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A transmission dielectric time domain spectroscopy method for aqueous systems
CHCMICAL
X TRANSMISSION
20 August 1982
PHYSICS LETTERS
DIELECTRIC TIME DOMAIN SPECTROSCOPY
METHOD
FOR AQUEOUS SYSTEMS
X ~3nsmb~1on mcthod in dielccuic umc domam spectroscopy. buitzblc ior aqueous systems, IS descrlbcd It IS drmon~t13t~d thJt the mrthod CXI bc applrsd IO aqueous clccrrol) IL‘S The dlclcculc spccrra oi solutions of the non-clecuoly tc glusosc and ~be clccuol~ ICSCUSOJ and sodmm carbotymc!h)l
1. Introduction In diclectrlc time domam spectroscopy (TDS), the mtluence of a dtelcctric sample on a pulss propagating in a coaual hnc IS studisd The most frequently used methods ar2 retlccuon measuremmts, III whch the first reflectlon agamst a long sample or the total rctlectlon from J short sample. 1s studed [ 11. The TDS technique has been apphed mamly TOthe study of nun-conductmg dielectrics of low or me&urn perrmttlvlty with critIcal frequenctes
ccUulosc arc gwcn 35 dlust.nt~rc spphcarrons.
Recently a computerized TDS system was described, suitable also for transmission methods [3]. Forth2 case of medium permitbvity dielectncs it was demonstrated that the good time-referencing stabllity (CO.5 ps) of this system makes It possible to improve the signal-to-noise ratio and to reach high frequencies. It is the purpose of this paprr to show how the total transmission method can be used in a straightforward manner to study the dielectrx properrles of aqueous systems, Including electrolytes, up into the GHz region.
2. Theory The mcident pulse IJ(~) and the transrmtted puke r(c) are Fourier transformed into the frequency domain F(w) = s f(t)e+” __
dr
(I)
and the transmission coefficient T(w) = R(W)/ V(w) is evaluated. Transmission-line theory gives the total transmission coefficisnt at frequency w as
0 009~3-614/81/OOOO-OCKIO/S 02.75 0 1982 North-Holland
CHCMIC-\L PHYSICS Lf-l-l-LRS
Volume 90. number 6
Here p = [ 1 - (~~)l/l]/[l + (e’)l/‘], 1is the sample length. c the spsed of light in free space and E‘ = E’ - IE” IS the complex pernuttlvlty of the sample. The solution oreq. (I?) for experimentally detrrmined r(t) and u(r) gives E*(W). However. in the study oiaqueous systems. where in fact the dewarlon in e’(w) from that of pure watzr is the interesting quantity, a relarlve measurement is preferable. Therefore a compsnson of the pulse transmitted through the unknown r(r) with the pulse transmitted through the same sample volume of pure water, w(f), should give a more duect measure of th2 desired quannty. The ratlo of the transforms of the pulses through the unknown and the water sample.
,
R (L?)/W(w) = T(w)/?-,(w)
(3)
&es an squatIon m e*(w), provided the transmission coeificiznt for water T,(w) is known. The dielectnc properties of water are well charac-
The pulse transmitted through a conductmg ssmplc wdl not reach the fiial level of the Incident s~cp pulse. lnstead its fial level will show an oft&t wiuch directly gives the conductwlty 0 The asymptotic value oi the time domxn transmlssron coefficient r(t)/u(r) IS given by 1, =
hm r(r)/o(r) = bm T(w) .
r-0
(7)
l-l-0
lnscrting eq (6) mto eq. (2) and lrttmg w - 0. on2 obrains I, = (I + ol/2Egc)- 1 .
