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Liquid-crystal molecules orient locally in response to external fields. When long-chain liquid-crystalline molecules are crosslinked together, changes in local orientation can lead to significant volume changes. Ware et al. made efficient microactuators that can change their shape from flat to three-dimensional structures (see the Perspective by Verduzco). By patterning volume elements so that each has a different preferred alignment for the liquid-crystalline molecules, they could fine-tune the volume changes. Science, this issue p. 982; see also p. 949 Dynamic control of shape can bring multifunctionality to devices. Soft materials capable of programmable shape change require localized control of the magnitude and directionality of a mechanical response. We report the preparation of soft, ordered materials referred to as liquid crystal elastomers. The direction of molecular order, known as the director, is written within local volume elements (voxels) as small as 0.0005 cubic millimeters. Locally, the director controls the inherent mechanical response (55% strain) within the material. In monoliths with spatially patterned director, thermal or chemical stimuli transform flat sheets into three-dimensional objects through controlled bending and stretching. The programmable mechanical response of these materials could yield monolithic multifunctional devices or serve as reconfigurable substrates for flexible devices in aerospace, medicine, or consumer goods.

The diffusion limitations on gas storage and catalytic reaction of microporous materials can often be overcome if they are incorporated into a mesoporous structure with much larger pores. Shen et al. grew ordered arrays of microcrystals of the ZIF-8 metal-organic framework, in which zinc ions are bridged by 2-methylimidazole linkers, inside a porous polystyrene template. These materials showed higher reaction rates for the Knoevenagel reaction between benzaldehydes and malononitriles and better catalyst recyclability. Science , this issue p. 206 A double-solvent method and templating are used to grow ordered arrays of metal-organic framework microcrystals. We constructed highly oriented and ordered macropores within metal-organic framework (MOF) single crystals, opening up the area of three-dimensional–ordered macro-microporous materials (that is, materials containing both macro- and micropores) in single-crystalline form. Our methodology relies on the strong shaping effects of a polystyrene nanosphere monolith template and a double-solvent–induced heterogeneous nucleation approach. This process synergistically enabled the in situ growth of MOFs within ordered voids, rendering a single crystal with oriented and ordered macro-microporous structure. The improved mass diffusion properties of such hierarchical frameworks, together with their robust single-crystalline nature, endow them with superior catalytic activity and recyclability for bulky-molecule reactions, as compared with conventional, polycrystalline hollow, and disordered macroporous ZIF-8.

Hierarchically porous materials with large pores in the micrometer range and small pores in the nanometer range, where the large pores facilitate mass transport and the small pores supply numerous active sites, show superiority to materials with unimodal pores in the fields of separation and adsorption. Among all the methods used to prepare hierarchically porous monoliths (HPMs), the sol–gel process accompanied by spinodal decomposition (or phase separation) shows its advantages such as facile method, no template, precise structural control, good reproducibility, and availability for various kinds of materials. This review focuses on the specific process to prepare various types of HPMs including silica, metal oxides, metal phosphates, and metal–organic hybrids, via the sol–gel process accompanied by spinodal decomposition. The HPMs composed of organic polymer and their carbonized derivatives prepared by polymerization-induced phase separation are also covered in this review as an example of similar morphological formation in purely organic crosslinking reactions. This review directs the most attention to the preparation of monolithic gels (sol–gel process) and the control of macroporous structure (phase separation). Highlights This review summarizes the preparation of hierarchically porous monoliths with various chemical compositions. The phase separation behaviors and methods of controlling pore structures are described in detail. Latest advances on the formation of porous monolith with low-valence metal oxides as well as metal–organic frameworks compositions are also introduced.

