Formaldehyde Controlling the Synthesis of Multishelled SiO2/Fe xO y Hollow Porous Spheres.

A concise and facile sol-gel method to prepare multiple magnetic SiO2/Fe xO y hollow porous spheres was developed. A series of SiO2/Fe xO y hollow porous spheres consisting of single shell, yolk-shell, double shells, and triple shells could be obtained by simply adjusting the formaldehyde amount, as Fe(acac)3 was used as the shell-forming promoter. As the formaldehyde amount increases, the morphology of the as-prepared hollow spheres changed from single-shelled, yolk-shelled, double-shelled, to triple-shelled and then turned back. The spheres possess a large specific surface area (∼966 m2/g), uniform mesopores (∼4.5 nm), and large pore volume (1.37 cm3/g). Moreover, the yolk-shelled spheres have been successfully used in in situ adsorbing and reducing heavy metal ions in aqueous solution; the results suggested that it was an efficient adsorbent and convenient to concentrate from water.

Enhancing thermal stability and mechanical properties of lyotropic liquid crystals through incorporation of a polymerizable surfactant.

We present a facile method to prepare thermally stable and mechanically robust crosslinked lyotropic liquid crystals (LLCs) through incorporation of a polymerizable amphiphile into a binary LLC system comprising commercially available surfactant Brij 97 and water. Thermal stability and mechanical properties of the polymerized LLCs were significantly enhanced after polymerization of the incorporated polymerizable surfactant. The effect of incorporating a polymerizable amphiphile on the phase behavior of the LLC system was studied in detail. In situ photo-rheology was used to monitor the change in the mechanical properties of the LLCs, namely the storage modulus, loss modulus, and viscosity, upon polymerization. The retention of the LLC nanostructures was evaluated by small angle X-ray scattering (SAXS). The ability to control the thermal stability and mechanical strength of LLCs simply by adding a polymerizable amphiphile, without tedious organic synthesis or harsh polymerization conditions, could prove highly advantageous in the preparation of robust nanomaterials with well-defined periodic structures.

Phase inversion of ionomer-stabilized emulsions to form high internal phase emulsions (HIPEs).

Herein, we report the phase inversion of ionomer-stabilized emulsions to form high internal phase emulsions (HIPEs) induced by salt concentration and pH changes. The ionomers are sulfonated polystyrenes (SPSs) with different sulfonation degrees. The emulsion types were determined by conductivity measurements, confocal microscopy and optical microscopy, and the formation of HIPE organogels was verified by the tube-inversion method and rheological measurements. SPSs with high sulfonation degrees (water-soluble) and low sulfonation degrees (water-insoluble) can stabilize oil-in-water emulsions; these emulsions were transformed into water-in-oil HIPEs by varying salt concentrations and/or changing the pH. SPS, with a sulfonation degree of 11.6%, is the most efficient, and as low as 0.2 (w/v)% of the organic phase is enough to stabilize the HIPEs. Phase inversion of the oil-in-water emulsions occurred to form water-in-oil HIPEs by increasing the salt concentration in the aqueous phase. Two phase inversion points from oil-in-water emulsions to water-in-oil HIPEs were observed at pH 1 and 13. Moreover, synergetic effects between the salt concentration and pH changes occurred upon the inversion of the emulsion type. The organic phase can be a variety of organic solvents, including toluene, xylene, chloroform, dichloroethane, dichloromethane and anisole, as well as monomers such as styrene, butyl acrylate, methyl methacrylate and ethylene glycol dimethacrylate. Poly(HIPEs) were successfully prepared by the polymerization of monomers as the continuous phase in the ionomer-stabilized HIPEs.

Graphene and graphitic derivative filled polymer composites as potential sensors.

