J. Phys. Chem. 1991, 95, 9579-9584
9579
Determination of Ion and Solvent Transport in an Osmium Polymer Film Uslng a Quartz Crystal Microbalance Andrew J. Kelly and Noboru Oyama* Department of Applied Chemistry, Faculty of Technology, Tokyo University of Agriculture and Technology, 2-24- 16, Nakamachi, Koganei, Tokyo 184, Japan (Received: April 29, 1991)
In situ ion and solvent contents within the osmium polymer complex [0~(bpy)~(PVP)Cl]+ [bpy = 2,2’-bipyridine and PVP = poly(4-vinylpyridine)] during redox of Os2+/’+were studied by using an electrochemical quartz crystal microbalance in various aqueous electrolytes. In C104- electrolyte, there is permselective movement of the anion only into the film during redox. The frequency response for other electrolytesshowed movement of anion with accompanyingwater. In ptoluenesulfonate (pTS-) at CO.1 M, 25 molecules of H 2 0 accompany each anion during oxidation. At 1 M pTS- the film is no longer rigid and considerable viscoelastic effects were observed in the conductance response. For other electrolyte anions, rigidity was confirmed, although the frequency changes correspond to quite large increases in polymer mass, (NO3- = 20%, CI- = 43%, and SO4*- = 54%). The water content of the initial Os2+state was measured ex situ. A simple relation between the initial water content of the [Os2+]+state and the [0s3+l2+state was established.
Experimental Section Introduction Polymer-modified electrodes1have been actively investigated Apparatus. AT cut-quartz crystals, 5 MHz, biconvex bevelled, over the last decade since the first reported examples appeared of 13-mm diameter (Toyo Kurafuto), were coated on both faces in the literature.* Metallopolymers based on poly(viny1pyridine) with Au (a. 300 nm) using a Cr adhesion layer (2 nm). In order (PVP) have proved synthetically attractive because either electo facilitate energy trapping,19 an asymmetric keyhole electrode trostatic binding3 or covalent attachment4 may be used to confine arrangement was used in which the piezoelectrically active area the electroactive center, a metal complex within the polymer. The (0.28 cm2) was smaller than the area of the working electrode charge-transport process has been shown to be influenced sigface (0.64 cm2). Typically after attachment of the working nificantly by the solvent in P V P * dand in metallopolymers based electrode face to the side arm of an electrochemical cell using on poly(~inylferrocene).~JThe nature of the solvent in contact silicone rubber, approximately 0.5-0.6 cm2 was exposed to the with the metallopolymer-coated electrode is known to determine solution. This arrangement was used to mitigate possible effects the permeability of substrates into polymer films in electrocatalytic reactiom6 The determination of ion and solvent content in thin polymer (1) (a) Albery, W. J.; Hillman, A. R. Chem. SOC.Annu. Rep. C 1981,371. films is fundamental to the successful characterization of these (b) Bard, A. J. J. Chem. Ed. 1983,60, 302. (c) Murray, R. W. Electroanal. systems. The quartz crystal microbalance (QCM) when operated Chem. 1984, 13, 191. in liquids7 has been shown to retain its high mass sensitivity, 5.66 (2) (a) Miller, L. L.; Van DeMark, M. R. J . Am. Chem. Soc. 1978,100, 3223. (b) Merz, A.; Bard, A. J. J. Am. Chem. SOC.1978, 100, 3222. (c) X lo7 Hz cm2 g-’ for 5-MHz AT cut quartz crystals8 Monolayer Wrighton, M. S.; Austin, R.G.; Bocarsly, A. B.; Bolts, J. M.; Haas, 0.;Legg, mass sensitivity has allowed the QCM to be used in the study of K. D.; Nadjo, L.; Palazzotto, M. C. J. Electroanal. Chem. 1978, 87, 429. (d) underpotential deposition9* and the adsorption of halidesgb Nowak, R.; Schulz, F. A.; Umana, M.; Abruna, H.; Murray, R. W. J. The QCM has therefore