NEUTRON DIFFRACTION STUDIES OF ICE NUCLEATION IN POROUS SILICA

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NEUTRON DIFFRACTION STUDIES OF ICE NUCLEATION IN POROUS SILICA

J. Dore, M. Dunn, P. Chieux

To cite this version:

J. Dore, M. Dunn, P. Chieux. NEUTRON DIFFRACTION STUDIES OF ICE NUCLE- ATION IN POROUS SILICA. Journal de Physique Colloques, 1987, 48 (C1), pp.C1-457-C1-463.

�10.1051/jphyscol:1987163�. �jpa-00226309�

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C o l l o q u e C1, s u p p l e m e n t a u n o 3 , Tome 48, m a r s 1987

NEUTRON DIFFRACTION STUDIES OF ICE NUCLEATION IN POROUS SILICA

J. C. DORE, M. DUNN and P. CHIEUX"

Physics Laboratory, University of Kent, GB-Canterbury CT2 7NQ, Great-Britain

* ~ n s t i t u t Laue-Langevin, B.P. 156 X , F-38042 Grenoble Cedex, France

Des mesures p a r d i f f r a c t i o n n e u t r o n i q u e o n t " e t 6 p r i s e s s u r D20 d a n s d e s s i l i c e s poreuges pour une gamme d e tempEratures. Pour l e S p h e r i s o r b S20W a v e c d e s p o r e s de - 90A ; l a g l a c e Ih q u i s e forme 2 - 1 3 ' ~ d e v i e n t p r i n c i p a l e m e n t d e l a g l a c e I, quand l a temperature a t t e i n t -21'~. ChauffFe, l a g l a c e cubique r e s t e s t a b l e j u s q u g a ' son p o i n t de f u s i o n v e r s 4'~. Les donnges i n d i q u e n t a u s s i l a p r g s e n c e d h n e forme dFsordonn7?e de g l a c e ou d q e a u d a n s t o u t e l a gamme S t u d i c e ( 2 -60'~).

Ces r?Zsultats c o n f i r m e n t . l e s i n d i c a t i o n s a n t 5 i r i e u r e s que l a f o r m a t i o n e t l a

s t a b i l i t g de l a g l a c e Ih e t l a g l a c e I, dgpendent s u r t o u t de f a c t e u r s c o n c e r n a n t l a t a i l l e d e s c r i s t a l l i t e s , b i e n que l e r a p p o r t e n t r e c e s deux formes semble z t r e p l u s s u b t i l q u q o n ne l e p e n s a i t jusquq'a p r s s e n t .

A b s t r a c t

Neutron d i f f r a c t i o n measurements have been made on D20 i n porous s i l i c a s f o r a r a n g e o f t e m p e r a t u r e s . I n S p h e r i s o r b S20W w i t h a p o r e s i z e o f - ^{90 ji t h e}

i n i t i a l f o r m a t i o n of i c e Ih a t -13OC becomes predominantly i c e I, a s t h e tempera- t u r e is reduced below -21°C. On h e a t i n g t h e c u b i c i c e remains s t a b l e u n t i l m e l t i n g i n t h e v i c i n i t y o f U°C. Th.e d a t a a l s o show e v i d e n c e f o r t h e p r e s e n c e o f a d i s o r d e r e d form o f i c e o r water o v e r t h e f u l l r a n g e s t u d i e d ( 2 -60°C). These r e s u l t s confirm t h e e a r l i e r s u g g e s t i o n s t h a t t h e growth and s t a b i l i t y o f i c e Ih and i c e Ic is p r i m a r i l y i n f l u e n c e d by c r y s t a l l i t e s i z e c o n s i d e r a t i o n s a l t h o u g h t h e b a l a n c e between t h e s e two forms seems t o be more s u b t l e t h a n p r e v i o u s l y r e a l i s e d .