(81
Thus the time domain dara will lmm2dlatsly gn2 1112 dc conductlvlty a. Consequsntly, 3 single TDS measurement on an electrolyte solution can g1v2 all the desaed data. The Fourier transiormxtlon and solution of cq. (3) g~vcs E;(W). from which tic conductmty contrlbutron deduced from the o value found UI the same me&urcment - IS subrracred to give the dlpolar dlelr’ctric oermittivity c’(w).
terized and a theoretical formula for E-(W) can bc used to evaluatz T, (w) from eq. (3) at the chosen frequencies. By fitting experunental permutlvity dara for pure water to 3 Cols-Cole function
3. Experimental
E.(W) = E, + (Es - E,)/[ 1 +
The maul features of the computer-controlled TDS spcctromeler were dzscnbcd and deta& of data acqw
(1w#-q .
(9
and results
Hasted [4] wx able to glv2 values for the parameters
sltion, time referencing and numernxl proxdurcs
es, E,, 7 and a at different temperatures. The dlelectric relaxation spread parameter is found to be very small, <0.02, implymg that the dlelectnc propertles Of water an very close to those of a Dsbye-type di-
given [3]
in fig. 1. Some modifications
in the system
snuni
electric characterized by a smgle relaxation time f*(w) = e, + (6, - e,)/( 1 + iw7) .
_A schematic diagram of the apparatus 1s
reproduced
CELL
(9
accuracy achevable in a TDS experiment
is not sufticient to differentiate between the functions (4) and (5). Therefore the Debyc model [eq. (j)] is quite adequate in the calculation from eq. (2) of the transmission coefficient T,,,(w) of pure water to be k2rted into eq. (3). In dielectrics showmg a dc conductivity u, the permittivity E*(W) has to be replaced by a total pemutt~vity The
E;(W) = E*(W) - lu/weo , where ho is the permntivity
(6) of a vacuum.
l-q 1. Schsmxic dlagnm of wmputcr-controkd chmncl TDS system : xd srmplc CCL
dual-
-113
VoIumL’ 90. number 6
CJIJMJCAL PJJTSICS LETKRS
can be noted. Addmw ofa disc memory to the minicomputer makes tt poss&le to S~VCrecorded puke shapes and transforms for further handlingat a later
stage. D~ferences between stored pulses can therefore be evahiaied by the computer and studied, either WSUaUy on a recorder or after Fourier transforr+on. The trisgermg schrm+z of the tunnel drade pulse generator has been altered. & m the standard arrangement of the r&xtometer, the tunnel drode 1sconnected to rhe current supply HPI IOSA. but it is directly frog. gored via a tugh-pass falter HP1 109B from rhe pre-tng output of the oscilloscope. This removes the slowiy _ yarying parts of the trig pulse. which IS added to the - tutmd diode output m the standard arrangement, and a leads to the output of a ncarIy Idea1step puke. This change in t~~germg scheme causes no addnional jrtermg m the time base. The semi-ngtd coaxtu!allmt bstwern rhe Power splitter and the s~ple-cont~g pre~s~on a~ bnr: allows a ume wmdow of 20 ns before the fist rereflechon bcrween the sample and power splitter adds IO the tract. In 011sscheme the uncenainry in the tune origm 1s <0.5 ps. If longer time windows are necdcd to reach low frequencies, two separate pulse generators can be used, tnggered by the same pulse from the osctioscop~. The uncerta~t~ in the time ongm B then larger. However, Uus can be accepted
when only low frequencres are of interest and the demands on a precise &me referencing are not as severe as m the ev~uation of hip-frequency transforms. r\ sznnple cell is mcluded in fig. 1. The teflon beads ire machmed to gi%eunpedance match. Holes are drilled m the coa~il hnc to al.lowcleaning of the cell Jnd the msertron and change of sample without dls~~selt~b~~ the fme. The line IS tilted to ~~c~tt~te the removal of air on fiig through the lower hole. A bboratory watermsuction pump is used to remove the wmple and to flush the cell w~t.h water and acetone
bctwccn changesof sample.The cell is surrounded by a thcrmostattcdjacket, As a ICS~case OIY il non-ekctrolyte, the dxeiectnc spectrum 3t 3°C of 3.2.8 hi glucosesolution was
studied. The sample length was 5 mm and the tune wmdow 20 ns. The dielectnc parameters of pure water as mrerpolatcd from the data in ref. {4[lr-J are es = 86.0, L = 4.7 and T = 14.8 ps. The spectrum is shown in fig. 2, where the refer. cnce spectrum of pure water is also included. No 414
005 01
a5
10
50 Y(C LI
TIE. 2. PerNMlVit~ Of ;ul
IqUCOUS solution of 2 8 M gluW$C The dots BNCch\: TDS d3ta. the iull tme Dfir to a n\o-Debye.proccss model and the broken lme the prmittmty s.~cLrunl of uwr at5“C
smoothing of transformed data was performed, before the pennittivitres were calculated. It can be seen that the spectrum of the @ucose solution differs considerably from that of pure water, ~~ca~g a significant influence of the solute on the rotational comic of water. Suggett 121, in his study of the dielectric relaxation ofsugar solutions, analysed his data in terms of a sum of two Debye-type processes.