been applied to the mass changes Electroanal. Chem. 1978, 94, 219. (3) (a) Oyama, N.; Anson, F. C. J. Electrochem. Soc. 1980,127,247. (b) occurring during redox in thin polymer films.I0 Solvent transport Oyama, N.; Anson, F. C. Anal. Chem. 1980, 52, 1192. (c) Oyama, N.; during electroneutrality requiring ion transport has been qualiShigehara, K.; Anson, F. C. Inorg. Chem. 1981, 20, 518. tatively demonstrated in the case of electrodes modified with thin (4) (a) Oyama, N.; Anson, F. C. J. Am. Chem. SOC.1979,101,739. (b) films of poly(vinylferrocene)’1.12 and p o l y a ~ ~ i l i n e . ’In~ .nitrated ~~ Oyama, N.; Anson, F. C. J. Am. Chem. SOC.1979,101, 3450. (c) Oyama, N.; Anson, F. C. J. Am. Chem. Soc. 1980,127,640. (d) Scott, N. S.; Oyama, polystyrene, the absence of significant dampening of the conN.; Anson, F. C. J. Electroanal. Chem. 1980, 110, 303. ductance frequency spectrum allowed the conclusion that the (5) (a) Daum, P.; Murray, R. W. J. Electroanal. Chem. 1979, 103, 289. observed frequency change, in excess of that expected for the ion (b) Daum, P.; Murray, R. W. J . Phys. Chem. 1981,85, 389. transport, could be correlated with solvent swelling of the film.I5 ( 6 ) (a) Anson, F. C. J. Phys. Chem. 1980,84,3336. (b) Rocklin, R. D.; Murray, R.W. J. Phys. Chem. 1981,85,2104. (c) Dumas-Bouchart, J. M.; Unambiguous quantitation of water transport in the nickel anaSaveant, J. M. J. Electroanal. Chem. 1980, 114, 159. logue of Prussian Blue in H 2 0 or D 2 0 showed that the frequency (7) (a) Kaufman, J. H.; Kanazawa. K. K.; Street, G. B. Phys. Rev. Lett. response corresponded with the increase in mass due to isotopic 1984,53,2461. (b) Bruckenstein, S.; Shay, M. Electrochim. Acta 1985.30, substitution of the solvent.17 1295. We have previously shown that the diffusion coefficient for (8) Sauerbrey, G. Z . Phys. Chem. 1959, 155, 206. charge transport, D,, , in thin films of [ 0 ~ ( b p y ) ~ ( P V P ) ~ ~ C l ] + (9) (a) Melroy, 0. R.;Kanazawa, K. K.; Gordon, J. G.; Buttry, D. A. Langmuir 1986, 2, 697. (b) Deakin, M. R.;Li, T. T.; Melroy, 0. R. J . during redox of the Osq+/’+couple is dependent on the supporting Electroanal. Chem. 1988, 243, 343. electrolyte anion” [bpy = 2,2’-bipyridyl and PVP = poly(4(10) Deakin, M. R.; Buttry, D. A. Anal. Chem. 1989,61, 1147A. vinylpyridine)]. In a preliminary report,18 it was shown that the (1 1) Varineau, P. T.; Buttry, D. A. J . Phys. Chem. 1987, 91, 1292. (12) Hillman, A. R.; Loveday, D. C.; Bruckenstein, S. J. Electroanal. QCM could, in thin films of this polymer, detect significant acChem. 1989, 274, 154. companying water transport, by H 2 0 / D 2 0substitution, with the (13) Orata, D.; Buttry, D. A. J. Am. Chem. SOC.1987, 109, 3574. p-toluenesulfonate anion at 25 molecules per anion. Solvent(14) Daifuku, H.; Kawagoe, T.; Yamamoto, N.; Ohsaka, T.; Oyama, N. transport effects were absent for the same anion using CH3CN J . Electroanal. Chem. 1989, 274, 313. (15) Borjas, R.;Buttry, D. A. J . Elecfroanal. Chem. 1990, 280, 73. as solvent. In this paper, we present a detailed examination of (16) Lasky, S. J.; Buttry, D. A. J. Am. Chem. SOC.1988, 110, 6258. mass transport in this polymer soaked in various supporting (17) Foster, R. J.; Kelley, A. J. Vos, J. G.; Lyons, M. E. G. J . Elecrroanal. electrolytes and examine whether the film rigidity is maintained Chem. 1989, 270, 365. even when the frequency response is far larger (10-20 times) than (18) Kelly, A. J.; Ohsaka, T.; Oyama, N.; Forster, R. J.; Vos, J. G. J. that expected on the basis of ion-transport considerations. Electroanal. Chem. 1990, 287, 185. To whom correspondence should be addressed.
(19) Salt, D. Hy-Q Handbook of Quartz Crystal Devices; Van-Nostrand Reinhold: Berkshire, England, 1987.
