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THE AUSTRALIAN NATIONAL UNIVERSITY

PESEARCH SCHOOL OF PHYSICAL ~CIENCES

DIFFUSION RESEARCH UNIT

Annual Report 1972

i,t,i.,o

12/1973

Head of Unit (Senior Fellow) Dr. P.. Mills, 11. Sc. (N. Z.) 9 Ph. D (Wash.

Fellow

Research Fellow

Research Assistant (II)

Staff Changes

St. Louis), D.Sc.

Dr. L.A. Woolf, M. Sc. (W.A.), Ph.D (N.E.)

Dr. R. O. Watts , B.Sc. (Lond.), Ph.D

Dr. D.S. Webster, B.Sc. Ph.D (N.S.W.)

GENERAL

At the beginning of the year the Unit was joined by Dr. D.S.Webster

from the University of New South Wales in the capacity of a research assist­

ant to set up a pulsed NMR machine. Hr. V.V. Morariu, a scholar , after

submitting his thesis returned to F~mania in November.

Conferences 2 Overseas Trave1 2 Lectures

Dr. L.A. Woolf left for a one- year sabbatical leave in October. He

is spending the first six months at Oxford University. Dr. R. O. Watts

spent three months from April to June at the I.B.M. Research Laboratories,

San Jose, California in order to carry out computer calculations on liquid

water. Whilst overseas he attended a Faraday Society Symposium in Manchester

in April and a Swnmer School on ' Molecular Motion in Liquids' at Menton,

France in early July. He also visited and lectured at research centres in

t he U.K., t he U.S. and Italy.

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Dr. Watts ?,ave a course of lectures on Dielectric Theory at the

School of General Studies during the third term. He also gave lectures on

his computer calculations on water to the Division of Physics and of

Environmental Mechanics 9 C. S.I.R. O. and in the School seminar programme.

I n RO UCTION

The research effort of the Unit centres on the study of self ­

diffusion in liquids although there are several projects concerned with

other properties of liquids also being undertaken. The pulsed NMR spin-echo

for self- diffusion has been under development during the year so that we now

have three techniques, isotopic tracers , spin- echo and molecular dynamics to

study this property. This year has been a very productive one in terms of

research output and this reflects the fact that t he Unit now has established

a proper balance between established techniques and developmental work.

Probably the most significant advance during the year is connected

with our studies on liquid water. It is a rather remarkable fact that of all

liquids , the self- diffus i on characteristics of water; which is undoubtedly the

most important , are l east well- kno~m . For the past t wenty years there have

been numerous attempts to measure t his quantity accurately without success

and there have been many appeals i n the literature for some definitive work

in this area. During the year data on the self - diffusion of liquid water of

the required accuracy and precision were produced in the Unit. Apart from

the intrinsic value of these self- diffus i on data i n rr any fields of science ,

two new research areas have been opened up. We have been able to s tudy the

isotopic effect in self - diffusion which although well- specified in gases

and solids has not been studied in liquids. Seconii ly , we can now calibrate

our NMR equipment and so obtain an accuracy of an order of magnitude better

than this method has been able to supply previously. Complementary 1ork on

high pressure diffusion in water has also begun.

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It should 'he reIM.rked 3lBo tha:: during the year theoretical studies

on liquid •,·ater have also been unc..ert:iken in the TJn:tt. These computer

simulation st'..ldies have revealed that long--range i!ipole-dipole interactions

between water molecules ~ay be accounted for by inclusion of a term fron1_

the Onsager react i on field and have sho vn that t~€ only other cowparablc

study made so far may be in error for not incorpora ting this f actor.

Progress in the various proj ·:.:c t s under study in the Unit arc detailed

below.

Self-diff-.ision in Liquid Water ; An n P.s heen indicated in the introduction

this project turned out most successfully. ~y careful ex&~ination of pro­

cedures and elimination of errors 9 u c have obtnined an accurate set of values

0 for the self-diffusion of water over t he temperature range 1- trS C.

Water-Silica Interactions · Work on this project was brought to a very

satisfactory conclusion this year. The many- sided attack on the problem

brought out many interesting phenomen3. One significant discovery was that

adsorption of a small amount of electrolyte on the surface completely

in.'1ibited the therm'3.l hysteresis effect which was reported last year . Although

there are several worthwhile leads to follow up on t his project, it is not

intended to do further r es earch in this area in the i1'1meniate future due to

precedence of other work.