Graphite and numerous graphitic-derived micro- and nano-particles have gained importance in current materials science research. These two-dimensional sheets of sp(2)-hybridized carbon atoms remarkably influence the properties of polymers. Graphene mono-layers, graphene oxides, graphite oxides, exfoliated graphite, and other related materials are derived from a parental graphite structure. In this review, we focus primarily on the role of these fillers in regulating the electrical and sensing properties of polymer composites. It has been demonstrated that the addition of an optimized mixture of graphene and or its derivatives to various polymers produces a record-high enhancement of the electrical conductivity and achieved semiconducting characteristics at small filler loading, making it suitable for sensor manufacture. Promising sensing characteristics are observed in graphite-derived composite films compared with those of micro-sized composites and the properties are explained mainly based on the filler volume fraction, nature and rate of dispersion and the filler polymer interactions at the interface. In short, this critical review aims to provide a thorough understanding of the recent advances in the area of graphitic-based polymer composites in advanced electronics. Future perspectives in this rapidly developing field are also discussed.

Reversible photorheological lyotropic liquid crystals.

We describe novel lyotropic liquid-crystalline (LLC) materials based on photoresponsive amphiphiles that exhibit rapid photoswitchable rheological properties of unprecedented magnitude between solidlike and liquidlike states. This was achieved through the synthesis of a novel azobenzene-containing surfactant (azo-surfactant) that actuates the transition between different LLC forms depending on illumination conditions. Initially, the azo-surfactant/water mixtures formed highly ordered and viscous LLC phases at 20-55 wt % water content. Spectroscopic, microscopic, and rheological analysis confirmed that UV irradiation induced the trans to cis isomerization of the azo-surfactant, leading to the disruption of the ordered LLC phases and a dramatic, rapid decrease in the viscosity and modulus resulting in a 3 orders of magnitude change from a solid (20,000 Pa) to a liquid (50 Pa) at rate of 13,500 Pa/s. Subsequent exposure to visible light reverses the transition, returning the viscosity essentially to its initial state. Such large, rapid, and reversible changes in rheological properties within this LLC system may open a door to new applications for photorheological fluids.

Does dynamic vulcanization induce phase separation?

Immiscible and miscible blends of poly(vinylidene fluoride) (PVDF) and acrylic rubber (ACM) were subjected to dynamic vulcanization to investigate the effect of crosslinking on phase separation. As a result of different processability, mixing torque behavior of miscible and immiscible blends was significantly different from one another. Scanning electron microscopy (SEM) was used to investigate the morphology of the system. After dynamic vulcanization, submicron ACM droplets were observed in the samples near the binodal curve of the system under mixing conditions. Small angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC) analysis were used to investigate the effect of dynamic vulcanization on the lamellar structure of the system. It was shown that for samples near the boundary of phase separation, increasing the crosslink density led to a decrease in the lamellar long period (L) as a sign of increment of crosslink density induced phase decomposition. Effects of shear rate on the final morphology of the system were investigated by changing the mixing temperature and by comparing the results of dynamic vulcanization at one phase and two phase regions.

A new approach for mechanisms of ferroelectric crystalline phase formation in PVDF nanocomposites.

This paper proposes a new mechanism for ferroelectric polymorph formation of poly(vinylidene fluoride) (PVDF) nanocomposites. Utilizing time-resolved Fourier transform infrared spectroscopy (FTIR), the real-time investigation of the conformational changes of the PVDF chain segment during crystallization of neat PVDF and the corresponding nanocomposite was performed. Whilst PVDF-clay nanocomposites exhibited mainly the ß crystal phase coexisting with the γ phase at low Tc (Tc < 155 °C), the coexistence of γ and ß crystalline phases was found at a high Tc temperature range (Tc > 155 °C). Experimental results were compared with predictions of the Lauritzen and Hoffman (LH) model and discrepancies were observed between model predictions and experiments. We then recalled the Brochard-de Gennes (BD) model and proposed that different crystalline polymorph formation should be inferred as a transition in the reeling-in rate dependence of the friction coefficient on nanocomposites rather than as a change in the relative rates of secondary nucleation and substrate completion. Combining LH and BD models we proposed a new mechanism to answer the contradictory questions associated with nanocomposite polymorphism. The coexistence of different polymorphs in nanocomposites was proposed to be associated with the coexistence of fast and slow moving chains, which were recognized as the free and adsorbed chains by nanofillers.