0022-3654/91/2095-9579%02.50/0 0 1991 American Chemical Society
9580 The Journal of Physical Chemistry, Vol. 95, No. 23, 1991
Kelly and Oyama
TABLE I: Equivalent Mass Cluage, M, Calctdated from tbe Steady-State Cyclic Voltammogram at 5 mV/sa
14
w
-
18 Hz
0
0.5 E / V vs. SSCE
Figure 1. Frequency and current responses of steady-state voltammogram at scan rate = 5 mV/s in 0.6 M NaC10, aqueous solution. Surface coverage of the osmium polymer is 16 pg/cm2.
due to compressional stress in thin films, which has been found to change the radial mass sensitivity of the crystal but not the overall integral mass sensitivity.20 The resonant frequency was measured on a Hewlett-Packard 5334B universal counter with the crystal as the active element of an oscillation circuit driven at 6-V dc. The frequency response of the crystal as a passive element was determined on a Hewlett-Packard 41 92A-LF impedance analyzer at 100-mV oscillator level. An operational amplifier based potentiostat/galvanostat (Polarization Unit PS-06, Toho Technical Research) was used to perform the electrochemical measurements in which the working electrode was at ground. A microcomputer (NEC, PC9801RX) was used to interface the above instruments. Materials. The osmium polymer complex was synthesized as previously describedS2I Thin films (0.1-0.5 r m ) of the polymer were coated on the working electrode surface until visibly smooth by spin coating or droplet evaporation from an ethanol stock solution. The polymer-coated quartz crystals were stored under ambient conditions. The geometric area of the film exposed to solution after attachment to the cell was measured accurately for each case. A standard three-electrode potentiostatic control arrangement was used for the electrochemical measurements, the counter electrode was a Pt wire in a frit-separated compartment, and the reference electrode was a saturated sodium chloride electrode. All supporting electrolytes used were of guaranteed reagent grade (>99%) and used as received. Doubly distilled deionized water and deuterium oxide (99.8%, Merck) were used to prepare aqueous electrolyte solutions. Procedure. Water absorption by thin films of the polymer was measured in a controlled-atmosphere container. Different ion exchanged forms of the complex were prepared reproducibly by continuous CV sweeping over the redox couple for 2 h at 10 mV/s, followed by 4 h at 1 mV/s in 0.1 M electrolyte. The crystals were rinsed with water before transfer to the controlled-atmosphere container in order to prevent the deposition of salt on the crystal. The amount of water absorbed was determined from the difference of the resonance frequency between the dry form of the film and under 97% relative humidity conditions.
Results and Discussion (a) Sodium Perchlorate. A typical steady-state frequency and current response by cyclic voltammetry is shown in Figure 1 for NaCIO4 as supporting electrolyte. The frequency response is stable at the level of f0.1 Hz with the absence of any noise influences. It can be seen that the frequency decrease during oxidation is indicative of an increase in the mass of the film as may be expected (20) 2341.
Ullevig, D. M.; Evans, J. E.;Albrecht, M.G. Anal. Chem. 1982,54,
(21) Forster, R. J.; VOS, J. G. Mucromolecules 1990, 23, 4372.