1 . I n t r o d u c t i o n

The behaviour o f w a t e r a t a h y d r o p h i l i c o r hydrophobic i n t e r f a c e h a s been a s u b j e c t o f i n t e r e s t f o r many y e a r s . It is w e l l r e c o g n i s e d t h a t t h e r e is some m o d i f i c a t i o n o f b o t h s t r u c t u r a l and dynamic p r o p e r t i e s b u t t h e d e g r e e t o which t h i s e x t e n d s i n t o t h e bulk l i q u i d phase remains a r e s e a r c h t o p i c o f c o n t i n u i n g i n t e r e s t and c o n t r o v e r s y . Experimental d a t a which p r i m a r i l y probe t h e m o l e c u l a r p r o p e r t i e s s u g g e s t a s h o r t - r a n g e e f f e c t which e x t e n d s over o n l y a few molecular l a y e r s whereas m e a p r e m e n t s on bulk thermodynamic p r o p e r t i e s . l e a d t o e s t i m a t e s r a n g i n g up t o 100 A o r more.

The p r o x i m i t y o f a n i n t e r f a c e i s expected t o i n f l u e n c e t h e n u c l e a t i o n p r o p e r t i e s . It is w e l l known t h a t t h e o n s e t of i c e f o r m a t i o n i s d e p r e s s e d below t h e normal f r e e z i n g p o i n t o f t h e bulk l i q u i d phase and is a l s o s t r o n g l y dependent on t h e p o r e s i z e . T h i s phenomenon p r o v i d e s a c o n v e n i e n t way o f s t u d y i n g w a t e r i n a weakly-supercooled s t a t e and e x t e n s i v e n e u t r o n d i f f r a c t i o n measurements have a l r e a d y been r e p o r t e d by S t e y t l e r e t a l . [1,2]. During t h e c o u r s e of t h i s work, some measurements were made below t h e n u c l e a t i o n t e m p e r a t u r e . The d i f f r a c t i o n

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987163

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p a t t e r n f o r t h e w a t e r / i c e C31 showed t h e c h a r a c t e r i s t i c s of cubic i c e (1,) r a t h e r than t h e normal hexagonal form, i . e . Ih, although t h e r e was a small admixture of t h i s component p r e s e n t i n t h e p a t t e r n and t h e peaks were super-imposed on an o s c i l l a t o r y form c h a r a c t e r i s t i c of a disordered m a t e r i a l . The following r e s u l t s a r e t h e preliminary f i n d i n g s from a more d e t a i l e d study of t h e same system using neutron d i f f r a c t i o n and show t h a t t h e behaviour is even more complex than f i r s t thought.

2. Experimental Procedure

a ) Samples

The main experiments were conducted on t h e porous s i l i c a Spherisorb S20W obtained from Phase Sep Ltd. The s u r f a c e h a s a low c o n c e n t r a t i o n of f r e e hydroxyl groups and can be completely d r i e d by h e a t i n g a t 200°C f o r s e v e r a l hours. To ensure t h a t hydrogen is f u l l y removed from t h e system t h e d r i e d sample is e q u i l i b r i a t e d w i t h excess D20 and then d r i e d again. The process is r e p e a t e d , a s r e q u i r e d , t o g i v e two samples comprising 'dry s i l i c a ' and 'wet s i l i c a ' i n which t h e pores a r e f u l l of D20 water.

The samples were s e a l e d i n a thin-walled vanadium c o n t a i n e r of 5mm diame t e r . The powdered m a t e r i a l i n i t i a l l y formed a loose-packed mass b u t a f t e r tap- ping, t h e l e v e l a d j u s t e d t o a s t a b l e p o s i t i o n of approximately c o n s t a n t packing d e n s i t y .

b ) Measurements

The neutron d i f f r a c t i o n d a t a were obtained with t h e D4B d i f f r a c t o m e t e r on t h e high f l u x r e a c t o r a t t h e I n s t i t u t Laue-Langevin (ILL) Grenoble. Angular scans were made f o r both t h e 'wett and 'dry' samples f o r a range of temperatures.

A f t e r c o r r e c t i o n f o r background, m u l t i p l e s c a t t e r i n g , . sample a t t e n u a t i o n e t c . , t h e s c a t t e r i n g p a t t e r n f o r t h e ice/water i s obtained following s u b t r a c t i o n of t h e s u b s t r a t e (Si02) c o n t r i b u t i o n .