A least-squares fit of the data m fig. 2 to such a model gives E, = 3.1,Asl = 55.5,5, = 25 ps, At-? = 15.5 and r2 = 0.14 ns. The chelcctnc parameters obtained correspond
Suggett. An ~terpre~~o~ of the two-component mode! is to attnbute the fast and slow relaxation processes to the bulk water and the rotation in the hyd~ted glucose complex, respe~t~ve~ k. k discussed above the total transistor method should be appkable to aqueous eiectrolyte &&tons, well with those of
Volume 90, number 6
CHChllCAL PHYSKS LElTERS
rg. 3 Pcrmntwty of an squeous solution of 0 043 hi CusoJ at PC (dots). The C” data arc corrected ior the conductnttj contribubon. The iull he corresponds to a nro-Dcbyc-process model and the broken lmc shows the pcrmittnltp spectrum of N ELtcr
two-Debye-process modd wath one process tdentral to that of pure water, and the other with Ae, = 6.6 and r1 = 0.74 ns. Pottel, m hn study of more concentrated bivaient molecutes, made an anallysrs in terms of three relaxation processes. The accuracy of the results in the present measurement does not allow such a detatled analysts. An interesting class oi conductrng aqueous systems IS polyelectrolyte solutions. Dtelectrrc studtes on such systems have shown the presence of dtsperslon regions m the MHz regton and below. An example of such a polyelectrolyte is sodium carboxymethyl cellulose (NaCMC). By measurements of the loss factor m the MHz region below 50 MHz, Allen et al. [61 found a dtelectrx disperston in thrs regton for N&MC solutions. The TDS method should give a stra~~tfor~~ard oppoltumty to confirm these fiidlngs, since in the TDS measurement both E’ and E” are d~ter~ned. The result of a nleasurement on a 20 mm s3mpIr of 15 NaChfC by volume at 25°C wtth a ttme wmdow of 100 ns IS shown m fig. 4. From the final pulse levels the dc conducttvtty was found to be 2.M X IO-3 R-t m-t. This conductivity rontributton has been subtracted from the data m fig. 5. The water parameters [J] used to calculate the reference spectrum were E, = 78.5. E, = -12 and 7 = 8.1 ps. The spectrum confums the exlstena;? of a broad secondary dlspcrsion with a critical frequency around 0.1 GHz. This is in agreement wrth extrapolations of
where the dc conductivity is obtained from the fmal pulse levels as t + a_ Tests on KC1 solutions gave the correct (I values and reproduced the spectrum of water. A more interestmg electrolyte is an aqueous CuSO, solution. The Spectrum from a 5 mm sampfe of 0.033 hl CuSOj at 5°C is shown in fig. 3. The ttme window used was 20 ns. The dc conducttvlty obtained from the ttmr dome data is 3.07 X 10-3 G-1 m-t. The conductivity contribution i&.x0 to the apparent permittivity has been subtracted in the data shown. The reference spectrum of pure water IS also included in the figure. Bestdes the main water dispersion, a secondary dispersion region is found below the GHz region. Such a relaxation process was previously observed in dtvalent electrolyte solutions by Pottel [S] who attributed it to ion paus in the solution. The theorettcal curve in fg. 3 is obtained by adopting a
Fig. 4. Permrttwity of a 1~sohttton by volumeof NKMCst 25°C. The e” data xc corrected for the conducu~lty contnbutren. The broken hoe shous the pcrmrtttvity spectrum of water
Volume 90 number 6
CHfhtICAL PH‘ISICS LIYMXRS
data from AUsn et al. 161 who studled solunons of iow2r concentmuon and lower conducIl~ty. Because of the broadness of the secondary &spersion. no artempt was mad2 to fit thr data in fg. -i to a dlelectnc model funcuon.
