Variation in size and shape of hexaoxyethylene dodecyl ether C 12E6 micelles with uptake of n-dodecane and n-dodecanol in dilute aqueous solution

Abstract

The size and shape of hexaoxyethylene dodecyl ether C12E 6 micelles in dilute aqueous solutions with oil (n-dodecane and n-dodecanol) uptake were investigated by static (SLS) and dynamic light scattering (DLS) experiments at 40.0°C for the C12E6 + water + n-dodecane system and at 25.0°C for the C12E6 + water + n-dodecanol system. The micelles collapse into the smaller ones by incorporating n-dodecane, implying that the incorporation of the oil weakens hydrophilic interactions among polyoxyethylene tail of the surfactant molecules and water too significantly to maintain the original micellar size. The inclusion of n-dodecanol causes growth in the micellar size, suggesting that n-dodecanol plays a role as a kind of co-surfactant. Accompanying size change, the micelles were found to alter their shape from the original wormlike shape to prolate ellipsoid with the oil uptake. The axial ratios determined are 17.4 and 9.2 for micelles containing n-dodecane and n-dodecanol, respectively. The volume allotted to each C12E6 molecule (including the oil) in the micelles does not vary much with oil content.