Polymer-functionalized polymer nanoparticles and their behaviour in suspensions†
Soft polymer nanoparticles can be functionalized with end-tethered polymer chains to control their solvent compatibility and stability. Controlling and understanding the behaviour of such functionalized latex suspensions are critical for their comprehensive applications. To investigate the effect of the nanoparticle architecture on their rheological behaviour, a library of polystyrene nanoparticles functionalized with a canopy of end-tethered poly(methyl acrylate) chains with different degrees of polymerization and grafting densities was prepared. When the end-tethered polymer chains were long enough, the suspensions of polymer-functionalized nanoparticles underwent a liquid to gel transition when the concentration of the nanoparticles was increased. The architecture of the polymer canopy was the determining factor for the mechanical properties of the resulting gels; nanoparticles with moderate grafting density where the polymer chains adopt a relaxed polymer brush conformation led to the formation of the strongest and most robust gels. In comparison with suspensions prepared with polymer functionalized nanoparticles, particles with a soft and swollen core formed gels with higher yield stress at a lower solid content.