Damping of water waves by "oil films" has already been appreciated since ancient times, however, knowledge regarding the causes of this effect has progressed only very slowly since the first attempted explanations in classical times. The first to describe this phenomenon was Aristotle in his Problemata Physica [1]:
Why is it that the sea, which is heavier than fresh water, is more transparent? Is it because
of its fattier composition? Now oil poured on the surface of water makes it more transparent,
and the sea, having fat in it, is naturally more transparent.
Furthermore, Plutarch in his Moralia: Quaestiones Naturales [2] ascribed to Aristotle (probably from lost parts of that author's Problemata):
Is it, as Aristotle says, that the wind, slipping over the smoothness so caused, makes no impression and raises no swell?......
They say that when (sponge) divers take oil into their mouths and blow it out in the depths they get illumination and see through the water. Surely it is impossible to adduce slipping of the wind as the cause there.
In addition to these astonishingly correct explanations Plutarch offered alternative but relatively obscure interpretations.
Another practical application of organic surface films added to the sea surface was reported by Pliny the Elder [3] describing the seamen's practice of calming water waves in a storm by pouring oil onto the sea, in order to prevent shipwrecking. A similar utilisation of oil was reported by Bede (Baeda Venerabilis º The Venerable Bede) who spent most of his life at the monastery Jarrow where he wrote the first comprehensive history book on British history Historia Ecclesiastica Brittanorum. He gives an account of one of Aidan´s miracles, as told to him by Cynemund, a priest of Jarrow. A priest named Utta, making a long sea journey, was instructed to pour oil on the sea in the event of a storm:
.... and the wind will immediately drop, giving you a pleasant, calm voyage.....He .... poured some of it over the sea, which immediately ceased its raging as Aidan had foretold (cited in the translation after Scott [4]).
Further early reports on wave damping by oil can be found in manuscripts by St. Germanus, Theophilact Simocrate, St. Nicholas, Erasmus Roterdamus, H. Canisius, S. Maiolus, M. Martin, V. Donati, T. Pennant, and L. Poinsinet de Sivry. The exact references are summarised in the bibliography by Scott [4], presumably the most comprehensive one with regard to this subject.
From a scientific point of view, Benjamin Franklin was the first to perform experiments with "oils" on natural waters. On June 20th, 1757, a convoy of ships set sail northwards from New York, bound for Louisburg, a French fortress near the eastern tip of Cape Breton Island, northeast of Nova Scotia [5] . The convoy consisted of transports carrying British troops, their escorting frigates, and some vessels carrying civilian passengers. One of these passengers happened to be watching the accompanying fleet when something unusual in the appearance of the sea around a vessel attracted his attention. This passenger was Benjamin Franklin, who had been appointed by the American House of Assembly in Philadelphia as their agent to petition George II against the action of the Proprietors of Pennsylvania. After a frustrating wait of nearly three months in New York until permission was given for the fleet to sail, he set out with about 40 others, passengers included, in one of three packet boats, which for protection sailed in convoy with the fleet and steered for England. The incident, which captured his attention, led to the first scientific recognition of the importance of surface films on water. Some years later he described it, and its sequel, in these words [6]:
In 1757, being at sea in a fleet of 96 sail bound against Louisburg, I observed the wakes of two of the ships to be remarkably smooth, while the others were ruffled by the wind, which blew fresh. Being puzzled with the differing appearance, I at last pointed it out to our captain, and asked him the meaning of it? "The cooks", says he, "have, I suppose, been just emptying their greasy water through the scuppers, which has greased the sides of those ships a little"; and this answer he gave me with an air of some little contempt as to a person ignorant of what everybody else knew. In my own mind I at first slighted his solution, tho' I was not able to think of another. But recollecting what I had formerly read in Pliny, I resolved to make some experiment of the effect of oil on water, when I should have opportunity......
At length being at Clapham where there is, on the common, a large pond, which I observed to be one day very rough with the wind, I fetched out a cruet of oil, and dropt a little of it on the water. I saw it spread itself with surprising swiftness upon the surface..... I then went to the windward side, where (the waves) began to form; and there the oil, though not more than a teaspoonful, produced an instant calm over a space several yards square, which spread amazingly, and extended itself gradually till it reached the lee side, making all that quarter of the pond, perhaps half an acre, as smooth as a looking glass (1 acre = 43 560 sq. feet = 63 x 63 m2).
