Facile Fabrication of Monolithic 3D Porous Silica Microstructures and a Microfluidic System Embedded with the Microstructure

Monolithic 3D porous silica structures are fabricated into a multilayer framework with a bimodal pore size distribution in the micrometer and sub‐micrometer range. The fabrication – which involves directed assembly of colloidal spheres, transfer printing, and removal of a sacrificial template – yields robust and mechanically stable structures over a large area. The structure becomes monolithic upon pyrolyzing the stacked layers, which induces necking of the particles. The monolithic microstructures can easily be embedded in microchannels with the aid of photolithography, leading to the formation of a microfluidic system with a built‐in microstructure in a site‐ and shape‐controlled manner. Utilization of the system results in a fourfold increase in the mixing efficiency in the microchannel.     

Polymer‐Based Porous Microcapsules as Bacterial Traps

Exposure to live bacteria and accumulation of dead bacteria during bactericidal processes can cause bacterial infectious diseases, implant failure, and antibacterial surface deterioration. Microcapsules with asymmetrically distributed, funnel‐shaped pores, which are capable of capturing, retaining, and killing bacteria are developed, offering a solution to bacterial contamination in liquids. It is found that bacterial isolation inside microcapsules is mainly driven by the bacteria's own motility and the microcapsules' geometry. After entry into the microcapsule cavity, the bacteria are stably retained inside. The microcapsules shield surrounding cells from exposure to bacterial toxins, as demonstrated by the coculture of rat embryonic fibroblast cells with microcapsules loaded with live Escherichia coli. The microcapsules can be enhanced with a bactericidal coating covering only the interior cavity. This confines the bacteria‐killing process, thereby further increasing biocompatibility. The microcapsules may offer a viable bacteria combatant approach as a potentially advantageous method to eradicate bacterial contamination.     

Composite Salt in Porous Metal‐Organic Frameworks for Adsorption Heat Transformation

Adsorptive heat transformation systems such as adsorption thermal batteries and chillers can provide space heating and cooling in a more environmental friendly way. However, their use is still hindered by their relatively poor performances and large sizes due to the limited properties of solid adsorbents. Here, the spray‐drying continuous‐flow synthesis of a new type of solid adsorbents that results from combining metal‐organic frameworks (MOFs), such as UiO‐66, and hygroscopic salts, such as CaCl₂ has been reported. These adsorbents, commonly named as composite salt in porous matrix (CSPM) materials, allow improving the water uptake capabilities of MOFs while preventing their dissolution in the water adsorbed; a common characteristic of these salts due to the deliquescence effect. It is anticipated that MOF‐based CSPMs, in which the percentage of salt can be tuned, are promising candidates for thermal batteries and chillers. In these applications, it is showed that a CSPM made of UiO‐66 and CaCl₂ (38% w/w) exhibits a heat storage capacity of 367 kJ kg^?1 , whereas a second CSPM made of UiO‐66 and CaCl₂ (53% w/w) shows a specific cooling power of 631 W kg^?1 and a coefficient of performance of 0.83, comparable to the best solid adsorbents reported so far.     

Nematic Liquid Crystals Embedded in Cubic Microlattices: Memory Effects and Bistable Pixels

The confinement of liquid crystals in geometries with frustrating boundary conditions gives rise to nontrivial effects such as bistability and memory. It is shown that large memory effects arise when nematic liquid crystals are embedded in cubic micrometer‐sized scaffolds made by two‐photon polymerization. The electric field alignment of the liquid crystals inside the porous medium is maintained when the applied field is above a threshold (approximately 2 V per micrometer of cell thickness). The onset of the memory is an on/off type process for each individual pore of the scaffold, and the memory typically starts emerging in one region of the structure and then propagates. The global memory effects in porous structures with controlled geometry are enhanced with respect to the case of random porous structures. This work is a proof of the “memory from topology” principle, which was previously suggested by computer simulations. These new materials can pave the way to new types of bistable displays.     