Photochemical activation routes are gaining the attention of the scientific community since they can offer an alternative to the traditional chemical industry that mainly utilizes thermochemical activation of molecules. Photoreactions are fast and selective, which would potentially reduce the downstream costs significantly if the process is optimized properly. With the transition towards green chemistry, the traditional batch photoreactor operation is becoming abundant in this field. Process intensification efforts led to micro- and mesostructured flow photoreactors. In this work, we are reviewing structured photoreactors by elaborating on the bottleneck of this field: the development of an efficient scale-up strategy. In line with this, micro- and mesostructured bench-scale photoreactors were evaluated based on a new benchmark called photochemical space time yield (mol·day −1 ·kW −1 ), which takes into account the energy efficiency of the photoreactors. It was manifested that along with the selection of the photoreactor dimensions and an appropriate light source, optimization of the process conditions, such as the residence time and the concentration of the photoactive molecule is also crucial for an efficient photoreactor operation. In this paper, we are aiming to give a comprehensive understanding for scale-up strategies by benchmarking selected photoreactors and by discussing transport phenomena in several other photoreactors.

The cellulose-based materials are new types of advanced materials combining pristine cellulose with functional materials for specific applications. In this study, a novel cotton fiber (CF)–covalent organic framework (COF) hybrid monolith was prepared for the efficient capture of iodine in vapor and solution. The cotton fibers were first modified with (3-aminopropyl)trimethoxysilane via silylation reaction to generate amino functions on the surface of the fibers, and then the COFs grafted subsequently. The obtained CF/COF hybrid monolith has been characterized by infrared spectra, powder X-ray diffraction, elemental analysis, scanning electron microscope, thermo-gravimetric analysis, and nitrogen adsorption–desorption analysis, and then it was used as adsorbent for removing iodine. The grafting of COFs on the cotton fiber matrix was calculated to be about 12.28 wt%, which increased the BET specific surface area of the cotton fiber from 1.9 to 166 m2/g. The CF/COF monolith displayed excellent capture ability for iodine vapor with adsorption capacity up to 823.9 mg/g, and it also showed remarkable adsorption ability for iodine in cyclohexane solution. The hybrid monolith can be easily regenerated by washing with methanol, and it showed good reusability. Moreover, the CF/COF monolith presented good thermal stability with a decomposition temperature above 300 °C. This strategy for combining COFs with cotton fibers will pave the way for the development of novel efficient adsorption materials for radioiodine during nuclear waste disposal.Graphic abstract

HighlightsConvincing candidates of flexible (stretchable/compressible) electromagnetic interference shielding nanocomposites are discussed in detail from the views of fabrication, mechanical elasticity and shielding performance.Detailed summary of the relationship between deformation of materials and electromagnetic shielding performance.The future directions and challenges in developing flexible (particularly elastic) shielding nanocomposites are highlighted.With the extensive use of electronic communication technology in integrated circuit systems and wearable devices, electromagnetic interference (EMI) has increased dramatically. The shortcomings of conventional rigid EMI shielding materials include high brittleness, poor comfort, and unsuitability for conforming and deformable applications. Hitherto, flexible (particularly elastic) nanocomposites have attracted enormous interest due to their excellent deformability. However, the current flexible shielding nanocomposites present low mechanical stability and resilience, relatively poor EMI shielding performance, and limited multifunctionality. Herein, the advances in low-dimensional EMI shielding nanomaterials-based elastomers are outlined and a selection of the most remarkable examples is discussed. And the corresponding modification strategies and deformability performance are summarized. Finally, expectations for this quickly increasing sector are discussed, as well as future challenges.

In recent years, molecularly imprinted polymers (MIPs) have become an excellent solution to the selective and sensitive determination of target molecules in complex matrices where other similar and relative structural compounds could coexist. Although MIPs show the inherent properties of the polymers, including stability, robustness, and easy/cheap synthesis, some of their characteristics can be enhanced, or new functionalities can be obtained when nanoparticles are incorporated in their polymeric structure. The great variety of nanoparticles available significantly increase the possibility of finding the adequate design of nanostructured MIP for each analytical problem. Moreover, different structures (i.e., monolithic solids or MIPs micro/nanoparticles) can be produced depending on the used synthesis approach. This review aims to summarize and describe the most recent and innovative strategies since 2015, based on the combination of MIPs with nanoparticles. The role of the nanoparticles in the polymerization, as well as in the imprinting and adsorption efficiency, is also discussed through the review.

