Barbara F. Howell
Notional Bureau of Standards Washington, D.C.20234
I
Anomalous Water: Fact or Figment
O n e of the more interesting scientific discoveries report,ed during t,he decade of the 60's is the announcement of t,he discovery of an allotropic modification of liquid wat,er which has a higher density and lower vapor pressure than ordinary water. Papers began to appear in Russian journals as early as 1960 stating t,hat water adsorbed on a hydrophilic surface undergoes a structural modificat,ion which extends out,ward for a distance of 10-6-10-s em. Prior to 1961, Deryagin (I) suggested a method for viscosit,y determination for thin layers of liquids adsorbed on solid surfaces. The method was developed by his associat,es, \vho found a fift,eenfold increase in viscosity for thin layers of adsorbed wat,er. The surface influence was found to end abruptly a short distance from the solid surface, providing a boundary a t which the enhanced viscosity suddenly disappeared. These discoveries were followed by the announcement by Fedyakin ( 1 ) that measurement. of the thermal expausion of water in a microcapillary did not s h o ~a minimum volume at 4'C. Instead theolength of water columns in capillaries of less than 200 A radius showed a linear decrease in length down to -12"C, at. which temperat,ure freezing had not yet occurred. These investigations of expansion aud contraction behavior of water columns in t,iny capillaries were continued until an entire family of curves was produced as shown in Figure 1. I n this figure relative length changes are plotted as a function of temperature. An interesting fact about these curves is that water in capillaries does not exhibit the same behavior on cooling that it does when warmed; instead hystersis loops are produced.
Figure 1. Freezing point curvet of moximolly modifled (11, mixtures of ordinary and onomolovr water I2 through 5 ) and ordinov water 161. (Adapted from 0 graph of 8. V. Deryagin (8)).
For t,heir capillary product, the Russians observed separation into t,wophases at -12" (8),but bot,h phases retain spherical menisci to t,emperat,ures of -50 to -60°C. This usual behavior was regarded by them as evidence for the existence of a new or anomalous modification of liquid water. Parenthetically, is it worth not,ing that supercooling of carefully purified water in capillaries is well known. Whereas large quantities of water freeze a t O°C, a small amount, such as that in a capillary, may be cooled to -72°C (5) if care is taken to remove "freezing nuclei," for example minute particles of dust. Furthermore, reduction in freezing point, separation into t,wo phases, and hyst,eresis type hehavior are observed for silica and other sols. By 1965, the Russian investigators had become convinced t,hat condensation of water vapor inside the capillary was essential for the product,ion of water with anomalous propert,ies and they observed that anomalous \vat,er exhibited a vapor pressure lowering amounting to as much as 7% below that of liquid wat,er. Liquid wat,er drawn up into capillaries, st,rangely enough, u7as not. found to exhibit unusual properties. Among t,hese workers, the belief was developing that wat,er was being struct,urally modified, that the molecular arrangement was somehow being altered during the process of coudensat,ion on a silica or glass surface. The alteration of properties was not believed to be due to glass-leaching since this would not explain the observed difference bet,ween liquid water entering t,he capillaries and water vapor condensing inside. The. results of elect,rical conductivit,~measurements made by Fedyakin (4) and others were published in 1965. Conductivity measurements were made by inserting platinum-wire electrodes into the capillary and measuring the electrical resistance of the water column wit,h a bridge circuit. Specific conductivity values found for anomalous water were higher than that of distilled >rater, but lower thau that of 0.1 N sodium hydroxide. Values for 207& suspensions of crushed glass in water were higher than the value for anomalous water, but. of the same order of magnitude. The arguments evinced for the exist,ence of anomalous water, as an allotropic modification of liquid water, were t,hat salt solutions in high enough concentration to produce the observed vapor pressure lowering, shorn electrical conductivities much larger thau that of anomalous water. (However, a hydrosol, or s solution of a nonelectrolyte is capable of exhibiting appropriate values of both conductivity and vapor pressure, simultaneously.) The Russian observers also compared elongation properties of a soiium hydroxide solution inside a capillary, with a similar column of anomalous water.. The sodium hydroxide column increases in length by Volume 48, Number 7 0, October 7 977
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condensation of additional water, whereas the anomalous water column shortens producing a gel "as shown by viewing the capillary under crossed Nicols in a polarizing microscope." Deryagin, Talaev, and Fedyakiu (5) published a paper in 1965 containing additional information about, anomalous water. Fedyakin had observed t,he groxth of secondary columns in glass capillaries in which a liquid column is already present,, and the secondary columns reportedly exhibited lowered vapor pressure and an increased viscosity. At this same time, because other invest,igators had suggested that the anomalous properties reported for capillary water might be caused by leaching, Deryagir~ ( 5 ) and coworkers began to attempt its preparation in highly purified fused silica capillaries. They believed that pure anomalous water would be produced if the water vapor pressure vere maintained a t less than 100% saturation, since ordinary water would not condense under this condition. (The vapor pressure loxering due to capillary curvature is negligible for capillaries above 1 fim in diameter.) A special vessel, shown in Figure 2, was designed by the
Figure 2. A ..hematic drawing d t h e opporotu. "red by Deryogin and coworkers to produce anomdous water. The chamber ir evacuated through the stopcock at the left. Woter temperature. of the upper and lower chambers ore reporotely controlled by m e o n r of thermostoned bothr, thermocouple (A) the temperature difference between the liquid woter reservoir ond the woter vapor which wrrounds the copillory (81.
