Flexible Porous Materials Research Articles

Molecular simulation of capillary phase transitions in flexible porous materials.

We used flat-histogram sampling Monte Carlo to study capillary phase transitions in deformable adsorbent materials. Specifically, we considered a pure adsorbate fluid below its bulk critical temperature within a slit pore of variable pore width. The instantaneous pore width is dictated by a number of factors, such as adsorbate loading, reservoir pressure, fluid-wall interaction, and bare adsorbent properties. In the slit pores studied here, the bare adsorbent free energy was assumed to be biparabolic, consisting of two preferential pore configurations, namely, the narrow pore and the large pore configurations. Four distinct phases could be found in the adsorption isotherms. We found a low-pressure phase transition, driven primarily by capillary condensation/evaporation and accompanied by adsorbent deformation in response. The deformation can be a relatively small contraction/expansion as seen in elastic materials, or a large-scale structural transformation of the adsorbent. We also found a high-pressure transition driven by excluded volume effects, which tends to expand the material and thus results in a large-scale structural transformation of the adsorbent. The adsorption isotherms and osmotic free energies can be rationalized by considering the relative free energy differences between the basins of the bare adsorbent free energy.

A Cooperative Pillar–Template Strategy as a Generalized Synthetic Method for Flexible Homochiral Porous Frameworks

AbstractA new strategy for creating homochiral metal–organic frameworks through a fusion of pillaring and templating concepts is demonstrated. This strategy makes use of the synergy among various chemical interactions during self‐assembly processes, and leads to the synthesis of a series of homochiral frameworks. In the presence of only pillar‐to‐pillar π–π interactions, inter‐pillar forces compete against metal–pillar interactions, resulting in mismatch between pillar‐to‐pillar and metal‐to‐metal separations and consequently 2D materials without pillaring. To create 3D materials, a method was developed to use various aromatic molecules, polycyclic aromatic hydrocarbons in particular, as templates to modulate the inter‐pillar interaction and separation, leading to the formation of 3D homochiral frameworks. The use of aromatic molecules, especially hydrocarbons, as structure‐directing agents, represents a new approach in the development of crystalline porous materials. Aromatic templates can be post‐synthetically extracted to yield flexible porous homochiral materials with gate‐opening gas sorption behaviors for both N2 and CO2 at partial pressures tunable by temperature.

A Cooperative Pillar-Template Strategy as a Generalized Synthetic Method for Flexible Homochiral Porous Frameworks.

A new strategy for creating homochiral metal-organic frameworks through a fusion of pillaring and templating concepts is demonstrated. This strategy makes use of the synergy among various chemical interactions during self-assembly processes, and leads to the synthesis of a series of homochiral frameworks. In the presence of only pillar-to-pillar π-π interactions, inter-pillar forces compete against metal-pillar interactions, resulting in mismatch between pillar-to-pillar and metal-to-metal separations and consequently 2D materials without pillaring. To create 3D materials, a method was developed to use various aromatic molecules, polycyclic aromatic hydrocarbons in particular, as templates to modulate the inter-pillar interaction and separation, leading to the formation of 3D homochiral frameworks. The use of aromatic molecules, especially hydrocarbons, as structure-directing agents, represents a new approach in the development of crystalline porous materials. Aromatic templates can be post-synthetically extracted to yield flexible porous homochiral materials with gate-opening gas sorption behaviors for both N2 and CO2 at partial pressures tunable by temperature.