Emerging Homochiral Porous Materials for Enantiomer Separation

Efficient resolution of racemates of chiral molecules is of great significance in the pharmaceutical, agrochemical, fragrances, and food additives industries. Emerging homochiral porous materials such as metal–organic frameworks, covalent-organic frameworks, porous-organic cages, and metal-organic cages with ultrahigh surface area, controllable pore chemistry and ample chiral recognition sites are promising for efficient chiral resolution, which display excellent properties for chiral separation applications. This review summarizes the design and synthesis strategies for the construction of homochiral porous materials, including direct synthesis, post-synthesis, and chiral induction synthesis. Following this, applications of emerging homochiral porous materials, including enantioselective adsorption, chiral chromatography, and membrane-based chiral separation are highlighted. Finally, the challenges in this area are discussed, with future perspectives provided.     

Porous Fibers Composed of Polymer Nanoball Decorated Graphene for Wearable and Highly Sensitive Strain Sensors

Wearable textile strain sensors that can perceive and respond to human stimuli are an essential part of wearable electronics. Yet, the detection of subtle strains on the human body suffers from the low sensitivity of many existing sensors. Generally, the inadequate sensitivity originates from the strong structural integrity of the sensors because tiny external strains cannot trigger enough variation in the conducting network. Inspired by the rolling friction where the interaction is weakened by decreasing interface area, porous fibers made of graphene decorated with nanoballs are prepared via a prolonged phase‐separation process. This novel structure confers the graphene fibers with high gauge factors (51 in 0–5% and 87 in 5–8%), which is almost 10 times larger than the same structures without nanoballs. A low detection limit (0.01% strain) and good durability (over 6000 circles) are obtained. By the virtue of these qualities, these fiber‐based textile sensors can recognize a pulse wave and eyeball movement in real‐time while keeping comfortable wearing sense. Moreover, by weaving such fibers, the electronic fabrics with a specially designed structure can distinguish the multilocation in real time, which shows great potential as wearable electronics.     

Room‐Temperature Micropillar Growth of Lithium–Titanate–Carbon Composite Structures by Self‐Biased Direct Current Magnetron Sputtering for Lithium Ion Microbatteries

Here, an unidentified type of micropillar growth is described at room temperature during conventional direct‐current magnetron sputtering (DC‐MS) deposition from a Li₄Ti₅O₁₂+graphite sputter target under negative substrate bias and high operating pressure. These fabricated carbon–Li₂O–TiO₂ microstructures consisting of various Li₄Ti₅O₁₂/Li₂TiO₃/Li_x TiO₂ crystalline phases are demonstrated as an anode material in Li‐ion microbatteries. The described micropillar fabrication method is a low‐cost, substrate independent, single‐step, room‐temperature vacuum process utilizing a mature industrial complementary metal–oxide–semiconductor (CMOS)‐compatible technology. Furthermore, tentative consideration is given to the effects of selected deposition parameters and the growth process, as based on extensive physical and chemical characterization. Additional studies are, however, required to understand the exact processes and interactions that form the micropillars. If this facile method is further extended to other similar metal oxide–carbon systems, it could offer alternative low‐cost fabrication routes for microporous high‐surface area materials in electrochemistry and microelectronics.     

Electric Field Assisted Microfluidic Platform for Generation of Tailorable Porous Microbeads as Cell Carriers for Tissue Engineering

Injection of cell‐laden scaffolds in the form of mesoscopic particles directly to the site of treatment is one of the most promising approaches to tissue regeneration. Here, a novel and highly efficient method is presented for preparation of porous microbeads of tailorable dimensions (in the range ≈300–1500 mm) and with a uniform and fully interconnected internal porous texture. The method starts with generation of a monodisperse oil‐in‐water emulsion inside a flow‐focusing microfluidic device. This emulsion is later broken‐up, with the use of electric field, into mesoscopic double droplets, that in turn serve as a template for the porous microbeads. By tuning the amplitude and frequency of the electric pulses, the template droplets and the resulting porous bead scaffolds are precisely produced. Furthermore, a model of pulsed electrodripping is proposed that predicts the size of the template droplets as a function of the applied voltage. To prove the potential of the porous microbeads as cell carries, they are tested with human mesenchymal stem cells and hepatic cells, with their viability and degree of microbead colonization being monitored. Finally, the presented porous microbeads are benchmarked against conventional microparticles with nonhomogenous internal texture, revealing their superior performance.     

