A Homochiral Porous Organic Cage-Polymer Membrane for Enantioselective Resolution

Membrane-based enantioselective separation is a promising method for chiral resolution due to its low cost and high efficiency. However, scalable fabrication of chiral separation membranes displaying both high enantioselectivity and high flux of enantiomers is still a challenge. Here, the authors report the preparation of homochiral porous organic cage (Covalent cage 3 (CC3)-R)-based enantioselective thin-film-composite membranes using polyamide (PA) as the matrix, where fully organic and solvent-processable cage crystals have good compatibility with the polymer scaffold. The hierarchical CC3-R channels consist of chiral selective windows and inner cavities, leading to favorable chiral resolution and permeation of enantiomers; the CC3-R/PA composite membranes display an enantiomeric excess of 95.2% for R-(+)-limonene over S-(-)-limonene and a high flux of 99.9 mg h-1 m-2. This work sheds light on the use of homochiral porous organic cages for preparing enantioselective membranes and demonstrates a new route for the development of next-generation chiral separation membranes.

Accurate prediction of solvent flux in sub-1-nm slit-pore nanosheet membranes

Nanosheet-based membranes have shown enormous potential for energy-efficient molecular transport and separation applications, but designing these membranes for specific separations remains a great challenge due to the lack of good understanding of fluid transport mechanisms in complex nanochannels. We synthesized reduced MXene/graphene hetero-channel membranes with sub-1-nm pores for experimental measurements and theoretical modeling of their structures and fluid transport rates. Our experiments showed that upon complete rejection of salt and organic dyes, these membranes with subnanometer channels exhibit remarkably high solvent fluxes, and their solvent transport behavior is very different from their homo-structured counterparts. We proposed a subcontinuum flow model that enables accurate prediction of solvent flux in sub-1-nm slit-pore membranes by building a direct relationship between the solvent molecule-channel wall interaction and flux from the confined physical properties of a liquid and the structural parameters of the membranes. This work provides a basis for the rational design of nanosheet-based membranes for advanced separation and emerging nanofluidics.

Effect of temperature on the conformation and functionality of poly(N-isopropylacrylamide) (PNIPAM)-grafted nanocellulose hydrogels

HYPOTHESIS

Poly(N-isopropylacrylamide) [PNIPAM]-grafted cellulose nanofibers (CNFs) are new thermo-responsive hydrogels which can be used for a wide range of applications. Currently, there is no clear understanding of the precise mechanism by which CNFs and PNIPAM interact together. Here, we hypothesize that the physical crosslinking of grafted PNIPAM on CNF inhibits the free movement of individual CNF, which increases the gel strength while sustaining its thermo-responsive properties.

EXPERIMENTS

The thermo-responsive behaviour of PNIPAM-grafted CNFs (PNIPAM-g-CNFs), synthesized via silver-catalyzed decarboxylative radical polymerization, and PNIPAM-blended CNFs (PNIPAM-b-CNFs) was studied. Small angle neutron scattering (SANS) combined with Ultra-SANS (USANS) revealed the nano to microscale conformation changes of these polymer hybrids as a function of temperature. The effect of temperature on the optical and viscoelastic properties of hydrogels was also investigated.

FINDINGS

Grafting PNIPAM from CNFs shifted the lower critical solution temperature (LCST) from 32 °C to 36 °C. Below LCST, the PNIPAM chains in PNIPAM-g-CNF sustain an open conformation and poor interaction with CNF, and exhibit water-like behaviour. At and above LCST, the PNIPAM chains change conformation to entangle and aggregate nearby CNFs. Large voids are formed in solution between the aggregated PNIPAM-CNF walls. In comparison, PNIPAM-b-CNF sustains liquid-like behaviour below LCST. At and above LCST, the blended PNIPAM phase separates from CNF to form large aggregates which do not affect CNF network and thus PNIPAM-b-CNF demonstrates low viscosity. Understanding of temperature-dependent conformation of PNIPAM-g-CNFs engineer thermo-responsive hydrogels for biomedical and functional applications.

Dual-Channel-Ion Conductor Membrane for Low-Energy Lithium Extraction

The development of energy-efficient and environmentally friendly lithium extraction techniques is essential to meet the growing global demand for lithium-ion batteries. In this work, a dual-channel ion conductor membrane was designed for a concentration-driven lithium-selective ion diffusion process. The membrane was based on a porous lithium-ion conductor, and its pores were modified with an anion-exchange polymer. Thus, the sintered lithium-ion conductors provided highly selective cation transport channels, and the functionalized nanopores with positive charges enabled the complementary permeation of anions to balance the transmembrane charges. As a result, the dual-channel membrane realized an ultrahigh Li+/Na+ selectivity of ∼1389 with a competitive Li+ flux of 21.6 mmol·m-2·h-1 in a diffusion process of the LiCl/NaCl binary solution, which was capable of further maintaining the high selectivity over 7 days of testing. Therefore, this work demonstrates the great potential of the dual-channel membrane design for high-performing lithium extraction from aqueous resources with low energy consumption and minimal environmental impact.

