Hydrogels, soft materials with 3D polymer networks in aqueous solution, have been developed for engineering and bio-related fields. However, these conventional hydrogels are weak and brittle due to lack of energy dissipation mechanisms. Recently, dual-network hydrogels have been proposed, combining rigid and flexible networks and exhibiting high strength, stretchability, and toughness. This paper explores the rheological properties of dual-network hydrogels based on acrylamide and sodium alginate under large deformations. This dual network is a combination of a covalently crosslinked polyacrylamide network and a supramolecular crosslinked sodium alginate network at the presence of divalent calcium cations. Small and large amplitude oscillatory shear methods with Fourier transform rheology, stress decomposition method, and Chebyshev polynomial analysis of large amplitude oscillatory shear (LAOS) data were employed to evaluate non-linearity limit, toughness, and network rigidity. The concentration of calcium ions affects (concentrations 0-80 mg/ml) the nonlinear transition and limit points, and all gel samples exhibit strain hardening, shear thickening, and shear densification.

When existing at emulsion interface and continuous phase, dispersibility of water-soluble flexible polymer chains has obvious effect on rheology and dielectric properties of whole emulsion. CNF Pickering emulsion is a good system to research these properties with respect to their microscopic phase structure, dielectric and rheological properties by using cellulose nanofibers (CNF) as water-soluble Pickering emulsifier, liquid Paraffin as oil phase and DDAB as a cationic auxiliary surfactant. The CNF- and DDAB-contents were systematically varied while the water to paraffin oil ratio remained constant to discern the influence of the Pickering emulsifiers. Polarized optical microscopic images revealed that the droplets have tendency to become smaller size for higher CNF content, but bigger size for higher DDAB content, which was proved by the fluorescent analysis for CNF dispersibility with varying DDAB content. The dielectric damping exhibits a minimum, whose value decreases with increasing DDAB- and CNF-content. Increasing the DDAB-content promotes solubilization of CNFs in the aqueous phase and will increase the overall viscosity and yield points. Similarly, a higher CNF-content leads to a higher viscosity and yield point, but at high DDAB-contents the viscosity function exhibits an S-shape at intermediate CNF-content. To evaluate the results further they were compared with CNF-dispersions (without oil-phase), which showed a surfactant effect slightly on maximum stress but strongly on yield stress τy, indicating DDAB can promote the formation of CNF network rather than the viscosity of whole system.