Inorganic materials have essential roles in society, including in building construction, optical devices, mechanical engineering and as biomaterials 1 – 4 . However, the manufacture of inorganic materials is limited by classical crystallization 5 , which often produces powders rather than monoliths with continuous structures. Several precursors that enable non-classical crystallization—such as pre-nucleation clusters 6 – 8 , dense liquid droplets 9 , 10 , polymer-induced liquid precursor phases 11 – 13 and nanoparticles 14 —have been proposed to improve the construction of inorganic materials, but the large-scale application of these precursors in monolith preparations is limited by availability and by practical considerations. Inspired by the processability of polymeric materials that can be manufactured by crosslinking monomers or oligomers 15 , here we demonstrate the construction of continuously structured inorganic materials by crosslinking ionic oligomers. Using calcium carbonate as a model, we obtain a large quantity of its oligomers (CaCO 3 ) n with controllable molecular weights, in which triethylamine acts as a capping agent to stabilize the oligomers. The removal of triethylamine initiates crosslinking of the (CaCO 3 ) n oligomers, and thus the rapid construction of pure monolithic calcium carbonate and even single crystals with a continuous internal structure. The fluid-like behaviour of the oligomer precursor enables it to be readily processed or moulded into shapes, even for materials with structural complexity and variable morphologies. The material construction strategy that we introduce here arises from a fusion of classic inorganic and polymer chemistry, and uses the same cross-linking process for the manufacture the materials. The crosslinking of oligomeric precursors, controlled by a capping agent, enables the production of moulded crystalline calcium carbonate with continuous structures.

Preterm birth (PTB) is defined as birth before the 37th week of pregnancy and results in 15 million early deliveries worldwide every year. Presently, there is no clinical test to determine PTB risk; however, a panel of nine biomarkers found in maternal blood serum has predictive power for a subsequent PTB. A significant step in creating a clinical diagnostic for PTB is designing an automated method to extract and purify these biomarkers from blood serum. Here, microfluidic devices with 45 μm × 50 μm cross-section channels were 3D printed with a built-in polymerization window to allow a glycidyl methacrylate monolith to be site-specifically polymerized within the channel. This monolith was then used as a solid support to attach antibodies for PTB biomarker extraction. Using these functionalized monoliths, it was possible to selectively extract a PTB biomarker, ferritin, from buffer and a human blood serum matrix. This is the first demonstration of monolith formation in a 3D printed microfluidic device for immunoaffinity extraction. Notably, this work is a crucial first step toward developing a 3D printed microfluidic clinical diagnostic for PTB risk.

The patterning of polydimethylsiloxane (PDMS) into complex two-dimensional (2D) or 3D shapes is a crucial step for diverse applications based on soft lithography. Nevertheless, mould replication that incorporates time-consuming and costly photolithography processes still remains the dominant technology in the field. Here we developed monolithic quasi-3D digital patterning of PDMS using laser pyrolysis. In contrast with conventional burning or laser ablation of transparent PDMS, which yields poor surface properties, our successive laser pyrolysis technique converts PDMS into easily removable silicon carbide via consecutive photothermal pyrolysis guided by a continuous-wave laser. We obtained high-quality 2D or 3D PDMS structures with complex patterning starting from a PDMS monolith in a remarkably low prototyping time (less than one hour). Moreover, we developed distinct microfluidic devices with elaborated channel architectures and a customizable organ-on-a-chip device using this approach, which showcases the potential of the successive laser pyrolysis technique for the fabrication of devices for several technological applications. A laser-based patterning method enables the fast fabrication of high-quality two- and three-dimensional features in polydimethylsiloxane for microfluidics and biomedical applications.