Antifreezes based on water eutectics are widely spread in engineering and by crio-preservation of biological objects as well. Salts of inorganic and organic acids, alcohols, glycols, glycol ethers, glycerin, acids, bases, amino-acids, and other chemical compounds are suitable here as supplementary means. Part of these compounds is capable to take part in the formation of H-bonds with water molecules, the others do not form H-bonds (CaCl2), but they are united into crystal-hydrates of CaCl2 • 6 Н2О type. In this case H-bond of water molecules can become the bond of intermolecular-cluster type. It is assumed that basic structural components of liquid water are cyclic penta- (H2O)5 and hexamers (H2O6), built with the participation of the long hydrogen bond and capable of producing the crown effect. Cyclic water clusters – short-range order of water in terms of cavity size and the number of oxygen atoms correspond to crown ethers: 15-crown-5 and 18-crown-6, sodium and calcium ions being absorbed into them. Energy estimation of water and ice (snow) interaction with the components of antifreezes: ethylene- and diethylene glycols, ethylene glycol ethers, hydrogen chloride and ammonia is made. Possibility of “ideal” solution formation with low freezing temperatures is shown. The analysis of the eutectics and diagrams of water antifreeze fusion based on the salts, alcohols, ethylene glycol, ethylene glycol ethers, hydrogen chloride and ammonia by comparison with an ideal solution of water concerning cryoscopic constant is carried out. It is established that the coefficient K in the equation of linear melting curve y = К•x + в for effective antifreezes, in terms of freezing temperature, exceeds the cryoscopic constant of water, that testifies to the destruction of long-range order of water. Penta- and hexamers of water responsible for short-range order of water pass into the eutectics as monomers or oligomers with the degree of cross linking equal to 2–4. To create effective antifreeze it is important to avoid the destruction of cyclic water clusters. It is desirable, as in the case with ethylene, to have the second component of water antifreeze in a cyclic form too. There is an analogy with naphthenic (cyclic) hydrocarbons of oil, which provide mobility of the condensed state. Promising are antifreezes based on mixtures of inorganic and organic compounds.
Water clusters, penta- and hexamers, H-bond, antifreeze, water cryoscopic constant, crown-effect
INTRODUCTION
Solutions with low freezing temperature based on water (antifreezes) are known in nature and are widely used in the technology of food production. The antifreeze composition comprises salts of inorganic and organic acids, alcohols, glycols, glycerin, acids and bases, amino acids and other compounds.
Formation of solutions is a spontaneous diffusion process proceeding from the thermal motion of constituent particles. Interaction force in the solution is evaluated by the osmotic pressure P, which depends on the concentration of the solute [1].
P = RT/V_1 ×ln(1-х) or after simplification P = RTc, where,
V1 – molar volume of the solvent, V1 = М/ρ;
М – molecular weight, ρ – density, х и с – mole fraction of the solute.
This equation describes the ideal, that is, rather diluted (thin) solutions (10-6 - 10-2 mole / dm3), in which osmotic pressure does not depend on the nature of the solvent and solute and is determined only by the number of interacting particles. Osmotic pressure is associated with the numerical average molecular weight of the solute:
М=RT m/П, where, m – molar concentration.
The osmotic properties of solutions include lowering the freezing point of the solvent (water) caused by the additive.
〖∆Т〗_(fr.)=К×m
K - cryoscopic constant of the solvent or the molar lowering of the solidification temperature of the solution. The indicator T characterizes the solvent and is independent of the nature of the solute (solid, liquid, gas). For water K = 1.86 ° C / mole.
For concentrated solutions, it is necessary to introduce osmotic correction factors that reflect the relationship of real and theoretical values. The composition of the resulting associates in the solution remains unknown, primary water clusters have not been established.
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