Tailoring the humidity response of cellulose nanocrystal-based films by specific ion effects

HYPOTHESIS

The optical properties and humidity response of iridescent films made of cellulose nanocrystal (CNC) and polyethylene glycol (PEG) can be tailored by the incorporation of electrolytes chosen based on specific ion effects (SIE).

EXPERIMENTS

A series of inorganic salts comprising five different cations and five anions based on the Hofmeister series were mixed with CNC/PEG suspensions, followed by an air-dried process into iridescent solid films. These films were tested in changing relative humidity (RH) environments from 30% to 90% and their photonic properties and mass change monitored. The underlying structures and the mechanism of their formation were quantified in terms of interparticle distance derived from small angle X-ray scattering experiment and pitch size quantified by scanning electron microscope (SEM).

FINDINGS

The specific color and color range of CNC/PEG based films are controlled by a specific anion effect achieved by selection of the salt while the specific cation effect is negligible. The salting-in type anions with the same valency result in a red-shift color when films are in the dried state. The salting-in type leads to a greater color changing range during RH changes than the salting-out type. The resultant mass gain/loss trend is consistent with the color change. In contrast, cations do not show any relationships between salting-in effect and the measured properties as observed for anions. The observed SIE can be used to engineer CNC/polymer-based humidity and bio-diagnostic colorimetric indicator devices.

Extrusion and 3D printing of novel lipid-polymer blends for oral drug applications

Lipids are interesting biological materials that can offer a number of pharmaceutical benefits when used as carriers for drug delivery. However, 3D printing of lipids alone by fused deposition processing techniques is very difficult as they have very poor mechanical properties that cause their filaments to fail when they are loaded into a fused deposition 3D printer. If this problem could be overcome, then lipids could be 3D printed into bespoke tablets and assist progress towards such personalised medicines. This work aims to improve the mechanical properties of lipid filaments by developing novel lipid-EVA (ethylene vinyl acetate) blends suitable for 3D printing. Different types of lipids in varying proportions were melt blended with EVA and extruded using a micro compounder. The ultimate printability of the materials was tested by feeding the filaments into a material extrusion 3D printer. Flexural testing of the extruded blends demonstrates that a good balance between the strength and flexibility is required for a material to be printable and it was found that a filament has to have a modulus/strength ratio between 8 and 25 in order to be printable. SEM analysis of the fracture surface shows a network structure within the lipid matrix that could be playing a role in the improved properties of the best performing blends. DSC thermograms show a shift in thermal transitions, suggesting some level of miscibility of the components that could have contributed to a more robust structure. The TGA results show an onset of degradation of the blends greater than 200 °C, indicating that the materials can readily withstand the extrusion and printing temperatures. This study demonstrates the successful extrusion and 3D printing of novel EVA-lipid blends with lipid contents of up to 90%.

Modulating the chiral nanoarchitecture of cellulose nanocrystals through interaction with salts and polymer

HYPOTHESIS

The conditions to allow self-assembly of cellulose nanocrystal (CNC) suspensions into chiral nematic structures are based on aspect ratio, surface charge density and a balance between repulsive and attractive forces between CNC particles.

EXPERIMENTS

Three types of systems were characterized in suspensions and subsequently in their solid dried films: 1) neat water dialyzed CNC, 2) CNC combined with polyethylene glycol(PEG) (CNC/PEG), and 3) CNC with added salt (CNC/Salt). All suspensions were characterized by polarized optical microscope (POM) and small angle X-ray scattering (SAXS), while the resultant dried films were analyzed by reflectance spectrometer, scanning electron microscope (SEM) and SAXS.

FINDINGS

The presence of chiral nematic (CN*) structures was not observed in dialyzed aqueous suspensions of CNC during water evaporation. By introducing salts or a non-adsorbing polymer, chirality was apparent in both suspensions and films. The interaxial angle between CNC rods increased when the suspensions of CNC/PEG and CNC/salt were dried to solid films. The angle was found to be dependent on both species of ions and ionic strength, while the inter-particle distance was only related to the salt concentration, as explained in terms of interaction energies. The CNC suspensions/film chirality can be modulated by controlling the colloidal forces.

Rapid Detection of Gram-Positive and -Negative Bacteria in Water Samples Using Mannan-Binding Lectin-Based Visual Biosensor

Waterborne bacterial infection is a health threat worldwide, making accurate and timely bacteria detection crucial to prevent waterborne disease outbreaks. Inspired by the intrinsic capability of mannan-binding lectin (MBL) in recognizing the pathogen-associated molecular patterns (PAMPs), a visual biosensor is developed here for the on-site detection of both Gram-positive and -negative bacteria. The biosensor was synthesized by immobilization of the MBL protein onto the blue carboxyl-functionalized polystyrene microparticles (PSM), which is then used in a two-step assay to detect bacterial cells in water samples. The first step involved a 20 min incubation following the MBL-PSM and calcium chloride solution addition to the samples. The second step was to add ethanol to the resultant blue mixture and observe the color change with the naked eye after 15 min. The biosensor had a binary (all-or-none) response, which in the presence of bacterial cells kept its blue color, while in their absence the color changed from blue to colorless. Testing the water samples spiked with four Gram-negative bacteria including Acinetobacter baumannii, Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa and two Gram-positive bacteria of Enterococcus faecalis and Staphylococcus aureus showed that the biosensor could detect all tested bacteria with a concentration as low as 10^1.5 CFU/ml. The performance of biosensor using the water samples from a water treatment plant also confirmed its capability to detect the pathogens in real-life water samples without the need for instrumentation.