to Aufust 1982
Admowledgement Financial support from the Swedish Natural Science Research Council is gratefully acknowledged.
References
From the dlustratlvz cases shown ir can be con-
ciuded that ths transmission method in &2lectnc time domain spectroscopy can be applied also to the study of aqueous di2Iectrics. The method has the mce featurr of dlr2ctIy givmg the de conductivity, makmg it possible to mvestlgate aqueous electrolytes. Further apphcxions of the method to other poly2l2ctroly1es wdl be pubkshed m a forthcoming paper.
416
[I) R H.Cok, r\nn. Rev. Phys. Chcm. 18 (1977) 2B3.3nd Rferences therem. I?] A. Suggctt snd AM. Clark, J. Solution Ch+zm.5 (1976) 1. [3] B. Cesrblom and B. Jonsson.J. Phys. El3 (1980t 1067 [Jj J.B. Hasted. m Water, a cornpr~b~~si~~trr’attsr’.Vol 1. ed. r. Fnnhs (Pknum. New Yo& 1972) ch. 7 [Sj R. Po~tei, Bcr. Bunengcs. Physrl. Chrm. 69 (1965) 363. [6] D.J. AUcn. S.hf. NC& and P J.T. Tat. J. Poll m. Sci A? 10 (1972) 433.
X TRANSMISSION
20 August 1982
PHYSICS LETTERS
DIELECTRIC TIME DOMAIN SPECTROSCOPY
METHOD
FOR AQUEOUS SYSTEMS
X ~3nsmb~1on mcthod in dielccuic umc domam spectroscopy. buitzblc ior aqueous systems, IS descrlbcd It IS drmon~t13t~d thJt the mrthod CXI bc applrsd IO aqueous clccrrol) IL‘S The dlclcculc spccrra oi solutions of the non-clecuoly tc glusosc and ~be clccuol~ ICSCUSOJ and sodmm carbotymc!h)l
1. Introduction In diclectrlc time domam spectroscopy (TDS), the mtluence of a dtelcctric sample on a pulss propagating in a coaual hnc IS studisd The most frequently used methods ar2 retlccuon measuremmts, III whch the first reflectlon agamst a long sample or the total rctlectlon from J short sample. 1s studed [ 11. The TDS technique has been apphed mamly TOthe study of nun-conductmg dielectrics of low or me&urn perrmttlvlty with critIcal frequenctes
ccUulosc arc gwcn 35 dlust.nt~rc spphcarrons.
Recently a computerized TDS system was described, suitable also for transmission methods [3]. Forth2 case of medium permitbvity dielectncs it was demonstrated that the good time-referencing stabllity (CO.5 ps) of this system makes It possible to improve the signal-to-noise ratio and to reach high frequencies. It is the purpose of this paprr to show how the total transmission method can be used in a straightforward manner to study the dielectrx properrles of aqueous systems, Including electrolytes, up into the GHz region.
