A Method for the Efficient Fabrication of Multifunctional Mosaic Membranes by Inkjet Printing

Challenges, Prospects, and Emerging Applications of Inkjet-Printed Electronics: A Chemist's Point of View

Driven by the development of new functional inks, inkjet-printed electronics has achieved several milestones upon moving from the integration of simple electronic elements (e.g., temperature and pressure sensors, RFID antennas, etc.) to high-tech applications (e.g. in optoelectronics, energy storage and harvesting, medical diagnosis). Currently, inkjet printing techniques are limited by spatial resolution higher than several micrometers, which sets a redhibitorythreshold for miniaturization and for many applications that require the controlled organization of constituents at the nanometer scale. In this Review, we present the physico-chemical concepts and the equipment constraints underpinning the resolution limit of inkjet printing and describe the contributions from molecular, supramolecular, and nanomaterials-based approaches for their circumvention. Based on these considerations, we propose future trajectories for improving inkjet-printing resolution that will be driven and supported by breakthroughs coming from chemistry. Please check all text carefully as extensive language polishing was necessary. Title ok? Yes.

Biocatalytic membranes for combating the challenges of membrane fouling and micropollutants in water purification: A review

Over the last few years, the list of water contaminants has grown tremendously due to many anthropogenic activities. Various conventional technologies are available for water and wastewater treatment. However, micropollutants of emerging concern (MEC) are posing a great threat due to their activity at trace concentration and poor removal efficiency by the conventional treatment processes. Advanced technology like membrane technology can remove MEC to some extent. However, issues like the different chemical properties of MEC, selectivity, and fouling of membranes can affect the removal efficiency. Moreover, the concentrate from the membrane filtration may need further treatment. Enzymatic degradation of pollutants and foulants is one of the green approaches for removing various contaminants from the water as well as mitigating membrane fouling. Biocatalytic membranes (BCMs), in which enzymes are immobilized on membranes, combines the advantages of membrane separation and enzymatic degradation. This review article discussed various commonly used enzymes in BCMs for removing MEC and fouling. The majorly used enzymes were oxidoreductases and hydrolases for removing MEC, antifouling, and self-cleaning ability. The various BCM synthesis processes based on entrapment, crosslinking, and binding have been summarized, along with the effects of the addition of the nanoparticles on the performances of the BCMs. The scale-up, commercial viability, challenges, and future direction for improving BCMs have been discussed and shown bright possibilities for these new generation membranes.

Hybrid Organic-Inorganic-Organic Isoporous Membranes with Tunable Pore Sizes and Functionalities for Molecular Separation

Accomplishing on-demand molecular separation with a high selectivity and good permeability is very desirable for pollutant removal and chemical and pharmaceutical processing. The major challenge for sub-10 nm filtration of particles and molecules is the fabrication of high-performance membranes with tunable pore size and designed functionality. Here, a versatile top-down approach is demonstrated to produce such a membrane using isoporous block copolymer membranes with well-defined pore sizes combined with growth of metal oxide using sequential infiltration synthesis and atomic layer deposition (SIS and ALD). The pore size of the membranes is tuned by controlled metal oxide growth within and onto the polymer channels, enabling up to twofold pore diameter reduction. Following the growth, the distinct functionalities are readily incorporated along the membrane nanochannels with either hydrophobic, cationic, or anionic groups via straightforward and scalable gas/liquid-solid interface reactions. The hydrophilicity/hydrophobicity of the membrane nanochannel is significantly changed by the introduction of hydrophilic metal oxide and hydrophobic fluorinated groups. The functionalized membranes exhibit a superior selectivity and permeability in separating 1-2 nm organic molecules and fractionating similar-sized proteins based on size, charge, and hydrophobicity. This demonstrates the great potential of organic-inorganic-organic isoporous membranes for high-performance molecular separation in numerous applications.

