Design of Intelligent Protective Composite Material with Stress Rate Sensitivity, Strong Interface Adhesion, and Recyclability.

Poly(dimethyl siloxane) (PDMS) elastomers play a significant role in smart materials, actuators, and flexible electronics. However, current PDMS lacks adhesion abilities and intelligent responsive properties, which limit its further application. In this study, the polydimethylsiloxane-ureidopyrimidinone impact hardening polymer (PDMS-UI) composites are manufactured by a dual cross-linking compositing tactic. PDMS, a chemically stable cross-linked network, acts as a framework owing to its excellent mechanical strength, whereas UI, a reversible dynamic physically cross-linked network with quadruple hydrogen bonding, endows the PDMS-UI with excellent self-healing ability (efficiency > 90%) and energy absorption (75.23%). Impressively, owing to multivalent hydrogen bonds, the PDMS-UI exhibits superior adhesion performance: the adhesion strength on various substrates exceed 150 kPa and that on the Ferrum substrate reaches 570 kPa. These outstanding properties make the PDMS-UI a potential candidate for application in both well-developed fields, such as, wearable protective materials, artificial skin and soft robotics.

A facile method to synthesize strong salt-enhanced hydrogels based on reversible physical interaction.

To overcome the adverse effects of salt on the mechanical properties of hydrogels, a facile double cross-linking method has been proposed to synthesize salt-enhanced tough hydrogels. Herein, a poly(hexafluorobutyl methacrylate-acrylamide) hydrogel [P(AAm-co-HFBMA) hydrogel] is prepared by the copolymerization of acrylamide (AAm) and hexafluorobutyl methacrylate (HFBMA) with N,N'-methylene bisacrylamide (NMBA) as a cross-linking agent in a dimethylformamide (DMF)/aqueous solution; DMF is then replaced by water. The results indicate that the tensile fracture stress of the P(AAm-co-HFBMA) hydrogel (20 mol% HFBMA) is as high as 0.43 MPa, which is far better than that of the PAAm hydrogel (ca. 30 kPa). Additionally, with a further increase in the hydrophobic structural units (25 mol% HFBMA), the tensile fracture stress of the P(AAm-co-HFBMA) hydrogel can be increased up to 2.34 MPa. The mechanical strength of the P(AAm-co-HFBMA) hydrogel is significantly enhanced to 3.50 MPa (2 M) from 2.34 MPa (0 M) after it is soaked in aqueous NaCl solutions with various salt concentrations. The mechanical properties and the results of the DSC analysis indicate that the main reason for its mechanical strength to exhibit a unique salt-enhancement trend can be explained as follows. After the P(AAm-co-HFBMA) hydrogel is soaked in the salt solution, the network gradually collapses with the penetration of the small molecules of salt. Thus, the hydrophobic C-F units easily form dynamic cross-linking junctions due to the switchable hydrophobic interaction between C-F groups, which can endow the P(AAm-co-HFBMA) hydrogel with a more effective dynamic energy dissipation mechanism in salt solution.

Polymer Brush Graft-Modified Starch-Based Nanoparticles as Pickering Emulsifiers.

We study biosourced core-shell particles with a starch-based core and thermo-responsive polymer brush shell using surface-initiated single-electron transfer living radical polymerization (SI-SET-LRP) as a Pickering stabilizer. The shell endows the Pickering stabilizer with reversible emulsification/demulsification of oil and water properties. The initiator attached to the starch-based nanosphere (Br-SNP) core particle was first fabricated using the precipitation method. Subsequently, dense poly( N-isopropylacrylamide) (PNIPAM) brush graft-modified starch-based nanoparticles (SNP- g-PNIPAM) were obtained via the SI-SET-LRP process. Interfacial properties of the resultant particles were analyzed by interfacial tensiometer measurements, as were the effects of the grafted polymer chain length and temperature on the interfacial activity. Pickering emulsion was obtained using SNP- g-PNIPAM particles as the stabilizer. The effect of the concentration of the Pickering stabilizer on the size of emulsion droplets was analyzed. The emulsification/demulsification process of the Pickering emulsion can be reversed and easily repeated by changing the temperature.

Interfacial Activity of Starch-Based Nanoparticles at the Oil-Water Interface.

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.

Tough, rapid-recovery composite hydrogels fabricated via synergistic core-shell microgel covalent bonding and Fe3+ coordination cross-linking.

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.

A novel poly(acrylic acid-co-acrylamide)/diatomite composite flocculant with outstanding flocculation performance.

