VOLUMETRIC PROPERTIES AND COMPRESSIBILITIES OF ALKYLTRIMETHYLAMMONIUMBROMIDES AND SODIUM ALKYLSULPHATES IN AQUEOUS-SOLUTION

Density and sound velocity data for aqueous solutions at 298.2 K conta ining alkyltrimethylammonium bromides and sodium alkylsulphates were a nalysed to yield partial molar volumes and isentropic compressions. Th e calculated contributions of methylene groups to the properties of al kyltrimethylammonium cations and alkylsulphate anions show no dependen ce on position in the alkyl chains and a common contribution to the io nic partial molar volumes over the range methyl less than or equal to n-octyl for the sulphates and n-propyl less than or equal to n-hexyl f or the alkyltrimethylammonium ions. However, a switch in head group fr om trimethylammonium to sulphate changes the contribution of methylene groups to estimated partial molar isentropic compressibilities. The r easons for this sensitivity are discussed in terms of hydration charac teristics. (C) 1998 John Wiley & Sons, Ltd.