Soft-soft nanocomposite adhesives made from colloidal particles*

Nanocomposites are often made with a dispersed hard phase in a soft matrix. In some cases however it might be interesting to obtain the stiffness from a continuous honeycomb structure and the toughness from the inside of the cells. Colloidal latex particles provide some unique opportunities to design nanocomposites. We have synthesized core-shell particles of acrylic copolymers where the outside shell contains a small amount of crosslinkable groups. These groups can then be used to introduce crosslinking points in and between the shells during the drying of the latex dispersion into a homogeneous film. The resulting films have very different large strain properties while the small and intermediate strain properties remain controlled by the viscoelastic properties of the inside of each particle. We show that films made in that way can have a very pronounced strain softening at intermediate strains (characteristic of viscoelastic liquids) while retaining a pronounced hardening at large strains (characteristic of viscoelastic solids'). This particular balance of properties results in a strong adherence to low energy surfaces while retaining a good resistance to creep.