3. R e s u l t s

a ) Temperature s t u d i e s with Spherisorb: i n i t i a l cooling.

The i n i t i a l measurements were made f o r t h e normal l i q u i d phase and t h e temperature was then reduced t o -2I0C. The r e s u l t i n g d i f f r a c t i o n p a t t e r n is shown i n t h e upper p a r t of Fig.1 and i s , s u r p r i s i n g l y , c h a r a c t e r i s t i c of hexago- n a l i c e ; t h e v a r i o u s peaks a r e indexed according t o known c h a r a c t e r i s t i c s C41.

The lower curve (Fig.1) shows t h e p a t t e r n which is observed a f t e r c o o l i n g t o -60°C where t h e f u r t h e r growth of t h e d i f f r a c t i o n peaks produces a c l e a r indica- t i o n o f t h e cubic i c e form. A small proportion of i c e Ih is s t i l l p r e s e n t , a s shown by t h e r e s i d u a l (1-02) peak although i t would appear from t h e e s t i m a t i o n of peak i n t e n s i t i e s t h a t t h e r e is p o s s i b l y a conversion of some i c e Ih t o i c e Ic i n t h i s process ( - 5 + ^{5 % ) .}

A c o n t i n u a t i o n o f t h e cooling shows an i n c r e a s i n g n u c l e a t i o n of i c e Ih but t h e r e is minimal change below -30°C. Figure 2 shows a comparison of d a t a taken a t -30°C and -60°C f o r t h e low s c a t t e r i n g - a n g l e region. There is c l e a r evidence f o r t h e e x i s t e n c e of a disordered t i c e / w a t e r t phase under t h e c r y s t a l l i n e peaks from t h e i c e I, and Ih s t r u c t u r e . T h i s i s well shown by t h e low l e v e l of s c a t t e r i n g below t h e main peaks ( < 2i-I ) which d e f i n e s t h e o v e r a l l l e v e l of incoherent

s c a t t e r i n g . Close examination of t h e s t r u c t u r e over t h e Q-range 3-6 A-' i n Fig. 1

suggests t h a t t h e peaks a r e superimposed on an o s c i l l a t o r y s t r u c t u r e which is

c h a r a c t e r i s t i c of a disordered m a t e r i a l but i t i s u n c l e a r from t h e p r e s e n t d a t a

what form t h i s disordered m a t e r i a l comprises. The o v e r a l l p a t t e r n t h e r e f o r e in-

d i c a t e s t h a t t h e r e is a complex admixture of up t o t h r e e d i s t i n c t phases which may

i n t e r c o v e r t a s t h e temperature is changed. I n Fig.2, it would seem t h a t a small

proportion (- 10%) o f t h e disordered phase is converted t o i c e I, a s t h e tempera-

t u r e is reduced from 243K t o 213K. The i n t e n s i t y o f t h e main peak is n o t much

a l t e r e d by t h e change, probably because t h e disordered/amorphous phase a l s o has a

peak a t t h i s p o s i t i o n which is buried underneath t h e Bragg peaks from t h e crys-

t a l l i n e phases. A f u r t h e r d i s c u s s i o n of t h i s e f f e c t is d e f e r r e d u n t i l t h e next

s e c t i o n .

{

C 8

- ¹

Q I A

Figure 1 . The i n i t i a l n u c l e a t i o n forming Figure 2. The v a r i a t i o n i n t h e i c e Ih (upper c u r v e ) and t h e lower temper- observed d i f f r a c t i o n p a t t e r n f o r a t u r e phase of i c e Ic (lower curve). D20 i c e i n Si02 when cooling

from 243K t o 213K.

Figure 3. The observed d i f f r a c t i o n Figure 4. An expanded s c a l e p l o t p a t t e r n on re-warming showing a r e d u c t i o n of t h e d i f f r a c t i o n p a t t e r n f o r i c e i n t h e i n t e n s i t y of t h e i c e I, peaks I, a t 213K showing t h e ' d i s o r d e r * and a c o n t r i b u t i o n from t h e c o - e x i s t i n g c o n t r i b u t i o n under t h e Bragg peaks;

l i q u i d phase. a corresponding p l o t f o r

low-density amorphous D20 i c e [81 is a l s o shown.

b ) Temperature s t u d i e s with Spherisorb: warming and re-cycling.