Thermoresponsive Poly(N-isopropylacrylamide) Grafted from Cellulose Nanofibers via Silver-Promoted Decarboxylative Radical Polymerization

A family of thermoresponsive poly(N-isopropylacrylamide) [PNIPAM]-grafted cellulose nanofibers (CNFs) was synthesized via a novel silver-promoted decarboxylative polymerization approach. This method relies on the oxidative decarboxylation of carboxylic acid groups to initiate free radicals on the surface of CNFs. The polymerization reaction employs relatively mild reaction conditions and can be performed in a one-step, one-pot fashion. This rapid reaction forms a C─C bond between CNF and PNIPAM, along with the formation of free polymer in solution. The degree of functionalization (DF) and the amount of PNIPAM grafted can be controlled by the Ag concentration in the reaction. Similar to native bulk PNIPAM, PNIPAM-grafted CNFs (PNIPAM-g-CNFs) show remarkable thermoresponsive properties, albeit exhibiting a slight hysteresis between the heating and cooling stages. Grafting PNIPAM from CNFs changes its cloud point from about 32 to 36 °C, influenced by the hydrophilic nature of CNFs. Unlike physical blending, covalently tethering PNIPAM transforms the originally inert CNFs into thermosensitive biomaterials. The Ag concentration used does not significantly change the cloud point of PNIPAM-g-CNFs, while the cloud point slightly decreases with fiber concentration. Rheological studies demonstrated the sol-gel transition of PNIPAM-g-CNFs and revealed that the storage modulus (G') above cloud point increases with the amount of PNIPAM grafted. The novel chemistry developed paves the way for the polymerization of any vinyl monomer from the surface of CNFs and carbohydrates. This study validates a novel approach to graft PNIPAM from CNFs for the synthesis of new thermoresponsive and transparent hydrogels for a wide range of applications.

A 3D-Printed Polymer-Lipid-Hybrid Tablet towards the Development of Bespoke SMEDDS Formulations

3D printing is a rapidly growing area of interest within pharmaceutical science thanks to its versatility in creating different dose form geometries and drug doses to enable the personalisation of medicines. Research in this area has been dominated by polymer-based materials; however, for poorly water-soluble lipophilic drugs, lipid formulations present advantages in improving bioavailability. This study progresses the area of 3D-printed solid lipid formulations by providing a 3D-printed dissolvable polymer scaffold to compartmentalise solid lipid formulations within a single dosage form. This allows the versatility of different drugs in different lipid formulations, loaded into different compartments to generate wide versatility in drug release, and specific control over release geometry to tune release rates. Application to a range of drug molecules was demonstrated by incorporating the model lipophilic drugs; halofantrine, lumefantrine and clofazimine into the multicompartmental scaffolded tablets. Fenofibrate was used as the model drug in the single compartment scaffolded tablets for comparison with previous studies. The formulation-laden scaffolds were characterised using X-ray CT and dispersion of the formulation was studied using nephelometry, while release of a range of poorly water-soluble drugs into different gastrointestinal media was studied using HPLC. The studies show that dispersion and drug release are predictably dependent on the exposed surface area-to-volume ratio (SA:V) and independent of the drug. At the extremes of SA:V studied here, within 20 min of dissolution time, formulations with an SA:V of 0.8 had dispersed to between 90 and 110%, and completely released the drug, where as an SA:V of 0 yielded 0% dispersion and drug release. Therefore, this study presents opportunities to develop new dose forms with advantages in a polypharmacy context.

Detecting subtle yet fast skeletal muscle contractions with ultrasoft and durable graphene-based cellular materials

Human bodily movements are primarily controlled by the contractions of skeletal muscles. Unlike joint or skeletal movements that are generally performed in the large displacement range, the contractions of the skeletal muscles that underpin these movements are subtle in intensity yet high in frequency. This subtlety of movement makes it a formidable challenge to develop wearable and durable soft materials to electrically monitor such motions with high fidelity for the purpose of, for example, muscle/neuromuscular disease diagnosis. Here we report that an intrinsically fragile ultralow-density graphene-based cellular monolith sandwiched between silicone rubbers can exhibit a highly effective stress and strain transfer mechanism at its interface with the rubber, with a remarkable improvement in stretchability (>100%). In particular, this hybrid also exhibits a highly sensitive, broadband-frequency electrical response (up to 180 Hz) for a wide range of strains. By correlating the mechanical signal of muscle movements obtained from this hybrid material with electromyography, we demonstrate that the strain sensor based on this hybrid material may provide a new, soft and wearable mechanomyography approach for real-time monitoring of complex neuromuscular–skeletal interactions in a broad range of healthcare and human–machine interface applications. This work also provides a new architecture-enabled functional soft material platform for wearable electronics.