2. Theory The mcident pulse IJ(~) and the transrmtted puke r(c) are Fourier transformed into the frequency domain F(w) = s f(t)e+” __
dr
(I)
and the transmission coefficient T(w) = R(W)/ V(w) is evaluated. Transmission-line theory gives the total transmission coefficisnt at frequency w as
0 009~3-614/81/OOOO-OCKIO/S 02.75 0 1982 North-Holland
CHCMIC-\L PHYSICS Lf-l-l-LRS
Volume 90. number 6
Here p = [ 1 - (~~)l/l]/[l + (e’)l/‘], 1is the sample length. c the spsed of light in free space and E‘ = E’ - IE” IS the complex pernuttlvlty of the sample. The solution oreq. (I?) for experimentally detrrmined r(t) and u(r) gives E*(W). However. in the study oiaqueous systems. where in fact the dewarlon in e’(w) from that of pure watzr is the interesting quantity, a relarlve measurement is preferable. Therefore a compsnson of the pulse transmitted through the unknown r(r) with the pulse transmitted through the same sample volume of pure water, w(f), should give a more duect measure of th2 desired quannty. The ratlo of the transforms of the pulses through the unknown and the water sample.
,
R (L?)/W(w) = T(w)/?-,(w)
(3)
&es an squatIon m e*(w), provided the transmission coeificiznt for water T,(w) is known. The dielectnc properties of water are well charac-
The pulse transmitted through a conductmg ssmplc wdl not reach the fiial level of the Incident s~cp pulse. lnstead its fial level will show an oft&t wiuch directly gives the conductwlty 0 The asymptotic value oi the time domxn transmlssron coefficient r(t)/u(r) IS given by 1, =
hm r(r)/o(r) = bm T(w) .
r-0
(7)
l-l-0
lnscrting eq (6) mto eq. (2) and lrttmg w - 0. on2 obrains I, = (I + ol/2Egc)- 1 .
(81
Thus the time domain dara will lmm2dlatsly gn2 1112 dc conductlvlty a. Consequsntly, 3 single TDS measurement on an electrolyte solution can g1v2 all the desaed data. The Fourier transiormxtlon and solution of cq. (3) g~vcs E;(W). from which tic conductmty contrlbutron deduced from the o value found UI the same me&urcment - IS subrracred to give the dlpolar dlelr’ctric oermittivity c’(w).
terized and a theoretical formula for E-(W) can bc used to evaluatz T, (w) from eq. (3) at the chosen frequencies. By fitting experunental permutlvity dara for pure water to 3 Cols-Cole function
3. Experimental
E.(W) = E, + (Es - E,)/[ 1 +
The maul features of the computer-controlled TDS spcctromeler were dzscnbcd and deta& of data acqw
(1w#-q .
(9
and results
Hasted [4] wx able to glv2 values for the parameters
sltion, time referencing and numernxl proxdurcs
es, E,, 7 and a at different temperatures. The dlelectric relaxation spread parameter is found to be very small, <0.02, implymg that the dlelectnc propertles Of water an very close to those of a Dsbye-type di-
given [3]
in fig. 1. Some modifications
in the system
snuni
electric characterized by a smgle relaxation time f*(w) = e, + (6, - e,)/( 1 + iw7) .
_A schematic diagram of the apparatus 1s
reproduced
CELL
(9
accuracy achevable in a TDS experiment
is not sufticient to differentiate between the functions (4) and (5). Therefore the Debyc model [eq. (j)] is quite adequate in the calculation from eq. (2) of the transmission coefficient T,,,(w) of pure water to be k2rted into eq. (3). In dielectrics showmg a dc conductivity u, the permittivity E*(W) has to be replaced by a total pemutt~vity The
E;(W) = E*(W) - lu/weo , where ho is the permntivity
(6) of a vacuum.
