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Anomalous water: a possible explanation of its formation and nature
Volume 12, number 1
CHEMICAL PHYS~S LETTERS.
1 December 1971
+NOMALOUS WATER: A POSSIBLE EXPLANATION ‘OF ITS FORMATION AND NATURE‘
._
M. PRIGOGD& and J J. FRIPIAT* Service de
Chink
Physique, FapWdes Sciences Ap&ue’es, de Bruxelles, Bmxelks, Be&m
Universite' Libre
Received30 September 1971
The origin and a phusible mechanism of the formation of the s&called anomalous wafer is proposed. It is based on particularities of the behaviour of water adsorbed,at low rektive pressure on hydroxylic silica surfaces. The main experimental results emerging from the study of “anomalous” water by various authors seem to be in qreement with the me&r&m de&bed in this note.
In the last years much effort has been devoted to the problem of “atiomalous” water, No agreement on its origii and mode of formation has been reached. It
As has been established [2,3], vicind hydroxyl groups play .a special sole in the adsorption of water molecules, due to the possibility of formation of dou-
is the pltipose of this letter to present what we believe is a plausible interpretation of.tbc interesting but of-
ble hydrogen bonds. They seem to read to localized
ten conflicting effects which ha= been observed. We shall give here only an outlice and stress some important features. Further details will be given elsewhere
region OP Iow re _ 1a t’Ive pre-e.
PI * The studies of infrared
Hair and Hertl [4j have shown th& in the :t $ prec:S? Iy I0 &d adsorprion.which is the nr&lomi.&nt phenomenon on surfaces. On the contrary, for higher relative pressure, it is the adsorption on the isolated hydroxyl groups, probably fdllowed (as soon as all OH groups are covadsorption.
spectra have shown that
silica surfaces freed,‘fiom the adsorbed water by heat-
ered), by capillary condensation, which dominates.
ing at 300°C-400°C in vacuum are composed of silanol groups and siloxane groups. The silariol groups
The physicochemical
may be classified according to the.following configurations ._
H I-
7. 9. 0-Si-0
-7)
H
H
A
I.’0 :
I
0: Iso!ated hy-
droxyl~oup .’
0’ da*
H
. 6/~~~o
0 Gemiml hy-
,,d,,
group
* laboratoke de Chimie,hkralq lWniversit0 de,@uvain. 1 ,, .’ .. .’ .. ,‘, ,. ;: : _.’ :,.
:
droxyl group
corrosion 6f glass surfaces has pointed .l.
cje
.f
:.
out the pbssi-.
bihty of the direct solubility of’silica in acidic water solution by electrtiphihc attack of protons. The re.semblance of the curx iepresenting the rate of the ~ initial solubility (that ti the qtiantity of silica liber-
attack in the solution of hydro-
chloi-ic acid) as a function of hydtogen id!? activity .@ the region ‘of pH +&en_ --Zar.d 2, with &ip~.~Ss ,I
: __:
in
,bulk. Fripiat et al. [S] have shown that the degree of dissociation is of the order of f%, that is 106 times that of water in bulk. This p‘roperti of adsorbed water
ated.after two ho& Iqstitut Agono,tiq&_
of water adsorbed
is very important for the’mechanism of formation of %n&nalous’?water we shall outline below; .The recent work by WI Damme et aI. [6] on the
I
,\P
I
.O-S-O-S-0
properties
the fust molecular-layers on the vicinal hydroxyl groups arc completely different from that of water in
..-,.
_,: : ,;. ‘. .‘,. _, .’; :.,
‘_ .
.
.’
:y
‘.