Diethyl sinapate-grafted cellulose nanocrystals as nature-inspired UV filters in cosmetic formulations

Inspired by nature’s photoprotection mechanisms, we report an effective UV-blocking nanomaterial based on diethyl sinapate-grafted cellulose nanocrystals (CNC-DES). The colloidal stability and UV-blocking performance of CNC-DES in aqueous glycerol (a common humectant in petroleum-free cosmetic formulations) and in a commercially available moisturizing cream were studied. Grafting the water-insoluble DES onto CNCs renders it dispersible in these water-based formulations, thanks to the excellent water-dispersibility of CNC nanoparticles. Glycerol dispersions containing 0.1 to 1.5 wt% CNC-DES display very high UV-blocking activity owing to the anti-UV DES moieties anchored onto CNCs. A facial cream blended with 1.5 wt% CNC-DES exhibits an SPF of 5.03, which is higher than a commercially available sunscreen with the same active ingredient concentration (SPF = 3.84). DPPH radical scavenging assay also showed the antioxidant potential of CNC-DES, albeit coinciding with a significant reduction in antioxidant activity after grafting DES onto CNCs. Cytotoxicity measurements revealed the CNC-DES not to cause significant cytotoxicity to murine fibroblast cells after 24 h of exposure. Overall, CNC-DES exhibits strong anti-UV and antioxidant properties and is water-dispersible, biocompatible, non-greasy, and lightweight. This study demonstrates the exceptional potential of DES-grafted CNCs as nature-inspired UV filters in the next generation of cosmetic formulations, including those for sensitive skins.

Grafting Nature-Inspired and Bio-Based Phenolic Esters onto Cellulose Nanocrystals Gives Biomaterials with Photostable Anti-UV Properties

Invited for this month's cover is the international collaborative work from the Bioresource Processing Research Institute of Australia (BioPRIA)-Monash University and URD Agro-Biotechnologies Industrielles (ABI)-AgroParisTech. The cover image shows how the grafting of Nature-inspired and bio-based phenolic esters on cellulose nanocrystals through click-chemistry provides materials with highly photostable UV-blocking properties. Cover art by David Mendoza. The Full Paper itself is available at 10.1002/cssc.202002017.

Grafting Nature-Inspired and Bio-Based Phenolic Esters onto Cellulose Nanocrystals Gives Biomaterials with Photostable Anti-UV Properties

New nature-inspired and plant-derived p-hydroxycinnamate esters and p-hydroxycinnamate diesters provide excellent protection against UV radiation when incorporated into a matrix. Herein, an efficient and sustainable pathway is reported to graft these phenolic compounds onto cellulose nanocrystals (CNCs) via click-type copper-catalyzed azide/alkyne cycloaddition (CuAAC) reaction. The successful grafting of the phenolic esters on CNC surface was evidenced by a range of chemical analyses, and the degrees of substitution (DS) of the CNC were found to depend on the structure of the phenolic ester grafted. Moreover, aqueous suspensions of the phenolic ester-grafted CNCs not only strongly absorb in both the UVA and UVB regions, but they also exhibit average to very high photostability. Their wide spectrum UV-absorbing properties and their stability upon exposure to UV are highly influenced by the structure of the phenolic ester, particularly by the extra ester group in p-hydroxycinnamate diesters. These findings demonstrate that cellulose nanocrystals decorated with such plant-derived and nature-inspired phenolic esters are promising sustainable nanomaterials for anti-UV applications.

Selective Permeation of Water through Angstrom-Channel Graphene Membranes for Bioethanol Concentration

Graphene-based laminate membranes have been theoretically predicted to selectively transport ethanol from ethanol-water solution while blocking water. Here, robust angstrom-channel graphene membranes (ACGMs) fabricated by intercalating carbon sheets derived from chitosan into thermally reduced graphene oxide (GO) sheets are reported. ACGMs with robust and continuous slit-shaped pores (an average pore size of 3.9 Å) are investigated for the dehydration of ethanol. Surprisingly, only water permeates through ACGMs in the presence of aqueous ethanol solution. For the water-ethanol mixture containing 90 wt% ethanol, water can selectively permeate through ACGMs with a water flux of 63.8 ± 3.2 kg m^-2 h^-1 at 20 °C and 389.1 ± 19.4 kg m^-2 h^-1 at 60 °C, which are over two orders of magnitude higher than those of conventional pervaporation membranes. This means that ACGMs can effectively operate at room temperature. Moreover, the ethanol can be fast concentrated to high purity (up to 99.9 wt%). Therefore, ACGMs are very promising for production of bioethanol with high efficiency, thus improving its process sustainability.

Electrolyte gating in graphene-based supercapacitors and its use for probing nanoconfined charging dynamics

Graphene-based nanoporous materials have been extensively explored as high-capacity ion electrosorption electrodes for supercapacitors. However, little attention has been paid to exploiting the interactions between electrons that reside in the graphene lattice and the ions adsorbed between the individual graphene sheets. Here we report that the electronic conductance of a multilayered reduced graphene oxide membrane, when used as a supercapacitor electrode, can be modulated by the ionic charging state of the membrane, which gives rise to a collective electrolyte gating effect. This gating effect provides an in-operando approach for probing the charging dynamics of supercapacitors electrically. Using this approach, we observed a pore-size-dependent ionic hysteresis or memory effect in reduced graphene oxide membranes when the interlayer distance is comparable to the ion diameter. Our results may stimulate the design of novel devices based on the ion-electron interactions under nanoconfinement.

