth of information about the freezing process, and also threw light on the difficulty of freezing water into ice. 

It should be clear from the above that because of sustained efforts over many decades, significant progress has now been achieved in the understanding of the freezing of water into ice. However, there stiU remain many unsolved problems in this area. For example, we do not yet have a quantitative theory of the nucleation of ice in supercooled water. The molecular models we use in simulations are perhaps too primitive, as most of them do not include the polarizabihty of water molecules. The polarizability of water is large due to the two lone pairs of electrons on the lone oxygen atom. Perhaps one would need to consider quantum simulations to fully understand the freezing of ice. 

Introduction and Section 19.1 In this chapter we examined some of the aspects of chemical thermodynamics, the area of chemistry that explores energy relationships. Most reactions and chemical processes have an inherent directionality They are spontaneous in one direction and not spontaneous in the reverse direction. The spontaneity of a process is related to the thermodynamic path the system takes from the initial state to the final state. In a reversible process, such as the melting and freezing of ice at 0° C, the system can go back and forth between states along the same path. In an irreversible process the system can t return to its original state along the same path. Any spontaneous process is irreversible. 

Crystallization of edible fats and oils in oil-in-water (OAV) emulsions is an important process in many industrial fields such as foods [1-4], cosmetics [5], and pharmaceuticals [6]. In the food industry, crystallization in the 0/W emulsion phase contributes to the de-emulsifying process in whipped creams, the freezing of ice creams, and coagulation of the 0/W emulsions at chilled states. Therefore, the production, quality, and stability of fat products in the emulsion state are highly influenced by crystallization of the oil phase [7], so much recent research has been aimed at the exploration of fat crystallization in O/W emulsions [8-13], Fat crystallization results in complex phenomena in O/W emulsions and affects such parameters as the rate and extent of crystallization, influences of emulsion droplet sizes, effects of emulsifiers, droplet-droplet interactions, polymorphism, and effects of cooling rate and subsequent temperature history. 

---