Neutron and\nX‑ray Scattering Characterization\nof Silica Nanoparticle-Stabilized Polymer Hybrid Latex Particles

A robust route to produce poly(methyl methacrylate) (pMMA)\nhybrid\nlatex particles (radius ∼250 nm) that are selectively “armored”\nwith silica nanoparticles (radius 12.5 nm) through addition of vinyltriethoxysilane\nwas previously shown (J.\nColloid Interface Sci. 2018, 528, 289–300).Depending\non synthesis conditions, the extent of nanoparticle attachment could\nbe varied; however, the mechanism behind this attachment during latex\ngrowth remained unclear. The dual population of particles present\n(silica + polymer) means that particle sizing by dynamic light scattering\nis ambiguous. Furthermore, the low glass transition temperature (<i>T</i><sub>g</sub>) of polymers such as poly(butyl acrylate)\n(pBA) typically used in film-forming applications for decorative coatings\n(i.e., paints) means that the hybrid latex particles are too “soft”\nfor robust analysis through atomic force microscopy (AFM) and scanning\nelectron microscopy (SEM). Here, we show that small- and ultrasmall-angle\nneutron scattering (SANS and USANS), along with complementary data\nfrom small-angle X-ray scattering (SAXS), reveals that these armored\nhybrid latex particles adopt a raspberry-type configuration, supporting\ntheir core–shell structure. The number of nanoparticles present\non the surface of the hybrid latex can be adjusted by addition of\none of a diverse range of alkyl- or perfluoroalkyl-silanes to alter\nsilica nanoparticle hydrophobicity, and quantified through analysis\nof scattering data. The approach therefore provides a novel, nonperturbative,\nand <i>in situ</i> method of quantifying nanoparticle attachment\nto polymer latex particles.