Communications to the Editor
References and Notes ( 1 ) C. B. Amphlett, "Inorganic Ion Exchangers", Elsevier, Amsterdam, 1964. (2)J. Inczedy, "Analytical Applications of Ion Exchangers", Pergamon Press, New York, N.Y., 1966. (3)H. F. Walton. Anal. Cbem.. 42, 86R (1970). (4)H.F. Walton, Anal. Cbem., 44, 256R (1972). (5)H. F. Walton, Anal. Cbem., 46,398R (1974). 66, 1380 (1944). (6)F. C. Nachod and W. Wood, J. Am. Cbem. SOC., (7)F. C. Nachod and W. Wood, J. Am. Cbem. SOC.,67,629 (1945). (8)C. Heitner-Wirguin and G. Markovits, J. fbys. Cbem., 67,2263 (1963). (9)G. H. Nancollas and R. Paterson, J. Inorg. Nucl. Cbem., 22, 259 (1961).
1387 (10)J. P. Rawat and S. Q. Mujtaba, Can. J. Cbem., 53, 2586 (1975). (1 1) R. Pribil. "Complexonii in Chimia Analitica", Edi. Tehn. Bucuresti, 1 ~ 6 1 , pp 254-255. (12)A. Vogel. "Quantitative Inorganic Analysis". Longmans, Green and Co., London, 1961. (13)E. B. Sandell. "Colorimetric Determination of Traces of Metals", Interscience, New York, N.Y., 1959,p 812. (14)G. E. Boyd. A. W. Adamson. and L. S.Myers, J. Am. Cbem. SOC.,69,2836 (1947). (15)D. Reichenberg, J. Am. Cbem. Soc., 75,589 (1953). (16)D. C. Freeman and D. N. Stamires, J. Cbem. fbys., 35, 799 (1961). (17)R. Turseand W. Rieman, 111, J. fbys. Cbem., 65, 1821 (1961). (18)R. M. Barrer and L. V. C. Rees, Nature (London), 167,768 (1960).
COMMUNICATIONS TO THE EDITOR
Polyelectrolyte Membrane Electrets. Evidence for High Degree of Charge Storage Capacity Publication costs assisted by the University of Illinois at Chicago Circle
Sir: In 1972 reported on persistent electrical polarization in membranes consisting of sodium polystyrenesulfonate in such polymer matrices as polyvinyl alcohol, polyacrylamide, and polyvinylpyrrolidone. In particular, we reported that a membrane consisting of the polyion in polyvinyl alcohol stored substantial amounts of electric charge in a stable fashion. In addition to the fact that the membranes stored several orders of magnitude more charge than did the usual dielectrics, these membranes also had substantial electrical conductivity. Typical values reported were polarizations of the order of C/cm2 with conductivities of t h e order of (ohm cm)-l. Both of these numbers were several orders of magnitude higher than the usual numbers reported in the literature for typical dielectric^.^*^ I t now appears t h a t as a result of a n unforseen contact resistance problem, the numbers we reported in 1972 were too low by almost 3 orders of magnitude. Recently we performed some experiments in which the same membrane formulation utilized in the 1972 work was used. In this membrane formulation the components were Dupont Elvanol71-30G (hot water soluble polyvinyl alcohol) and Dow sodium polystyrenesulfonate (mol wt = 6 X 106).T h e polystyrenesulfonate was washed with methanol six times and dialyzed against distilled water five times to remove such impurities as sodium bromide and unreactive monomer. T h e polyvinyl alcohol was similarly dialyzed for purification purposes. Appropriate mixtures of these ingredients in aqueous solution were cast on glass plates and dried a t 70 "C in a circulating oven. Up to this point, the procedure was exactly t h e same as reported in 1972. However, in the recent work, the dried membranes were then coated with a suspension of purified colloidal graphite in chloroform. In addition, t h e electrodes were similarly coated.
10
0
02
04
06
08
MOLE FRACTION PSSNa
10 In
PL'A
Figure 1. Membrane conductance as a function of mole fraction PSSNa in PVA.
After the membranes were dried, experiments were performed, utilizing several membrane formulations, in which the membranes were thermally charged and discharged using t h e same procedures and apparatus reported by Linder e t al. In these experiments the membranes (ca. 0.005 cm thick) were charged by placing them in an electric field (22.5 V) a t 66 "C, cooled t o room temperature, after which the field was removed, and then reheated to about 76 "C while the membranes discharged through an electrometer (Keithley Model The Journal of Physical Chemistry. Vol. 80, No. 72, 1976
1388
Communications to the Editor
present membranes will store approximately 30 C/g a t room temperature. T h e charged membranes (ca. 0.005 cm thick) retain a potential of about 2.5 V. For purposes of comparison, a commercial mercury battery, rated a t 1.35 V, stores approximately 270 C/g. Taken in this light, the present results appear very promising. O=Linder et al (66°C) O=This work (65.5'C)
Acknowledgment. We hereby acknowledge t h e generous support of t h e National Science Foundation under terms of grant GK 43294.
