Mass transport characteristics of alkyl amines in a water/n-decane system.

Water-in-decane emulsions can be applied as reaction system for the precipitation of nanoparticles. Herein the precipitation reaction is induced once an oil as well as water soluble compound (here: alkyl amines) diffuses from the continuous oil phase into a water based droplet, loaded with the reaction partner. Thus, the mass transfer and adsorption characteristics of the alkyl amine at the interface are key parameters to understand particle formation in emulsion droplets. For this reason, the effective diffusion coefficients and the interfacial tension of different alkyl amines in a water/n-decane system were estimated. Furthermore, emulsifiers necessary for the stability of the emulsion might represent a diffusion barrier. In order to determine its influence, diffusion experiments were also conducted in the presence of emulsifier. The effective diffusion coefficients were measured using an adapted photometric method. To identify relevant adsorption characteristics of the water/n-decane/alkyl amine systems, the interfacial tension was studied with the pendant drop technique. According to the results, we can draw three conclusions: First, the effective diffusion coefficient depends on the molecular structure of the amines. Second, regarding our materials, the surface activity and surface coverage proved to be a governing parameter to describe differences in the transport mechanism. And third, the presence of additional surface active compounds leads to a decrease of the effective diffusion coefficient.