.’.: :
107 ._
Volume
12, rplmber
CHEMICALPHYSICSLElTERS
1
adsorptionisothermof the hydrogen ions, suggests that the hydrogen ions indeed play an important role inthe corrosion process. These authors show also that in the region ofpH between G and 2 after two hours attack, the rate of dissolution of silica becomes constant. This limiting rate increases with the cqncentration of hydrogen ions. The results given in refs. [7-g] indicate a remarkable similitude of the conditions most favourable for the formation of “anomalous” water to those conditions most favourable for the superficial soIubility of silica by water adsorbed in the first molecular layers. This observation leads us to suggest the following mechanism for the formation of “anomalous” water. We suppose that the first stage consists of the adsorption of water moleEules on a capihary surface, under conditions which favour adsorption on vicinal hydroxyl groups. This corresponds to the situations where the surface contains initially only siloxane and silanol groups and no adsorbed water, and moreover is exposed to a low relative pressure. The adsorbed water molecu!es then form a highly organized struc-
ture, The enhanced degreeof dissociationof water moleculesin the first adsorbed layers creates a favourable medium for the solubility of silica and other constituents of glass. The solution formed in this way will dilute itself by adsorption of normal water. The foal concentration of this solution will be such that its equilibrium vapour pressure is equal to the pressure established at ?he beginning of the experiment. The quantity of silica dissolved in the first stage of the experiment is determhed by the initial conditions, notably by tht! acidity of the adsorbed water and the state of the capillary surface. Thz decrease of the acidity of a medium due to the adsorption of a normal water reduces the solubility of silica. There are other experimental data which seem to be in complete agreement with these ideas. As has been shown through measurements of refractive indexes and optical ankotropy by Castellion et al. IlO] in the first stage of the experiment “anomalous” water grows near the capillary surface forming-highly ordered layers. As the distance from the wall increases the extent of ordering decreases. The f&t that the aging of “anomalous” water in capillaries gives‘rise to a very strong decreaseof order and even to its complete disappearance can be explained by a polymerizaticn of silicic acid present &the
108 ..
golution:it
then forms a
1 December 1971
sol or a gel of silica, What seems to be vr&~significanr in the experiments of Castellion et al. istlre fact that the high refractive index corresponds always to the : high initial order. This shows then that the higher the .or+r and the dissociation degree of adsorbedwater, the higher the concentration of silica is which is dis-
sohed .
Everett, Haynes and Elroy [ll] , studying the phase behavicur and the vapour pressure of “anomalous” water, reached the conclusion that the “anomalous” water is not a single chemical species but a polydisperse polymer which forms a so1 which coagulates to gel over a certain range of p/p* and within the gelled state ages with reduction in solubility. Everett et al. have shown that all the properties discussed by them were consistent with that of a silicic acid sol and geI. Therefore they concluded that because it was not likely that substances other than silica and water would be cobundin the capillary, it is indeed the silicic acid sol which is responsible for the properties of “anomalous” water. In addition, the solubility of silica estimated by Everett et al. was greater than that usually quoted for aqueous solutions. The mechanisms of formation of the “anomalous” water proposed by Everett et al. is very similar to ours. There are also analytical arguments available. De Paz& al. [12] have found that the mass spectrum of “anomalous” water contains mass triplets typical of silica isotopes. Also the electron probe analyses of residues from the condensation of “anomalous” water by Bascom, Brooks and Worthington 1131 indicate a significant amount of silica and sodium_
The argumentwhich, accordingto Deryaginand his coworkers [14], seems to be the most important for the existence of “anomalous” water, comes, on one side, from the fact that the “anomalous” water can be transferred by distillation at a temperature to 7OO’C without losing it9 anomalous properties and, on the other side, the product of a distillation at 700800°C appears to be normal water. If one accepts, what is well known to geologists and engineers (for an interesting bibliography see [ 15]), that silica can be carried by steam, one can try to give an alternative explanation of this behaviour. First, according to Heitman [ 161, the solubility of silica in water and water wpour increases with the density of the solvent and with the &nperature. On the other hvd, Ekady [17j has show&&at the quantity of sili-,
Volume 12. number
1
L Deaxnber
CHEMIC4L PHYSICS LETTERS
ca carried by steam increases with the acidity of the ,solution. As all of these favourable conditions are realised in the distillation experiment of Deryagin et al., one may imagine that the coIumn of “anomalous” water can be restored after distillation in the sense that the distillate may contain a non-negligible quantity of silica. It is known [18] that heating of a silica surface above 800°C causes drastic, and irreversible elimination of the hydroxyl groups. The impossibility of a formation of hydrated species of silica at temperatures above 8OO”C,would explain the fact that the product of distillation at such temperatures appears to be normal water. In conclusion, when an appropriate configuration of hydroxyl groups is present on a surface of silica, adsorbed molecules of water can form a hi&~ly organized structure, but this structure exists only in intimate contact with the surface. The physical properties of water in this structure are quite different from that of water in bulk and may lead to enhanced solubiIity of silica. Even if in agreementwith these views “anomalous” water in the usual sense does not exist, these phenomena are quite remarkable.and unexpected and deserve further study. We thank Professor Ceorges Thomaes of the Faculty of Applied Science of Brussels Free University for helpful discussions; we wish to thank D.H. Everett, J.M. Haynes and PJ. McElroy of the Dapartment of Physical Chemistry, Bristol University, whose article “Coll&tive properties of anomalous water” was very useful in the development of our thesis. We would iike to e,xpress our gratitude to Dr. D. Oriani, Professor I. Prigogine and Professor R. Schechter for discussions and advice.