.
Russians to maintain a precise water vapor saturation, and nyas used to produce anomalous water. The upper portion of the chamber, in which the fused silica capillary was placed, contained water vapor a t a slightly higher temperature than that of the liquid water reservoir t,en~peralurein order to produce the desired undersaturation. Temperature control for the two chambers was effected by me:ins of water jackets supplied with waber from temperature-controlled baths. The growth of a liquid column in the capillary was observed through the optically-flat window in the end of t,he upper chamber with the aid of a microscope. The Russian investigators concluded that leaching of the capillary mat,eri,zl canuol play a n essent,ial role in 'anomalous uat,er formation because of the short time (= 1 hr) required for water to condense inside a rapillary when air has been removed. This group observed a much sloxer growth rate in the presence of air, and assumed that the rate is cotitrolled primarily by the 664
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diffusion of vapor t,hrough theair in the column. With all the advantages that come from hindsight, it is possible to say t,hat the Russian group apparently overloolred the fact t,ho.t nit,rogen gas from air is strongly adsorbed by a fresh silica or glass surface (6), and the presence of nitrogen on t,he capillary surface interferes with the adsorption of wat,er. The Russians also apparently vere unaware of the p~ssibilit~y t,hat freshly drawn fused silica capillaries often contain fine silica particles vhich serve as nuclei for the formation of droplets of liquid water and lead to the productionof silica sols. Further, as soon as rapillaries are pulled, they become partially coated with whatever substances are present in the air surrounding them, so that it is possible for these materials to go into solution in water which later fills t,he capillaries. By 1967 the Russiaris had pretty n-ell characterized their alleged stable allotrope of liquid xater. They believed it could be distilled at temperatures up to 400°C ~ i t h o u losing t its anomalous characteristics (as can a silica sol (7) or a borate solution). Use of a densky gradient column has produced values for its specific gravit,y xhichvaried, but ran as high as 1.4 times that of wat,er. Refractive index values, ranging upvard to 1.46, had been determined by using a microscope to measure the apparent inside diameter of a liquid filled capillary. Measurement of the distance the microscope objective travels between sharp focus positions on the upper and lower capillary walls, and utilization of the "foreshortening effect," which causes objects to appear to be closer when vie\ved through a material of higher refractive index, alloms calculat,ion of the refractive index. Besides these, a viscosit,y value 15 times that, of normal wat,er had been ohtained from measurements made inside a capillary. For this purpose measurements were made of the pressure necessary to cause a liquid column to move inside a capillary and of the velocity of the motion. These were used to calculate t,he viscosit,y. As t,ime passed, additions to t,he list of properties reported by the Russians (8) included the heat. of vaporization (6 kcal-mole-') and a value for the molecular weight of 180-200 obtained by cryoscopic methods. The surface tension for a mixture of anomalous and ordinary water with a mole fraction of anomalous water equal to 0.3, was 75 ergs-~m-~. This surface t,ension elevation indicates that organic substances are probably not responsihte for the observed properties of anomalous water, since organics usually lower the surface tension. One problem in characterization, which the Russians had, stemmed from the fact that. very miuute portions of anomalous water were produced a t one t,ime, and of necessity property measurements were made on different samples. Afeauwhile, Bellamp, Osborne, Pethica, and Finnie in lhgland had become excited over the possible significanoe of the Russian discovery, and Tvere attempting to grow aarromalous water in vacuum desiccators which lacked precise temperature control, although in a t least some of their attempts a potassium sulfat,e solut,ion v a s used to produce a lover xvater vapor pressure (9). Shorlly thereafter, numerous articles appeared in journals postulating structures for this elusive form of \vat,er. Such arrangements as a rhomhic dodecahedra1 structure, one consisting of four water molecules a t the corners of a tet,rahedron, a highly branched net.work
Figure 4. The infrored spectrum of polywatar obtained by Lippincott I1 31 (Adopted).