l-q 1. Schsmxic dlagnm of wmputcr-controkd chmncl TDS system : xd srmplc CCL
dual-
-113
VoIumL’ 90. number 6
CJIJMJCAL PJJTSICS LETKRS
can be noted. Addmw ofa disc memory to the minicomputer makes tt poss&le to S~VCrecorded puke shapes and transforms for further handlingat a later
stage. D~ferences between stored pulses can therefore be evahiaied by the computer and studied, either WSUaUy on a recorder or after Fourier transforr+on. The trisgermg schrm+z of the tunnel drade pulse generator has been altered. & m the standard arrangement of the r&xtometer, the tunnel drode 1sconnected to rhe current supply HPI IOSA. but it is directly frog. gored via a tugh-pass falter HP1 109B from rhe pre-tng output of the oscilloscope. This removes the slowiy _ yarying parts of the trig pulse. which IS added to the - tutmd diode output m the standard arrangement, and a leads to the output of a ncarIy Idea1step puke. This change in t~~germg scheme causes no addnional jrtermg m the time base. The semi-ngtd coaxtu!allmt bstwern rhe Power splitter and the s~ple-cont~g pre~s~on a~ bnr: allows a ume wmdow of 20 ns before the fist rereflechon bcrween the sample and power splitter adds IO the tract. In 011sscheme the uncenainry in the tune origm 1s <0.5 ps. If longer time windows are necdcd to reach low frequencies, two separate pulse generators can be used, tnggered by the same pulse from the osctioscop~. The uncerta~t~ in the time ongm B then larger. However, Uus can be accepted
when only low frequencres are of interest and the demands on a precise &me referencing are not as severe as m the ev~uation of hip-frequency transforms. r\ sznnple cell is mcluded in fig. 1. The teflon beads ire machmed to gi%eunpedance match. Holes are drilled m the coa~il hnc to al.lowcleaning of the cell Jnd the msertron and change of sample without dls~~selt~b~~ the fme. The line IS tilted to ~~c~tt~te the removal of air on fiig through the lower hole. A bboratory watermsuction pump is used to remove the wmple and to flush the cell w~t.h water and acetone
bctwccn changesof sample.The cell is surrounded by a thcrmostattcdjacket, As a ICS~case OIY il non-ekctrolyte, the dxeiectnc spectrum 3t 3°C of 3.2.8 hi glucosesolution was
studied. The sample length was 5 mm and the tune wmdow 20 ns. The dielectnc parameters of pure water as mrerpolatcd from the data in ref. {4[lr-J are es = 86.0, L = 4.7 and T = 14.8 ps. The spectrum is shown in fig. 2, where the refer. cnce spectrum of pure water is also included. No 414
005 01
a5
10
50 Y(C LI
TIE. 2. PerNMlVit~ Of ;ul
IqUCOUS solution of 2 8 M gluW$C The dots BNCch\: TDS d3ta. the iull tme Dfir to a n\o-Debye.proccss model and the broken lme the prmittmty s.~cLrunl of uwr at5“C
smoothing of transformed data was performed, before the pennittivitres were calculated. It can be seen that the spectrum of the @ucose solution differs considerably from that of pure water, ~~ca~g a significant influence of the solute on the rotational comic of water. Suggett 121, in his study of the dielectric relaxation ofsugar solutions, analysed his data in terms of a sum of two Debye-type processes.