Series of anionic flocculants with outstanding flocculation performance, poly(acrylic acid-co-acrylamide)/diatomite composite flocculants (PAAD) were successfully prepared through aqueous solution copolymerization and applied to flocculate from oil-field fracturing waste-water. The structure of PAAD was characterized by Fourier transform infra-red spectroscopy, (13)C nuclear magnetic resonance and X-ray diffraction tests, and its properties were systematically evaluated by viscometer, thermogravimetry analysis and flocculation measurements. Furthermore, the influences of various reaction parameters on the apparent viscosity of flocculant solution were studied, and the optimum synthesis condition was determined. The novel composite flocculants exhibited outstanding flocculation properties. Specifically, the dosage of composite flocculants that could make the transmittance of treated wastewater exceed 90% was only approximately 12-35 ppm, which was far lower than that of conventional flocculants. Meanwhile, the settling time was lower than 5 s, which was similar to that of conventional flocculants. This was because PAAD flocculants had a higher absorption capacity, and larger chain extending space than conventional linear flocculants, which could refrain from the entanglement of linear polymer chains and significantly improve flocculation capacity.

Fabrication of an Amino Functionalized Paper-Based Material for Highly Efficient Detection and Adsorption of Formaldehyde.

An amino functionalized paper-based material that utilized amino functionalized polymer particles as sensing probes and adsorption sites was fabricated via internal sizing technology for application in formaldehyde detection and adsorption. A large specific surface area and the porous structure of the paper fibers enable the application of the composite paper-based material as a sensor at low concentrations of primary amine groups. The material reacts with low levels of formaldehyde, resulting in a concentration-based change in the pH, which is rapidly expressed as a color change. After exposure to formaldehyde (0.02 mg/m3) for 10 min, the color of the composite paper-based material changed from pink to brown, demonstrating the high sensitivity of the material, and this transition could be clearly observed using the naked eye. Additionally, the composite paper-based material acts as an adsorbent at a high content of amino groups, owing to a rapid addition reaction with formaldehyde, exhibiting a high adsorption capacity. Considering the high sensitivity, adsorption capacity, and adsorption speed for formaldehyde, the as-developed composite paper-based material exhibits promising application potential in the field of formaldehyde detection and adsorption.

New Approach for Preparation of Porous Polymers with Reversible Pore Structures for a Highly Safe Smart Supercapacitor.

Porous polymers have many industrial applications, but their pore structures (open or closed) are usually fixed during polymerization. In this study, polymers with reversible and controllable pore structures, namely, thermosensitive porous hydrogels with regulated volume phase transition temperature, were prepared using a Pickering high-internal-phase emulsion as the template. Upon heating, the hydrogels transformed not only in their wettability (between hydrophilicity and hydrophobicity with water contact angles of 21.8 and 100.9°) but also their pore structure (between open through-holes and closed holes with pore throat sizes of 15.58 and 0 µm, respectively) in a short time (<10 s). When the hydrogel was used as a separator in smart supercapacitors (SCs), this behavior effectively limited the path of electrolyte migration, reducing the chance of conflagration accidents. Moreover, by utilizing the highly reversible pore structures and wettability of the porous hydrogel, reversible charging and discharging were restored after the system cooled down. This work not only provides great guidance for preparing porous polymers with reversible pore structures but also paves the way for designing smart SCs with enhanced safety.

Temperature-responsive Pickering high internal phase emulsions for recyclable efficient interfacial biocatalysis.

The field of biocatalysis is expanding owing to the increasing demand for efficient low-cost green chemical processes. However, a feasible strategy for achieving product separation, enzyme recovery, and high catalytic efficiency in biocatalysis remains elusive. Herein, we present thermoresponsive Pickering high internal phase emulsions (HIPEs) as controllable scaffolds for efficient biocatalysis; these HIPEs demonstrate a transition between emulsification and demulsification depending on temperature. Ultra-high-surface-area Pickering HIPEs were stabilized by Candida antarctica lipase B immobilized on starch particles modified with butyl glycidyl ether and glycidyl trimethyl ammonium chloride, thus simplifying the separation and reuse processes and significantly improving the catalytic efficiency. In addition, the switching temperature can be precisely tuned by adjusting the degree of substitution of the modified starches to meet the temperature demands of various enzymes. We believe that this system provides a green platform for various interfacial biocatalytic processes of industrial interest.

Robust cellulose-based composite adsorption membrane for heavy metal removal.