Growth of a Highly Porous Coordination Polymer on a Macroporous Polymer Monolith Support for Enhanced Immobilized Metal Ion Affinity Chromatographic Enrichment of Phosphopeptides

A simple room temperature solution‐based method for the preparation of highly porous iron(III) benzenetricarboxylate coordination polymer films on the internal surface of a macroporous polystyrene‐divinylbenzene‐methacrylic acid polymer is reported. The resulting metal‐organic polymer hybrid (MOPH) maintains a high specific micropore surface area of 389 m² g^‐1 and thermal stability above 250 °C in air. The MOPH preparation is readily adapted to a capillary column, yielding a flow‐through separation device with excellent flow permeability and modest back‐pressure. The excellent separation capability of the MOPH column is demonstrated by enriching phosphopeptides from mixtures of digested proteins. This approach to MOPH synthesis is easily implemented and likely adaptable to a wide range of coordination polymers and metal‐organic frameworks.     

Porous Polymer Films with Gradient‐Refractive‐Index Structure for Broadband and Omnidirectional Antireflection Coatings

Porous polymer films that can be employed for broadband and omnidirectional antireflection coatings are successfully shown. These films form a gradient‐refractive‐index structure and are achieved by spin‐coating the solution of a polystyrene‐block‐poly(methyl methacrylate) (PS‐b‐PMMA)/PMMA blend onto an octadecyltrichlorosilane (OTS)‐modified glass substrate. Thus, a gradient distribution of PMMA domains in the vertical direction of the entire microphase‐separated film is obtained. After those PMMA domains are removed, a PS porous structure with an excellent gradient porosity ratio in the vertical direction of the film is formed. Glass substrates coated with such porous polymer film exhibit both broadband and omnidirectional antireflection properties because the refractive index increases gradually from the top to the bottom of the film. An excellent transmittance of >97% for both visible and near‐infrared (NIR) light is achieved in these gradient‐refractive‐index structures. When the incident angle is increased, the total transmittance for three different incident angles is improved dramatically. Meanwhile, the film possesses a color reproduction character in the visible light range.     

Hierarchically Structured Porous Materials for Energy Conversion and Storage

Materials with hierarchical porosity and structures have been heavily involved in newly developed energy storage and conversion systems. Because of meticulous design and ingenious hierarchical structuration of porosities through the mimicking of natural systems, hierarchically structured porous materials can provide large surface areas for reaction, interfacial transport, or dispersion of active sites at different length scales of pores and shorten diffusion paths or reduce diffusion effect. By the incorporation of macroporosity in materials, light harvesting can be enhanced, showing the importance of macrochannels in light related systems such as photocatalysis and photovoltaics. A state‐of‐the‐art review of the applications of hierarchically structured porous materials in energy conversion and storage is presented. Their involvement in energy conversion such as in photosynthesis, photocatalytic H₂ production, photocatalysis, or in dye sensitized solar cells (DSSCs) and fuel cells (FCs) is discussed. Energy storage technologies such as Li‐ions batteries, supercapacitors, hydrogen storage, and solar thermal storage developed based on hierarchically porous materials are then discussed. The links between the hierarchically porous structures and their performances in energy conversion and storage presented can promote the design of the novel structures with advanced properties.     