A least-squares fit of the data m fig. 2 to such a model gives E, = 3.1,Asl = 55.5,5, = 25 ps, At-? = 15.5 and r2 = 0.14 ns. The chelcctnc parameters obtained correspond
Suggett. An ~terpre~~o~ of the two-component mode! is to attnbute the fast and slow relaxation processes to the bulk water and the rotation in the hyd~ted glucose complex, respe~t~ve~ k. k discussed above the total transistor method should be appkable to aqueous eiectrolyte &&tons, well with those of
Volume 90, number 6
CHChllCAL PHYSKS LElTERS
rg. 3 Pcrmntwty of an squeous solution of 0 043 hi CusoJ at PC (dots). The C” data arc corrected ior the conductnttj contribubon. The iull he corresponds to a nro-Dcbyc-process model and the broken lmc shows the pcrmittnltp spectrum of N ELtcr
two-Debye-process modd wath one process tdentral to that of pure water, and the other with Ae, = 6.6 and r1 = 0.74 ns. Pottel, m hn study of more concentrated bivaient molecutes, made an anallysrs in terms of three relaxation processes. The accuracy of the results in the present measurement does not allow such a detatled analysts. An interesting class oi conductrng aqueous systems IS polyelectrolyte solutions. Dtelectrrc studtes on such systems have shown the presence of dtsperslon regions m the MHz regton and below. An example of such a polyelectrolyte is sodium carboxymethyl cellulose (NaCMC). By measurements of the loss factor m the MHz region below 50 MHz, Allen et al. [61 found a dtelectrx disperston in thrs regton for N&MC solutions. The TDS method should give a stra~~tfor~~ard oppoltumty to confirm these fiidlngs, since in the TDS measurement both E’ and E” are d~ter~ned. The result of a nleasurement on a 20 mm s3mpIr of 15 NaChfC by volume at 25°C wtth a ttme wmdow of 100 ns IS shown m fig. 4. From the final pulse levels the dc conducttvtty was found to be 2.M X IO-3 R-t m-t. This conductivity rontributton has been subtracted from the data m fig. 5. The water parameters [J] used to calculate the reference spectrum were E, = 78.5. E, = -12 and 7 = 8.1 ps. The spectrum confums the exlstena;? of a broad secondary dlspcrsion with a critical frequency around 0.1 GHz. This is in agreement wrth extrapolations of
where the dc conductivity is obtained from the fmal pulse levels as t + a_ Tests on KC1 solutions gave the correct (I values and reproduced the spectrum of water. A more interestmg electrolyte is an aqueous CuSO, solution. The Spectrum from a 5 mm sampfe of 0.033 hl CuSOj at 5°C is shown in fig. 3. The ttme window used was 20 ns. The dc conducttvlty obtained from the ttmr dome data is 3.07 X 10-3 G-1 m-t. The conductivity contribution i&.x0 to the apparent permittivity has been subtracted in the data shown. The reference spectrum of pure water IS also included in the figure. Bestdes the main water dispersion, a secondary dispersion region is found below the GHz region. Such a relaxation process was previously observed in dtvalent electrolyte solutions by Pottel [S] who attributed it to ion paus in the solution. The theorettcal curve in fg. 3 is obtained by adopting a
Fig. 4. Permrttwity of a 1~sohttton by volumeof NKMCst 25°C. The e” data xc corrected for the conducu~lty contnbutren. The broken hoe shous the pcrmrtttvity spectrum of water
Volume 90 number 6
CHfhtICAL PH‘ISICS LIYMXRS
data from AUsn et al. 161 who studled solunons of iow2r concentmuon and lower conducIl~ty. Because of the broadness of the secondary &spersion. no artempt was mad2 to fit thr data in fg. -i to a dlelectnc model funcuon.
to Aufust 1982
Admowledgement Financial support from the Swedish Natural Science Research Council is gratefully acknowledged.
References
From the dlustratlvz cases shown ir can be con-
ciuded that ths transmission method in &2lectnc time domain spectroscopy can be applied also to the study of aqueous di2Iectrics. The method has the mce featurr of dlr2ctIy givmg the de conductivity, makmg it possible to mvestlgate aqueous electrolytes. Further apphcxions of the method to other poly2l2ctroly1es wdl be pubkshed m a forthcoming paper.
416
[I) R H.Cok, r\nn. Rev. Phys. Chcm. 18 (1977) 2B3.3nd Rferences therem. I?] A. Suggctt snd AM. Clark, J. Solution Ch+zm.5 (1976) 1. [3] B. Cesrblom and B. Jonsson.J. Phys. El3 (1980t 1067 [Jj J.B. Hasted. m Water, a cornpr~b~~si~~trr’attsr’.Vol 1. ed. r. Fnnhs (Pknum. New Yo& 1972) ch. 7 [Sj R. Po~tei, Bcr. Bunengcs. Physrl. Chrm. 69 (1965) 363. [6] D.J. AUcn. S.hf. NC& and P J.T. Tat. J. Poll m. Sci A? 10 (1972) 433.