The composition of polymeric colloidal particle mixtures made from polyacrylates and polyurethanes can be determined at the single nanoparticle level in their solid state using infrared (IR) based Photo-induced Force Microscopy (PiFM). The morphological differences between (1) a blend of two individual polymer dispersions and (2) a hybrid dispersion created by incorporating polyacrylate phases during the preparation of polyurethane particles can be clearly elucidated by detecting the photo-induced force responses originating from materials under irradiation of a tunable IR laser at a wavelength at which one of the polymers shows a strong characteristic IR absorption peak. The hybrid dispersion shows a high degree of mixing between the two chemically distinct species, which would otherwise phase separate in a physical blend. PiFM, with its excellent spatial resolution down to the nanometer scale and spectroscopic similarity to the FT-IR technique, shows strong potential in materials characterization for research areas such as colloids in water-based coatings and micro/nano-plastics.