Hexadecyltrimethylammonium chloride and bromide in aqueous solutions containing urea and several alkylureas: a differential scanning calorimetric study

Abstract

With increase to the concentration of urea over the range 0 ⩽[urea]/mol dm^–3⩽ 3.0, the extremum in the differential heat capacity, δC_p, of hexadecyltrimethylammonium bromide (CTAB; aq; 0.02 mol dm^–3; reference, water) moves from 45 °C to lower temperatures and the associated enthalpy change characterising cluster reorganisation decreases. Addition of ethylurea to this CTAB solution produces a more dramatic shift in the extremum; the effect is even more striking when 1, 3-diethylurea is added. Addition of other alkylureas including, 1,1-diethylurea both shifts the extremum in δC_p and reduces its magnitude. A similar pattern emerges for aqueous solutions containing hexadecyltrimethylammonium chloride (CTAC). The effect of these ureas on CTAB(aq) is attributed to adsorption and penetration of the alkylureas into the CTAB micelles and clusters.