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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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