Cryogenic Self··diffus :i.on : Progress in this aree. has been ~ little disappoint·~

ing. During the year as operati on of thF.! machine proce eded ~ it was found

necessary to make two major alterations. These wer e to change from

scintillation to gas counting and from solenoid to rotatine magnets for

stirring. The apparatus ~,orks well mechanically and electronically in a

genere.l sense and does produce diffusion coef £:i.d.ents. Rowev8r. ther e is

a significant discrepancy with the values obtained by other metho ds and

before committing ourselves to public~tion of these results , we ar c carry­

ing out a series of difficult and time delaying t ests on every aspect of om:

procedures.

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NMR Self-diffusion: The setting up of a pulsed MMP. machine has proceeded

during the year and the apparatus is now operational. A great deal of care

has been taken to embody recent research findings and it is antici~ated

that this machine will be able to produce data of greater accuracy anc

precision than those already in the literature. As steted earlier the

availability of our self-diffusion ata for water should b~ a very important

factor in increasing the accuracy attainabl8 by the !~1R method.

Hieh Pressure :t)j_ffusion ~ The experimental results obtained by :.kCool

(1971 Report) ~ave been published together with a rigorous theoretical

analysis of the experimental method. Also the results have been used to

show the inadequacy of a theoretical interpretation of transport properties

which was proposed by overseas workers early in 1972.

To provide room for new equipment the high pressure apparatus has

been removed to another laboratory. While it was being re-ossembled sub­

stantial modificat:bnswere made to impro,re its versatility and, particularlyt

to enable it to be used at much higher pressures than before. A new

diffusion cell was designed and constructed (by the mein workshop). P,csults

have been obtained with the new cell for the tracer diffusion of HTO in

H2o. The measurements extend to 2500 bar which is close to the useable limit

of the pressure vessel. They provide a verification of earlier 9 less

accurate 9 results obtained by workers using a completely diff erent experi­

mental method. The latter results were in serious disagreement with the

only previously existing independent data for the self- diffusion of water.

An extension of the new data is being made to obtain results under

pressure over a wide range of temperatures anc thereby complement other

work of the Unit at atmospheric pressure. Suc'.1 data arc necessary for

the testing of transport theories and for comparison with computer- simulated

diffusion experiments based on theoretical model s of the water potential.

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Diffunion in Electrolytes : A theoretical analysis has been completed and

published of multicomponent diffusion in solutions composed of a solvent which

ionizes and a strong electrolyte. The analysis provides the first theoret­

ical confirmation of a type of diffusional behaviour predicted in 1962 and

observed experimentally in these laboratories in that year.

Thermodynrunic Excess Property Mee.surements ; Measurements are being made at

Oxford University in liquid mixtures of xenon and polar molecules (approx ­

imately point dipoles). The measurements are being made during sabbatical

leave to obtain experience in such cryogenic measurements and their

theoretical interpretation for possible related studies with cryogenic liquid

mixtures in the Unit.

Statistical Mechanics of Dense Systams ~ A most pleasing aspect of this

year has been the general acceptance overseas of the work on argon-argon

interactions. In last year's report it was stated that a very accurate

potential function had been developed for argon, excellent agreement being

obtained with a considerable amount of experimentel data. This year new

experimental data has become available that confirms several of our

predictions of inaccuracies in previous measurements. Consequently the

theoretical work on argon carried out in this Unit is being u3ed in

several overseas laboratories as a standard by which cxperim~ntal work

must be interpreted.

Early in the year the work on the gas and liquid phases of helium-4

was completed. Agreement with experiment was P,ood~ and th£ work has been

published. At present phase shift programmes are being developed to enable

low temperature calculations for gaseous helium to be performed. These

programmes are also being used to analyse single channel ion-atom clustering

reactions. It is expected that the results of this second study will be of

particular relevance to problans bein3 examined experimentally in the Ion

Diffusion 1Jnit.

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The work on the third virial coefficient of hard spheres with

embedded dipoles was successfully completed and has been used by

Professor R. H. Stokes? University of New Englcmd, to improve his theory

of mixtures of polar molecules in non-polar solvents. At the end of

the year the work on benzene interations, nentioned last year, was being

restarted.

Four months of this year were spent ~vorking on the computer

simulation of liquid water at the I.B.M. Research Laboratories 9 San Jose.

