Determination of CTAB CMC in mixed water + short-chain alcohol solvent by surface tension, conductivity, density and viscosity measurements

We considered the mutual influence of cetyltrimethylammonium bromide (CTAB) and methanol, ethanol as well as 1-propanol on their behaviour in the aqueous solution. This consideration was based on the surface tension, density, viscosity and conductivity measurements of the aqueous solutions of CTAB and alcohol mixture at 293 K in the whole range of alcohol concentration and in the presence of the surfactant in the monomeric and aggregated forms in the solution. Additionally, the dynamic light scattering measurements were made at the surfactant and alcohol concentration at which the aggregation of their molecules can be expected. CTAB practically does not influence the possibility of the formation of the small aggregates of alcohols and slightly affects the partial and apparent molar volumes of water and alcohols, but alcohols considerably affect the critical micelle concentration (CMC) of CTAB and the degree of counterions bound to its micelles. The mixed micelles of CTAB and methanol are probably formed in the whole range of alcohol concentration but those of CTAB and ethanol or 1-propanol only in their concentration range in which they are present in the monomeric form in the solution.

Graphical abstractInfluence of alcohol molecules form on specific conductivity of the aqueous solution of CTAB mixture with methanol, ethanol and propanol. (1) – Conductivity at the critical aggregation concentration of alcohol (CAC). (2) – Conductivity at the constant concentration of alcohols equal to CAC of methanol. (3) – Conductivity at the constant concentration of alcohols equal to CAC of ethanol. (4) – Conductivity at the constant concentration of alcohols equal to CAC of 1-propanol. (5) – Conductivity at the constant concentration of alcohols equal to 1.07 mol/dm3. (6) – Conductivity in ``pure'' alcohols.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Short-chain alcohols form aggregates in the aqueous solutions of their mixture with CTAB. ► Ethanol and 1-propanol decrease the CMC of CTAB at their low concentrations. ► CTAB forms micelles in the whole range of methanol concentration. ► CTAB slightly affects the apparent and partial molar volume of alcohols and water. ► The contraction minimum of the sum of alcohol and water volumes exists at their 1:1 ratio.