Polycrystalline Advanced Microporous Framework Membranes for Efficient Separation of Small Molecules and Ions

Advanced porous framework membranes with excellent selectivity and high permeability of small molecules and ions are highly desirable for many important industrial separation applications. There has been significant progress in the fabrication of polycrystalline microporous framework membranes (PMFMs) in recent years, such as metal-organic framework and covalent organic framework membranes. These membranes possess small pore sizes, which are comparable to the kinetic diameter of small molecules and ions on the angstrom scale, very low thickness, down to tens to hundreds of nanometers, highly oriented crystalline structures, hybrid membrane structures, and specific functional groups for enhancing membrane selectivity and permeability. Recent advances in the fabrication methods of advanced PMFMs are summarized. Following this, four emerging separation applications of these advanced microporous framework membranes, including gas separation, water desalination, ion separation, and chiral separation, are highlighted and discussed in detail. Finally, a summary and some perspectives of future developments and challenges in this exciting research field are presented.

Development of a Paper-Based Microfluidic System for a Continuous High-Flow-Rate Fluid Manipulation

The current study describes the development of a disposable paper-based microfluidic system, which unlike its predecessors that are only capable of processing a small amount of fluid, can continuously process the fluid at a high flow rate of up to 1.5 mL/min. The fabrication procedure was clean-room-free and robust, involving the use of a CO₂ laser to engrave the microchannels on a paper substrate, followed by alkenyl ketene dimer treatment to hydrophobize the paper and lamination. The microchannel down to a minimum depth of ∼80 μm with an average roughness of ∼8 μm was engraved on the substrate. As a proof of concept, the applicability of this system to enrich the microparticles based on the inertial focusing mechanism was tested. This new generation of paper-based microfluidic system can be potentially used for the diagnostic applications where the analyte is low in quantity and processing a large volume of fluid sample is required.

Light-Switchable Self-Healing Dynamic Linear Polymers: Reversible Cycloaddition Reactions of Thymine-Containing Units

A dynamic linear polymer was formed by the [2π+2π] reversible cycloaddition reaction of a thymine-based monomer under topochemical conditions and was used in self-healing applications. The reversible polymerisation of the thymine monomer was confirmed by UV and GPC analysis. Irradiation at 302 nm resulted in polymerisation of the monomer, and irradiation with wavelengths lower than 240 nm resulted in depolymerisation and the production of oligomeric units. This leads to a reduction in the glass transition temperature, and promoted healing of surface scratches due to the increased chain mobility. The self-healing ability of scratched samples was assessed based on the visual disappearance of the damage. In addition, the mechanical properties of the polymer before and after healing were found to be similar.

Voltage-Gated Ion Transport in Two-Dimensional Sub-1 nm Nanofluidic Channels

Voltage-gated nanofluidic systems have shown a wide range of potential applications in biosensors, energy harvest, and separation. Two-dimensional (2D) nanofluidic membranes fabricated with electrically conductive nanosheets have high ion conductivity and voltage-gated ion transport behaviors. However, the voltage-gating effect of the sub-nanometer-sized 2D channel membranes has not been well-investigated. In this work, a high-performance voltage-gated 2D nanofluidic device is constructed by assembling MXene nanosheets into a laminar membrane with sub-1 nm interlayer channels. By applying external voltage to the membrane, the ion conductivity of the device is enhanced by positive voltages and reduced by negative voltages, exhibiting a high voltage-gating on-off ratio of ∼10. The on-off ratio is found to be dependent on ion concentration and ion species. This work demonstrates that 2D membranes with interlayer spacings comparable to those of hydrated ion diameters can achieve high and tunable voltage-gating function, which provides a strategy to construct devices for highly efficient on-demand ion transport.

Light-Healable Epoxy Polymer Networks via Anthracene Dimer Scission of Diamine Crosslinker

Two anthracene-based diamine crosslinkers were used to cure a range of commercially available monomers to produce four highly photoreversible crosslinked epoxy polymers. Through careful selection of the epoxy monomers used, the properties of the resultant polymer networks were varied to create a coating material that possessed room-temperature light-stimulated healing. Of the four coatings created, the best healing performance was exhibited by the two most flexible systems, both of these also exhibited the thermal and mechanical performance necessary for coatings. By using anthracene, the utilization of a wide range of wavelengths in the healing process is possible, which in applications such as industrial coatings would be of significant benefit.

How rheological behaviors of concentrated starch affect graft copolymerization of acrylamide and resultant hydrogel

Corn starches with different amylose/amylopectin ratios were used to explore the effect of rheological behaviors of concentrated system on the graft copolymerization of acrylamide and resultant hydrogels, which sheds a light on their reactive extrusion process. The viscoelastic moduli of starch melts increased with increasing amylose content (AC), leading to a decreased extent of micro-mixing detected by a reduced rheokinetic rate. With increasing AC, the graft efficiency was decreased but with almost similar monomer conversion (about 87.5%) and nearly equivalent graft content. XRD and SAXS spectra revealed that the extent of retrogradation of the starches were increased and two-phase separation was enhanced for hydrogels with increasing AC. Interestingly, microscopic analysis showed the superabsorbent hydrogel from the starch with AC of 50% exhibited a gridding membrane porous structure, resulting in a higher water absorbent capacity of 550 g/g. This was attributed to the moderate crosslinking and the slightly greater graft content.

