surfactant concentration profile at interface
 

Hi there - I am looking to generate a surfactant concentration profile at the interface of another fluid.

I am performing a simulation on multiphase flow, VOF model. I am able to generate the volume fraction in my simulation. Now, I am supposed to diffuse a soluble surfactant into one of the fluid phase. This reduces the surface tension between the two phases. Based on the volume of surfactant added the surface tension changes according to the Gibbs equation. I am trying to solve the convective diffusion equation by defining UDF. Making interfacial tension a function of surfactant concentration. But unsuccessful. I am unable to generate a concentration profile at the interface. What alternatives? Thanks in advance.

-Sripad