100th Anniversary of Macromolecular Science Viewpoint: Integrated Membrane Systems

Membranes fabricated from self-assembled materials are one recent example of how polymer science has been leveraged to advance membrane technology. Due to their well-defined nanostructures, the performance of membranes made from these materials is pushing the boundaries of size-selective filtration. Still, there remains a need for higher performance and more selective membranes. The advent of functional membrane platforms that rely on mechanisms beyond steric hindrance (e.g., charge-selective membranes and membrane sorbents) is one approach to realize improved solute-solute selectivity and further advance membrane technology. To date, the lab-scale demonstration of these platforms has often relied on fabrication schemes that require extended processing times. However, in order to translate lab-scale demonstrations to larger-scale implementation, it is critical that the rate of the functionalization scheme is reconciled with membrane manufacturing rates. In this viewpoint, it is postulated that substrates lined by reactive moieties that are amenable to postfabrication modification would enable the production of membranes with controlled nanostructures while providing access to a diverse array of pore wall chemistries. A comparison of reaction and manufacturing rates suggests that mechanisms that exhibit second-order reaction rate constants of at least 1 M^-1 s^-1 are needed for roll-to-roll processing. Furthermore, for mechanisms that exhibit rate constants greater than 300 M^-1 s^-1, it may be possible to integrate multiple functional domains over the membrane surface such that useful properties emerge. These multifunctional systems can expand the capabilities of membranes when the patterned chemistries interact at the heterojunctions between domains (e.g., Janus and charge-patterned mosaic membranes) or if they exhibit cooperative responses to external operating conditions (e.g., membrane pumps).

Towards single-species selectivity of membranes with subnanometre pores

Synthetic membranes with pores at the subnanometre scale are at the core of processes for separating solutes from water, such as water purification and desalination. While these membrane processes have achieved substantial industrial success, the capability of state-of-the-art membranes to selectively separate a single solute from a mixture of solutes is limited. Such high-precision separation would enable fit-for-purpose treatment, improving the sustainability of current water-treatment processes and opening doors for new applications of membrane technologies. Herein, we introduce the challenges of state-of-the-art membranes with subnanometre pores to achieve high selectivity between solutes. We then analyse experimental and theoretical literature to discuss the molecular-level mechanisms that contribute to energy barriers for solute transport through subnanometre pores. We conclude by providing principles and guidelines for designing next-generation single-species selective membranes that are inspired by ion-selective biological channels.

Resistance and Permselectivity of 3D-Printed Micropatterned Anion-Exchange Membranes

It has been demonstrated that a micropatterned surface can decrease the resistance of anion-exchange membranes (AEMs) and can induce desirable flow properties in devices, such as mixing. Previously, a model that related the resistance of flat and patterned membranes with the same equivalent thickness was proposed, which used the patterned area and thickness ratio of the features to describe the membrane resistance. Here, we explored the validity of the parallel resistance model for a variety of membrane surface designs and area ratios. We demonstrated that the model can predict the resistance of a wide range of patterned AEMs. We showed that the resistance is independent of the spatial ordering of the design by examining random patterns, which is relevant for applications that require, for example, increased mixing in multilayered devices. Some experimental values of resistance obtained for patterned membranes presented deviations from the model. Scanning electron microscopy (SEM) images of the patterned membranes revealed resolution variations and pattern replication errors due to the stereolithographic process. A geometric correction of the target ratios improved the fit of the modeled data to the experimental values, showing that light bleeding during curing was a source of error. Two additional experimental factors were not accounted for in the model: a distinct interface between the bottom and top layer and overcuring of the bottom layer during successive steps. These sources of error were investigated by examining the resistance of single- and double-layered membranes, as well as single-layer membranes with different curing times. The differences obtained in the resistances for control samples demonstrated that both the interface and the overcuring influenced the resistance of the membrane. The results obtained in this study enlighten the discussion relating membrane-surface morphology and transport properties, as well as the optimization of 3D-printed membranes using a stereolithography process.