Nanofibrillar micelles and entrapped vesicles from biodegradable block copolymer/polyelectrolyte complexes in aqueous media.

Here we report a viable route to fibrillar micelles and entrapped vesicles in aqueous solutions. Nanofibrillar micelles and entrapped vesicles were prepared from complexes of a biodegradable block copolymer poly(ethylene oxide)-block-poly(lactide) (PEO-b-PLA) and a polyelectrolyte poly(acrylic acid) (PAA) in aqueous media and directly visualized using cryogenic transmission electron microscopy (cryo-TEM). The self-assembly and the morphological changes in the complexes were induced by the addition of PAA/water solution into the PEO-b-PLA in tetrahydrofuran followed by dialysis against water. A variety of morphologies including spherical wormlike and fibrillar micelles, and both unilamellar and entrapped vesicles, were observed, depending on the composition, complementary binding sites of PAA and PEO, and the change in the interfacial energy. Increasing the water content in each [AA]/[EO] ratio led to a morphological transition from spheres to vesicles, displaying both the composition- and dilution-dependent micellar-to-vesicular morphological transitions.

Largely enhanced thermal and mechanical properties of polymer nanocomposites via incorporating C60@graphene nanocarbon hybrid.

Although considerable progress has been achieved to create advanced polymer nanocomposites using nanocarbons including fullerene (C60) and graphene, it remains a major challenge to effectively disperse them in a polymer matrix and to fully exert their extraordinary properties. Here we report a novel approach to fabricate the C60@graphene nanocarbon hybrid (C60: ~47.9 wt%, graphene: ~35.1%) via three-step reactions. The presence of C60 on a graphene sheet surface can effectively prevent the aggregation of the latter which in turn helps the dispersion of the former in a polymer matrix during melt-processing. C60@graphene is found to be uniformly dispersed in a polypropylene (PP) matrix. Compared with pristine C60 or graphene, C60@graphene further improves the thermal stability and mechanical properties of PP. The incorporation of 2.0 wt% C60@graphene (relative to PP) can remarkably increase the initial degradation temperature by around 59 ° C and simultaneously enhance the tensile strength and Young's modulus by 67% and 76%, respectively, all of which are higher than those of corresponding PP/C60 (graphene) nanocomposites. These significant performance improvements are mainly due to the free-radical-trapping effect of C60, and the thermal barrier and reinforcing effects of graphene nanosheets as well as the effective stress load transfer. This work provides a new methodology to design multifunctional nanohybrids for creating advanced materials.

Individual dispersion of carbon nanotubes in epoxy via a novel dispersion-curing approach using ionic liquids.

The effective dispersion of carbon nanotubes (CNTs) in a thermoset was achieved using ionic liquid as the dispersion-curing agent. We preferentially dispersed multiwalled carbon nanotubes (MWCNTs) down to individual tube levels in epoxy resin. Here the dispersion is ruled by the depletion of physical bundles within the MWCNT networks, for which molecular ordering of ionic liquids is considered responsible. The quantitative analyses using ultra small angle X-ray scattering (USAXS) confirmed the dispersion of individual MWCNTs in the matrix. The distance between the dispersed nanotubes was calculated at different nanotube loadings using the power law fitting of the USAXS data. The fine dispersion and subsequent curing, both controlled by ionic liquid, lead to composites with substantially enhanced fracture mechanical and thermomechanical properties with no reduction in thermal properties. Merging processing techniques of nanocomposites with ionic liquid for efficient dispersion of nanotubes and preferential curing of thermosets facilitates the development of new, high performance materials.

A simple and effective approach to vesicles and large compound vesicles via complexation of amphiphilic block copolymer with polyelectrolyte in water.