INaCI0,lIM 0.02 0.05 0. I 0.4
M,/g
mol-’
lNaClO.1 /M 0.8
86 96
1 .o 3.0
91
m3-I/8 95
85 85
91
“Surface coverage of the polymer film = 16 pg/cm2. for electroneutrality requiring anion transport into the film. The reduction process reverses the frequency change, leading to a cyclical steady-state process. The mass change may be calculated from the observed frequency change by using the Sauerbrey equationlo
Af = -[2h2/(Pqrq)1’21AM/A
(1)
where Ajis the change in resonance frequency,h, for mass change AM. pq and p are the density and shear modulus of quartz. A is the area of &e resonating quartz. The calculated equivalent mass change (eq 1) per faraday of charge, M, (Table I), is close to that of the perchlorate anion molecular mass, 99 g/mol, over most of the concentration range examined. The M, reaches a maximum of 0.4 M, where it equals the anion molecular mass, but decreases with further increases in concentration of the supporting electrolyte. This may indicate that the transport number of the anion, t-, is not unity as would be expected for an ideally permselective anion exchange film and that there may be some cation transport in the opposite direction, possibly from small amounts of undissociated supporting electrolyte pairs within the film. Also if there are changes in the amount of water transport into or out of the film, this may also lead to deviations of My from the anion molecular mass, even though the film may be ideally permselective. The transport numbers, t+ and t- may also be determined from the apparent shift of the formal potential, (El,),, of the polymer-bound redox couple with concentration of t i e supporting electrolyte.22 This behavior is caused by a Donnan potential difference between the anion-exchange polymer film and the contacting supporting electrolyte. The complete half-reaction required to maintain electroneutrality within the polymer film is for the simple case of a 1:l supporting electrolyte
OS^+),^+ + 2X;
+ t+C,+ + e * (Os2+):
+ tX,- + (1 + t+)Xp- + t+Cp+ (2)
where p and s represent the polymer and solution phases and OS^+)^, and (Os2+): are the oxidized, Os’+, and reduced, Os2+, forms of the polymer-bound osmium complex, where the charges on the complex are 2+ and +, respectively. X- and C+ are the anion and cation species present, which have transferance numbers t- and t+, respectively. The apparent formal potential of the Os2+I3+couple in the polymer, (E,?,,,, is then given by R T [c+]‘~ R T (Efp)app = E‘, - - In -- -(tF [X-Itp F
- t+) In [X-1, (3)
where Efp is the formal potential of the couple in the coating and the brackets mean ionic activities. A plot of the apparent formal potential of the osmium polymer complex, the midpoint of the anodic and cathodic peaks determined from the cyclic voltammogram at 1 mV/s, with the activity of the supporting electrolyte can be used to check the applicability of this approach. The plot in Figure 2 shows that the shift of the apparent formal potential is -52.0 f 1 mV/decade of activity change. The behavior for an ideally permselective anion exchange polymer is -59 mV/decade. A comparison indicates a 1- of 0.87, showing predominantly anion (22) (a) Naegli, R.; Redepenning, J.. Anson, F. C. J . Phys. Chem. 1986. 90,6227. (b) Redepenning, J.; Anson, F. C. J . Phys. Chem. 1987,91,4549.
The Journal of Physical Chemistry, Vol. 95, No. 23, 1991 9581
Determination of Ion and Solvent Transport
TABLE 11: Concentration Dependence of QCM Parameters8 pwhme/Hz [NapTS]/M
Apl/Hz
Afb/Hz
AQ/mC
M,/g mol-'
Gd/mS
0.0 V
0.005 ... 0.02 0.10 0.50
27 I 27 I 258 362
275 280 240 375 -310
0.378 0.392 0.387 0.418 0.468
666 64 1 619 804 -616
1.49 1.46 1.44 I .29 1.60
2550 2550 2650 2850 6200
I .oo
0.6 V 2600 2500 2750 3000 6400
(E:),&' 0.329 0.299 0.282 0.241 0.227
'Change in frequency at steady state from minimum to maximum, IO mV s-l. *Change in frequency between conductance maximum at 0.60 and 0.0 V versus SSCE. 'Change in charge, average of anodic and cathodic charges, IO mV s-l. dConductancemaximum. ePeak width at half-maximum, pwhm f 50 Hz. fMq calculated from conductance AJ #Surface coverage of the polymer film = 24 pg/cm2.
"
0
-2.0
-1.0
0.0
Log(aCloi /mol.dmq3)
Figure 2. Dependence of the apparent formal potential, (Ep?spp,on NaCIO, activity in aqueous solution. Surface coverage of the osmium polymer = 16 &m2. Activities were calculated by the Debye-Hiickel
equation. transport but not ideal permselectivity. It is also possible to determine t- and t+ from
Mq = t-M- - t+M+
0.5
1.0
1.5
A r x 108/m 01.c m-2 Figure 3. Dependence of the steady-state frequency change at IO mV/s in 0.1 M NapTS on differing thickness of the osmium polymer represented by AI'a(rrI),which is the surface coverage of the Os3+sites in the film during oxidation of Os(I1).
