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Liquid-Like (Transition) Layer on Ice 1 JOURNAl, OF COLLOID AND INTERFACE SCIENCE 25, 192--205 (1967) Liquid-Like (Transition) Layer on Ice 1 H. H. G. JELLINEK Department of Chemistry, Clarkson College of Technology, Potsdam, New York Received August 1, 1966 The concept of a liquid-like layer on ice even below the freezing point of water has become of increasing importance, because it can account for the surprising surface properties of ice. This concept has a very interesting history involving many famous scientists of the last century such as Faraday, Lord Kelvin, J. Thomson, Helmholtz, and Tyndall. Actually, an appreciable amount of research was carried out on ice about 100 years ago. A survey of the concept of the liquid-like layer covering approximately the last hundred years will be given here. A. EARLY WORK at that time and Faraday carried out a In 1850, M. Faraday (1,2) described a number of experiments with other substances phenomenon shown by ice, which soon at their melting points, but they did not became the object of a lively controversy show this behavior. between such famous scientists as Faraday Tyndall accepted Faraday's view, and and Tyndall, on the one side, and J. Thom- the term regelation (refreezing) was first son, his brother W. Thomson (later Lord coined by him in a paper with Huxley (3). Kelvin), and Helmholtz, on the other side. Tyndall attempted to explain the '.'flow" of Faraday's observation was a very simple glaciers by regelation. His idea was that the one: If two pieces of ice at 0°C. or at a higher ice in glaciers fractures in many places, ambient temperature are brought into slight takes up new positions, and reunites by contact, they freeze together. Faraday regelation. points out in various papers that water can Somewhat before Faraday's discovery of be supercooled and superheated. However, regelation, J. Thomson (4) (a brother of when an ice crystal is placed into supercooled W. Thomson (5), later Lord Kelvin) made water, crystallization takes place at once. a quantitative theoretical study of the effect He ascribes this freezing to the effect of of pressure on the melting point of ice by "cohesive" forces exerted on the neighboring thermodynamic reasoning. The final result water "particles." This effect is intensified, is in the form of the Clausins-Clapeyron according to him, if a water film is situated equation. Thomson tried at once to explain between two ice surfaces--a situation which regelation by pressure melting and opposed is brought about by contacting two pieces Faraday's and Tyndall's views. J. D. Forbes of ice; the cohesive forces are then so effec- (6,7) was also interested in regelation phe- tive that freezing takes place even when the nomena at that time, but his theory of ambient temperature is above 0°C. This regelation was certainly incorrect and is of property of ice was a very remarkable one only historical interest today. In response to Thomson's criticisms of 1 This survey appeared as special report $70, Faraday's views on regelation, the latter October 1964, U. S. Army Cold Region Research (2) performed a number of simple but very and Engineering Laboratories, Hanover, New Hampshire. The author wishes to express his ap- ingenious experiments. However, J. Thom- preciation for support of this work by the above son (5) was not convinced. organization. Thus, Faraday and Thomson were dead- 192 LIQUID-LIKE (TRANSITION) LAYER ON ICE 193 locked, although Faraday conceded that, 2.86,~ under appropriate conditions, pressure melt- i ~---,~ ing could play a role. Helmholtz (3) also o Oo ,0 supported Thomson's views and carried out I experiments on regelation, but Tyndall (3) C' remarks in his book that he and Helmholtz © ¢ eventually agreed that regelation could not be properly explained at that time. It is clear that if only experiments at 0°C. I or above are considered, a definite decision o + cannot be made. Thomson's views eventually I I prevailed and found their way into the © o textbooks. I i ii~--o, 2o A Further progress came when more became © known about crystal lattices and forces acting in the surface of solids and when experiments were carried out at tempera- 2.81A tures below the melting point of ice. Fie. 1. Surface layer of a sodium chloride B. RECENT WORK crystal lattiee showing displacement of anions and cations forming an electrical double layer, 0.20 A Progress was made concerning the problem thick (9). of regelation by Weyl (8) in 1951. He pointed out that in an ionic crystal lattice there is reaching consequences for the surface prop- polarization in the surface distorting the erties of water and ice. Thus for water, there lattice in the uppermost surface layer. A