This work reports for the first time a simple and effective approach to trigger a spheres-to- vesicles morphological transition from amphiphilic block copolymer/polyelectrolyte complexes in aqueous solution. Vesicles and large compound vesicles (LCVs) were prepared via complexation of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) with poly(acrylic acid) (PAA) in water and directly visualized using cryo-TEM. The complexation and morphological transitions were driven by the hydrogen bonding between the complementary binding sites on the PAA and PEO blocks of the block copolymer. The findings in this work suggest that complexation between amphiphilic block copolymer and polyelectrolyte is a viable approach to vesicles and LCVs in aqueous media.

Thermoreversible Polymer Gels in DMF Formed from Charge- and Crystallization-Induced Assembly.

Polymer organogels formed through dynamic interactions are interesting for various applications. The fabrication of polymer organogels in polar solvents through ionic interaction is rare, although such organogels in non-polar organic solvents have been well studied. Herein, polymer organogels in a polar solvent N,N-dimethyl formamide (DMF) were fabricated from a triblock copolymer, poly(4-vinyl pyridine)-block-poly(ethylene glycol)-block-poly(4-vinyl pyridine) (4VPm-EGn-4VPm), and a fluorinated surfactant, perfluorooctanoic acid (PFOA), and their microphase separation and properties were studied. Ordered microphase separation and the crystalline structures were revealed by small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS), respectively. All the 4VPm-EGn-4VPm/PFOA organogels are sensitive to temperature, and the ratio of PFOA to pyridine groups reversibly. The polymer organogels are also responsive to triethylamine and triethylammonium acetate.

Effect of Molecular Weight of Self-Emulsifying Amphiphilic Epoxy Sizing Emulsions on the Carbon Fibres and Interfacial Properties of Their Composites.

The molecular weight of self-emulsifying amphiphilic epoxy sizing emulsions has a big effect on the carbon fibres and interfacial properties of their composites. Novel amphiphilic epoxy sizing emulsions with four different molecular weights (7500, 11,000, 15,000 and 17,000) were successfully prepared by a self-emulsifying method and applied to improve interfacial bonding between carbon fibres (CFs) and an epoxy resin (EP). The effect of molecular weight on the quality of emulsions, the sized CFs and the interfacial properties of the CF/EP composite system were studied. The results reveal that these novel sizing emulsions exhibited strong emulsifying ability and high processability. The most favourable wettability and adequate CF surface free energy were obtained by the emulsion with a molecular weight of 7500. Compared with unsized CFs, the monofilament fibre tensile performance was remarkably improved when increasing the shape parameter from 5.08 to 7.20. The interfacial sheer strength (IFSS) of the CF/EP composite was greatly increased by 96% with the emulsion of 7500. The enhanced interfacial adhesion benefits were attributed mainly from the enhanced charge interaction between CFs and the sizing layer as well as the compatibility and the mechanical interlock between the sizing layer and the epoxy matrix.

2,4-Dinitrophenol as an effective cocatalyst: greatly improving the activities and enantioselectivities of primary amine organocatalysts for asymmetric aldol reactions.

Seven primary amine organocatalysts 1a-g were readily prepared from natural primary amino acids via two steps and then were used to catalyze the direct asymmetric aldol reaction, but they showed very poor enantioselectivities and activities. As an effective cocatalyst, 2,4-dinitrophenol (DNP) dramatically elevated the activities and enantioselectivities of these very inefficient primary amine organocatalysts. This remedial course to the very inefficient organocatalysts by selection and employment of the optimal cocatalyst was particularly cost-effective and environment-beneficial compared with de novo development of catalysts. The highest efficient organocatalytic system that was composed of 1f and DNP showed high enantioselectivities and good to high diastereoselectivities with a broad spectrum of seven ketones. The linear ketones and cyclopentanone got predominant syn products whereas cyclohexanone mainly gave anti products.

N-primary-amine-terminal beta-turn tetrapeptides as organocatalysts for highly enantioselective aldol reaction.

