Yang Wang

Strong nanocomposite reinforcement effects in poly(vinyl alcohol) with melanin nanoparticles

Poly(vinyl alcohol)/melanin nanocomposites with improved tensile strength, Youngs modulus and heat distortion temperature (HDT) were prepared by using simple aqueous solution mixing. When incorporated into PVA with low content (0.5–2 wt%), melanin nanoparticles dramatically enhanced the mechanical properties of PVA. With addition of 2 wt% melanin, the nanocomposites exhibited a tensile strength (σ) of 155 MPa and a Youngs modulus (E) of 2.95 GPa, which were much higher than these of neat PVA. HDT was enhanced from 56.5 °C to 100 °C. TEM indicated that melanin nanoparticles were uniformly dispersed in PVA without aggregation. The strong hydrogen bonding between the –OH (or –NH–) of melanin and –OH of PVA confirmed by FTIR, which played a key factor to prevent the aggregation of nanoparticles in PVA matrix and made a contribution to the high performance of PVA.

Superior mechanical properties of double-network hydrogels reinforced by carbon nanotubes without organic modification.

A facile method is developed to fabricate nanocomposite double-network (DN) gels with excellent mechanical properties, which do not fracture upon loading up to 78 MPa and a strain above 0.98, by compositing of carbon nanotubes (CNTs) without organic modification. Investigations of swelling behaviors, and compressive and tensile properties indicate that equilibrium swelling ratio, compressive modulus and stress, fracture stress, Young’s modulus, and yield stress are significantly improved in the presence of CNTs. Scanning electron microscopy (SEM) reveals that the pore size of nanocomposite DN gels is decreased and some embedded micro-network structures are observed on the fracture surface in comparison to DN gels without CNTs, which leads to the enhancement of mechanical properties. The compressive loading-unloading behaviors show that the area of hysteresis loop, dissipated energy, for the first compressive cycle, increases with addition of CNTs, which is much higher than that for the successive cycles. Furthermore, the energy dissipation mechanism, similar to the Mullins effect observed in filled rubbers, is demonstrated for better understanding the nanocomposite DN polymer gels with CNTs.

A Novel UV-Shielding and Transparent Polymer Film: When Bioinspired Dopamine–Melanin Hollow Nanoparticles Join Polymers

Ultraviolet (UV) light is known to be harmful to human health and cause organic materials to undergo photodegradation. In this Research Article, bioinspired dopamine-melanin solid nanoparticles (Dpa-s NPs) and hollow nanoparticles (Dpa-h NPs) as UV-absorbers were introduced to enhance the UV-shielding performance of polymer. First, Dpa-s NPs were synthesized through autoxidation of dopamine in alkaline aqueous solution. Dpa-h NPs were prepared by the spontaneous oxidative polymerization of dopamine solution onto polystyrene (PS) nanospheres template, followed by removal of the template. Poly(vinyl alcohol) (PVA)/Dpa nanocomposite films were subsequently fabricated by a simple casting solvent. UV irradiation protocols were set up, allowing selective study of the extra-shielding effects of Dpa-s versus Dpa-h NPs. In contrast to PVA/Dpa-s films, PVA/Dpa-h films exhibit stronger UV-shielding capabilities and can almost block the complete UV region (200-400 nm). The excellent UV-shielding performance of the PVA/Dpa-h films mainly arises from multiple absorption because of the hollow structure and large specific area of Dpa-h NPs. Moreover, the wall thickness of Dpa-h NPs can be simply controlled from 28 to 8 nm, depending on the ratio between PS and dopamine. The resulting films with Dpa-h NPs (wall thickness = ∼8 nm) maintained relatively high transparency to visible light because of the thinner wall thickness. The results indicate that the prepared Dpa-h NPs can be used as a novel UV absorber for next-generation transparent UV-shielding materials.

Enhanced Thermal Stability and UV-Shielding Properties of Poly(vinyl alcohol) Based on Esculetin

In this article, PVA composites with outstanding thermal stability, UV shielding, and high transparency were fabricated on the basis of traditional Chinese medicine (esculetin). Characterization data have suggested in which the resulting PVA/esculetin (ESC) composites display excellent thermal stability compared to pure PVA and most of the PVA nanocomposites. The pyrolysis mechanism of PVA before and after modification with esculetin varies from chain unzipping degradation followed by chain random scission. The DPPH scavenging activity and FTIR measurements have illustrated that esculetin can scavenge reactive radicals, which leads to improvements in thermal stability and a change in the pyrolysis mechanism of PVA. More importantly, the resulting composites can almost completely block the whole UV region (200-400 nm) without any deterioration of the high transparency of the composites. Therefore, the composites can convert harmful UV light into blue light effectively, which is beneficial for their application as optical materials and devices.