Figure 3. A, The rhombic dodecahedra1 model of Danohve (10). B , The tetrohedrol rlwchlre of Bolonder 11 1). C, The branched network contoining partial hexogonol rings 1131. D, The stacked hexogonol Toyers of Allen (141.
containing partial hexagonal rings, and a layered structure, composed of planar, fused hexagonal rings with alternative starking patterns were proposed (Fig. 3). -,
At the same time new names for anomalous water proliferated. Erlander (12) proposed super water;
Lippincott (IS), poly\vater; and Allen (14) proposed the name cgclimetric ~vater. Somehow the names orthowater and v a t e r I1 Tvere also acquired. Federal agencies in t,he United States appropriated money for the characterization and large scale production of this intriguing substance, and many laboratories undertook its investigation without financial support. I n June of 1969 Lippincott (IS) and co~vorkerspublished an infrared (Fig. 4) and a Raman spectrum for this sobstance, along xvith an electron microprobe analysis which sho~vedthe presence of oxygen, (hydrogen cannot, be detected by this method) and traces of silicon and sodium. Lippincot,t interpreted the infrared absorption a t 1595 cm-' to be the OH-stretching mode ~vhich is normally observed as a broad band a t approximately 3400 em-' in liquid water. I t is ell known that 'hydrogen bonding shifts the OH-stretching vibrational mode toward longer ~vavelengths. For example, water vapor shows this absorption a t 3756 and 3651 cm-' and the increase in hydrogen bonding due t o liquefaction causes the shift to t,he 3400 cm-' position. Lippincott, considered the very strong hydrogen bonds which exist in alkali bifluorides, e.g., RHF, which s h o m H-F stretching a t 1450 em-', and reasoned that an extremely strong hydrogen bond in water could produce the addit,ional shifting of t,he 0-H stretching to 159.5 cnl-'. The 0-H-0 structural unit is isoelectronic wit,h the F H F unit which has an F-F distance of 2.26 A. Correlations (15) of the magnihde of t,he shift in O H stretching absorption have been made with oxygen t o oxygen distances for hydrogen bonded systems, and hydrogen bond sbrengths have also been estimated from the magnit,udes of t,he shift. On this basis Lippincott suggested that polywater might have oxygen to oxygen distances of 2.3 A, with the hydrogen atom located midway on the line joining the t,wo oxygen atoms. Reasoning similarly, he estimated the hydrogen bond strength to be 30-50 kcal-mole-' per bond unit, rather than the usual value of approximately 6 kcal-mole-' for liquid water. I n this paper he also published t,he netlike st,ructure shown in Figure 3. While the interest and enthusiasm surrounding this mysterious form of wat,er were a t their heights, various other papers appeared. Petsko (16) and Page, Jakohsen, and Lippincott (17) published paramagnetic resonance spectra which showed a resonance 300 Hz downfield from the normal water resonance. A distincVolume 4 8 , Number 10, October 1971
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tive X-ray diffraction pattern v a s also reported (18). Calculations n-ere made of the "possihility of p-electron delocalization" (lo), an infrared vibrational mode analysis was done on the structure proposed by Lippincott (SO), molecular orbital calculations (81) \yere made, and the electronic structure of polyxater \\-aselucidated by means of CND0/2 calculations (14). While these sophisticated theoretical approaches !yere being made, mnch effort was expended in attempts to prepare greater than microgram amounts of polgwater. But the bubble of belief was soon to burst. As early as April of 19G9, aud during the spring and summer of 1970, papeis began to appear in ~vhichthe existeuce of anomalous 11-ateras a stable allotropic. modificatiou of liquid water was qnestioned. Rabidenu and Florin ( 8 collected 11-ater in fused quartz capillaries by condensation of vater vapor in an unsaturated atmosphere. After concentration, this material exhibited the same density, refractive index, and freezing point, behavior as anomalous xater. Electron microprobe analysis of the concentrated material showed the pre5 ence of sodium, boron, and oxygen. Rabideau (89) also performed experiments which shoved that anomalous ~yaterdid not form inside ca~illariesmaintained a t undersaturation if special care, i.e., suspending capillaries from wires, \I-as used to prevent liquid rater from creeping inside. Rousseau (83) reported that, his samples, prepared by "standard methods," shoxed the same physical and spectroscopic properties as other anomalous 11-atersamples, but contained large amounts of impurities. He attributed the ir absorption band a t 1100 cm-' to S O P ion, and suggested that bands at 1600 and 1400 cm-I vere likely due to earboxyl groups and bicarbonates. At this same time certain Russian investigators began to publish doubts about the validity of the