Gradient Porous Elastic Hydrogels with Shape‐Memory Property and Anisotropic Responses for Programmable Locomotion

Programmable locomotion of responsive hydrogels has gained increasing attention for potential applications in soft robotics, microfluidic components, actuators, and artificial muscle. Modulation of hydrogel pore structures is essential for tailoring their mechanical strength, response speeds, and motion behaviors. Conventional methods forming hydrogels with homogeneous or stepwise‐distributed pore structures are limited by the required compromise to simultaneously optimize these aspects. Here, a heterobifunctional crosslinker enabled hydrothermal process is introduced to synthesize responsive hydrogels with well‐defined gradient pore construction. According to gradient porosity controls, the hydrogels simultaneously exhibit rapid responses to external stimuli, high elasticity/compressibility, and programmable locomotion capability. By incorporating polypyrrole nanoparticles as photothermal transducers, photo/thermal responsive composite hydrogels are formed to enable programmable control of locomotion such as bending, curving, twisting, and octopus‐like swimming under near‐infrared laser stimulation. The tunable pore structures, mechanical properties, and locomotion of this new class of materials make these gradient porous hydrogels potentially suitable for a variety of applications.     

Immobilization of Quantum Dots in Nanostructured Porous Silicon Films: Characterizations and Signal Amplification for Dual‐Mode Optical Biosensing

Highly sensitive dual‐mode labeled detection of biotin in well‐characterized porous silicon (PSi) films using colloidal quantum dots (QDs) as signal amplifiers are demonstrated. Optimization of the PSi platform for targeted QD infiltration and immobilization is carried out by characterizing and tuning the porosity, film depth, and pore size. Binding events of target QD‐biotin conjugates with streptavidin probes immobilized on the pore walls are monitored by reflective interferometric spectroscopy and fluorescence measurements. QD labeling of the target biotin molecules enables detection based on a distinct fluorescent signal as well as a greater than 5‐fold enhancement in the measured spectral reflectance fringe shift and a nearly three order of magnitude improvement in the detection limit for only 6% surface area coverage of QDs inside the porous matrix. Utilizing the QD signal amplifiers, an exceptional biotin detection limit of ≈6 fg mm^?2 is demonstrated with sub‐fg mm^?2 detection limits achievable.     

周期性多孔低介电常数材料机械特性的表面波测量模型

研究了纳米通孔的分布对于表面波方法测量多孔低介电常数薄膜机械特性的影响,提出了用横观各向同性表征周期性多孔介质材料结构特性的表面波传播理论模型,给出了表面波在low-k薄膜/Si基底分层结构中的传播方程.通过数值算例揭示出表面波在不同传播方向的频散特性,以及low-k薄膜的弹性常数即杨氏模量E,E'和剪切模量G'对频散特性的影响.结果表明E'和G'在垂直于通孔的传播方向不能被测出.     

Dramatic Morphology Control in the Fabrication of Porous Polymer Films

Highly ordered, porous honeycomb films are prepared by the breath‐figure (BF) technique using dendron‐functionalized star polymers as precursors. By changing the nature of the dendritic end groups, dramatically different porous morphologies can be produced. Three series of star polymers are prepared with both the size of the 2,2‐bis(methoxy)propionic acid (bis‐MPA)‐based dendron end group and the dendron functionality being varied. Star polymers end‐functionalized with acetonide‐protected dendrons (generations 1 to 4) are initially prepared and the acetonide groups subsequently deprotected to yield hydroxyl‐functionalized star polymers. Modification of these hydroxyl groups with pentadecafluorooctanoyl chloride yields a third series of functionalized star polymers. The resulting star polymers have surface groups with very different polarity and by utilizing these star polymers to form honeycomb films by the BF technique, the morphology produced is dramatically different. The star polymers with amphiphilic character afford interconnected porous morphologies with multiple layers of pores. The star polymers with pentadecafluorooctanoyl end groups show highly ordered monolayers of pores with extremely thin walls and represent a new porous morphology that has previously not been reported. The ability to prepare libraries of different dendronized star polymers has given further insights into the BF technique and allows the final porous morphology to be controllably tuned utilizing the functional chain ends and generation number of the dendronized star polymers.