Nucleation of ice

As mentioned in Section IX-2A, binary systems are more complicated since the composition of the nuclei differ from that of the bulk. In the case of sulfuric acid and water vapor mixtures only some 10 ° molecules of sulfuric acid are needed for water oplet nucleation that may occur at less than 100% relative humidity [38]. A rather different effect is that of passivation of water nuclei by long-chain alcohols [66] (which would inhibit condensation note Section IV-6). A recent theoretical treatment by Bar-Ziv and Safran [67] of the effect of surface active monolayers, such as alcohols, on surface nucleation of ice shows the link between the inhibition of subcooling (enhanced nucleation) and the strength of the interaction between the monolayer and water. 

Cavitation bubbles work as nucleation sites of particles. For example, in a supercooled sucrose solution, nucleation of ice crystals induced by cavitation bubbles has been experimentally observed [72], This phenomenon has been called sonocrys-tallization [73]. Although there are some papers on the mechanism of sonocrystal-lization, it has not yet been fully understood [74, 75]. It has been reported that the distribution of crystal size in sonocrystallization is narrower than that without ultrasound [73]. It may be related to the narrower size distribution of sonochemi-cally synthesized particles compared to that without ultrasound [76, 77]. Further studies are required for the mechanism of particle nucleation by ultrasound. 

Chow R, Blindt R, Chivers R, Povey M (2005) A study on the primary and secondary nucleation of ice by power ultrasound. Ultrasonics 43 227-230... 

Burke and Lindow [1.13] showed, that certain bacteria (e. g. Pseudomonas syringae) can act as nuclei for crystallization if their surface qualities and their geometric dimensions are close to those of ice. Rassmussen and Luyet [1.14] developed a connection for solutions of water with ethyleneglycol (EG), glycerol (GL) and polyvinylpyrrolidone (PVP) between the subcooling down to the heterogeneous and homogeneous nucleation of ice. 

Talsma et al. [1.34] described the freezing behavior of certain liposomes by DSC measurements. Besides the expected influences of freezing and rewarming speeds, and of the CPAs (mannitol and mannitol in Tris-buffer solutions) it was shown, that the heterogeneous and homogeneous crystallization in mannitol solutions exists and the nucleation of ice depends also on the liposome size In small liposomes (e. g. 0.14 pm) mannitol suppressed the heterogeneous crystallization more effectively than in large (0.87 pm) liposomes. If in certain substances no crystallization or eutectic mixtures can be found by DSC (cephalosporin, Williams [1.35]) with the used experimental conditions, one has to seek different conditions [1.32]. 

Independent of the growth of ice crystals (Section 1.1.2), which can be observed down to approx. -100 °C, and a possible recrystallization (Section 1.1.3), this chapter describes only such developments or changes of structures that can be influenced by additives. The addition of CPAs to albumins, cells or bacteria influences the nucleation of ice - or at least its growth - in such a way that their natural structures are retained as much as possible. On the other hand, additives are introduced to crystallize dissolve substances. If this method does not help, e. g. with antibiotics, the solution concentrates increasingly until a highly viscous, amorphous substance is included between ice crystals. This condition has disadvantages ... 

These sulfuric acid particles become less concentrated as the temperature decreases or the water vapour increases. Under very cold stratospheric conditions, these liquid aerosols may take up water and HNO, forming ternary solutions H,S0/HN0,/H,0, which eventually freeze [19,24,26], Below 192 K, HNO, becomes the dominant condensed acid, and H,S04 drops to below 3 wt %. The thermodynamics and freezing nucleation of ice and H,S04 or HNO, hydrates from such solutions are however not well understood [27,28]. Other types of solid particles, such as the less stable nitric acid dihydrate (NAD, HN0,.2H,0) [29], sulfriric acid tetrahydrate (SAT, H S04.4H,0) [18,30], sulphuric acid hemihexahydrate (SAH, H2S04.6.5H20) [18], nitric acid penta-hydrate (NAP, HN03.5H,0) [31] and more complex sulfuric acid/nitric acid mixed hydrates [32] may also be a key to understanding Type IPSC nucleation and evolution [28],... 