After this, I contrived to take with me, whenever I went into the country, a little oil in the upper hollow joint of my bamboo cane, with which I might repeat the experiment as opportunity to succeed...... In these experiments, one circumstance struck me with particular surprize. This was the sudden, wide and forcible spreading of a drop of oil on the face of the water, which I do not know that anybody has hitherto considered. If a drop of oil is put on a polished marble table, or on a looking-glass that lies horizontally; the drop remains in its place, spreading very little. But when put on water it spreads instantly many feet around, becoming so thin as to produce the prismatic colours, for a considerable space, and beyond them so much thinner as to be invisible, except in its effect of smoothing the waves at a much greater distance. It seems as if a mutual repulsion between its particles took place as soon as it touched the water, and a repulsion so strong as to act on other bodies swimming on the surface, as straws, leaves, chips, etc., forcing them to recede every way from the drop, as from a center, leaving a large clear space. The quantity of its force and the distance at which it will operate, I have not yet ascertained, but I think it a curious enquiry, and I wish to understand whence it arises.....
Benjamin Franklin's experiments with a "teaspoonful of oil" on Clapham pond in 1773 inspired many investigators to consider sea surface phenomena or to conduct experiments with oil films. This early work was reviewed by Scott [4], Giles [5], Giles and Forrester [7], and Tanford [8]. Franklin's studies with experimental slicks can be regarded as the beginning of surface film chemistry. His speculations on the wave damping influence of oil induced him to perform the first qualitative experiment with artificial sea slicks at Portsmouth (England) in October of 1773. Although the sea was calmed and very few "white caps" appeared in the oil-covered area, the swell continued through the oiled area to Franklin's great disappointment.
In addition to early experiments on the open sea, basic studies were performed in the laboratory, in order to gain basic insight into the wave damping mechanism induced by surface-active oil film materials ("slicks"). The first to carry out systematic wave tank investigations appears to have been Achard in the year 1778 who used a trough 4.3 m long, 1.2 m wide, and 1.2 m deep, in which standing waves were generated by a hand-cranked rotating-cylinder assembly [9]. The effect of the waves on a model ship, 15 cm long, was observed, and the action of an oil film in suppressing the breaking of waves over the ship was demonstrated. The effect of oil was, however, not remarkable, and the greater wave-suppressing action of air-filled glass spheres tethered to the model ship led the author to the conclusion that the effect of both oil and floating solid bodies was a result of the mass they added to the surface.
Otto gave perhaps the earliest comprehensive account of the classical and medieval authors, and in his descriptions of uses he draws heavily on Franklin and Lelyveld (see [4]). In explaining the effect he favours the hypothesis that the oil discourages the natural affinity of water for air, and prevents the force of the wind from being transmitted to the water. He does not, however, reject the hypothesis of Achard that floating solid bodies may have a similar, and more permanent, calming effect. Kries described his reasons for scepticisms regarding all of the mechanisms so far proposed for explaining the action of oil on waves [11]: Achard's work with a model system is criticised as unrealistic; Otto`s belief in the chemical effect, waves being generated by the affinity between water and air, was thought to be unlikely compared with the mechanical effect of the fluctuating force of the wind, and Müller's suggestion (see [4]) that the viscous skin on the surface hinders wave breaking, although felt to be plausible, was seen to require more experiments to determine whether the oil layer is sufficiently strong for this effect. Principally concerned with explaining the damping of large amplitude waves observed by Franklin at an oil/water interface, Robinet [12] suggested that an oil film can only exert a marked effect on waves whose amplitude is less than the film thickness. Since all waves must start from small amplitudes, however, he considered that the effect on storm waves is credible. By the way of contrast, Weber and Weber conjectured that an oil layer does not adhere to the water, and thus absorbs the horizontal component of the wind stress [13]. Van Beek [14] concurred with Franklin and Aristotle that the effect of oil is in the prevention of small waves which would allow the wind to grip the breakers. He attempted to explain this damping action, his argument being based on some effect of the oil on horizontal components of the wind velocity.