Tetrapeptides, containing a terminated primary amine and conformationally restricted D-Pro-Gly or D-Pro-Aib (2-aminoisobutanoic acid) segment as a strongly beta-turn-nucleating element, were designed and synthesized with condensation of N-module dipeptides with C-module dipeptides in solution. They were first applied to catalyze aldol reactions, and were found to be effective catalysts for the transformations. The tetrapeptide Val-D-Pro-Gly-Leu-OH (1g) was the optimal organocatalyst. It was shown that the intensive beta-turn conformation, indicated by CD and NOESY spectra, contributed to the (R)-aldol and high enantioselectivity of the reaction of acetone in MeOH, whereas the sharply varied conformation should contribute to the low enantioselectivity and (S)-product of the reaction in 1,2-dichloroethane (DCE). The asymmetric induction in the reaction of hydroxyacetone was not affected by solvents, and predominant anti products were achieved by 1g in MeCN with the additive (S)-BINOL.

Microphase separation through competitive hydrogen bonding in self-assembled A-b-B/C diblock copolymer/homopolymer complexes.

We present a study of microphase separation induced by competitive hydrogen bonding in A-b-B/C diblock copolymer/homopolymer complexes where the diblock copolymer A-b-B is immiscible and the homopolymer C can interact unequally with both A and B blocks through hydrogen bonding. A model system containing poly(2-vinyl pyridine)-block-poly(methyl methacrylate) (P2VP-b-PMMA) and poly(4-vinyl phenol) (PVPh) in tetrahydrofuran was investigated. In these self-assembled complexes, microphase separation takes place due to the disparity in intermolecular interactions. Specifically, PVPh and P2VP blocks interact strongly to form complex, whereas PVPh and PMMA blocks interact weakly. The hydrogen bonding interactions were revealed by infrared spectroscopy and analyzed in terms of the difference in interassociation constants (K), i.e., interaction parameters of each blocks of the block copolymer to the homopolymer and according to the random phase approximation. The phase behavior of the complexes was investigated with small-angle x-ray scattering and transmission electron microscopy. A series of morphologies including lamellae, hexagonal cylinders, wormlike microdomains, and hierarchical structures was documented as a function of the copolymer concentration. Moreover, we outlined how hydrogen bonding determines the self-assembly and causes morphological transitions in different A-b-B/C diblock copolymer/homopolymer systems with respect to the K values.

Nanofibrous, Emulsion-Templated Syndiotactic Polystyrenes with Superhydrophobicity for Oil Spill Cleanup.

A series of syndiotactic polystyrene (sPS) monoliths with controllable shapes, nanofibrous structures, hierarchical pores, superhydrophobicity, high specific surface area, and high strength have been fabricated for the first time by solidifying nonaqueous high internal phase emulsions (HIPEs) through crystallization-induced gelation. The nonaqueous HIPEs were formed by dispersing glycerol in 1,2,4-trichlorobenzene stabilized by sulfonated sPS at a high temperature of 120 °C, and with sPS in the continuous phase, these HIPEs were solidified by cooling at room temperature to obtain sPS monoliths. The shapes of the sPS monoliths were controllable, and excitedly, nanofibrous structures were found at void walls, with fiber diameters ranging from 20 to 100 nm. The sPS monoliths exhibited pores in different scales: emulsion-templated voids at nearly 10 µm with pore throats ranging from 1 to 2 µm and macropores and mesopores between nanofibers, enabling the monoliths to exhibit extremely high specific surface area of up to 420 m2·g-1. The porous sPS monoliths were robust, and they did not fail even at a compressive strain of 70%, with Young's moduli ranging from 157.7 to 2638.0 kPa. The monoliths were superhydrophobic and oleophilic, with water contact angles over 150° and with oils absorbed rapidly. The superhydrophobicity and oleophilicity enabled the porous sPS monoliths to absorb bulk oils on the water surface, underwater oils, and even oils within oil-in-water emulsions. The monoliths absorbed a large amount of organic solvents, edible oils, and fuel oils with equilibrium liquid uptakes up to 81.3, 44.4, and 41.9 g·g-1 for chloroform, olive oil, and diesel, respectively. The liquid absorption was rapid, and the monoliths exhibited a relatively high reusability. These porous sPS monoliths were demonstrated to be a candidate for the applications of oil/water separation and/or oil spill cleanup.