1971
Reference5
[l] M. Rigogine’and J_I. Fripiat, Bull_ Sac. Chim. France, to be pubtished.
[2] A.V. Kiselevand V.T. Lygin. ColIoidI. 2r
(Buttetworths,
Fripht, M.C. Ganuche and R. Brichad. 5. Phys 66 (1962) 805. [4] W. Hertland M.L. Hair, Nature 223 (19691 1150. [5] J.J. Fripit, A. Jelli, G. Poncdet and J. Am+& I. Phw.
[3]
J.J.
Chem.
Chem. 69 (1965) 2185. [6] ‘Van Damme, Charlet, Wauters and
[7] [8] [9] [lo]
[ 1l] (121
IelIi,O.C9.E., Pro-
jet III, Rapport de ctiture pour Ies dexx premi@res at&es d’activite’, pr&ntd Ie 24 novemb:e 1970. S.B. Brumrner, F.H. Cocks,G. Entine and J.I. Bradspies, J. COIL Intern. Sci., to be published. S.B. Brummer,G. Entine, J.I. Bradspies, H. Lingertat and C. Leung. Science, to he published. M. Rigogine and C. Thomaes, Compt. Rend. Aud. Sci (Paris) 269B (1969) 999. Gh. Castellion, D.G. Grabar, J. Hession and H. Burkhard, Science 167 (1970) 865. D.H. Everett, J.H. Haynes and PJ. hfcEiroy, Nature 226 (1970) 1033. H. de Py. A. POUO and ME. Va&uri.Chem. Phys.
Letters 7 (1970) 23. [13] W.D. Bascom, E.J. Brooks and BN. Worthington III, Nature 228 (1970) 1290. (141 B.V. Deryagin, Z.M. Zorin, Ya.I. Rnbinotictr, XV. Talayev and N.V. Churayev, DokL Akad. Nauk SSSR 191 (1970) 4,859. [15 ] O.H. Krikorian, Thermodynamics of tie sificz-steam system, Lawrence Radiaiion laboratory, University of &Iiforr;ia, Livermore, Reprint. [16] H-G. Heitman, Chemiker Ztg. 88.22 (f964) 891. [17] E,L,Brady, J, Phys. Chem. 57 (1953) 706. [18] G.L. Young, J.ColIoid Sci. 13 (1956) 67.
109
CHEMICAL PHYS~S LETTERS.
1 December 1971
+NOMALOUS WATER: A POSSIBLE EXPLANATION ‘OF ITS FORMATION AND NATURE‘
._
M. PRIGOGD& and J J. FRIPIAT* Service de
Chink
Physique, FapWdes Sciences Ap&ue’es, de Bruxelles, Bmxelks, Be&m
Universite' Libre
Received30 September 1971
The origin and a phusible mechanism of the formation of the s&called anomalous wafer is proposed. It is based on particularities of the behaviour of water adsorbed,at low rektive pressure on hydroxylic silica surfaces. The main experimental results emerging from the study of “anomalous” water by various authors seem to be in qreement with the me&r&m de&bed in this note.
In the last years much effort has been devoted to the problem of “atiomalous” water, No agreement on its origii and mode of formation has been reached. It
As has been established [2,3], vicind hydroxyl groups play .a special sole in the adsorption of water molecules, due to the possibility of formation of dou-
is the pltipose of this letter to present what we believe is a plausible interpretation of.tbc interesting but of-
ble hydrogen bonds. They seem to read to localized
ten conflicting effects which ha= been observed. We shall give here only an outlice and stress some important features. Further details will be given elsewhere
region OP Iow re _ 1a t’Ive pre-e.
PI * The studies of infrared
Hair and Hertl [4j have shown th& in the :t $ prec:S? Iy I0 &d adsorprion.which is the nr&lomi.&nt phenomenon on surfaces. On the contrary, for higher relative pressure, it is the adsorption on the isolated hydroxyl groups, probably fdllowed (as soon as all OH groups are covadsorption.
spectra have shown that
silica surfaces freed,‘fiom the adsorbed water by heat-
ered), by capillary condensation, which dominates.
ing at 300°C-400°C in vacuum are composed of silanol groups and siloxane groups. The silariol groups
The physicochemical
may be classified according to the.following configurations ._
H I-
7. 9. 0-Si-0
-7)
H
H
A
I.’0 :
I
0: Iso!ated hy-
droxyl~oup .’
0’ da*
H
. 6/~~~o
0 Gemiml hy-
,,d,,
group
* laboratoke de Chimie,hkralq lWniversit0 de,@uvain. 1 ,, .’ .. .’ .. ,‘, ,. ;: : _.’ :,.
