Isotherms for the binding of dodecyltrimethylammonium (DTA+) ions by sodium dextran sulfate (NaDxS) and sodium poly(styrenesulfonate) (NaPS) in the presence of added NaCl are reported. The binding isotherms were determined by using a potentiometric technique based on surfactant ion selective solid-state electrodes. The solid membranes used in the electrodes consist of poly(vinyl chloride) (PVC) plasticized by bis(2-ethylhexyl) phosphate with a DTA-dodecyl sulfate carrier complex. The electrodes exhibit Nernstian response for DTA+ down to concentrations as low as 1 X "5 mol kg"1 even in the presence of a large excess of NaCl, allowing for sensitive and accurate free surfactant ion determinations. The binding of DTA+ to both polyanions is shown to be highly cooperative. The cooperativity parameter from the Zimm-Bragg theory may be estimated at 650 ± 100 and 200 ± 100 for the NaDxS and NaPS cases, respectively, and is independent of the NaCl concentration in both cases. The binding constant K of DTA+ to an isolated site on the polyanion is considerably larger in the PS-DTA system than in the DxS-DTA system, presumably because of differences in the hydrophobic/ hydrophilic properties of the two polymers. K is found to decrease strongly with increasing NaCl concentration; this decrease is similar in magnitude to the decrease in the critical micelle concentration (cmc) of dodecyltrimethylammonium bromide (DTABr) with increasing total counterion concentration in the presence of added NaCl.

Binding isotherms are reported for dodecyl-and tetradecyltrimethylammonium (DTA+ and TTA+) ion binding to polyacrylate (PA), alginate, pectate, and (carboxymethyl)cellulose (CMC) in the presence and absence of added NaCl at 30 °C, determined by using a potentiometric technique based on surfactant cation selective solid-state membrane electrodes. The results indicate a highly cooperative nature of the binding process of DTA+ and TTA+ by PA, alginate, and pectate but a lower cooperativity in the CMC system. TTA+ binding results in a larger cooperative binding constant (Ku) in all systems. The differences between DTA+ and TTA+ in the free energy of surfactant binding are 2.19kT for PA, 2.50kT for alginate, 2.56kT for pectate, and 2.64kT for CMC without NaCl and 2A2kT for PA with 0.01 m NaCl. These differences are comparable to the free energy of transfer of two methylene groups from water to a hydrocarbon medium or to a micelle. The presence of 0.01 m NaCl results in smaller Ku values and higher cooperativity.

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B3H 4JSA N D MICHAEL FALKAtlorltir R P S P ( I I .~.~~ L(rbot.trfor?~, Nntior~nl R~.setrr.rh Corrrlcil of' Cnritrdtr, Hol;fir.r, N.S., Ctrritrdo B3H 321 Rcccivcd August 30, 1983 SYLVIO QUEZADO. JAN C. T. KWAK. and MICHAEL FALK. Can. J. Chcm. 62. 958 (1984). We havc studicd thc infrarcd spcctra of Nafion mcmbrancs in twcnty diffcrcnt cationic forms, in ordcr to charactcrizc thc watcr-anion-cation interactions at low watcr contents. Spcctra in thc OH strctchinp rcgion and in thc H-0-H bcnding region allow thc distinction bctween hydrogcn-bondcd and non-hydrogen-bondcd water rnolcculcs, and yicld information on the modc of attachment of watcr molcculcs to the anion-cation pairs. Whcn thcrc is a good match bctwccn the Lcwis acid strcngth of the cation and thc Lcwis basc strcngth of thc anion. ion pairs are rclativcly stablc and watcr rnolccules tcnd to attach on the outsitlc. Whcn thc acid strcngth of thc cation and thc basc strcngth of thc anion arc mismatched, as is thc case for small cations of high charge or for largc cations of low chargc. watcr molcculcs tcnd to bc inscrtcd bctwccn thc ion pairs cvcn at thc lowcst watcr contcnts.

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