The study was made possible by a very generous grant of computer time

from I.B .H. Huch of the work was concerned with the long-range effects of

the dipole-dipole interr->.ct:J.onsbetwcen water molacules. It was discov0red

that these interactions can be satisfactorily included in the simulation by

assuming that the water molecules beyond about 12 i from a given molecule

can be treated as a continuum. Using this assumption the long-range

effects can be accounted for by including a contribution from the Cnsager

reaction field arising from the polarisation of the innnediate environment

of the given molecule. There were several qualitative differences between

the ce.lculations carricn out with and without the inclusion of this

reaction field. The work gave a satisfactory qualitative description of

many properties of liquid water. Also at the I.B.H. :r.'.escarch Laborato-ries

a number of other problems were examined :; including the development of a

xenon-xenon potenti~l function. Aithough this function has not yet reached

the accuracy of the argon function it gives reasonable agreement •,Tith such

disparate properties as the transport coefficients of the gas and the phonon

dispersion curves of the solid.

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PUBLICATONS

+ Barker, J.A. andWntts, R.O.,

12/1973

'Onsager reaction field and the machine simulation of polar liquids.v

Disc. Far. Soc. 53, 000· ·1 (1972).

* Fisher R.A. and Watts, R.O.,

'Friction coefficient formalism in the statistical mechanics of

transport processes. 1 Aust. J. Ptys. 25, 21-31 (1972).

* 3. Fisher R.A. and Watts, R.O.,

4.

'Solid argon ~ Monte Carlo cc,lculations along the solid-vapour

co-existence curve. v Holec. Phys. ~' 1051-1069 (1972).

* Fisher R.A. and Watts, R.O ••

1 Calculated self-diffusion coefficients for liquid argon.' Aust.

J. Phys.~. 529-538 (1972).

* * 5. Mccool, M.A. , Collings, A.F. and Woolf, L.A.,

'Pressure and temperature dependence of the self-diffusion of

benzenc. 1 J. Chem. Soc. (Faraday I), 68 , 1489··14n (1972).

* 6. I1cCool, M.A. and Woolf, L.A.,

1 Pressure and temperature dependence of the self-diffusion of carbon

tetrachloride.' J. Chem. Soc. (Faraday I), 68, 1971-1981 (1972).

* 7. Mccool, M.A. and Woolf, L.A.,

7 Self-diffusion measurements under pressure with a diaphragm cell

theory of the method, end cxnerimental results for cyclohexane.'

High Temperatures-High Pressures,!, llpp. (in press) (1972).

8. Uorariu. V. V. and Mills, R. ,

'S f d b d · 1 · b 1 o0 c. 1 tate o a.sore wat~r on s1 ica at temperatures e ow

J. Colloid and Interface Science, 39, 406-408, (1972).

9. Morariu, V.V. and Mills , R.~

'A study of water adsorbed on silica by adsorption, DTA and NMR

techniques, I.' Zcitschrift fur Physikalische Chemie, l!}_s 298-310s(1972).

;'; Former mellhler. n..1.sed on l ·10r~ done Hhile a member of the Unit.

+mot a member of this University.

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10. Morariu, V. V. and Mills s R.,

1 Self diffusion of water adsorbed on silic~. 7 Zeitschrift fur

Physikal ische Chemie , 79, 1-9, (1972).

11. Morariu V. V. and !.fills , R. ,

12.

' A study of water adsorbed on silica. The eff ect of surface water ,

temperature and coverage on the spin-spin relaxation time . II . '

Zeitschrift fur Physikalische Chemie, ]J_; 0000 (1972). , Snook , LK. and Watts, R.O. ,

vAb initio cal culations for helium-4 of thermodynamic and transport

properties of the gas and the ground state energy of the liquid. 1

Aust. J. Phys. E , 000-006 (1972).

13. Watts , R.O. ,

'Perturbation theory of therma l transport coefficients. ' J. Chem.

Phys.~. 3731- 3733 (1972).

14. Watts, R. O. ,

' Third virial coefficient of hard spher es with er.ibedded dipoles .

Mclee. Phys. 23s 445-447 (1972).

15. Woolf, L.A.,

' Multicomponent diffusion in e system consisting of a strong

electrolyte solute a t low concentra tions in an ionizing solvent .'

J. Phys. Chem. , Ji!., 1166-1169 {1972).

16. Woolf , L.A. ,

vRelationship between diffusion co ef f icients in a three- component

system in which two components are isotopicall y related. 7 J. Chem.

Phys., 56, 2489-2490 (1972).

111ember of the Research School of Chemstry.

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17. Woolf , L.A. 9

1 ?-.elations hip between th~ transport coeffictents of dense fluids. 1

J. Chem. Phys., 2._9 3013- 3814 (1972).

Thesis submitted

V.V. Morariu

' The silica/water interface'. (1972)