:
droxyl group
corrosion 6f glass surfaces has pointed .l.
cje
.f
:.
out the pbssi-.
bihty of the direct solubility of’silica in acidic water solution by electrtiphihc attack of protons. The re.semblance of the curx iepresenting the rate of the ~ initial solubility (that ti the qtiantity of silica liber-
attack in the solution of hydro-
chloi-ic acid) as a function of hydtogen id!? activity .@ the region ‘of pH +&en_ --Zar.d 2, with &ip~.~Ss ,I
: __:
in
,bulk. Fripiat et al. [S] have shown that the degree of dissociation is of the order of f%, that is 106 times that of water in bulk. This p‘roperti of adsorbed water
ated.after two ho& Iqstitut Agono,tiq&_
of water adsorbed
is very important for the’mechanism of formation of %n&nalous’?water we shall outline below; .The recent work by WI Damme et aI. [6] on the
I
,\P
I
.O-S-O-S-0
properties
the fust molecular-layers on the vicinal hydroxyl groups arc completely different from that of water in
..-,.
_,: : ,;. ‘. .‘,. _, .’; :.,
‘_ .
.
.’
:y
‘.
.’.: :
107 ._
Volume
12, rplmber
CHEMICALPHYSICSLElTERS
1
adsorptionisothermof the hydrogen ions, suggests that the hydrogen ions indeed play an important role inthe corrosion process. These authors show also that in the region ofpH between G and 2 after two hours attack, the rate of dissolution of silica becomes constant. This limiting rate increases with the cqncentration of hydrogen ions. The results given in refs. [7-g] indicate a remarkable similitude of the conditions most favourable for the formation of “anomalous” water to those conditions most favourable for the superficial soIubility of silica by water adsorbed in the first molecular layers. This observation leads us to suggest the following mechanism for the formation of “anomalous” water. We suppose that the first stage consists of the adsorption of water moleEules on a capihary surface, under conditions which favour adsorption on vicinal hydroxyl groups. This corresponds to the situations where the surface contains initially only siloxane and silanol groups and no adsorbed water, and moreover is exposed to a low relative pressure. The adsorbed water molecu!es then form a highly organized struc-
ture, The enhanced degreeof dissociationof water moleculesin the first adsorbed layers creates a favourable medium for the solubility of silica and other constituents of glass. The solution formed in this way will dilute itself by adsorption of normal water. The foal concentration of this solution will be such that its equilibrium vapour pressure is equal to the pressure established at ?he beginning of the experiment. The quantity of silica dissolved in the first stage of the experiment is determhed by the initial conditions, notably by tht! acidity of the adsorbed water and the state of the capillary surface. Thz decrease of the acidity of a medium due to the adsorption of a normal water reduces the solubility of silica. There are other experimental data which seem to be in complete agreement with these ideas. As has been shown through measurements of refractive indexes and optical ankotropy by Castellion et al. IlO] in the first stage of the experiment “anomalous” water grows near the capillary surface forming-highly ordered layers. As the distance from the wall increases the extent of ordering decreases. The f&t that the aging of “anomalous” water in capillaries gives‘rise to a very strong decreaseof order and even to its complete disappearance can be explained by a polymerizaticn of silicic acid present &the
108 ..
golution:it
then forms a
1 December 1971
sol or a gel of silica, What seems to be vr&~significanr in the experiments of Castellion et al. istlre fact that the high refractive index corresponds always to the : high initial order. This shows then that the higher the .or+r and the dissociation degree of adsorbedwater, the higher the concentration of silica is which is dis-
sohed .