The basis for our present models describing wave damping by monomolecular surface films was formed by a paper published by Marangoni in 1872 [15]:
Spargendo dell'olio sul mare si sostituische alla superficie elastica dell'aqua la superficie non elastica dell'olio; sicche il vento smuoverá localmente le particelle dell'olio senza che il movimento venga a communicarsi per una grande estensione, e di qui il cessare dell'increspamento della superficie coll'effusione dell'olio.
Marangoni described investigations which showed that motions of bodies at the surface of a liquid may be opposed by elastic forces associated with a surface layer. The conclusion of Plateau that such effects are due to an increased viscosity of the surface layer was shown to be inadequate. The importance of the surface elasticity (or more precise visco-elasticity in modern terms) in the damping of wind waves was pointed out (Abbonacciamento delle onde, pp 268-270) and the explanation of the effect that the change of elasticity associated with the oil is sufficient to prevent excitation of waves by the wind, is essentially that still held today. However, it should be noted that Marangoni´s conclusions are rather confused from a modern point of view, the water being found to be elastic and the oil surface not elastic. On the other hand, Marangoni´s views inspired many models related to the influence of surface-active chemical compounds on the motion of fluids (Marangoni effect, Marangoni damping), including models in the field of Applied and Technical Chemistry. It may also be of interest to the readers that several observations of daily life are closely associated with the Marangoni effect. For example, if wine is poured into a wine glass, and then moderately shaken around such that the wine is moving along the outer parts of the glass, one can observe the wine creeping up the walls. This upward movement is driven by surface tension gradients (Marangoni effect) caused by different intense evaporation of ethanol at the lower and upper parts of the walls.
A more precise interpretation of water wave damping through the elastic nature of a spread oil film was given by Reynolds. The full text is as follows [16]:
The paper contained a short account of an investigation from which it appeared that the effect of oil on the surface of water to prevent wind-waves and destroy waves already existing, was owing to surface-tension of the water over which the oil spread varying inversely as the thickness of the oil, thus introducing tangential stiffness into the oil-sheet, which prevented the oil taking up the tangential motion of the water beneath. Several other phenomena were also mentioned. The author hopes shortly to publish a full account of the investigation.
This full account apparently never appeared, except for a few lines given in Reynolds 1884 [4]. Lord Rayleigh carried out very detailed laboratory experiments, which showed the damping of wind-excited ripples by a drop of oil. The phenomenon was explained in terms of the resistance to wave motion associated with the differences in surface tension, which arise during the periodic extensions and contractions of the surface. Related experiments on the properties of soap films and the spreading of organic materials were also described. The very comprehensive work was published in three papers [17-19].
The first to perform wave-damping measurements in a kind of Langmuir trough, i.e., under different compression status of the monolayer, was Agnes Pockels [20]. Ironically, she described for the first time an apparatus that was later also used by Langmuir and named after him (according to a publication in 1917). Pockels performed relatively delicate experiments on the contamination of water surfaces by organic materials. A shallow trough divided by a movable barrier was used to vary the area of a water surface and thus the compression status of the monolayer, and marked variations of the damping of ripples were found. A rapid increase in damping with increasing surface concentration was found.
The earliest available hydrodynamic theory of water wave damping by elastic surface films was published by Lamb [21]. He refers to Reynolds [16] and the experiments by Aitken (see [4, 7]), but prior publication of the detailed theory is not indicated. All but the outline of the theory was omitted from later editions of this book, and it is likely that Lamb assumed that damping was greatest with an inextensible film, and that intermediate elasticities, therefore, had less effect (cited after Scott [4]). This conclusion was shown by Dorrestein to be incorrect [22]. The paper by Levich [23] was the first to present in detail the linearised hydrodynamics of waves on a water surface with surface dilational elasticity. The only cases considered in detail concern insoluble films, and represent the clean and incompressible-film-covered surface. A detailed treatment of the hydrodynamic theory of surface waves, including the effect of an elastic surface film, was published by Levich in 1962 [24]. In addition, the damping caused by dissolved surface-active material was considered. Further laboratory experiments performed until 1978 were briefly reviewed by Scott [4].
In recent years, experimental sea slicks are being utilised for basic studies of air-sea interaction processes including wind wave generation [27-35], wind-induced drift response of the ocean surface [36], and gas exchange [37] as well as for the investigation of the modification of remote sensing signals by biogenic and anthropogenic surface-active chemicals on the ocean surface [38-41].
