Understanding the interfacial activity of polysaccharide nanoparticles adsorbed at oil–water interfaces is essential and important for the application of these nanoparticles as Pickering stabilizers. The interfacial properties of starch-based nanospheres (SNPs) at the interface of an n-hexane–water system were investigated by monitoring the interfacial tension at different bulk concentrations. The three-phase contact angle (θ) and the adsorption energy (ΔE) increased with increasing size and degree of substitution with octenyl succinic groups (OSA) in the particles. Compared with the OSA-modified starch (OSA-S) macromolecule, the SNPs effectively reduced the interfacial tension of the n-hexane–water system at a relatively higher concentration. These results and the method reported herein are useful for selecting and preparing polysaccharide nanoparticles as Pickering stabilizers for oil–water emulsions.

We developed tough, rapid-recovery composite hydrogels that are fabricated via core–shell microgel covalent bonding and Fe3+ dynamic metal coordination cross-linking. First, core–shell microgels are used as cross-linking agents and initiators to prepare homogeneous hydrogel networks with rapid recovery in the absence of an organic cross-linking agent. The toughness and recoverability of the composite hydrogels can be improved by adding the dynamic reversibility of ionic cross-linking. Owing to the synergistic effect of microgel covalent bonding, Fe3+ coordination cross-linking, and H-bond cross-linking, the multi-cross-linked composite hydrogels exhibit excellent toughness and a fast recovery rate. These characteristics demonstrate that the dynamic reversibility of the ionic cross-linking can significantly improve the toughness and recoverability of the hydrogels. In addition, the core–shell microgels play a key role in toughening the hydrogels and accelerating their recovery by transferring stress to grafted polymer chains and homogenizing the hydrogel network.

In this study, multi-sensitive hydrogels with high mechanical strength were successfully prepared by in situ free-radical polymerization of acrylamide, acrylic acid and acryloyloxyethyl trimethyl ammonium chloride monomers in the presence of microgels in aqueous media. Microgels with amine groups on the surface were used as polyfunctional initiating and cross-linking centers to fabricate a network. The microgel-based hydrogels synthesized did not fracture upon loading up to 30 MPa and a strain above 99 % when the water content was about 84 wt%. As for the swelling behaviors of the microgel-based hydrogels, they were susceptible to pH and salt concentration. Meanwhile, deswelling tests indicated that the microgel-based hydrogels had thermo-sensitive properties and under high temperature exhibited a faster shrinking rate, which could be attributed to the solvent channels caused by the shrinkage of microgels due to their thermo-sensitive core. And microgel-based hydrogels with various deswelling rates can be determined by regulating the content and species of microgel. Furthermore, the low extensibility of microgel-based polyampholyte hydrogels could be improved by creating a hybrid network with microgels and a small amount of N,N’-methylenebisacrylamide served as the chemical cross-linkers. The hybrid hydrogels possessed superior compressive strength and simultaneously showed abnormal elongation of up to 1000 %.

Novel microgel composite hydrogels characterized with the structural evolution of crosslinking junctions were prepared. Under the pH stimulus, the high-strength hydrogels exhibit a drastic and sudden volume phase transition, which derives from the dissociation and association of crosslinks.

High strength, stimuli-responsive poly(acrylamide) composite hydrogels (PAAm CH gels) were prepared by grafting polymerization of acrylamide (AAm) onto temperature-sensitive core–shell microgels. These microgels, composing of poly(N-isopropylacrylamide) as core and polyvinylamine (PVAm) as shell, were used as both initiator and crosslinker to form a robust three-dimensional network via bonding the poly(acrylamide) (PAAm) backbone. The CH gels exhibited a remarkably rapid shrinking rate and transmittance switch in response to the environmental temperature change, which the conventional chemically cross-linking PAAm hydrogels (PAAm OR) were short of. Even compared to the bulk PNIPAAm hydrogels (PNIPAAm OR) crosslinked with N,N′-methylenebisacrylamide (MBA), the CH gels were featured with faster responsive rate, which could be attributed to the formation of interconnected water transportation channels between the microspheres and PAAm gel matrix due to the fast shrinking of microgels. Moreover, the effects of microgel species and content on swelling and mechanical properties of CH gels were also systematically investigated. The results elaborated that the CH gels could be compressed almost 99% without breaking and completely recovered their original shape when the stress was removed. And the optimized compressive strength of CH gels could be up to 21.94 MPa. Based on the analysis of CH gel mechanical properties, the influence of microsphere content on effective network chains density of CH gels was discussed through rheology measurements. Finally, the essential reinforcement on mechanical properties was mainly contributed to the homogeneous microstructure of hydrogel network and the energy dissipation mechanism of microgels in gel matrix.