An investigation of dynamic surface tension, critical micelle concentration, and aggregation number of three nonionic surfactants using NMR, time-resolved fluorescence quenching, and maximum bubble pressure tensiometry.
Several physicochemical properties have been determined for N-dodecyllactobionamide (LABA), maltose 6'-O-dodecanoate (C12-maltose ester), and tetra(ethylene oxide) dodecyl amide (TEDAd). The increase in the flexibility of the sugar headgroup, enabling more possible molecular conformations, reduces the minimum area/molecule at the liquid-vapor interface obtained at the critical micelle concentration (cmc). The obtained cmc's were 0.35 mM (LABA), 0.3 mM (C12-maltose ester), and 0.5 mM (TEDAd). The monomer diffusion coefficient decreased with the molecular weight and increasing headgroup flexibility of the sugar headgroup, and values were in the range from 3.1 x 10(-10) to 3.6 x 10(-10) m2/s. The micelle diffusion coefficients (0.46 x 10(-10) to 0.68 x 10(-10) m2/s) indicated that the TEDAd micelles deviated most from spherical shape. The micelle aggregation numbers determined by time-resolved fluorescence quenching (TRFQ) were estimated to be 120+/-10 (LABA), 90+/-10 (C12-maltose ester), and 130+/-10 (TEDAd). The dynamic surface tension measurements show that the adsorption of TEDAd onto the liquid-vapor interface at short surface lifetimes is diffusion-limited, whereas an adsorption barrier is present for the sugar surfactants. The analysis of the dynamic surface tension data above the cmc shows that the rate of demicellization is faster for TEDAd than for the two sugar-based surfactants.
Kjellin
U R Mikael
UR
Department of Chemistry, Surface Chemistry, Royal Institute of Technology, Drottning Kristinas väg 51, SE-100 44 Stockholm, Sweden. mikael.kjellin@surfchem.kth.se
Reimer
Johan
J
Hansson
Per
P