2 research outputs found
STAND: Surface Tension for Aggregation Number Determination
Taking
advantage of the extremely high dependence of surface tension
on the concentration of amphiphilic molecules in aqueous solution,
a new model based on the double equilibrium between free and aggregated
molecules in the liquid phase and between free molecules in the liquid
phase and those adsorbed at the air/liquid interface is presented
and validated using literature data and fluorescence measurements.
A key point of the model is the use of both the Langmuir isotherm
and the Gibbs adsorption equation in terms of free molecules instead
of the nominal concentration of the solute. The application of the
model should be limited to non ionic compounds since it does not consider
the presence of counterions. It requires several coupled nonlinear
fittings for which we developed a software that is publicly available
in our server as a web application. Using this tool, it is straightforward
to get the average aggregation number of an amphiphile, the micellization
free energy, the adsorption constant, the maximum surface excess (and
so the minimum area per molecule), the distribution of solute in the
liquid phase between free and aggregate species, and the surface coverage
in only a couple of seconds, just by uploading a text file with surface
tension vs concentration data and the corresponding uncertainties