Effect of Organic Modification on Multiwalled Carbon Nanotube Dispersions in Highly Concentrated Emulsions

Highly concentrated water-in-oil emulsions incorporating multiwalled carbon nanotubes (MWCNTs) are prepared. Homogeneous and selective dispersions of MWCNTs throughout the oil phase of the emulsions are investigated. The practical insolubility of carbon nanotubes (CNTs) in aqueous and organic media necessitates the disentanglement of CNT "agglomerates" through the utilization of functionalized CNTs. The design and synthesis of two tetra-alkylated pyrene derivatives, namely, 1,3,6,8-tetra(oct-1-yn-1-yl)pyrene (TOPy) and 1,3,6,8-tetra(dodec-1-yn-1-yl)pyrene (TDPy), for the noncovalent organic modification of MWCNTs are reported. The modifier molecules are designed in such a manner that they facilitate an improved dispersion of individualized MWCNTs in the continuous-oil phase of the highly concentrated emulsion (HCE). Transmission electron microscopic analyses suggest that the alkylated pyrene molecules are adsorbed on the MWCNT surface, and their adsorption eventually results in the debundling of MWCNT agglomerates. Fourier transform infrared, Raman, and fluorescence spectroscopic analyses confirm the π-π interaction between the alkylated pyrene molecules and MWCNTs. The noncovalent modification significantly improves the effective debundling and selective dispersion of MWCNTs in HCEs.

Electrochemically-derived graphene oxide membranes with high stability and superior ionic sieving

Crosslinker-free electrochemically-derived graphene oxide membranes are found to be extraordinarily stable in aqueous solutions and exhibit superior ionic sieving performance because of their unique chemical structure.

Enokitake Mushroom-like Standing Gold Nanowires toward Wearable Noninvasive Bimodal Glucose and Strain Sensing

We have recently demonstrated that Enokitake mushroom-like gold with nanoparticles as the "head" and nanowires as the "tail" could grow directly on elastomeric substrates, which are extremely stretchable electrodes that can be used as wearable sensors for detecting strain and pressure. In this work, we show that such electrodes can also be used as intrinsically stretchable glucose biosensors. By modifying the vertical gold nanowire electrodes with glucose oxidase and Prussian blue nanoparticles, a limit of detection of 10 μM, sensitivity of 23.72 μA·mM^-1·cm^-2, and high selectivity can be achieved. The as-obtained glucose biosensors were able to maintain a high sensing performance under various mechanical deformations. Even for 30% strain, a sensitivity of 4.55 μA·mM^-1·cm^-2 toward glucose detection in the artificial sweat was possible. Furthermore, it was found that strains could be simultaneously detected with a gauge factor of 2.30 (strain 0-10%) and 22.64 (strain 10-20%), demonstrating the potential of such bimodal sensors to allow simultaneous monitoring of physical and biological signals.

Development of bio-acrylic polymers from Cyrene™: transforming a green solvent to a green polymer

A bio-based methacrylic polymer derived from a green solvent, Cyrene™ through a green synthesis pathway with very high glass transition temperature, thermal stability and high reactivity.

Atomistic insights into the adsorption and stimuli-responsive behavior of poly(N-isopropylacrylamide)-graphene hybrid systems

Non-covalent functionalization of graphene materials with responsive polymers is a promising approach for synthesizing new, hybrid composites with improved dispersibility and functional properties. However, the interplay between various components of the hybrid systems, their structural configurations, and stimuli-responsive behavior are not yet well understood at the atomic level. Here, we investigate the temperature-responsive behavior of physisorbed poly(N-isopropylacrylamide) (PNIPAM) on to graphene (G) and graphene oxide (GO) sheets in aqueous solution using large scale molecular dynamics simulations. It was observed that PNIPAM can be spontaneously anchored to the surfaces of both G and GO at 290 K with a macromolecular coil shape. However, the configuration of PNIPAM on G is markedly different in comparison with that on GO, leading to its distinct thermoresponsive behavior. Specifically, the adsorption on G gives rise to an increase in the temperature of the coil-to-globule transition when compared to the native polymer, the origin of which can be interpreted in terms of the interactions and the solvation behavior. The results obtained here are of significance to the design and manipulation of graphene-based stimuli-responsive hybrid systems with optimal functional properties.

Functionalized Boron Nitride Nanosheets: A Thermally Rearranged Polymer Nanocomposite Membrane for Hydrogen Separation

Amino functionalized boron nitride nanosheets (FBN) were incorporated into a crosslinked, thermally rearranged polyimide (XTR) to fabricate FBN-XTR nanocomposite membrane. The FBN-XTR membrane exhibited a small decrease in H₂ permeability but demonstrated a remarkably increased H₂ gas selectivity over other gases, compared with XTR. The XTR membrane heat-treated at 425 °C had a H₂ permeability of 210 Barrers and a H₂ /CH₄ separation factor of 24.1, whereas the nanocomposite membrane with 1 wt % FBN exhibited a H₂ permeability of 110 Barrers and H₂ /CH₄ separation factor of 275, an order of magnitude greater. At 1 wt % FBN loading, the FBN-XTR membrane showed three times higher tensile strength and 60 % higher elongation than pristine XTR membrane. In addition, FBN-XTR was found to be able to be readily processed into thin-film membranes for practical H₂ separation applications.