(4)
where M-and M+ are the molecular mass of the anion and cation, respectively. The r- for 2 M NaClO,, which shows the largest deviation of Mq from the perchlorate molecular mass, is 0.87, in good agreement with the t- determined from the Donnan potential shift. At other concentrations there may be small amounts of accompanying water movement with anion leading to deviations. (b) Sodium p-Tolwnesulconate (NapTS). In a previous paper,'* we showed that in the case of NapTS as supporting electrolyte the M , = 620 g/mol, determined from the steady-state frequency, and the charge change was composed of two contributions. A mass contribution from the pTS anion, 171 g/mol, and from the movement of water together with the anion during oxidation and reduction. A change of the solvent, D 2 0 for H20, produced an 1 1% increase in this water movement contribution to M,, which was consistent with that based on a H / D isotope shift in the molecular mass of water. Figure 3 shows the dependence of the measured steady-state frequency change on the surface coverage change, Arosclrl,, as Os2+is oxidized to Os3+for films of differing thickness. It can be seen that the plot of the frequency change with AI' is a straight line with a zero intercept and that the determined Mq remains constant for films of differing thickness. This clearly indicates that the Uqreflects a bulk process and not an interfacial or surface process. A surface process would have an M , that is dependent on film thickness. Surface morphology could contribute to the observed frequency change if the film morphology is different between the Os2+and Os3+forms of the polymer film. For example, if the surface of the polymer film is smooth in the Os2+form and uneven or rough in the Os3+form, then the amount of water trapped in surface irregularities would differ between the rough and smooth forms, leading to an observed frequency change during redox not associated with the ion movement required to maintain electroneutrality. If a surface morphological change is present, its contribution to the total
frequency change should be constant, irrespective of film thickness. This would lead to a nonzero intercept in a plot of frequency change with thickness and Meq would not be constant for films of different thickness. Surface morphology changes have been shown to contribute to the QCM frequency behavior during redox of A u , C~ U ~ ~,and ~ ~Ag23b ~ electrodes in alkaline solutions. A measure of the film rigidity may also be determined from the conductance response of the crystal/film/liquid composite resonator. Mechanoelectrical coupling due to the piezoelectric effect allowed the QCM when operated in a liquid to be modeled in terms of an equivalent either mechanical or electrical circuit.24 Using this approach, mechanical effects such as viscosity or elasticity were observed in terms of their effect on the equivalent electrical circuit parameters, which can be determined by using an impedance analyzer. Although exact relationships do not yet exist for the case of a crystal/polymer film/liquid composite resonator, this approach has been used to allow qualitative observations of film rigidity.I5 A significant increase in the polymer film viscosity is expected to be manifested by a decrease in the conductance maximum and a broadening of the conductance response determined from the peak width at half-maximum (pwhm). The conductance response with frequency was measured at fixed potentials, 0.0 and 0.6 V versus SSCE (Table II), where the films are in the Os2+and Os3+states, respectively, judging from the formal potential, Ef(Os2+/Os3+)= 0.260 V. There is only a small change in the peak height and in the pwhm, showing that there is no significant change in the rigidity of the film upon oxidation. The change in the position of the frequency of maximum conductance corresponds with the frequency change measured by the active oscillator method. The conductance response clearly supports the conclusion that the film rigidity is not compromised a t this concentration of NapTS, which has been previously shown by H 2 0 / D 2 0 solvent substitution and represents an alternative and more realistic method for confirming the absence of viscoelastic changes in the frequency response. Although, the Mq remains constant with film thickness, it does have a marked concentration dependence as shown in Figure 4. (23) (a) Schumacher, R.;Borges, G.; Kanazawa, K. K. Sur/. Sci. 1985, L621. (b) Schumacher, R.;Gordon, J . G.; Melroy, 0. R. J . Electroanal. Chem. 1987, 216, 127.
(24) Muramatsu, H.;Tamiya, E.; Karube, 1. Anal. Chem. 1988,60, 2142.
The Journal of Physical Chemistry, Vol. 95, No. 23, 1991
9582 a
b
C
d
e
Kelly and Oyama TABLE 111: Frequency and Charge Changes Evaluated from
Steady-State Cyclic Voltnmmogrnms in Various Supporting Electrolvtes. 10 mV
electrolyte, 0.1 M NaN03 NaCl Na2S0,C NaCIO4
s-ld
Af”/Hz
A@/mC
600 1387 1713 41
0.825 0.864 0.716 0.409
M,/g
mol-’ 674 1491 2220 94
(E,?,&’ 0.295 0.330 0.315 0.240
‘Change in frequency at steady state from maximum to minimum. bChange in charge, average of anodic and cathodic charges. ‘0.05 M Na2S04. dSurface coverage = 55.7 pg cm-’.