References and Notes (1) C. Linder and I. F. Miller, J. Phys. Chem.. 76, 3434 (1972)
(2)C.Linder and I. F. Miller, J. Nectrochem. SOC..120, 498 (1973). (3) S.Bini and R. Capelletti in "Electrets", M. M. Perlman. Ed.. Electrochemical Society, N.J., 1973, p 66. (4) E. B. Podgorsak, G. E. Fuller, and P. R. Moran, ref 3, p 172.
College of Engineering University of lllinois at Chicago Circle Chicago, lllinois 60680
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10-q
0
Irving F. Miller' Joaquin Mayoral
Received October 28. 7975
I
I
I
I
,
0.2
0.4
0.6
0.8
1.0
MOLE FRACTION PSSNa in P V A Figure 2. Membrane polarization in PVA.
as a function of mole fraction PSSNa
SlOC). Figures 1 and 2 represent the results obtained. Each point reported is an average of a minimum of four experiments involving a t least two separate membranes. T h e average standard deviation was 20.1% while the maximum standard deviation found was 36.4%. Figure 1 is a comparision of the membrane conductance obtained in this work with t h e work of Linder e t al. It should be noted that although the curves have essentially the same shape, the present curve is displaced upward by more than 2 orders of magnitude. This displacement is almost certainly a result of the reduced contact resistance between t h e electrodes and the membranes brought about by t h e presence of colloidal graphite. Figure 2 shows the membrane polarization obtained by integrating the measured current vs. time curves as compared with those of Linder e t al. Again, it should be pointed out t h a t although the curves have roughly t h e same shape, t h e present curve is displaced upward by more than 2 orders of magnitude. T h e fact that the polarization curves now obtained have essentially the same shape as those reported by Linder e t al. indicates that the model formulated to explain those results is still valid. T h e model (involving an electret formation and stabilization mechanism in which an ion became displaced in t h e direction of t h e applied field via a positive feedback between a local field and its reactive field components and the stabilization of these displacements by hydrogen bonding) was dependent on the shape of a polarization curve but not on the absolute values obtained. T h e significance of the values now obtained lies in the very real possibility that membrane electrets of this type might prove to be practical sources of electrical power. On a weight basis the 0.6 mole fraction membrane stores approximately I C/g. Linder found that raising the polarization temperature from 66 to 93 OC increased the polarization of the membranes by about 1.5 orders of magnitude. I t is reasonable to expect, therefore, that if the polarization temperature is 90 "C, t h e The Journal of Physical Chemistry, Vol. 80, No. 72, 7976
Nonideality of Mixing of Micelles of Fluorocarbon and Hydrocarbon Surfactants and Evidence of Partial Miscibility from Differential Conductance Data Publication costs assisted by the Petroleum Research Fund
Sir: Although fluorocarbons and hydrocarbons are individually typical nonpolar substances, they exhibit considerable departure from ideality in their so much so t h a t heptane and perfluoroheptane, for example, are only partially miscible a t room temperature.' We wish to report some critical micellization concentrations (cmc) and differential conductance data on mixtures of sodium perfluorooctanoate (SPFO) with some hydrocarbon chain surfactants in aqueous solution which point out how intense this nonideality effect is in small systems such as micelles. These observations, along with some others recently made regarding the anomalous behavior of partially fluorinated surfactants,* suggest t h a t such nonideality effects may be widespread and may significantly affect the properties of (a) carbon-fluorine compounds in biological systems,3 (b) fluorine-labeled molecules for probing or studying hydrophobic environments of proteins, of enzymes, or of lipid membra ne^,^-^ and, (c) surfactants a t interfaces where fluorocarbon-hydrocarbon interactions are involved. Figure 1 shows the cmc values of mixtures of S P F O with sodium laurate (SL) and sodium decyl sulfate (SDeS), in presence of 0.001 N NaOH added to suppress any hydrolysis. T h e data were obtained from plots of equivalent conductance against t h e square root of the concentration, C, in equivalentsfliter, a procedure particularly useful for mixtures of ionic surfactants.l0 T h e conductance was corrected for the contribution of the NaOH." Its effect on the high cmc values of Figure 1 through the common-ion effect13 may be considered negligible for comparative purposes. Previous studies have shown that the cmc's of binary mixtures of ionic hydrocarbon chain surfactants fall within the range of the values of the individual pure ~ o r n p o n e n t s , ' ~ J ~ - ' ~ and that the mixing of the chain moieties is nearly idea1,l4J5J8
