Jan Czapkiewicz

Adsorption isotherms of homologous alkyldimethylbenzylammonium bromides on sodium montmorillonite

The adsorption of homologous alkyldimethylbenzylammonium bromides, [C(6)H(5)CH(2)N(CH(3))(2)R]Br, on sodium montmorillonite from aqueous NaCl solutions at room temperature has been studied. R stands for the methyl-, butyl-, hexyl-, octyl-, decyl-, and dodecyl-group, and the corresponding ammonium cations will be denoted as C1+, C4+, C6+, C8+, C10+, and C12+, respectively. C1+, the reference cation, attains the plateau region of adsorption at a level close to the cation exchange capacity (CEC) of the clay. The chain-length dependence on adsorptivity of the homologous cations exhibits an unexpected peculiarity. In the case of short-chain homologues of C1+ their adsorption onto sodium montmorillonite decreases in the order C1+>C4+>C6+. This behavior is due, presumably, to the growing steric hindrances at the surface of clay, which occur because of the limited area available for the bulky organic cations at the exchange sites. These limitations appear to be out-balanced in the case of higher homologues for which the increasingly growing hydrophobic effects lead to the expected sequence of adsorptivity of the cations, i.e., C1+<C8+<C10+<C12+. The extent of adsorption of the long-chain homologous cations at the plateau region exceeds the CEC value and indicates the commencement of formation of a bilayer or admicelle. As expected, the adsorption data for the short-chain homologues fit fairly well to the Langmuir isotherm, whereas the data for the C10+ and C12+ cations show an increasing departure from linearity of the corresponding plots. Results of X-ray analysis of organo-clays fully loaded with C1+, C4+, and C12+ cations suggest that in the case of short-chain homologues, the ammonium cations lay flatly and interact relatively strongly with the montmorillonite packet surface, whereas the long-chain homologue forms an interdigitated system of coiled hydrocarbon chains.

Micellization of decyldimethylbenzylammonium chloride at various temperatures studied by densitometry and conductivity

Abstract The critical micelle concentration (cmc), ionization degree of micellization, β , and standard free energy of micellization, Δ G 0 m , of decylbenzyldimethylammonium chloride in aqueous solution at 15, 25, 35, 45 and 55°C have been estimated from conductivity data. A shallow minimum of the cmc value appears at around 35°C. The apparent molar volumes of the monomeric and micellized surfactant were estimated from density data measured at 15, 25 and 35°C. It is suggested that release of water molecules from the hydration shell of the counter-ions may be an important contribution to the observed apparent expansion of the surfactant upon micellization.

Conductivity and dynamic light scattering studies on homologous alkylbenzyldimethylammonium chlorides in aqueous solutions

Abstract The critical micelle concentration and ionization degree of micelles formed by decyl-, dodecyl- and tetradecylbenzyldimethylammonium chlorides in aqueous solutions at 298 K have been determined conductometrically. The hydrodynamic radii of the micelles have been estimated from quasi-elastic light scattering data obtained for the surfactants in aqueous sodium chloride solutions. Both techniques yield results indicating a high degree of ionization of the micelles, suggesting that the benzyl group acts as a second hydrophobic substituent at the head group of the surfactant and plays a role similar to that of a second alkyl chain in double-chained cationic surfactants.

Micellar behavior of tetradecyldimethylbenzylammonium chloride in water-alcohol mixtures.

The effect of butanol and benzyl alcohol on the critical micelle concentration and the degree of ionization of micelles of tetradecyldimethylbenzylammonium chloride has been studied conductometrically in the temperature range of 5 to 40 degrees C at 5 degrees C intervals. The results indicate that some self-association process of benzyl alcohol in the aqueous phase commences when its concentration amounts to ca 0.05 m. By applying the theoretical treatment suggested by Motomura for binary surfactant systems, the molar fraction of alcohol in the micelle and the standard free energy of solubilization were estimated from the dependence of cmc on temperature and alcohol concentration. For comparative purposes the micellar properties of tetradecyltrimethylammonium bromide in water-alcohol systems at 25 degrees C have also been studied.