Adsorptive membranes offer an effective mode to remove heavy metal ions from contaminated water, due to the synergies made possible by low-cost, high-affinity adsorbents and highly scalable filtration in one system. However, the development of adsorptive membranes is hampered by their instability in the aqueous phase and low binding affinity with a broad spectrum of heavy metals in a reasonable flux. Herein, a regenerated cellulose support membrane is strongly grafted with stable and covalent-bonded polyelectrolyte active layers synthesized by a reactive layer-by-layer (LBL) assembly method. The LBL assembled layers have been successfully tested by scanning electron microscopy, Fourier-transform infrared spectroscopy and X-ray photo-electron spectroscopy. The covalent bonding provides the membrane with long-term stability and a tunable water flux compared to a membrane assembled by electrostatic bonding. The maximum adsorption capacity of the membrane active layers can reach up to 194 mg/g, showing more efficient adsorption at lower heavy metal concentration and higher pH value of feed solution. The membrane can remove multiple ions, such as Cu, Pb, and Cd, by adsorption and is easy to be regenerated and recovered. The strong covalent bonding can extend the membrane lifetime in water purification to remove multiple heavy metals at high efficiency.

Multifunctional starch-based material for contaminated emulsions separation and purification.

Stable water-in-oil (W/O) emulsions can produce at many industrial production occasions. However, most materials for its separation have serious fouling problems. To overcome this shortcoming, we fabricated an easy cleaning multifunctional starch-based material with unique wetting behavior which could realize efficient separation and purification of W/O emulsions. This material has a hierarchical structure and superoleophilic and under oil superhydrophobic surfaces which could separate various W/O emulsions in a high separation efficiency and flux without external pressure. In addition, the decrease of separation flux was not observed for this material, which can be reused more than 10 times after washing with ethanol and drying after each separation cycle. Furthermore, this material also could realize efficient removal of dyes and heavy-metal and rare-earth ions simultaneously during a separation process. The material shows great potential for separating and purifying stable W/O emulsions produced during the industrial production.

Starch-based nanospheres modified filter paper for o/w emulsions separation and contaminants removal.

There is a pressing need around the world to develop novel functional biodegradable materials to separate oil/water mixtures and emulsions completely. Recently, superhydrophilicity and underwater superoleophobicity materials have been attracted attention due to their high efficiency in oil/water separation. However, it is still a challenge to prepare materials that combine oil/water separation and water purification in an environment-friendly way. In this work, biodegradable starch-based nanospheres (SNPs) coated filter paper was prepared in a low-cost, simple, and environmentally friendly manner. The SNPs coating could not only help to change the wettability of the substrate material but also build the hierarchical micro and nano structures which are conducive to separation and purification process. After modification by coating SNPs, the filter paper exhibited excellent performance in a wide range of oil/water mixtures or emulsions separation and the wettability of the filter paper could be regulated by adjusting the pH value. The modified filter paper presented good recyclability after several separation process. Furthermore, the as-prepared filter paper could also remove water-soluble contaminants during the oil/water separation process, thus realizing to combine separation and purification process in one single step. This biodegradable starch-based separating material with good separation performance, stability and recyclability has significant application potential in practical separation and purification process.

Thermoresponsive starch-based particle-stabilized Pickering high internal phase emulsions as nutraceutical containers for controlled release.

Pickering high internal phase emulsions (HIPEs) stabilized solely by bioderived starch-based particles hold potential for application in the food and pharmaceutical fields. This paper reports the use of a thermoresponsive 2-hydroxy-3-butoxypropyl starch (HBPS) particle as a representative natural biocompatible material for use as an effective stabilizer for HIPE formation. HBPS is synthesized by using butyl glycidyl ether as a hydrophobic reagent to change the hydrophobic-hydrophilic balance of starch, and then starch-based particles are fabricated by a simple nanoprecipitation procedure. The size of particles increased with an increase in temperature, and the particles are essentially monodisperse with a PDI of about 0.1 when the temperature was above 15 °C. These HBPS particles were subsequently used as an effective stabilizer to fabricate stable oil-in-water (o/w) Pickering HIPEs with an internal phase volume of 80% at different stabilizer concentrations. The results demonstrated that increasing the particle concentration is conducive to the formation of stable Pickering HIPEs with greater stiffnesses. In addition, the nutraceutical material (ß-carotene) was encapsulated into HIPEs and in vitro release experiments revealed that the release in this system can be controlled by adjusting the temperature.

Water-in-oil Pickering emulsion polymerization of N-isopropyl acrylamide using starch-based nanoparticles as emulsifier.

Inverse Pickering emulsions stabilized by naturally derived particles are of interesting during the past decade. In this study, starch-based nanoparticles were used as a particulate emulsifier to stabilize a w/o Pickering emulsion. The effects of particle concentration and oil volume fraction on the emulsion type and stability were investigated in detail. Catastrophic phase inversion from o/w to w/o emulsions occurred at a volume fraction of oil of 0.3-0.4, without altering the particle wettability. Further, a linear relation existed between the average droplet diameter and total amounts of starch-based nanoparticles. The obtained starch-based nanoparticles also served as a Pickering stabilizer to conduct a w/o Pickering polymerization. Raspberry-like thermoresponsive starch-poly(N-isopropyl acrylamide) nanocomposites with a well-defined structure were synthesized.

