The influence of silica nanoparticles on the lower critical solution temperature (LCST) phase behavior and phase-separation kinetics of a blend consisting of poly(methyl methacrylate) (PMMA) and poly(styrene-co-acrylonitrile) (SAN), is studied via a high-throughput experimentation (HTE) approach, which combines a composition (φ) and a temperature (T) gradient. The evolution of the phase-separation process is studied by optical microscopy (OM), small-angle light scattering (SALS), and transmission electron microscopy (TEM). Depending on the specific interaction between the silica surface and the polymers, the distribution of silica particles during phase separation can be controlled to be either in one of the polymer phases or at the PMMA/SAN interface. The hydrophilic silica nanoparticles preferentially migrate to the PMMA phase, leading to a slow down of the coarsening rate, which may be related to a reduction of the mobility of PMMA due to an increase of the silica concentration. The hydrophobic silica nanoparticles are localized at the PMMA/SAN interface, and the inhibition of coalescence corresponds to the presence of a solid barrier (the nanoparticles) between the polymers, which prevents the coarsening process.