Dye-labeled poly(organosiloxane) microgels with core-shell architecture

Poly(organosiloxane) microgels are highly cross-linked rather monodisperse spherical particles of radius about 10 nm. Using a functionalized silane comonomer, i.e., (chlorobenzyl)trimethoxysilane, model particles suitable for studies in colloid physics are available: photoreactive and fluorescent dyes can be covalently bound within the microgels to prepare tracers for diffusion studies using forced Rayleigh scattering (FRS) and fluorescence correlation spectroscopy (FCS). For the application as tracer particles, it is important not to influence the diffusion behavior by the coupled chromophores. Therefore, functionalized precursors with a core-shell architecture are used to minimize labeling effects. The photochromic dye ortho-nitrostilbene (ONS) and the fluorophores rhodamine B, coumarin 343, and pyrene, respectively, were then coupled to the functionalized cores. The dye content of the labeled mu-gels strongly decreases with increasing thickness of the protective shell. A higher polarity of the used chromophores also lowers the dye content significantly, while differences in the size of the used label molecules are less important. The fluorescence intensity of the dye-labeled spheres is also influenced by the size of the protective shell which has been explained by differences in mobility of the labels (caging effects) and, at high dye concentration (thinner shell), by reabsorption.