Spontaneous volume transition of polyampholyte nanocomposite hydrogels based on pure electrostatic interaction.

A circular system is employed in this paper to investigate the swelling behaviors of polyampholyte hydrogels; this circular system can effectively eliminate the disturbance of various factors and keep the surrounding environment constant. It is found that there exists a spontaneous volume transition to the collapsed state of polyampholyte hydrogels, which is attributed to the overshooting effect, and the transition can occur repeatedly under certain conditions. (13)C NMR is employed to investigate the swelling behavior of polyampholyte hydrogels. The swelling kinetics of polyampholyte hydrogels under various circular media and various circular runs are also investigated in this paper. All the results suggest that the spontaneous volume transition to the collapsed state of polyampholyte hydrogels is dominated by pure electrostatic interaction between different charges in polymer chains.

Fabrication of shape-tunable macroparticles by seeded polymerization of styrene using non-cross-linked starch-based seed.

Nonspherical colloidal particles with various geometries and different compositions have attracted tremendous attention and been widely researched. The preparation of polymer colloidal particles with controlled shapes by seeded polymerization is recognized as the most promising technique owing to the precise control of various morphologies and using non-cross-linked seed particles are of particular interest. Seeds particles derived from natural biopolymers are seldom applied. Hence, non-cross-linked starch-based seed could be used to fabricate the anisotropic particles by soap-free seed polymerization. Non-cross-linked starch-based seed particles were prepared by a nanoprecipitation method. Starch/polystyrene composite colloidal particles with shape-tunable were fabricated by soap-free seeded polymerization using starch-based seed. The effect of the polymerization time, monomer feed ratio and seed type were investigated. The seed particles with a single- or multi-hole structure were obtained after swelling with styrene. The resulting particles including golf-like, raspberry-like, octahedron-like and snowman-like structures, was fabricated on the polymerization process. This study firstly reports that the morphology of composite particles from golf-like to snowman-like at high monomer feed ratio using starch-based seed. At low monomer feed ratio, raspberry-like particles were obtained by surface nucleation increasing process. In addition, seed type also effect the morphology of composite particles.

Synthesis of poly(2-(2-methoxyethoxy)ethyl methacrylate) hydrogel using starch-based nanosphere cross-linkers.

Biodegradable thermosensitive hydrogels have attracted great interest because of their potential in biomedical applications. Herein, we present a novel, thermoresponsive poly(2-(2-methoxyethoxy)ethyl methacrylate) hydrogels with starch-based nanospheres as cross-linkers (NMH). NMHs exhibit a narrow lower critical phase transition temperature (LCST) range and high mechanical strength compared with conventional, small molecular cross-linked hydrogels (CMH). Fourier transform infrared (FT-IR) spectroscopy confirms that the NMHs are degradable in aqueous medium. The phase transition temperature of the NMHs is ∼4°C compared with ∼25°C for CMH. The NMHs can sustain strength of 12.2MPa, 10 times more than that of CMH. Moreover, the deswelling rate of NMHs is faster than CMH. The different concentrations of nanospheres can efficiently regulate the various properties of NMHs. The NMHs have excellent properties because of its even network structure formed by nanosphere cross-linkers.

In situ hydrogel constructed by starch-based nanoparticles via a Schiff base reaction.

Polysaccharide-based hydrogels are remarkable materials for the biomedical fields because of its excellent biodegradation and biocompatibility. In this work, a novel polysaccharide-based hydrogel was fabricated by in situ crosslinking of starch-based nanoparticles and polyvinylamine. Starch was decorated with cholesterol group and aldehyde groups. TEM and DLS showed that the cholesterol modified oxidation starch (OCS) exhibited a core-shell nanoparticles with mean size of ∼143 nm in aqueous. The hydrogel was then synthesized via Schiff base reaction. Rheological measurements demonstrated the incorporation of cholesterol groups not only reduced the gel time but also improved the storage modulus of the hydrogel compared with the oxide starch crosslinked hydrogel. SEM showed the OCS based hydrogels possess a well-defined porous structure. Furthermore, doxorubicin (DOX) was used as model drug to investigate the control and release properties of OCS hydrogels. This OCS hydrogel would be a promising drug carrier for biomedical applications.

A robust route to fabricate starch esters vesicles.

Starch-based vesicles with controlled size have been successfully achieved by a simple nanoprecipitation procedure from starch mixed ester.