To try to understand the variation in surface tension as a function of functionalized gold nanoparticle particle and SDS concentration, we will make measurements of the specular neutron reflectivity from the air/water interface of gold nanoparticle dispersions. We also propose an indirect measurement of the surface free energy of functionalized gold nanoparticles from a direct measurement of the interfacial structure he surface free energy of gold nanoparticles functionalized with different short-chain thiols. Our recent SANS measurements on these particles, lead us to expect that there maybe lateral ordering of the particles with a characteristic length-scale in the range 10-40 nm, depending on pH. We will use the spin-echo capability of Offspec to look for this ordering and to correlate it with the the particle structures identified by SANS.