•Monodisperse starch-polystyrene core-shell nanoparticles are fabricated.•The mechanism Pickering transform to seeded emulsion polymerization is proposed.•The particles size is regulated by pH value, styrene content, the SNP content and size.The convenient synthesis of core-shell nanoparticles containing degradable components is very desirable given the potential applications of such nanoparticles in biomaterials. A facile approach for producing monodisperse starch-polystyrene nanocomposites with well-defined core-shell structures in the absence of a surfactant was developed. The initially-formed Pickering emulsions underwent conversion into seeded emulsions during the polymerization, wherein the amphiphilic starch-based nanospheres (SNPs) serve as stabilizer and seed. A possible mechanism for this transition was explored based on the morphology and size variations of the emulsion droplets and the resultant nanospheres. The effects of the monomer concentration, SNP content and size, and pH on the core-shell nanospheres were investigated. With increasing monomer concentration, the core size of the particles remained almost unchanged, while the shell layer thickness increased almost linearly. The size of the core-shell nanospheres can be regulated by adjusting the pH and the SNP content and size.

•Core-shell microspheres are used as both initiator and cross-linker.•Synergic effect of homogeneous network and energy dissipating mechanism of H-bonding.•The reversible deformation of core–shell microspheres due to the flexibility of PBMA.•The cavitations between the microspheres and matrix.A series of chemically cross-linked microgel composite hydrogels (MCH gels) with excellent toughness and stretchability were prepared using core–shell polymer microspheres as cross-linking junctions. In our strategy, MCH gels are obtained by connecting microspheres with polyacrylamide (PAAm) chains chemically grafted onto their surfaces, where an organic cross-linking agent is completely unnecessary. The mechanical behavior of the MCH gels was analyzed, and superresolution fluorescence microscopy and scanning electron microscopy were used to investigate their toughening mechanism. The results indicated that the homogeneous network structure resulting from the good compatibility between the core–shell microspheres and matrix was an important reason for the excellent toughness of the MCH gels. In addition to interactions among H bonds in the grafted PAAm chains, reversible deformation of the core–shell microspheres acting as cross-linking junctions, which arises from the flexibility of the microspheres, and the effect of cavitation between the microspheres and matrix could also effectively dissipate energy during deformation of the MCH gels.Download high-res image (189KB)Download full-size image

Here, we present a novel nanoparticle derivate from natural polysaccharide as a stabilizer for the Pickering polymerization of styrene. In this process, amphiphilic starch-based nanospheres (SNPs) were fabricated from starch octenyl succinic ester through a nanocoprecipitation process as a Pickering stabilizer. The effects of the SNP concentration, size and pH value on the Pickering polymerization are investigated in detail. The polystyrene (PS) particle morphology transforms from bare PS particles to raspberry-like structures with an increase in the SNP content. The linear relationship between the inverse diameter of the PS particles and the SNP content allows for an estimation of the coverage of SNPs on the PS particle surface. Moreover, the size of the PS particles can be regulated by the SNP size. The microstructure of the PS particles can also be regulated by the pH value of the reaction medium. Finally, a possible mechanism for the formation of the PS particles with different morphologies is proposed.

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 %.

An in situ hydrogel based on oxidation cholesterol starch (OCS) and O-carboxymethyl chitosan (CMCT) that is completely devoid of potentially cytotoxic small molecule cross-linkers and does not require complex manoeuvres or catalysis has been formulated and characterized. The network structure was created by Schiff base formation. The mechanical properties, internal morphology and swelling ability of the injectable hydrogel were examined. Rheological measurements demonstrated that increasing the concentration of the monomer improved the storage modulus. SEM showed that the hydrogel possessed a well-defined porous structure. In addition, the Schiff base reaction was acid sensitive. Under acid conditions, the hydrogel could hydrolyse quickly compared with high pH conditions. Doxorubicin (DOX) was used as a model drug to investigate the control and release properties of the hydrogel. The cytotoxic potential of the hydrogel was determined using an in vitro viability assay with L929 cells as a model and the results revealed that the hydrogel was non-cytotoxic.

Although lots of impact protective materials reported exhibited better impact protective performance thanking to their excellent mechanical performance, their applications were still seriously impeded due to absence of soft–stiffness switch smartness. Herein, a novel impact hardening polymer (IHP) with negative Poisson's ratio was synthesized via a condensation polymerization, followed by a simple thermal annealing to achieve a perfect soft–stiffness switch characteristic and self-healing capacity. Its soft–stiffness switch ability σ, defined as G′max/G′min in rheological analysis, can reach 9000, which is never reported so far. The result of laser speckle scatter measurement elucidates that IHP has negative Poisson's ratio, which is the root cause why IHP exhibits soft–stiffness switch capacity. Finally, 3D composite anti-impact fabrics were prepared by dip–coating IHP dispersion onto a 3D porous polyester fabric. Not only the impact protective performance of anti-impact fabrics finished with the IHP is significantly improved, but also the flexibility and hand feeling of anti-impact fabrics finished with the IHP are obviously very good because the IHP is flexible without impact.A novel impact hardening polymer (IHP) with negative Poisson's ratio was synthesized via a condensation polymerization, followed by a simple thermal annealing to achieve a perfect soft–stiffness switch characteristic and self-healing capacity. Its soft–stiffness switch ability σ, defined as G′max/G′min in rheological analysis, can reach 9000, which is never reported so far. The result of laser speckle scatter measurement elucidates that IHP has negative Poisson's ratio, which is the root cause why IHP exhibits soft–stiffness switch capacity.

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.

A series of amphoteric hydrophobic-associative flocculants with outstanding flocculation efficiency and salt tolerance, poly(acrylamide/acrylic acid/dimethyl benzyl aminoethyl acrylate chloride), are successfully prepared (named AAB series) and used to flocculate the montmorillonite suspensions. The solution properties of AAB copolymer are systematically evaluated by viscometer, rheology and steady-state fluorescence analysis. The results suggest that the space network structure forming via hydrophobic-associating interaction can increase solution viscosity and improve the bridging capacity of copolymers. Meanwhile, the apparent viscosity in salt solution increases with increase in the concentration of salt stemming from the anti-polyelectrolyte effect of polyampholyte. Further, the flocculation performances of flocculants in 1 wt% montmorillonite suspensions are evaluated by turbidity, optimal dosage and settlement rate measurement. The results elaborate that the flocculation performances of amphoteric hydrophobic-associating AAB flocculants are better than that of commercial flocculants (cationic and anionic polyacrylamide) and homemade cationic flocculant (AAB-0-5) independent of the type and concentration of salt. The novel ampholyteric hydrophobic-associative flocculants will exhibit intriguing prospective in industry water treatment, in that the anti-polyelectrolyte effect of polyampholyte and hydrophobic-associating interaction can endow excellent flocculation efficiency and salt tolerance.

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.