Following the f i r s t temperature reduction run, t h e sample was warmed

u n t i l t h e l i q u i d phase was regained. Due t o v a r i a b l e h e a t conduction i n t h e

sample, i t was impossible t o d e f i n e t h e exact temperature a t which melting oc-

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curred but t h e r e s u l t s i n d i c a t e d t h a t t h e i c e 1, phase was s t a b l e over a tempera- t u r e range extending up t o t h e normal melting p o i n t of i c e I a t approximately U0C. Figure 3 shows a s h o r t scan taken when p a r t of t h e i c e had melted s o t h a t t h e d i f f r a c t i o n p a t t e r n c o n s i s t s of a mixture of both t h e i c e I, and t h e water p a t t e r n . There is no evidence of conversion from i c e Ic t o i c e Ih s o t h a t t h i s temperature i s t h e h i g h e s t value a t which i c e I, has been observed.

A f u r t h e r r u n was made with reducing temperature b u t t h e d a t a have not y e t been analysed. I n t h e course of t h i s second temperature c y c l e t h e r e was a sudden unexpected change i n t h e o v e r a l l s c a t t e r i n g i n t e n s i t y which h a s n o t y e t been ex plained and could p o s s i b l y i n d i c a t e some s t r u c t u r a l damage t o t h e porous network of t h e s i l i c a s u b s t r a t e . These r e s u l t s w i l l be presented a t a l a t e r s t a g e when t h e d a t a have been f u l l y evaluated.

4. I n t e r p r e t a t i o n of d a t a

The p r e s e n t experiments demonstrate a number of i n t e r e s t i n g phenomena which can only be p a r t i a l l y explained. The presence o f i c e I, r a t h e r than i c e Ih can be accounted f o r by t h e s i z e of t h e c r y s t a l l i t e s which presumably cannot grow beyond t h e s i z e of an i n d i v i d u a l c a v i t y . Nucleation s t u d i e s i n quenched amorphous samples o f aqueous i o n i c s o l u t i o n s by C51 have shown t h a t t h e balance of cubic and hexagonal i c e i s dependent on t h e number of n u c l e a t i o n c e n t r e s i n t h e mate- r i a l and t h a t t h i s can be c o n t r o l l e d i n t h e amorphous phase by an 'annealing procedure' based on temperature c o n t r o l . I n Spherisorb t h e r e is a n a t u r a l re- s t r i c t i o n t o the c r y s t a l l i t e s i z e due t o t h e pore characteristics and t h i s is such a s t o favour t h e formation of i c e I,. Subsequent changes i n temperature have no f u r t h e r i n f l u e n c e on t h e r a t i o s o t h a t once formed, t h e c r y s t a l l i t e s remain s t a b l e u n t i l t h e normal melting p o i n t . T h i s observation confirms t h a t t h e r e l a - t i v e s t a b i l i t y is based on an energy c r i t e r i a which depends p r i m a r i l y on t h e s u r f a c e t o volume r a t i o and not on k i n e t i c f a c t o r s a s s o c i a t e d with t h e r a t e of formation. It should a l s o be noted t h a t t h e f i r s t peak i n t h e d i f f r a c t i o n pat- t e r n i s never a sharp s i n g l e peak and t h i s f e a t u r e has r e c e n t l y been explained by Kuhs [ 6 ] a s r e s u l t i n g from s t a c k i n g i r r e g u l a r i t i e s i n t h e c r y s t a l l i n e l a t t i c e . The shape of t h i s peak i s very s i m i l a r i n a l l s t u d i e s and does not appear t o be s i g n i f i c a n t l y a f f e c t e d by the d i f f e r e n t p r e p a r a t i o n methods although t h e r e i s c l e a r l y an i n t e r e s t i n making f u r t h e r i n v e s t i g a t i o n s . I t would a l s o seem t h a t pure cubic i c e is never formed and t h e r e i s always an admixture of i c e Ih i n t h e s e p r e p a r a t i o n techniques.