Everett, Haynes and Elroy [ll] , studying the phase behavicur and the vapour pressure of “anomalous” water, reached the conclusion that the “anomalous” water is not a single chemical species but a polydisperse polymer which forms a so1 which coagulates to gel over a certain range of p/p* and within the gelled state ages with reduction in solubility. Everett et al. have shown that all the properties discussed by them were consistent with that of a silicic acid sol and geI. Therefore they concluded that because it was not likely that substances other than silica and water would be cobundin the capillary, it is indeed the silicic acid sol which is responsible for the properties of “anomalous” water. In addition, the solubility of silica estimated by Everett et al. was greater than that usually quoted for aqueous solutions. The mechanisms of formation of the “anomalous” water proposed by Everett et al. is very similar to ours. There are also analytical arguments available. De Paz& al. [12] have found that the mass spectrum of “anomalous” water contains mass triplets typical of silica isotopes. Also the electron probe analyses of residues from the condensation of “anomalous” water by Bascom, Brooks and Worthington 1131 indicate a significant amount of silica and sodium_
The argumentwhich, accordingto Deryaginand his coworkers [14], seems to be the most important for the existence of “anomalous” water, comes, on one side, from the fact that the “anomalous” water can be transferred by distillation at a temperature to 7OO’C without losing it9 anomalous properties and, on the other side, the product of a distillation at 700800°C appears to be normal water. If one accepts, what is well known to geologists and engineers (for an interesting bibliography see [ 15]), that silica can be carried by steam, one can try to give an alternative explanation of this behaviour. First, according to Heitman [ 161, the solubility of silica in water and water wpour increases with the density of the solvent and with the &nperature. On the other hvd, Ekady [17j has show&&at the quantity of sili-,
Volume 12. number
1
L Deaxnber
CHEMIC4L PHYSICS LETTERS
ca carried by steam increases with the acidity of the ,solution. As all of these favourable conditions are realised in the distillation experiment of Deryagin et al., one may imagine that the coIumn of “anomalous” water can be restored after distillation in the sense that the distillate may contain a non-negligible quantity of silica. It is known [18] that heating of a silica surface above 800°C causes drastic, and irreversible elimination of the hydroxyl groups. The impossibility of a formation of hydrated species of silica at temperatures above 8OO”C,would explain the fact that the product of distillation at such temperatures appears to be normal water. In conclusion, when an appropriate configuration of hydroxyl groups is present on a surface of silica, adsorbed molecules of water can form a hi&~ly organized structure, but this structure exists only in intimate contact with the surface. The physical properties of water in this structure are quite different from that of water in bulk and may lead to enhanced solubiIity of silica. Even if in agreementwith these views “anomalous” water in the usual sense does not exist, these phenomena are quite remarkable.and unexpected and deserve further study. We thank Professor Ceorges Thomaes of the Faculty of Applied Science of Brussels Free University for helpful discussions; we wish to thank D.H. Everett, J.M. Haynes and PJ. McElroy of the Dapartment of Physical Chemistry, Bristol University, whose article “Coll&tive properties of anomalous water” was very useful in the development of our thesis. We would iike to e,xpress our gratitude to Dr. D. Oriani, Professor I. Prigogine and Professor R. Schechter for discussions and advice.
1971
Reference5
[l] M. Rigogine’and J_I. Fripiat, Bull_ Sac. Chim. France, to be pubtished.
[2] A.V. Kiselevand V.T. Lygin. ColIoidI. 2r
(Buttetworths,
Fripht, M.C. Ganuche and R. Brichad. 5. Phys 66 (1962) 805. [4] W. Hertland M.L. Hair, Nature 223 (19691 1150. [5] J.J. Fripit, A. Jelli, G. Poncdet and J. Am+& I. Phw.
[3]
J.J.
Chem.
Chem. 69 (1965) 2185. [6] ‘Van Damme, Charlet, Wauters and
[7] [8] [9] [lo]
[ 1l] (121
IelIi,O.C9.E., Pro-
jet III, Rapport de ctiture pour Ies dexx premi@res at&es d’activite’, pr&ntd Ie 24 novemb:e 1970. S.B. Brumrner, F.H. Cocks,G. Entine and J.I. Bradspies, J. COIL Intern. Sci., to be published. S.B. Brummer,G. Entine, J.I. Bradspies, H. Lingertat and C. Leung. Science, to he published. M. Rigogine and C. Thomaes, Compt. Rend. Aud. Sci (Paris) 269B (1969) 999. Gh. Castellion, D.G. Grabar, J. Hession and H. Burkhard, Science 167 (1970) 865. D.H. Everett, J.H. Haynes and PJ. hfcEiroy, Nature 226 (1970) 1033. H. de Py. A. POUO and ME. Va&uri.Chem. Phys.
Letters 7 (1970) 23. [13] W.D. Bascom, E.J. Brooks and BN. Worthington III, Nature 228 (1970) 1290. (141 B.V. Deryagin, Z.M. Zorin, Ya.I. Rnbinotictr, XV. Talayev and N.V. Churayev, DokL Akad. Nauk SSSR 191 (1970) 4,859. [15 ] O.H. Krikorian, Thermodynamics of tie sificz-steam system, Lawrence Radiaiion laboratory, University of &Iiforr;ia, Livermore, Reprint. [16] H-G. Heitman, Chemiker Ztg. 88.22 (f964) 891. [17] E,L,Brady, J, Phys. Chem. 57 (1953) 706. [18] G.L. Young, J.ColIoid Sci. 13 (1956) 67.
109