To explore this hypothesis, various amounts of ethanol were added to the dispersion. The presence of ethanol has a strong influence on the CMC of CTAC, increasing it from ~1.1 mM in aqueous media to ~125 mM in equimolar mixtures of H2O/EtOH . Furthermore, a previous study combining experiment and molecular simulation showed that the presence of ethanol as a co-solvent favored the assembly of AuNRs due to the stripping of interfacial surfactant micelles, thus decreasing interparticle repulsion. Thus, the mechanism of particle attachment to the surface appears to be the polymer-induced destabilization of the nanoparticles in the vicinity of the thermal gradient, which is inaccessible without the presence of co-solvent due to the increased density of CTA + adsorbed at the nanoparticle faces (Figure ). Beyond the effect of co-solvent on the CMC of CTAC, many studies have shown sign changes in the Soret coefficient of several polymers when introducing a co-solvent.