Long-chain branching hydrogel with ultrahigh tensibility and high strength by grafting via photo-induced polymerization

A novel long-chain branching (LCB) hydrogel, polyacrylamide grafted from poly(2-acrylamido-2-methylpropanesulfonic acid) via photo-induced polymerization, has been developed with excellent mechanical properties such as ultrahigh tensibility and high strength. Investigations of tensile and compressive properties indicate that the Youngs modulus, ultimate strength and strain, toughness, compressive modulus and stress are significantly improved by introduction of LCB. Scanning electron microscopy (SEM) reveals that the amount of embedded micro-network structures in LCB gels is increased with an increase in the length of LCB. The compressive loading–unloading behaviour shows that the area of the hysteresis loop (the dissipated energy) for the first compressive cycle increases with the introduction of LCB and is higher than that for subsequent cycles. The energy dissipation mechanism is demonstrated for a better understanding of LCB gels. Furthermore, rheological measurements are also studied. Dynamic shear measurements show that both the storage modulus and the complex viscosity increase in the presence of LCB.

Hierarchical structural double network hydrogel with high strength, toughness, and good recoverability

Hierarchical structural double network hydrogel (H-DN gel) was fabricated by inducing ferric coordination crosslinkers in the second network of PAMPS/P(AAm–AAc) double network hydrogel. Investigations of the tensile and compressive properties indicated that the H-DN gel exhibited a dramatic enhancement in the Youngs modulus, tensile ultimate strength, toughness, compressive modulus and stress, compared to traditional double network hydrogels. H-DN hydrogel exhibited good recoverability that remained at ∼70% of the initial dissipated energy after resting at 60 °C for 15 min. Finally, scanning electron microscopy (SEM) revealed that the amount of embedded micro-network structures in H-DN gel became more intensive and the walls got thicker.

Graphene-assisted fabrication of poly(ε-caprolactone)-based nanocomposites with high mechanical properties and self-healing functionality

Herein, high-performance and self-healing poly(e-caprolactone) (PCL) nanocomposites were fabricated using polydopamine-capped reduced graphene oxide (PDG) as a nanofiller with the aid of fold-thermal compression (termed “mechanical annealing”) cycle effect. To improve the dispersion and interfacial interactions between the PDG nanosheets and PCL matrix, PCL chains were first grafted on PDG nanosheets by ring-opening polymerization of e-caprolactone. Notably, superior mechanical performances were successfully achieved by tailoring the periodic mechanical annealing process. The tensile strength of the PCL nanocomposite reaches up to 41.6 MPa, and the yield strength is as high as 22.7 MPa after 10 cycles of mechanical annealing, which are 2.4 and 2.6 times higher than those of pure PCL, respectively. Moreover, the photothermal conversion ability of polydopamine endowed the nanocomposite with self-healing functionality. The temperature of nanocomposites can rapidly surpass the melting temperature of the polymer upon exposure to near-infrared (NIR) light and thus allows fast NIR light-induced self-healing and recovery of the mechanical properties of the nanocomposites; this finding provides a facile method to obtain and explore new graphene-based NIR light-induced self-healing nanocomposites.

Effects of Melanin on Optical Behavior of Polymer: From Natural Pigment to Materials Applications

Melanin is a kind of ubiquitous natural pigment, which serves a variety of protective functions in many organisms. In the present study, natural melanin and synthetic melanin nanoparticles (NPs) were systematically investigated for its potential application in polymeric optical materials. A significant short-wavelength shielding and high visible light transparency polymer nanocomposite was easily obtained via tuning the melanin particle size. In particular, the nanocomposite film with melanin NPs (diameter ≈ 15 nm) loading even as low as 1 wt % blocks most ultraviolet light below 340 nm and still keeps high visible light transparency (83%) in the visible spectrum. More importantly, because of the excellent photoprotection and radical scavenging capabilities of melanin, the resulting polymer nanocomposite exhibits outstanding photostability. In effect, such fantastic melanin NPs is promising for applications in various optical materials.