should be a disturbance in the surface layers; good example is a crystal of sodiunl chloride in other words, the properties of water in (9). The anions are more polarizable than the surface are different from the bulk the cations, and the surface free energy is properties of water. decreased when the anions are displaced A transition layer several hundred Ang- with respect to the cations in the surface stroms thick is needed, according to Weyl layer as shown in Fig. 1. to pass from the configuration of the outer- An electrical double layer is formed owing most layer to the proper bulk ice structure. to the distortion of the lattice. The actual Thus, he assumes a liquid-like layer, which values for this distortion depend, of course, on the one side has the properties of a water on assumptions made about potential energy surface which changes continuously across curves, etc. This introduces uncertainties in a certain film thickness until the crystal the quantitative evaluation. However, it structure of ice is reeehed. Such a layer, seems to be agreed that such distortion and according to him, exists not only very near double !ayer formation actually take place. the melting point but considerably below An appreciable decrease in surface free the melting point, eventually disappearing energy accompanies such distortion. Weyl as the temperature decreases. Such a film suggested a similar phenomenon for the is in equilibrium with water vapor on the structure of the ice surface. Water molecules one side and bulk ice on the other. It is consist of dipoles, and the surface free energy neither liquid water nor ordinary ice, but is of a water surface and also of an ice surface a transition film which has properties some- in contact with air or in a vacuum would where between those of ice and water. He be considerably reduced if the water dipoles goes even further and postulates that such a were oriented in such a way that the negative liquid-like transition film exists not only at charges (the oxygen atoms) were situated an ice/air interface but also on ice/solid at the outer surface, directed towards the interfaces. The properties and thickness of air or vacuum. In such a way an electrical the transition film will then be influenced by double layer would be formed at the surface the nature of the respective solid. of the water or ice. This postulate has far- The assumption of a liquid-like layer on 194 JELLINEK ice below 0°C. throws new light on all regela- sodium chloride will, of course, have thicker tion phenomena and allows a distinction to transition films and the rolling action will be made between the views of Faraday and be increased. Tyndall on the one side and those of Thom- It will be very difficult to explain this son on the other. In other words, regelation phenomenon in any other way; for instance, phenomena should occur say at -5°C., by pressure melting. It could be assumed where 615 kg./em. 2 are needed to depress that on contact, large pressures are devel- the melting point of ice to such a value. oped owing to the small contact area and Nakaya and Matsumoto (10) were the that some melting and refreezing takes first to carry out some experimental work place; however, breaks should take place in order to verify Weyl's assumptions. They without any rolIing action, although there prepared ice spheres, which were suspended is a small rotational momentum. Similar from cotton threads like pendulums. One of experiments, more accurately controlled, these pendulums could be moved laterally however, were carried out by Hosler, Jensen, making the two spheres touch each other and Goldshlak (11). under a ve[y slight force estimated by the Their apparatus is shown in Fig. 2. It authors to be less than 0.01 dyne. The ice consists of a heated insulated box which spheres prepared from distilled water had could be cooled to -80°C. Here A and B diameters ranging from 1.5 to 4 mm. are the ice spheres, C a microscope, D a Separation of the two spheres was wormserew, and E a calibrated knob. Lateral achieved by moving the suspension point movements to an accuracy of 0.001 inch of one sphere laterally. This separation took could be measured. The force of separation place when each thread formed an angle 0 is again measured by finding the angle 0, with the vertical. An interesting phe- nomenon was observed by these authors. It happened quite frequently at the angle 0, I H that the two spheres started sliding or rolling over each other before finally separating. Rotation was more frequent near the melting point but also occurred at -7.0°C. The strength tended to decrease with increasing temperature, but increased (larger contact c tl'f:],ltl Z.
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