Bioinspired nanoparticle spray-coating for superhydrophobic flexible materials with oil/water separation capabilities

Much of the inspiration for the creation of superhydrophobic surfaces has come from nature, from plants such as the sacred lotus (Nelumbo nucifera), where the micro-scale papillae epidermal cells on the surfaces of the leaves are covered with nano-scale epicuticular wax crystalloids. The combination of the surface roughness and the hydrophobic wax coating produces a superhydrophobic wetting state on the leaves, allowing them to self-clean and easily shed water. Here, a simple scaled-up carbon nanoparticle spray coating is presented that mimics the surface of sacred lotus leaves and can be applied to a wide variety of materials, complex structures, and flexible substrates, rendering them superhydrophobic, with contact angles above 160°. The sprayable mixture is produced by combining toluene, polydimethylsiloxane, and inherently hydrophobic rapeseed soot. The ability to spray the superhydrophobic coating allows for the hydrophobisation of complex structures such as metallic meshes, which allows for the production of flexible porous superhydrophobic materials that, when formed into U-shaped channels, can be used to direct flows. The porous meshes, whilst being superhydrophobic, are also oleophilic. Being both superhydrophobic and oleophilic allows oil to pass through the mesh, whilst water remains on the surface. The meshes were tested for their ability to separate mixtures of oil and water in flow conditions. When silicone oil/water mixtures were passed over the meshes, all meshes tested were capable of separating more than 93% of the oil from the mixture.

Further proof for the theory of elastic sound absorption about flexible porous materials

A new theory about porous materials has evolved in recent years, and it differs from traditional theories to a large extent. In this paper, by referring to documents to test the new theory experimentally and theoretically, we make analysis of the relationship between thickness of porous materials and the frequency of incident sound wave, so as to further discuss about the new theory. Results prove that the new sound absorption theory is of great significance in the sound absorption mechanism of porous material and very useful in practical application.

Further proof for the theory of elastic sound absorption about flexible porous materials

A new theory about porous materials has evolved in recent years, and it differs from traditional theories to a large extent. In this paper, by referring to documents to test the new theory experimentally and theoretically, we make analysis of the relationship between thickness of porous materials and the frequency of incident sound wave, so as to further discuss about the new theory. Results prove that the new sound absorption theory is of great significance in the sound absorption mechanism of porous material and very useful in practical application.

Microstructure Design of Lightweight, Flexible, and High Electromagnetic Shielding Porous Multiwalled Carbon Nanotube/Polymer Composites.

Multiwalled carbon nanotube/polymer composites with aligned and isotropic micropores are constructed by a facile ice-templated freeze-drying method in a wide density range, with controllable types and contents of the nanoscale building blocks, in order to tune the shielding performance together with the considerable mechanical and electrical properties. Under the mutual promotion of the frame and porous structure, the lightweight high-performance shielding is achieved: a 2.3 mm thick sample can reach 46.7 and 21.7 dB in the microwave X-band while the density is merely 32.3 and 9.0 mg cm-3 , respectively. The lowest density corresponds to a value of shielding effectiveness divided by both the density and thickness up to 104 dB cm2 g-1 , far beyond the conductive polymer composites with other fillers ever reported. The shielding mechanism of the flexible porous materials is further demonstrated by an in situ compression experiment.

Biomass-derived flexible porous carbon materials and their applications in supercapacitor and gas adsorption

In this work, biomass-related fabrics (cotton, cotton–flax, and flax fabrics) were used as precursors to synthesize a series of flexible porous carbon materials through simple carbonization at different temperatures. The porosities of these materials were then studied in detail. Physicochemical and texture properties, such as morphology, elemental composition, degree of structural order, and functional group, were also comprehensively characterized to supply basic information with regard to the utilization of these materials. Furthermore, flexible heteroatom-doped porous carbon materials were obtained through a “dipping and drying” process. Given that these biomass-derived carbon materials are flexible and porous, the applications of these materials as flexible and free-standing electrodes in supercapacitors and gas adsorbents were investigated.