discovery of anomalous water (84). In an effort. to validate hi discovery, Deryagin proposed mass spectrometric analyses. Twent,y-five samples weighing from 10-6 to lo-= g mere analyzed under the directorship of V. L. Tal'rose. The mass spectra showed that the samples cont,ained lipids and phospholipids (compounds which are exuded in human sweat) in amounts as large as the amount of sample itself. Ions of mass 19 (HaO+),36 and 37 ((H20)2+ and (H20)2H+) were absent, whereas mass 18 (HtO) was present in large amount. Polywater samples prepared in the United States, and concentrated by evaporation, have been analyzed by ESCA ($5) (electron spectroscopy for chemical analysis). Results show that 95% of the total photoelectron spectrum consists of sodium and potassium salts of sulfate, chloride, nitrate, horates, and carbonate compounds. Davis (86) has produced ir spectra of polyHz0 and poly-DzO which show the same absorption peals. These provide strong evidence that the spectrum published by Lippincott does not, indicate the existence of "super-strong" hydrogen bonds, since if this were the case, the 2500 cm-' OD stretching mode of DzO would also show a large shift toward lower frequencies when it became poly-DpO. The aut,hor has been able to reproduce the vapor pressure behavior of anomalous water with a mixture of silica gel and water and obtain the report,ed boiling point by extrapolation of a plot of the logarit.hm of vapor pressure as a function of the reciprocal of the 666
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Journal of Chemical Education
absolute temperature. The slope of this line yielded a value for the heat of vaporization very close to the value obtained by Deryagin for anomalous water. We have also reproduced many of the freezing point curves attribut,ed to anomalous water by using mixtures of water, Cabosil (a colloidal form of silica), and sodium hydroxide. I n addit,ion, a water solution, which was shown by electron microprobe analysis t,o contain sodium, silicon, and oxygen, showed an increased surface tension of the same magnitude as that of anomalous water. We have constructed a chamber in xhich accurate temperature control is possible, and we find that. vater fails to condense in freshly-drawn, fused silica capillaries a t less than 100% water vapor saturrttion in agreement with the results of Rabideau (88). Bascom, Brooks, and Worthington (87) have suggested that anomalous xyater owes its properties to the presence of silicates and Kurtin, et al., (88), have stated that all the properties of anomalous wat.er are also those of hydrosols. As the last fell- years have passed, more and more disturbing questions concerning the existence of anomalous water have arisen. No one to date has succeeded in preparing this material in its pure state, and property measurements vary widely from sample to sample as xould be expected for a mixture. The heat of vaporization reported by Deryagin (S), as previously stated, is G Ircal-mole-', u-hich is less than the value for ordinary water; yet anomalous ~vat,er reportedly boils at. a temperature much higher than ordinary water. How can this be explained? Signs cmtly, evaporation of anomalous water produces a nonvolatile residue amounting to as much as 15% of the init,ial sample mass. Deryagin suggests that the residue is the most highly polymerized portion of polyxater, but a silicate mixture seems a far more likely possibility! Furthermore, since anomalous wat,er has a lower vapor pressure than ordinary xater, thermodynamics predicts t,hat the free energy is lower for the anomalous phase and t,hat it, is the more stable. Since t,his is t,he case, why is ordinary water the prevalent form? A final quest.ion in regard to anomalous water concerns growth on itself. Once a small amount is formed one would expect growth to cont,inue,in t,he manner of supercooled vat,er changing to ice after an ice crystal is dropped into it, but no such behavior is observed. These objections have apparently proved insurmountable. More' and more the tide of belief is receding, and has now reached such a low ebb t>hatNatuve, which along with Science has been a faithful chronicler of polywater research, has published its obituary (89). In a half page article entitled "Polywater Drains Away," t.he evidence set forth by Bascom (84), who found polywat,er residues t.o contain principally sodium and silicat,e ions, and that of Barnes (86) are cit,ed, as examples of the increasing volume of evidence that polywater owes its properties to impurities. The author acknowledges support from the Office of Naval Research, grant No. N0001469A-0141-0002 and project THEMIS, N0001468-A-0497. Literature Cited (1) Translatedfrom Kolloidnyy~hurnd.24 (No. 4 ) . 361 (1962). (2) D.;nr*am. D. V.. E n a r o v ~ .E. G.. Znsr.mmrr. B. V.. A N D C a u e r w . N. V.. Translated from Doklady Akodemit Noun 8SSR. 172 (No. 5) 1121 (1867).