Vertical Gold Nanowires Stretchable Electrochemical Electrodes

Conventional electrodes produced from gold or glassy carbon are outstanding electrochemical platforms for biosensing applications due to their chemical inertness and wide electrochemical window, but are intrinsically rigid and planar in nature. Hence, it is challenging to seamlessly integrate them with soft and curvilinear biological tissues for real-time wearable or implantable electronics. In this work, we demonstrate that vertically gold nanowires (v-AuNWs) possess an enokitake-like structure, with the nanoparticle (head) on one side and nanowires (tail) on the opposite side of the structure, and can serve as intrinsically stretchable, electrochemical electrodes due to the stronger nanowire-elastomer bonding forces preventing from interfacial delamination under strains. The exposed head side of the electrode comprising v-AuNWs can achieve a detection limit for H₂O₂ of 80 μM, with a linear range of 0.2-10.4 mM at 20% strain, with a reasonably high sensitivity using chronoamperometry. This excellent electrochemical performance in the elongated state, in conjunction with low-cost wet-chemistry fabrication, demonstrates that v-AuNWs electrodes may become a next-generation sensing platform for conformally integrated, in vivo biodiagnostics.

Effect of Incorporation of Multiwalled Carbon Nanotubes on the Microstructure and Flow Behavior of Highly Concentrated Emulsions

Multiwalled carbon nanotubes (MWCNTs) were incorporated into highly concentrated water-in-oil emulsions with the ultimate aim of achieving a uniform and effective dispersion of MWCNTs within the emulsion matrix. The emulsion was formulated in such a way, wherein the internal phase consists of higher than 90 wt %. By keeping the same aqueous-to-oil phase ratio, the amount of MWCNTs in the oil phase was systematically adjusted to investigate their effects on the microstructure development and rheological behavior of the emulsion. The addition of MWCNTs led to a reduced droplet size and also resulted in a narrower distribution of the droplet size. The rheological behavior of nanotube-incorporated emulsions was characterized with varying MWCNT concentrations and also as a function of the emulsification time. The rheological characteristics of the nanotube-incorporated emulsions were identical to those of the neat emulsion and were primarily governed by the variation in the droplet size and droplet-size distribution. However, the yield strain and cross-over strain were independent of the mean droplet size and polydispersity of the emulsion. Emulsions that have smaller droplets exhibited higher storage modulus (G'), yield stress (τ_Y), and apparent viscosity (η). For all refining times investigated, nanotube-incorporated emulsions have higher G', τ_Y, and η values when compared to the neat emulsion, and these values further increased with the MWCNT concentration. This was primarily due to the decrease in the droplet size with MWCNT addition. Furthermore, our findings suggest that the incorporated MWCNTs did not induce any significant change in the rheological behavior of emulsions with identical droplet sizes, and it remained essentially unchanged with the concentration of MWCNTs. However, the nanotube-incorporated emulsions possessed solidlike behavior up to a higher applied stress when compared to a neat emulsion of identical droplet size.

Standing Enokitake-like Nanowire Films for Highly Stretchable Elastronics

Stretchable electronics may enable electronic components to be part of our organs-ideal for future wearable/implantable biodiagnostic systems. One of key challenges is failure of the soft/rigid material interface due to mismatching Young's moduli, which limits stretchability and durability of current systems. Here, we show that standing enokitake-like gold-nanowire-based films chemically bonded to an elastomer can be stretched up to 900% and are highly durable, with >93% conductivity recovery even after 2000 stretching/releasing cycles to 800% strain. Both experimental and modeling reveal that this superior elastic property originates from standing enokitake-like nanowire film structures. The closely packed nanoparticle layer sticks to the top of the nanowires, which easily cracks under strain, whereas the bottom part of the nanowires is compliant with substrate deformation. This leads to tiny V-shaped cracks with a maintained electron transport pathway rather than large U-shaped cracks that are frequently observed for conventional metal films. We further show that our standing nanowire films can serve as current collectors in supercapacitors and second skin-like smart masks for facial expression detection.

Self-assembled gold nanorime mesh conductors for invisible stretchable supercapacitors

Thin, skin-conformal, transparent and stretchable energy devices are ideal for powering future wearable and implantable electronics. However, it is difficult to achieve such "unfeelable" and "invisible" devices with traditional materials and design methodologies because of the challenge of simultaneously achieving high optical transparency, high electrical conductivity and high mechanical stretchability. Here, we report a two-step nanowire growth approach for fabricating gold nanorime mesh conductors, enabling skin-thin, transparent and stretchable supercapacitors. Solution-state oleylamine-capped 2 nm-thin gold nanowires self-assemble into highly transparent nanomeshes, which then serve as templates for growing highly conductive vertically aligned nanowires. This two-step solution-plus-surface nanowire growth strategy leads to elastic gold nanorime mesh conductors with an optical transparency up to 90.3% at 550 nm, a low sheet resistance as low as 1.7 ± 0.8 Ω sq-1, and a stretchability of over 100% strain. Such elastic conductors are successfully used to construct symmetrical supercapacitors that can simultaneously achieve high areal capacitance and high stretchability, demonstrating the potential to power future bio-integratable electronics.