Superhydrophobic melamine sponge with excellent surface selectivity and fire retardancy for oil absorption

Flexible porous materials have been widely used as precursors for preparing superhydrophobic oil absorbents due to their high capacity and extraordinary recyclability. A final product with multiple characteristics such as superhydrophobicity, fire retardancy, good elasticity, low cost, and environmental friendliness is highly needed for practical applications. In this study, superhydrophobic melamine sponges (SMSs) with the above characteristics were prepared by modifying melamine sponges with polymethylsilsesquioxane via an immersion method. A villiform layer of organosilane was coated on the surface of the melamine fibers and disclosed by scanning electron microscopy. The superhydrophobicity of the sponge with a water contact angle of 156° is due to the increased surface roughness and methyl terminal groups exposed at the interface. Polycondensation reaction between the secondary amine groups on the raw sponge surface and silanol is identified by ATR-FTIR and EDX spectra. The SMS effectively absorbs various organic solvents and oils from water with excellent absorption rate. In addition, it maintains stable superhydrophobicity in extreme environments, including strong acid/alkali conditions, high/low temperatures, and prolonged immersion in organic solvents. Importantly, the SMS retains the intrinsic fire retardancy of the raw melamine sponge. In simulating oil spill environments, the SMS shows good performance in blocking spread of crude oil spill and separating surfactant-free water-in-oil emulsions. These advantages make it a promising material for oily wastewater treatment and oil spill clean-ups.

Active through-mask electrochemical machining with its interelectrode gap filled with flexible porous material

It has been one of issues that conventional through-mask electrochemical machining is very hard to fabricate surface texture efficiently on the non-planar workpiece. To solve this problem, a modified active through-mask electrochemical machining process (active TM-ECM) with its interelectrode gap filled with flexible porous material was proposed on the basis of development of a special tool cathode. The newly developed tool cathode allows for inlet and distributing of electrolyte as well as discharging of solution. The flow field within the interelectrode was analyzed and optimized numerically, and the effects of key process parameters including mask thickness, flexible porous layer thickness, clamping force and pulsed current parameter on the geometric profiles and their distributing characteristics of the machined microdimple were investigated experimentally. The arrays of microdimples with a fairly good distribution of geometric dimensions were successfully machined on both the stainless steel planar substrate and cylindrical workpiece by using the optimal process conditions. It is showed that the modified active TM-EMM process exhibits favorable machinability and applicability to produce microdimples on the planar and non-planar surfaces.

Superior thermoelasticity and shape-memory nanopores in a porous supramolecular organic framework.

Flexible porous materials generally switch their structures in response to guest removal or incorporation. However, the design of porous materials with empty shape-switchable pores remains a formidable challenge. Here, we demonstrate that the structural transition between an empty orthorhombic phase and an empty tetragonal phase in a flexible porous dodecatuple intercatenated supramolecular organic framework can be controlled cooperatively through guest incorporation and thermal treatment, thus inducing empty shape-memory nanopores. Moreover, the empty orthorhombic phase was observed to exhibit superior thermoelasticity, and the molecular-scale structural mobility could be transmitted to a macroscopic crystal shape change. The driving force of the shape-memory behaviour was elucidated in terms of potential energy. These two interconvertible empty phases with different pore shapes, that is, the orthorhombic phase with rectangular pores and the tetragonal phase with square pores, completely reject or weakly adsorb N2 at 77 K, respectively.

Transformation of iron oxides on PI electrospun membranes

Iron oxides/PI fiber membranes, especially magnetic PI membranes, are important flexible porous materials available application in the field of wave absorption, magnetic recording, membrane separation and catalysts. Therefore, α-Fe2O3 loaded PI composite fibers were prepared by electrospinning of poly(amic acid) PAA solution followed by loading Fe3+ on the PAA membrane by ion-exchange and then imidization. Then the α-Fe2O3 on PI membrane were reduced by H2 to give magnetic PI membranes. The content of α-Fe2O3 and Fe3O4 on PI can be controlled by adjustment the ion-exchange time. The saturation magnetization of the composite membranes can reach up to 4emu/g and the final composite membranes have magnetic response ability.