R m . W.. Department of Commerce Microfilm PB-27773 (Shriften d e Dnrlachan Akodernis dm Luftfocachunu. 8, No. 2 (1944)). FEDYAKIN, N. N.. DEBYAOIN,B. V., N O Y I I ~ V A A., V., AND TALAEV, M. V., Tranelated from DoXlody Abodarnii Nouk SSSR, 165 (No. 4). 878 (1965). D m r a o m , B. V., T=*ev. M. V.. *No F ~ o r m r x N. , N.. Translated fromDoklady Akodemii Notrl. SSSR. 165 (No. 3). 597 (1965). HAIR,MICUE= L.. "Infrared Speatrosaopy in Surface Chemistry." M a e l Dekksr. New York. 1967, pp 92ff. soar*^, R.. "The Phase. of Siliclioa;' Rutgem Univ. Press, 1965, p. 338. D ~ R Y ~ IB.NV., . AND CIORAIW. N. V., "Investigation of the Prop erties of Weter 11." a paper presented t o the 44th National Colloid Symposium. Lshigh Univemity. June. 1970. FINNET. JOXN.W v a t e Communication (1968). Dol**num. J.. Scicncc. 166,1000 (1969). BOLAND~R. R. W..Kt.88NER. J. L.. JR., A N D ZYNO, J. T.. Notule. 221, No. 5187. 1233 (1969). EXLANDER. S. R.. Phy8. Em. Ldlma, 22 (No. 5). 177 (1969). L r p ~ m o o n .E. R.. 8Taorsnxa. R. R., G u m . W. H., AND C m s ~ c . G . L.,Seianea, 164, 1482 (1969). ALLEN,L. C.. AND KOLLXAN. P. A,, S e i e m , 167, 1443 (1970).
(15) PrrslrT*~.G. W., A N D M o C ~ m ~ m w A.. L.. "The Hydrogen Bond:' W. H. Freeman. San Francisco. 1960, pp 82 ff. (16) PETBHD, G . A., Science. 167, 171 (1970). E. R., S e i ~ w e . (17) Pme, T. F.. Jn., J o m s s e n . R. J.. A N D LIPPINCOTT. 167.61 . 119701. . . (18) PETSKO,G . A.. AND MABBEY, W. R.. I... L .%RPV . DiErwtion -1., vestigations of Anomalous Water." b paber pres&tad a t the 44th National Colloid Symposium. Lehigh Univ., June, 1970. (19) M6881EB. 8.P.. S ~ i a m .e167.479 . - ~ llP70)~ ~ ~ (20) B*TBS. J . B . , ~ & ~ c o r r E. , R.. MIKAWA.Y.. A N D J A ~ B B E NR., J., J . Chcnt. Phys., 52 (No. 7). 3731 (1970). . S. N., A N D Rho, C. N. R., Cham. Comm., No, (21) Go.=. A,. M o s ~ a r A.
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R*nms*u. S. W.. A N D FLORIN.A. E.,Schwa. 169,48 (1970). Roussmu, D. L., AND Porno, 8. P. S., Scienra, 167,1715 (1970) Z ~ r s n m V.. , Khimiyo i zhinn. NO. 12.37 (1969). R o o s s s ~ uD, . L., A N D DAVXB, R. L.. Seiancc, 171.170 (1971). C. and E. News o. 7. June 29. 1970. B ~ s o o r W. . D.;B&OKS. E.'J., ARD WORTXM~TON.B. N. 111, NSIYI.. 228, 1290 (1970). . H.. K U B T ~ NB. , C., A N D (28) Kunvm. S. L.. Mmn. C. A,, M U ~ L E BW. WOLB, E.D.. Science, 167, 1720 (1970). (29) Nature. 230.11 (1971).
(22) (23) (24) (25) (26) (27)
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