[1] Aristotle, Problemata Physica , Book XXIII "Problems connected with salt water and the sea", No. 38.
[2] Plutarch, Moralia: Quaestiones Naturales, Vol. 11, No. 12.
(see also Plutarch, Moralia: De Primo Frigido, No. 950).
[3] C. Plinius Secundus (Pliny the Elder), Historia Naturalis, Book 2, Chapter 49 (completed A.D. 77).
(see also C. Plinius Secundus, Historia Naturalis, Book 2, Chapter 106).
[4] Scott J C (1979) Oil on troubled waters. A bibliography on the effects of surface-active films on surface-wave motions. Multi-Science Publishing Co. Ltd, The Old Mill, Dorset Place, London, 1979. ISBN 0 906522 00 5
[5] Giles C H (1969) Franklin's teaspoonful of oil. Studies in the early history of surface chemistry, part 1. Chem. Ind., 1616-1624.
[6] Franklin B (1774) Of the stilling of waves by means of oil. Phil. Trans. Roy. Soc. 64, 445-460.
[7] Giles C H, Forrester S D (1970) Wave damping: the Scottish contribution. Studies in the early history of surface chemistry, part 2. Chem. Ind., 80-87.
[8] Tanford C (1989) Ben Franklin stilled the waves. Duke University Press, Durham and London, 227 pp.
[9] Achard F C (1778) Mémoire sur la manière de calmer l'agitation d'une partie de la surface d'un fluide,.(Concerning the means of reducing the motion of part of the surface of a fluid...). Nouveaux Mémoires de l'academie Royale des Sciences et Belles-Lettres, Berlin, 19-26 (in French).
[10] Otto J F W (1798) Das Öl, ein Mittel die Wogen des Meeres zu besänftigen (Oil as a means of calming waves at sea). Allgemeine Geographischen Ephemeriden, Vol. 2, 516-527 (in German).
[11] Kries F C (1799) Einige Bemerkungen über J.F.W. Otto's Aufsatz: das Öl, ein Mittel die Wogen des Meeres zu besänftigen (Some comments on J.F.W. Otto`s article: Oil as a means of calming waves at sea). Allgemeine Geographischen Ephemeriden, Vol 3, 242-251 (in German).
[12] Robinet (1807) Explication d'un phénomène d'hydrostatique observè par Franklin (Explanation of a hydrostatic phenomenon observed by Franklin). Journal de Physique, de Chimie et d'Histoire Naturelle, 277-282 (in French).
[13] Weber E H, Weber W (1825) Über die Besänftigung der unter dem Einflusse des Windes erregten Wellen durch die Ausbreitung von Ölen auf der Oberfläche von Wasser (On the calming of wind-generated waves by the spreading of oil on the surface of water). Wellenlehre, auf Experimente gegründet, Leipzig, 60-90 (in German).
[14] van Beek A (1842) Mémoir concernant la propriété des huiles de calmer les flots, et de rendre la surface de l'eau parfaitement transparente (Memoir concerning the property of oils to calm waves, and to make the surface of water perfectly transparent). Annales de chimie et de Physique, 3me Série, Vol 4, 257-289.
[15] Marangoni C (1872) Sul principio della viscosita superficiale dei liquidi stabilito dal sig.
J. Plateau (On the principle of the surface viscosity of liquids, established by J. Plateau).
Nuovo Cimento, Series 2, Vol. 5/6, 239-273 (in Italian).
(Further evidence was given Marangoni in Nuovo Cimento, Series 3, Vol. 3, 50-68, 97-115, 193-211.
[16] Reynolds O (1880) On the effect of oil in destroying waves on the surface of water. Report of the British Association for the Advancement of Science, 489-490.
[17] Lord Rayleigh (1890) Foam. Proceedings of the Royal Institution, Vol. 13, 85-97.
[18] Lord Rayleigh (1890) On the superficial viscosity of water. Proceedings of the Royal Society, Vol. 48, 127-140.
[19] Lord Rayleigh (1890) On the tension of water surfaces, clean and contaminated, investigated by the emthod of ripples. Philosophical Magazine, Vol. 30, 386-400.
[20] Pockels A (1891) Surface tension. Nature, 43, 437-439.