Solution blowing of thermoplastic polyurethane nanofibers: A facile method to produce flexible porous materials

ABSTRACTSolution blowing (SB) is a promising and scalable approach for the production of nanofibers. Air pressure, solution flow‐rate, and nozzle‐collector distance were determined as effective process parameters, while solution concentration was also reported as a material parameter. Here we performed a parametric study on thermoplastic polyurethane/dimethyl formamide (TPU/DMF) solutions to examine the effect of such parameters on the resultant properties such as fiber diameter, diameter distribution, porosity, and air permeability of the nanofibrous webs. The obtained solution blown thermoplastic polyurethane (TPU) nanofibers had average diameter down to 170 ± 112 nm, which is similar to that observed in electrospinning. However, the production rate per nozzle can be 20 times larger, which is primarily dependent on air pressure and solution flow rate (20 mL/h). Moreover, it was even possible to produce nanofibers polymer concentrations of 20%; however, this increased the average nanofiber diameter. The fibers produced from the TPU/DMF solutions at concentrations of 20% and 10% had average diameters of 671 ± 136 nm and 170 ± 112 nm, respectively. SB can potentially be used for the industrial‐scale production of products such as nanofibrous filters, protective textiles, scaffolds, wound dressings, and battery components. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43025.

Direct Guest Exchange Induced Single-Crystal to Single-Crystal Transformation Accompanying Irreversible Crystal Expansion in Soft Porous Coordination Polymers

Two flexible porous coordination materials, [Mn(pybimc)2]·2H2O·G (G = toluene, 1tol; THF, 1thf), where pybimc = 2-(2′-pyridyl)-benzimidazole-5-carboxylate, featuring identical one-dimensional chain structure have been characterized. Guest exchange studies have exhibited that 1tol cannot be converted to 1thf through direct replacement of guest toluene molecules by THF molecules, but, of particular interest, 1thf is actually converted to 1tol and 1aromatic (where aromatic = o-, m-, p-xylene) upon the exchange of THF to toluene and other aromatic molecules, respectively. This signifies a single-crystal to single-crystal transformation accompanied irreversible crystal expansion. In-depth analyses reveal that the nature of the weak yet sufficiently strong framework–guest C–H···π interactions, rather than the guest size, observed in this system plays a key role in guiding the adsorption of liquid-phase aromatics in the soft crystalline materials.

Fabrication of Micro-Dimple Arrays Using Modified Through-Mask Electrochemical Micromachining

It has been found that well-defined surface textures (such as micro-dimple arrays, micro groove arrays) can reduce friction, wear and improve heat transfer, fluid motion state effectively. To produce micro-dimple arrays on the metal surface with a high efficiency and low cost, this paper proposed a modified through-mask electrochemical micromachining method with flexible porous material filled in the interelectrode gap. The feasibility of the process and the most important process factor which affects the depth of the micro-dimple were investigated by orthogonal experiments. The results showed that micro-dimple arrays can be obtained efficiently using both direct current (DC) and pulsed current and the qualities of the micro-dimples generated by pulsed power were much better than those formed by DC. Electrolyte concentration was the most important factor that affected the depth of the micro-dimple in the selected process parameters.

Molecular simulation of gas adsorption and diffusion in a breathing MOF using a rigid force field.

Simulation of gas adsorption in flexible porous materials is still limited by the slow progress in the development of flexible force fields. Moreover, the high computational cost of such flexible force fields may be a drawback even when they are fully developed. In this work, molecular simulations of gas adsorption and diffusion of carbon dioxide and methane in NH2-MIL-53(Al) are carried out using a linear combination of two crystallographic structures with rigid force fields. Once the interactions of carbon dioxide molecules and the bridging hydroxyls groups of the framework are optimized, an excellent match is found for simulations and experimental data for the adsorption of methane and carbon dioxide, including the stepwise uptake due to the breathing effect. In addition, diffusivities of pure components are calculated. The pore expansion by the breathing effect influences the self-diffusion mechanism and much higher diffusivities are observed at relatively high adsorbate loadings. This work demonstrates that using a rigid force field combined with a minimum number of experiments, reproduces adsorption and simulates diffusion of carbon dioxide and methane in the flexible metal-organic framework NH2-MIL-53(Al).

