Static and dynamic structural probing of swollen polyacrylamide ferrogels

Abstract

The local structure of hybrid ferrogels resulting from the incorporation of γ-Fe₂O₃ nanoparticles into a polyacrylamide polymeric network is probed from a static and a dynamic point of view, under various synthesis conditions and at swelling equilibrium. Relaxation of magneto-optical birefringence and small-angle neutron scattering measurements show adsorption of the nanoparticles onto the polymer, which is ascribed to H-bonding. These measurements allow one to identify the conditions leading either to a homogeneous scaffold reinforced by the nanoparticles, or to a nano-structured composite with 2D nanoparticle decoration on the walls of percolating pockets, initially filled by the ferrofluid during the synthesis and leaking out during the swelling. Two parameters rule the structure and the properties of these ferrogels – the osmotic pressure ratio R_Π (ratio of the osmotic pressure of the initial ferrofluid to that of the hydrogel) and the steric parameter R_S (ratio of the nanoparticle volume to the mesh volume of the polymeric hydrogel).