Fig. 6. Hertzian contact mechanics describe the pairwise interactions between microgels in the jammed state.
(A) Microgel building blocks come into contact in the jammed state where nonzero contact areas are generated. The depth of indentation, δ, on surfaces can be estimated via Hertzian contact based on the properties of the building blocks. In calculations, the normal force upon contact, FN, was fixed to 0.1 μN for each pair of microgels. (B) δ as a function of microgel stiffness rises sharply as a result of the highly deformable surfaces of soft microgels. Elasticity of microgels will resist further deformation, developing repulsive potentials, V(r), that are stored as elastic energy in the system. (C) V(r) of microgels at a fixed δ increases as a function of polymer content cross-linking density and size due to higher elasticity that resists microgel deformation. For comparison, we have included the hard sphere (HS) limit (gray) showing that δ = 0 for all microgel stiffnesses and V(r) → ∞ for all nonzero δ.