Interfacial Junctions Control Electrolyte Transport through Charge-Patterned Membranes

Distinct transport mechanisms emerge when nanostructured substrates are patterned with multiple chemistries. For example, charge-patterned mosaic membranes possess surfaces functionalized with discrete domains of both positive and negative charge. These oppositely charged domains provide pathways for both the cation and anion from a dissolved salt to permeate through the membrane without violating the macroscopic constraint of electroneutrality. Here, by systematically varying the geometry and size of the charge pattern, we elucidate the molecular interactions that promote the transport of salts under the action of pressure-driven flow. For patterns that consist of equivalent areal coverages of positively charged and negatively charged domains, the effects of the geometric parameters were encapsulated in a single variable, the interfacial packing density, that quantified the fraction of the membrane surface covered by junctions between oppositely charged domains. Experimentally, the transport of symmetric electrolytes (i.e., KCl and MgSO₄) increased with the value of the interfacial packing density, while the interfacial packing density did not significantly affect the transport of asymmetric electrolytes (i.e., K₂SO₄ and MgCl₂). Simulations of the electrical potential near the membrane surface demonstrate that for symmetric electrolytes the structural charge heterogeneity reduces the barrier to ion partitioning, thereby promoting salt transport through the membranes. For asymmetric electrolytes, the charge heterogeneity skews the local availability of ions from the stoichiometric ratio of the salt, thus hindering salt transport. These findings demonstrate the promise of accessing transport mechanisms, which could find utility in a diverse range of chemical separations and sensing applications, through chemical patterning of membranes.

Recent Advances in the Fabrication of Membranes Containing "Ion Pairs" for Nanofiltration Processes

In the face of serious environmental pollution and water scarcity problems, the membrane separation technique, especially high efficiency, low energy consumption, and environmental friendly nanofiltration, has been quickly developed. Separation membranes with high permeability, good selectivity, and strong antifouling properties are critical for water treatment and green chemical processing. In recent years, researchers have paid more and more attention to the development of high performance nanofiltration membranes containing “ion pairs”. In this review, the effects of “ion pairs” characteristics, such as the super-hydrophilicity, controllable charge character, and antifouling property, on nanofiltration performances are discussed. A systematic survey was carried out on the various approaches and multiple regulation factors in the fabrication of polyelectrolyte complex membranes, zwitterionic membranes, and charged mosaic membranes, respectively. The mass transport behavior and antifouling mechanism of the membranes with “ion pairs” are also discussed. Finally, we present a brief perspective on the future development of advanced nanofiltration membranes with “ion pairs”.

Pinch-off dynamics and dripping-onto-substrate (DoS) rheometry of complex fluids

Liquid transfer and drop formation/deposition processes involve complex free-surface flows including the formation of columnar necks that undergo spontaneous capillary-driven instability, thinning and pinch-off. For simple (Newtonian and inelastic) fluids, a complex interplay of capillary, inertial and viscous stresses determines the nonlinear dynamics underlying finite-time singularity as well as self-similar capillary thinning and pinch-off dynamics. In rheologically complex fluids, extra elastic stresses as well as non-Newtonian shear and extensional viscosities dramatically alter the nonlinear dynamics. Stream-wise velocity gradients that arise within the thinning columnar neck create an extensional flow field, and many complex fluids exhibit a much larger resistance to elongational flows than Newtonian fluids with similar shear viscosity. Characterization of pinch-off dynamics and the response to both shear and extensional flows that influence drop formation/deposition in microfluidic and printing applications requires bespoke instrumentation not available, or easily replicated, in most laboratories. Here we show that dripping-onto-substrate (DoS) rheometry protocols that involve visualization and analysis of capillary-driven thinning and pinch-off dynamics of a columnar neck formed between a nozzle and a sessile drop can be used for measuring shear viscosity, power law index, extensional viscosity, relaxation time and the most relevant processing timescale for printing. We showcase the versatility of DoS rheometry by characterizing and contrasting the pinch-off dynamics of a wide spectrum of simple and complex fluids: water, printing inks, semi-dilute polymer solutions, yield stress fluids, food materials and cosmetics. We show that DoS rheometry enables characterization of low viscosity printing inks and polymer solutions that are beyond the measurable range of commercially-available capillary break-up extensional rheometer (CaBER). We show that for high viscosity fluids, DoS rheometry can be implemented relatively inexpensively using an off-the-shelf digital camera, and for many complex fluids, similar power law scaling exponent describes both neck thinning dynamics and the shear thinning response.