Unconventional Janus Properties of Enokitake-like Gold Nanowire Films

We report on unconventional Janus material properties of vertically aligned gold nanowire films that conduct electricity and interact with light and water in drastically different ways on its two opposing sides. These Janus-like properties originate from enokitake-like nanowire structures, causing the nanoparticle side ("head") to behave like bulk gold, yet the opposing nanowire side ("tail") behaves as discontinuous nanophases. Due to this Janus film structure, its head side is hydrophilic but its tail side is hydrophobic; its head side reflects light like bulk gold, yet its tail side is a broadband superabsorber; its tail side is less conductive but with tunable resistance. More importantly, the elastomer-bonded Janus film exhibits unusual mechatronic properties when being stretched, bent, and pressed. The tail-bonded elastomeric sheet can be stretched up to ∼800% strain while remaining conductive, which is about 10-fold that of head-bonded film. In addition, it is also more sensitive to bending forces and point loads than the corresponding tail-bonded film. We further demonstrate the versatility of nanowire-based Janus films for pressure sensors using bilayer structures in three different assembly layouts.

Novel In-situ Precipitation Process to Engineer Low Permeability Porous Composite

Inspired by the natural precipitation of minerals in soil and rocks, a novel, simple and industrially scalable in-situ precipitation process to produce low permeability porous composites is presented. This process relies on capillary flow in wettable porous composites to absorb and store liquid. In this process, a porous composite first absorbs a salt solution, after which the composite is dipped in a second salt solution. Salts are selected such as they react to form an insoluble precipitate. As big pores absorb more liquid than small pores, the precipitated particles are formed specifically for each pore. In this paper, precipitation of CaCO3 nanoparticles in cellulose nanofibre (CNF) films was demonstrated as an example. Precipitation of 1 wt% of CaCO3 nanoparticles in the CNF film reduced the pore volume by 50%, without changing the density. This reduced the water vapour and oxygen transmission rates by one order of magnitude to 4.7 g/m2.day and 2.7 cc/m2.day, respectively. The barrier properties of in-situ precipitated composites showed superior performance to previously reported CNF films in literature. The concept is general and of very high industrial interest as it can easily be retrofitted to current continuous industrial processes.

Thermoresponsive Amphoteric Metal-Organic Frameworks for Efficient and Reversible Adsorption of Multiple Salts from Water

Regenerable, high-efficiency salt sorption materials are highly desirable for water treatment. Here, a thermoresponsive, amphoteric metal-organic framework (MOF) material is reported that can adsorb multiple salts from saline water at room temperature and effectively release the adsorbed salts into water at elevated temperature (e.g., 80 °C). The amphoteric MOF, integrated with both cation-binding carboxylic groups and anion-binding tertiary amine groups, is synthesized by introducing a polymer with tertiary amine groups into the cavities of a water-stable MOF such as MIL-121 with carboxylic groups inside its frameworks. The amphoterized MIL-121 exhibits excellent salt adsorption properties, showing stable adsorption-desorption cycling performances and high LiCl, NaCl, MgCl2 , and CaCl2 adsorption capacities of 0.56, 0.92, 0.25, and 0.39 mmol g-1 , respectively. This work provides a novel, effective strategy for synthesizing new-generation, environmental-friendly, and responsive salt adsorption materials for efficient water desalination and purification.

Carbon Nanotube Networks as Nanoscaffolds for Fabricating Ultrathin Carbon Molecular Sieve Membranes

Carbon molecular sieve (CMS) membranes have shown great potential for gas separation owing to their low cost, good chemical stability, and high selectivity. However, most of the conventional CMS membranes exhibit low gas permeance due to their thick active layer, which limits their practical applications. Herein, we report a new strategy for fabricating CMS membranes with a 100 nm-thick ultrathin active layer using poly(furfuryl alcohol) (PFA) as a carbon precursor and carbon nanotubes (CNTs) as nanoscaffolds. CNT networks are deposited on a porous substrate as nanoscaffolds, which guide PFA solution to effectively spread over the substrate and form a continuous layer, minimizing the penetration of PFA into the pores of the substrate. After pyrolysis process, the CMS membranes with 100-1000 nm-thick active layer can be obtained by adjusting the CNT loading. The 322 nm-thick CMS membrane exhibits the best trade-off between the gas permeance and selectivity, a H₂ permeance of 4.55 × 10^-8 mol m^-2 s^-1 Pa^-1, an O₂ permeance of 2.1 × 10^-9 mol m^-2 s^-1 Pa^-1, and an O₂/N₂ ideal selectivity of 10.5, which indicates the high quality of the membrane produced by this method. This work provides a simple, efficient strategy for fabricating ultrathin CMS membranes with high selectivity and improved gas flux.