The i n i t i a l formation of i c e Ih a t t h e o n s e t o f n u c l e a t i o n is s u r p r i s i n g . A p o s s i b l e r a t i o n a l i s a t i o n of t h i s behaviour could be t h a t t h e r e is some water expelled from t h e pores due t o t h e change i n d e n s i t y with temperature. I f t h e pore8 a r e completely f u l l a t 20°C t h i s excess volume would presumably lead t o t h e presence of s u r f a c e water on t h e o u t s i d e of t h e s i l i c a p a r t i c l e s which could possi b l e explain i t s d i f f e r e n t behaviour. The proportion of i c e Ib can be assessed by t h e s i z e of t h e 102 peak although t h e r e is some uncertaxnty i n t h e e s t i m a t i o n o f t h e background s c a t t e r i n g . There is some evidence f o r a small r e d u c t i o n i n s i z e a s t h e temperature f a l l s suggesting t h a t t h e r e could be some conversion o f i c e Ih t o i c e Ic. This behaviour is very puzzling because t h e r e a r e no o t h e r c a s e s where t h e normal hexagonal i c e changes t o t h e metastable cubic form d i r e c t l y .

I n a d d i t i o n t o t h e c r y s t a l l i n e forms of i c e t h e r e i s c l e a r evidence f o r t h e presence of a disordered form of w a t e r / i c e over t h e f u l l temperature range s t u d i e d . I n Fig. 5 t h e p a t t e r n f o r amorphous D20 i c e C71 grown by vapour deposi- t i o n a t 10 K i s shown. Although t h e r e i s some s i m i l a r i t y i n t h e o v e r a l l

o s c i l l a t o r y s t r u c t u r e it i s c l e a r t h a t t h e observed p a t t e r n could n o t be

re-constructed by s u p e r p o s i t i o n of Bragg peaks on t h e p a t t e r n of t h i s low-density

anorphous i c e . Comparison of t h e ' d i s o r d e r ' p a t t e r n shown under t h e Bragg peaks

of Fig.5 with r e c e n t neutron d i f f r a c t i o n p a t t e r n s of h i g h d e n s i t y amorphous i c e

C91 i n d i c a t e s t h a t t h e w a t e r / i c e s t r u c t u r e a t t h e i n t e r f a c e is not o f t h i s type.

The presence of t h e d i s o r d e r e d c o n t r i b u t i o n remains an important and controver- s i a l a r e a f o r f u r t h e r d i s c u s s i o n but i t would appear t h a t t h e preliminary calcu- l a t i o n s o f Kuhs, B l i s and Finney [ t h i s conference] r e p r e s e n t a p o s s i b l e means of explanation. Under t h e s e circumstances t h e d i s o r d e r would r e s u l t p r i m a r i l y from s t a c k i n g f a u l t s i n t h e s e q u e n t i a l o r d e r i n g of t h e planes w i t h i n t h e predominantly cubic c r y s t a l phase. The e x i s t i n g c a l c u l a t i o n of t h e s t r u c t u r e f a c t o r f o r a f i x e d sequence (abcababc) shows some f e a t u r e s which a r e s i m i l a r t o those of t h e p r e s e n t r e s u l t s but t h e study of f u r t h e r ordered and random sequences d e f i n i n g v a r i o u s kinds of polytypes w i l l be necessary t o c h a r a c t e r i s e t h e d e t a i l e d behaviour. It t h e r e f o r e appears p o s s i b l e t h a t c u b i c i c e is i n t r i n s i c a l l y d i s o r - dered on a c r y s t a l l o g r a p h i c b a s i s and t h e r e l a t i o n s h i p between i c e Ic and i c e Ih is more s u b t l e than had previously been considered. Furthermore, t h e balance of o r d e r / d i s o r d e r may be s e n s i t i v e t o r e l a t i v e l y minor p e r t u r b a t i o n s so t h a t t h e d a t a f o r t h e second c o o l i n g cycle ( y e t t o be analysed) should be p a r t i c u l a r l y i n s t r u c t i v e . D i f f r a c t i o n measurements can only provide information on t h e time-averaged s t r u c t u r e and t h e r e f o r e measurements, such a s nmr, which probe t h e proton mobility w i l l be needed t o a s c e r t a i n whether t h i s m a t e r i a l should be regarded a s s o l i d - l i k e o r l i q u i d - l i k e i n i t s p r o p e r t i e s .

