Good morning,
Thanks for your attention. I would like to know other methods to estimate the effective interfacial area per surfactant molecule in a monodisperse emulsion without using the Gibbs adsorption isotherm and tensiometry experiments. Could it be done by any groups contribution method? Thanks
If you know:
- the surfactant molecular weight (easy if you know the structure)
- the surface-weighted droplet size (measure with low angle light scattering, e.g. Mastersizer)
- the oil volume fraction (you know that),
- the total amount of surfactant (you know that) and
- the surfactant remaining in the continuous phase, (tricky part, need to measure after removing the droplets)
you can estimate the area per molecule in a straightforward calculation :-).
Dear Antonio,
I agree to Alan Parker. You will find an example for this approach in the attached publication.
I also agree, that the removal of the oil droplets is the tricky part. If you use ultrafiltration devices, you will have to make sure that surfactant adsorption at the membrane does not lead to an underestimation of surfactant in the continuous phase. If you separate your emulsion by centrifugation, you might significantly disturb the partitioning equilibrium of the surfactant. I prefer UF - just collect as much filtrate as you need for the quantification of the surfactant and maybe particle size measurements.
It is also adviseable to check for very small oil droplets / swollen micelles in the filtrate / supernatant, because they might contribute to the total surface area (see paper by C. Berton-Carabin).
For sufficiently low ionic surfactant concentration you may assume that all surfactant is at the interface until saturation of the interface, because monomer concentration is at least one order smaller than that at the interface (see pdf provided by Kathleen). Merely different the situation for nonionic surfactants (and oil soluble ionic ones) where a fraction of surfactant will partition into the oil phase.
Thank you all for your answers, they have been really useful for me. If i could help you in someway please let me know. Antonio
Dear Antonio,
I hope my paper could be of use to you not only as a direct answer to your query but generally as well.
Journal of Dispersion Science and Technology
Publication details, including instructions for authors and subscription information:
http://www.informaworld.com/smpp/title~content=t713597266
THE ADSORPTION OF AN ANIONIC SURFACTANT AT THE OIL
WATER INTERFACE DURING EMULSION HOMOGENIZATION
P. Dokića; Lj. Djakovića; V. Sovilja
a Faculty of Technology University of Novi Sad, Yugoslavia
Online publication date: 21 June 2010