Preparation and characterization of nanocomposite films based on gum arabic, maltodextrin and polyethylene glycol reinforced with turmeric nanofiber isolated from turmeric spent.

Turmeric nanofibers (TNF) were used as reinforcement in the gum arabic (GA), maltodextrin (MDX) and polyethylene glycol (PEG) matrices to enhance the physicochemical properties. The TNF were prepared from turmeric spent by acid hydrolysis accompanied by high pressure homogenization. The thermal and mechanical properties, structure morphology and antimicrobial activities of the prepared nanocomposites were investigated. Differential scanning calorimetry (DSC) data indicate that the addition of TNF significantly increased the onset temperature (To), peak temperature (Tp) and conclusion temperature (Tc) of the melting peaks of nanocomposites, but considerably decreased the enthalpy change values. The tensile properties showed that the addition of TNF enhanced mechanical properties due to the formation of networks within the GA, MDX and PEG. The scanning electron microscopy (SEM) images revealed the films of GA-TNF and MDX-TNF show smooth, homogenous surface due to intermolecular hydrogen bonding, and the film of PEG-TNF shows good dispersion of TNF with PEG matrix with rough surface because of strong interfacial adhesion between TNF and PEG and strong hydrogen bonding, which are further confirmed by the FT-IR spectroscopy. XRD results exhibited the disappearances of peaks of TNF indicating the reinforcement of TNF in the prepared nanocomposite matrices. The antibacterial tests show the prepared nanocomposites exhibited excellent antibacterial performance against Bacillus cereus, Escherichia coli, Staphylococcus aureus and Salmonella typhimurium.

Effect of the Chain Structure of Self-Emulsifying Polyester Sizing Agent on ILSS of Carbon Fiber/Unsaturated Polyester Resin Composites.

Herein, we report self-emulsifying anionic unsaturated polyester emulsions with different chain segments as novel sizing agents. The epoxy modified unsaturated polyester emulsions were synthesized via a self-emulsifying technique with no organic solvents. Emulsions were characterized by dynamic light scattering (DLS), Zeta potential, centrifuge, and cryo-scanning electron microscopy (Cryo-SEM). The results showed that the emulsions obtained were mono-dispersed nanospheres that had adequate colloidal stability. The maximum Zeta potential of the sizing agent is -52.88 mV. In addition, these emulsions were investigated as the sizing agents in order to improve interfacial adhesion between carbon fibers (CFs) and unsaturated polyester resin (UPR). Compared with the CFs sized with the commercial epoxy sizing agent, the interlaminar shear strength (ILSS) of CF/UPR composites from the CFs sized by these emulsion sizing agents with three different chain structures were enhanced by 25%, 29%, and 42%, respectively. The emulsion sizing agent composed of a flexible segment synthesized from adipic acid, neopentyl glycol, and maleic anhydride is most effective and can achieve the highest enhancement of the ILSS of CF/UPR composites.

Granular Nanostructure: A Facile Biomimetic Strategy for the Design of Supertough Polymeric Materials with High Ductility and Strength.

The realization of high strength, large ductility, and great toughness for polymeric materials is a vital factor for practical applications in industry. Unfortunately, until now this remains a huge challenge due to the common opposing trends that exist when promoting improvements in these properties using materials design strategies. In the natural world, the cuticle of mussel byssus exhibits a breaking strain as high as 100%, which is revealed to arise from an architectural granular microphase-separated structure within the protein matrix. Herein, a facile biomimetic designed granular nanostructured polymer film is reported. Such biomimetic nanostructured polymer films show a world-record toughness of 122 (± 6.1) J g-1 as compared with other polyvinyl alcohol films, with a breaking strain as high as 205% and a high tensile strength of 91.2 MPa, which is much superior to those of most engineering plastics. This portfolio of outstanding properties can be attributed to the unique nanoscale granular phase-separated structure of this material. These biomimetic designed polymer films are expected to find promising applications in tissue engineering and biomaterials fields, such as artificial skin and tendon, which opens up an innovative methodology for the design of robust polymer materials for a range of innovative future applications.