The effective degree of ionization of micelles as determined from partition data of colloidal electrolytes

Abstract The partition isotherms of pentadecyl-, tetradecyl-, and dodecyltrimethylammonium bromides in the water-1,2-dichloroethane system measured over a concentration range covering the critical micelle concentration (cmc) are presented. A phase separation model of the micelles was proposed to account for the abrupt change of slope of the isotherms at cmc, and an expression was derived relating the effective degree of ionization ( z ′) of the micelle with the analytical equilibrium partition concentrations of the long-chain electrolyte. The z ′ values for the micelles of the alkyltrimethyl-ammonium bromides as determined from the partition data amount to only 0.04. It is suggested that the strong binding of the bromide counterions to the micelles is due to the penetration of ion pairs into the core of the micelle, modified by solubilized 1,2-dichloroethane, as well as to the adsorption of the solubilizate at the micelle-water interface.

Surface tension studies on the complexation of dodecylpyridinium chloride byβ-cyclodextrin in aqueous electrolyte solutions

Surface tension measurements have been performed at 25° C for aqueous mixtures of dodecylpyridinium chloride and β-cyclodextrin in 0.1 M NaCl. Data analyses assuming 1:1 stoichiometry were applied to estimate the complexation constant of the host-guest complex formation. The technique yields consistent results for solutions with a swamping, constant concentration of a simple inorganic electrolyte.

Langmuir monolayers of polyphenylene carboxylic acids

Abstract A series of polyphenyl carboxylic acids with 3–6 uncondensed benzene rings and some of their analogues with a nitro and/or cyano group were synthesized and investigated at the air-water interface. They all can be treated as substituted m-terphenyls. It is determined that a system with at least four phenyl groups with the carboxyl group at a peripheral position are a prerequisite for the ability of monolayer formation. Their isotherms exhibit a large plateau attributed to the formation of bilayers.

Apparent molar volumes of benzyltrimethylammonium bromide and its homologs in aqueous solution at 15, 25, and 35° C

Apparent molar volumes at infinite dilution of benzyltrimethylammonium bromide and its butyl and hexyl homologs at 15, 25, and 35°C and of dibenzyldimethylammonium bromide at 25°C in aqueous solution were estimated from density measurements. The additivity rule for the contribution of the methylene groups to the apparent molar volumes was found to be obeyed within a broad range of homologs, which covers the parent salt and the dodecyldimethylbenzylammonium bromide. The volumetric contribution of the phenylene (–C6H4–) group was estimated to be 61 cm3-mol−1 at 25°C. A value of −16.9 ± 0.3 cm3-mol−1 was suggested for the volumetric contribution of the N+ fragment to the apparent molar volume of alkylbenzyldimethylammonium salts.

Evaluation of surfactant ion activity in micellar solutions of dodecylpyridinium chloride from partition data and counter ion activity measurements

The partition isotherm of dodecylpyridinium chloride in the water-1,2-dichloroethane system, measured over a broad concentration range, served for the evaluation of the critical micelle concentration and of the effective concentration and mean activity of the surfactant ions in the micellar concentration range. On the basis of the charged phase separation model for the micelles and EMF measurements of counter-ion activity, the surfactant cation activity and the apparent degree of counter ion association to the micelle (β) of 0.69 were estimated. The results indicate a gradual decrease of surfactant cation activity with increasing total concentration in the micellar range and support literature data derived from EMF measurements that apply surfactant selective plastic exchange membrane electrodes.

Vapor pressure osmometry studies on aggregation of low molecular weight quaternary ammonium bromides in chloroform

Abstract Vapor pressure osmometry was used to estimate apparent mean aggregation numbers of n-propyl-n-butyl-, and n-octyltrimethyl-ammonium bromides, and of tetraethyl- and n-tetrapropylammonium bromides in chloroform at 298 and 310 K, at the concentration range of 0.02 to 0.2 mol kg−1. Aggregation increases strongly with the decrease in the molecular weight of the bromides and appears to increase slightly upon elevation of the temperature, presumably due to desolvation effects. The Simple Stepwise Aggregation Model (I) with equal equilibrium constants for the addition of each monomer unit does not fit to the data. The Modified Model (II), which allows the association equilibrium constant for the first step to be different from the general stepwise constant, fits fairly well to the aggregation pattern of the weakly associating salts. At higher concentrations, the data for all studied salts conform as well to the Mass-Action Model (III) for the equilibrium between monomers and q-mers.