Liquid balance monitoring inside conventional, Retrofit, and bio-reactor landfill cells

The Outer Loop landfill bioreactor (OLLB) in Louisville, KY, USA has been the site of a study to evaluate long-term bioreactor performance at a full-scale operational landfill. Three types of landfill units were studied including a conventional landfill (Control cell), a new landfill area that had an air addition and recirculation piping network installed as waste was being placed (As-Built cell), and a conventional landfill that was modified to allow for liquids recirculation (Retrofit cell). During the monitoring period, the Retrofit, Control, and As-Built cells received 48, 14, and 213LMg−1 (liters of liquids per metric ton of waste), respectively. The leachate collection system yielded 60, 57 and 198LMg−1 from the Retrofit, Control, and As-Built cells, respectively. The head on liner in all cells was below regulatory limits. In the Control and As-Built cells, leachate head on liner decreased once waste placement stopped. The measured moisture content of the waste samples was consistent with that calculated from the estimate of accumulated liquid by the liquid balance. Additionally, measurements on excavated solid waste samples revealed large spatial variability in waste moisture content. The degree of saturation in the Control cells decreased from 85% to 75%. The degree of saturation increased from 82% to 83% due to liquids addition in the Retrofit cells and decreased back to 80% once liquid addition stopped. In the As-Built cells, the degree of saturation increased from 87% to 97% during filling activities and then started to decrease soon after filling activities stopped to reach 92% at the end of the monitoring period. The measured leachate generation rates were used to estimate an in-place saturated hydraulic conductivity of the MSW in the range of 10−8 to 10−7ms−1 which is lower than previous reports. In the Control and Retrofit cells, the net loss in liquids, 43 and 12LMg−1, respectively, was similar to the measured settlement of 15% and 5–8% strain, respectively (Abichou et al., 2013). The increase in net liquid volume in the As-Built cells indicates that the 37% (average) measured settlement strain in these cells cannot be due to consolidation as the waste mass did not lose any moisture but rather suggests that settlement was attributable to lubrication of waste particle contacts, softening of flexible porous materials, and additional biological degradation.

Preliminary Research on Damping Material Composed of Flexible Porous Material and Liquid

This paper presents a new type of damping material composed of flexible porous material such as polyurethane foam and liquid such as water. This new type of damping material costs less than viscoelastic materials such as Sorbothane, and is anticipated to have a better damping effect. At the same time, installation of the new type of damping material is as easy as that of usual viscoelastic materials. The damping effect of this material on the vibration of a cantilever iron plate is experimentally compared with the one of a viscoelastic material. The damping effect on a rail piece with a length of 1.2m and a weight of 72kg is also experimentally investigated. The experimental results show a good damping effect. The design variables of this new damping material such as the liquid viscosity and the hardness of the porous material are thought to influence the damping effect, consequently are investigated by carrying out vibration testing of a cantilever iron plate (material:SS400, size:300×440×5mm, weight:5.2kg).

有機アルコキシシランを用いた柔軟多孔体の開発

有機アルコキシシランを用いた柔軟多孔体の開発

531 柔軟多孔質材と液体による制振材開発のための基礎的研究(制振材・非線形減衰,OS-3 ダンピング,総合テーマ「伝統を,未来へ!」)

This paper presents a new type of damping material composed of flexible porous material and liquid. Lower cost and better damping effect are anticipated for the new damping material rather than viscoelastic materials. The damping effect of the new damping material on the vibration of an iron plate is experimentally compared with that of a viscoelastic material. The damping effect of the new material on a rail piece (length of 1.2m) is also investigated. Finally, the influence of some design variables for the damping effect, such as liquid viscosity, is investigated experimentally.