0.5
0
E/Vvs. SSCE
Figure 4. Frequency at IO mV/s active oscillator and current responses of steady-statecyclic voltammogram at (a) 0.005 M. (b) 0.02 M, (c) 0.1 M, (d) 0.5 M, and (e) 1.0 M NapTS. Frequency response (e) obtained is determined by the position of conductance maximum, since the electrode fails to resonate at 1 .O M NapTS solution. Surface coverage of the osmium polymer = 24 pg/cm2. 1.60
r
1
-
0
0.5 E/ V~SSSCE
0.5 E / VVS.SSCE
0
(dl
v,
E
\
0
- 0.5 E/Vvs.SSCE
0 5.002
4.990
Frequency/ M Hz Figure 5. Conductance response with frequency of the crystal/polymer film/liquid oscillator at 0.0 V versus SSCE at varying concentrationsof NapTS: (a) 0.005 M, (b) 0.02 M, (c) 0.1 M, (d) 0.5 M, and (e) 1.0 M. Surface coverage of the osmium polymer = 24 pg/cm2. The determined Mq,as shown in Table 11, decreases slightly with increasing concentration of NapTS in the range 0.005-0.1 M NapTS. In 0.5 M NapTS, frequency response is initially larger than in lower concentrations but decreases to a stable value as shown in Figure 4d. In 1 M NapTS, the polymer-coated crystal does not oscillate in the active mode, but in the absence of the film, a stable resonance response is observed. The dependence of the conductance response with frequency on the concentration of NapTS is shown in Figure 5 , it can be seen that the peak height and width (Table 11) change only slightly in the range 0.0054.1 M. The same changes were observed for a bare electrode, which is due to the increase in viscosity and density of the contacting liquid phase in this concentration range.24 At further increases in the concentration of NapTS, the conductance peak is decreased and becomes broader, indicating an increase in the losses or damping of acoustic energy of vibration in the polymer matrix due to an increase in the viscosity. As the pwhm is increased significantly at concentrations greater than 0.1 M, this shows that considerable viscoelastic effects are present. This makes all determinations of mass from frequency invalid at concentrations greater than 0.1 M. The bare Au electrode crystal/liquid composite over the range 0.005 to 1 .O M shows only a small increase in pwhm of 190 Hz, whereas in the presence of the film the increase is 4380 Hz. Resonance of the QCM always occurs when there is no difference in phase between the applied voltage sine wave and the resulting current sine wave. In our experiment, the crystal/film/liquid composite fails to resonate at 1 M NapTS. By use of the impedance analyzer, it was confirmed by measuring
0.5 E / Vvs.SSCE
0
Figure 6. Frequency and current response of the steady-state cyclic voltammogram at 5 mV/s in (a) 0.1 M NaNO,, (b) 0.1 M NaCI, (c) 0.05 M Na2S04,and (d) 0.1 M NaCIO,. Surface coverage of the osmium polymer = 55.7 pg/cm2. the dependence of the phase difference with frequency that there was no frequency of zero phase difference. The variation in the frequency at maximum conductance, fG, in 1 M NapTS as the film is held a t different potentials is shown in Figure 4e. The frequency response having a Mq of -610 g/mol is clearly the opposite of those at the lower concentrations with comparison in Figure 4d,e. We are unaware of whether or not this frequency can be related to a mass change by using eq 1, because there is a significant viscoelastic contribution. It should be noted that at 1 .O M NapTS in both the peak maximum and pwhm responses only a small change is observed between the Os2+and Os3+forms. It is a surprising finding that swelling in the NapTS solution increased with the concentration of supporting electrolyte. This is not usually the case. Rather, the salt concentration increase usually causes deswelling. (c) Other Anions. The steady-state current and frequency response for the same polymer film when the supporting electrolyte anion only is changed is shown in Figure 6. Table 111 shows the determined Mq in each case. It can be observed that the frequency as anion was also as response obtained for NO3-, CI-, or similarly observed for pTS, much larger than that expected on the basis of the movement of only the anion into the polymer film. However, in C104-as the anion the same film showed behavior that is near permselective Clod- anion movement with little or no accompanying solvent ingress. The excess mass change after subtraction of that expected for the movement of anion only corresponds to 20%, 43%, and 54% of the polymer dry mass for NO3-, CI-, and SO4*-,respectively. The effect of replacing K+ for Na+ in the case of a polymer film in the nitrate form shows
The Journal of Physical Chemistry, Vol. 95, No. 23, 1991 9583
Determination of Ion and Solvent Transport
F
TABLE IV: Effect of Water Absorption by the Film on Conductance Parameters for the Os2+ State pwhm/Hzb anion
wateP/%
dry
c1-
27
60
NO
