The osmotic coefficient, the apparent molar volume, and the electrical conductivity of aqueous solutions of the homologous series of decyl-, undecyl-, dodecyl-, tridecyl-, tetradecyl-, pentadecyl-, and hexadecylpyridinium bromides (CnPyBr) have been determined at 25 °C. From these data the variation of the critical micelle concentration (cmc) with the chain length of the surfactant has been obtained. Measurements were performed usually at concentrations from well below to well above the cmc. From osmotic coefficient and conductivity measurements, the degree of counterion binding to micelles, β, has been calculated. It has been found that the values of β are rather insensitive to the chain length, and as expected, the values determined from transport measurement are lower than those from the osmotic pressure measurements. From the apparent molar volumes the aggregation numbers of alkylpyridinium bromides have been estimated, following simple geometrical considerations suggested by Tartar and Tanford.

Following the procedure given in the literature, we prepared water-soluble T h symmetric derivative of fullerene C60, at which six malonic acid molecules have been attached, T h -C60(C(COOH)2)6. The sample has been characterized by some fundamental physicochemical data and properties:  13C NMR chemical shifts for the acid and its sodium salt, solubility data, potentiometric and conductometric titration curves, the electrical conductivity, the osmotic coefficient, and the apparent molar volume. It has been found that fullerenehexamalonic acid (FHMA), C66(COOH)12, behaves as a diprotic acid. The first carboxylic group, COOH(1), of the malonic acid functional group behaves as an almost strong acid, whereas the second COOH(2) group is a weak acid with pK 2 of about 5.5. The molar conductivity extrapolated to zero concentration yielded Λ0 = 395.0 Ω-1 cm2 mol-1 COOH(1) and the molar conductivity of half-ionized fullerenehexamalonate ion Λ0 (1/6C66(COOH)6(COO-)6) = 45.2 Ω-1 cm2 mol-1. Due to the low solubility of the acid (about 11.8 g/L) the measurements were restricted to a narrow concentration range from about 0.0018 to 0.000 01 mol FHMA/L. In this concentration range, the apparent molar volume was found to be constant and equal to φV = 557 mL/mol FHMA. The osmotic coefficient, which we succeeded in determining only at the highest concentration, is comparable to the fraction of free hydrogen ions calculated from conductivity data and pH measurements.

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The addition of simple salt to a solution of conjugated polyelectrolyte can lead to substantial changes in its optical properties caused by the conformational change of the polymer chain. The effect of the addition of alkali metal and tetraalkylammonium chlorides to solutions of lithium salt of poly(thiophen-3-ylacetic acid) is investigated by NMR. The fractions of free alkali metal counterions are in agreement with predictions of the cylindrical Poisson-Boltzmann cell model. On the other hand, the fractions of free tetraalkylammonium counterions deviate from the prediction of this model and diminish with increasing size of these counterions. This trend is consistent with observed ultraviolet-visible absorption spectra and measured self-diffusion coefficients of the polyion in mixtures with tetraalkylammonium salts. A transition to more constricted conformation of the polyion chain becomes more pronounced with the lengthening of alkyl groups in the added tetraalkylammonium cation. Taking into account the obtained fractions of free counterions, existing thermodynamic data are reanalysed in order to determine thermodynamic parameters for binding of different counterions to the polyion. This analysis shows that standard enthalpies of binding of alkali metal counterions are distinctively different, which is most probably related to differences in hydration shells of counterions. On the other hand, such an analysis fails in the case of tetraalkylammonium chlorides where obviously more complex changes take place.