5. Acknowledgements

T h i s work was c a r r i e d o u t with t h e support o f t h e Neutron Beams Research Committee of SERC. One of u s , (M.D.) acknowledges t h e support of t h e SERC i n t h e form of a r e s e a r c h fellowship.

References

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1031 -1 051 .

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3 . ^D.C. S t e y t l e r , J.C. Dore and C.J. Wright, J. Phys. Chem., 3, (19831, 2458-2459.

4. W. Kuhs and M. Lehmann i n "Water Science ReviewsI1, Vol. I1 (1986) Ed. F.

Franks.

5. A . Elarby-Aouizerat, J-F J a l , C. Farradou, J . Dupuy, P. Chieux and A.

Wright, J . Phys. Chem., 3, (19831, 4170-4173.

6. W. Kuhs, P r i v a t e Communication.

7. M.R. Chowdhury, J.C. Dore and J.T. Wenzel, J. Non. Cryst. S o l i d s , 53,

(19821, 247-265

8. L. Bosio, G.P. J o h a r i and J . T e i x e i r a , Phys. Rev. L e t t . , 56, ^(1986),

460-463.

9. M-C. Bellisent-Funel and J . T e i x e i r a , P r i v a t e Communication.

COMMENTS

N. FUKUTA

The pore s i z e corresponds t o t h e r e l a t i v e humidity. What was t h e average r e l a t i v e

humidity of your sample ?

JOURNAL DE PHYSIQUE

Answer :

The samples were equilibrated over several days with the normal vapour at room temperature and were therefore completely filled. Several cycles were necessary to ensure that and residual hydrogen atoms were exchanged with deuterium atoms.

Comment :

Some 25 years ago, we cooled silica gel of know relative humidity and observed dielectric constant change when the temperature reached between -40 and -6oDC. I thought it was due to homogeneous nucleation of hexagonal ice. Water used was H20.

Answer :

I would need to know more details of the pore size to answer this question but if the pore size was small it is unlikely to be nucleation to hexagonal ice. The region of -40°C to -60°C is an interesting one because it is below the anomalous temperature for liquid water.

Comment of J. DUPUY

Ic can be form from pure water by supersonic jet (see Torchet, Forges and al.

Orsay,J. Physical Chemistry).

Question : Which is the size dispersion of the pores ?

Answer :

The detailed morphology of the pore structure is not known but is presumably an irregular surface resulting from the gel precipitation process. Small-angle scattering techniques are being used to study the pore structures and to characterize them in times of fractal networks but this may not give the detailed information required. One presumes that the overall structure is one of large irregularly-shaped cavities with connecting channels.

B. HALE

Have you estimated critical cluster size for heterogeneous liquid -to- solid (ice I, or Ice Ih) for a model of your "water in micropore" system ? Could the fact that critical cluster sizes are larger than the size of your pores be inhibiting a phase transition ?

Answer :

The present indications are that the crystallite size is limited by the size of the pores. We can obtain some information from the diffraction broadening of the single peaks and this is consistent with the known pore size. For Spherisorb the main features of the diffraction pattern are retained but in the case of Casil there is considerable broadening so it would seem that the nucleation front cannot propagate through the connecting channels. Ue believe this feature is responsible for the stabilization of the cubic ice phase up to the melting point.

Y. MIZUNO

Have you ever made experiments using other porous materials 7 I suppose that your

small size cubic ice is influenced strongly by the crystalline structure of the

substrate.

Answer :

These experiments were the first ones we have made. The silica gel system is

convenient because we need a high surface area and pore volume to ensure that we are

able to substract the substrate scattering to obtain information on the liquid/ice

phase. It would be possible to study other surfaces but I do not know of any

materials with the required characteristics. Another possibility is to coat the

internal silica surface with another substrate but we have not yet investigated this

technique. The basic silica pattern is amorphous and we do not expect the surface to

have a crystalline form.