[21] Lamb H (1895) The calming effect of oil on water waves. Hydrodynamics, 2nd Edition, Cambridge University Press, Article 304, 552-555.
[22] Dorrestein R (1951) General linearised theory of the effect of surface films on water ripples. Proceedings, Koninklijke Nederlandse Akademie van Wetenschappen, Series B, Vol. 54, 260-272.
[23] Levich V G (1940) The damping of waves by surface-active materials. Zhurnal Eksperimentalnoi
i Teoretcheskoi Fiziki, Vol. 10, No. 11, 1296-1304 (in Russian).
(English language version: Acta Physiochimica URSS, Vol.14, 307-328 (1941)).
[24] Levich V G (1962) Waves on a liquid surface. Physicochemical Hydrodynamics, Prentice Hall, Chapter 11, 591-626.
[25] La Mer V K (1962) Retardation of evaporation by monolayers: transport processes. Academic Press, New York.
[26] Davies J T, Rideal E K (1963) Interfacial Phenomena. Academic Press, New York and London, 480 pp.
[27] Hühnerfuss H., Garrett W D (1981) Experimental sea slicks: their practical applications and utilization for basic studies of air-sea interactions. J. Geophys. Res., 86, 439-447.
[28] Hühnerfuss H, Alpers W, Jones W L, Lange P, Richter K (1981) The damping of ocean surface waves by a monomolecular film measured by wave staffs and micro-wave radars. J. Geophys. Res., 86, 429-438.
[29] Hühnerfuss H, Alpers W, Lange P A, Walter W (1981) Attenuation of wind waves by artificial surface films of different chemical structure. Geophys. Res. Lett., 8 , 1184-1186.
[30] Hühnerfuss H, Alpers W, Garrett W D, Lange P A, Stolte S (1983) Attenuation of capillary and gravity waves at sea by monomolecular organic surface films. J. Geophys. Res., 88 , 9809-9816.
[31] Hühnerfuss H, Walter W, Lange P A, Alpers W (1987) Attenuation of wind waves by monomolecular sea slicks and the Marangoni effect. J. Geophys. Res., 92 , 3961-3963.
[32] Alpers W, Hühnerfuss H (1989) The damping of ocean waves by surface films: A new look at an old problem. J. Geophys. Res., 94, 6251-6265.
[33] Barger W R, Garrett W D, Mollo-Christensen E L, Ruggles K W (1970) Effects of an artificial sea slick upon the atmosphere and the ocean. J. Appl. Meteorol. 9, 396-400.
[34] Mallinger W D, Mickelson T P (1973) Experiments with monomolecular films on the surface of the open sea. J. Phys. Oceanogr. 3, 328-336.
[35] Alpers W, Hühnerfuss H (1989) The damping of ocean waves by surface films: A new look at an old problem. J. Geophys. Res., 94, 6251-6265.
[36] Lange P, Hühnerfuss H (1978) Drift response of monomolecular slicks to wave and wind action. J. Phys. Oceanogr., 8, 142-150.
[37] Brockmann U H, Hühnerfuss H, Kattner G, Broecker H-Ch, Hentzschel G (1982) Artificial surface films in the area near Sylt. Lymnol.Oceanogr., 27, 1050-1058.
[38] Hühnerfuss H, Gericke A, Alpers W, Theis R, Wismann V, Lange P A (1994) Classification of sea slicks by multi-frequency radar techniques: new chemical insights and their geophysical implications. J. Geophys. Res., 99, 9835-9845.
[39] Hühnerfuss H, Alpers W, Dannhauer H, Gade M, Lange P A, Neumann V, Wismann V (1996) Natural and man-made sea slicks in the North Sea investigated by a helicopter-borne 5-frequency radar scatterometer. Int. J. Remote Sensing, 17, 1567-1582.
[40] Gade M, Alpers W, Hühnerfuss H, Masuko H, Kobayashi T (1998) Imaging of biogenic and anthropogenic ocean surface films by the multifrequency/multipolarization SIR-C/X-SAR. J. Geophys. Res., 103, 18851-18866.
[41] Gade M, Alpers W, Hühnerfuss H, Wismann V R, Lange P A (1998) On the reduction of the
radar backscatter by oceanic surface films: scatterometter measurements and their theoretical
interpretation. Rem. Sens. Environ., 66, 52-70.