L.H. Seeley, G.T. Seidler, Two-dimensional nucleation of ice from supercooled water. Phys. Rev. Lett. 87, 055702/1 (2001)... 

The practical independence of Li-0 and Li-D distances with temperature shows the strong orientational correlation of water molecules around Li it is most likely that an average orientation of the coordinated water molecules is such that the four atoms in a Li -D20 unit is pyramidal. The strong orientational correlation of the bound water molecules rationalizes the anisotropic reorientational motion of the water molecules in the hydration shell found by nuclear magnetic relaxation data of supercooled LiCl solutions. The evolution of the secondary hydration shell of Li may be a hint of nucleation of ice, glass transition, and partial recovery of hydrogen bonds in the supercooled state. 

This happened because of our investigation of the rate of nucleation of ice in deeply supercooled water. Previous laboratory studies of the freezing of water occurred in substantially warmer water and were blind to the phase of ice obtained. We studied water undergoing nucleation at roughly the temperature of nucleation in cirrus clouds, I believe. I understand that what happens in cirrus clouds has an important effect on the climate. Moreover, we showed directly that the ice first nucleated was the metastable cubic ice, not the ordinary hexagonal ice. Atmospheric scientists had inferred that result from indirect evidence. Previously it had not been possible to carry out experiments like ours in the laboratory, which is why our work attracted the attention of atmospheric scientists. 

Remaining parts of solvents (e.g., dimethylsulfoxide (DMSO), ethanol, dichlormethane, and acetone) influence, even in small quantities, the nucleation of ice crystals and its growth. Normally they will also reduce 7, [5-7]. The solvents will also change the pressure reading on a thermoelectric (TM) instrument and... 

As was the case with ozone, aerosols also occur naturally in the atmosphere. Aerosols play an important role in the atmosphere s hydrologic cycle. Formation of cloud droplets occurs on hygroscopic aerosols, and nucleation of ice also needs a particle to initiate ice formation. Precipitation, which is enhanced by the presence of large aerosols or ice, strongly depends on these ice and cloud condensation nuclei. Most (though not... 

Franks, F. Mathias, S.F. Trafford, K. The nucleation of ice in undercooled water and aqueous polymer solutions. Colloids Surf 1984,11, 275-285. 

Nucleation has a number of important practical consequences. In metallurgy, the rate of nucleation of molten metals and metal alloys affects the structural and mechanical properties of the solid metals that are formed upon casting. In the preparation of high-quality crystalline semiconductors through laser melting and resolidification the nucleation step affects the resulting microstructures. In the atmospheric sciences, nucleation of ice in clouds is a widely studied process, while biologists are interested in the ways in which certain plants appear to inhibit nucleation of ice from water and thus show increased resistance to cold. 

However, Zettlemoyer (1968) has more recently shown that such a macroscopic treatment is inadequate to explain the nucleation of ice by well known nucleators, such as Agl. Conceptually, Zettlemoyer s results show that hydrophilic sites invariably present on hydrophobic surfaces are necessary for initiation of the crystalline phase. 

Although AF(G)Ps and LDHIs are distinct, they both inhibit the growth of crystals. Neither AFGP nor PVP are reported to significantly affect ice nucleation, and similary, we have shown that AFPs and PVP did not affect homogeneous nucleation of THF hydrate. It is not known if these two types of inhibitors can adsorb to other hydrophilic surfaces, however silica is an ubiquitous impurity and common to both these systems. Thus, it is of interest to determine the effects of these inhibitors on heterogeneous nucleation of ice/clathrate hydrate. 

One has to distinguish our studies here from the more popular studies on the adsorption of AFPs or LDHIs on ice or gas hydrate since the former focuses on the effect of AFP/LDHI on heterogeneous nucleation of ice/gas hydrate and the later focuses on the effect on the effects on the ice/hydrate growth. Thus, the studies represented in this study deals with impurity surfaces but not ice/hydrate surface. The authors think that this is an important aspect for the understanding of good ice/hydrate inhibition since the nucleation process is heterogeneous and must involve impurity surfaces. 

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