Foam Template Research Articles

Flexible, conductive, and highly pressure-sensitive graphene-polyimide foam for pressure sensor application

Three-dimensional porous graphene foams have received increasing attention in the fields of sensors, flexible conductors, and energy storage. Mechanical stability, flexibility, and electrical conductivity are prerequisites for materials used in these fields. In this paper, novel polyimide-based graphene foam was prepared by dip-coating a polyimide foam template followed by chemical reduction and thermal reduction. The prepared foam displayed excellent mechanical stability and flexibility (elastic modulus: ∼5 kPa). The synergistic effects of chemical and thermal reduction led to a foam with high electrical conductivity of ∼0.4 S m−1. By controlling the dip-coating times, the foam achieved a high pressure sensitivity of 0.36 kPa−1. Experiments show that the prepared foam can be used as effective pressure sensor to measure heartbeat, joint activity, and airflow.

Carbon-bonded alumina foam filters produced by centrifugation: A route towards improved homogeneity

An alternative route for producing carbon-bonded alumina filters was analyzed and compared with the state of the art, both based on the replica method. The latter comprises a dip coating and subsequent rolling and spraying steps (R+S). The proposed route is based on dip coating and centrifugation (CF-T1). Aiming to investigate the influence of an additional thermal treatment on the ceramic coating homogeneity, a modified centrifugation route was analyzed (CF-T2). Computer tomography (CT) analyses provided a targeted evaluation of the spatial material distribution after each processing step. It was found that log-normal functions fitted well the wall thickness values attained for all investigated filters. Qualitative surface evaluation was conducted using a digital (optical) microscope. The R+S and CF-T1 filters exhibited surface macro-cracks and hollow struts, due to the release of the polyurethane foam template during firing. The CF-T2 presented partly filled struts with a high amount of micro-cracks on the surface, being a potential alternative to increase the filtration efficiency, as the filter surface area was raised. However, in preliminary mechanical tests, the surface micro-cracks seemed to considerably reduce the cold crushing strength of the CF-T2 filters. Based on the CT data, it was possible to conclude that the centrifuged filters presented a more homogeneous material distribution, as a consequence of higher automation level of the process.

Enhanced specific surface area and thermal conductivity in ultrathin graphite foams grown by chemical vapor deposition on sintered nickel powder templates

The specific surface area and effective thermal conductivity of ultrathin graphite foams (UGFs) grown by chemical vapor deposition (CVD) have been limited by the large pore sizes of reticulated nickel foam templates. Here we show that nickel templates formed by sintering of low-cost nickel powder can reduce pore size and increase specific surface area. Accordingly, the effective density of a free-stranding graphite foam grown on the high-surface area templates can be increased by an order of magnitude relative to one grown on a reticulated nickel foam template. This increase is accomplished without increasing the thickness of the CVD graphite or decreasing the structural quality of the graphite. Based on experiments with nickel powder with and without the reticulated nickel template present, we found that both the particle size and sintering temperature influenced template morphology. Because of a 68-times increase in the volumetric specific surface area of a graphite foam synthesized on a sacrificial sintered powder template compared to a UGF grown on a reticulated template, we have been able to increase the relative graphite density and effective thermal conductivity from 0.87 ± 0.09% to 8.4 ± 0.3% and from 2.1 ± 0.3 Wm−1K−1 to 16.3 ± 1.1 Wm−1K−1, respectively.

One‐Step In Situ Synthesis of Three‐Dimensional NiSb Thin Films as Anode Electrode Material for the Advanced Sodium‐Ion Battery

A low‐cost, facile and highly efficient in situ solvothermal reaction has been developed for the first time to synthesize, by using a 3D Ni foam template, three‐dimensional nickel‐antimony (3D NiSb) thin films as anode electrode materials for use in sodium‐ion batteries (SIBs). The structure design and preparation have proved reasonable and efficient, leading to excellent electrochemical properties. At current densities of 100, 200 and 400 mA g–1, specific capacities of 643.8, 520.5 and 378.6 mA h g–1, respectively, could be obtained. Additionally, a specific capacity of 420 mA h g–1 could be achieved after 100 cycles at a current density of 100 mA g–1. This could be attributed to the special 3D binder‐free conductive network connecting the NiSb nanoparticles and the 3D contact area with the electrolyte, which is beneficial for the charge‐transfer kinetics and electrochemical performance. Moreover, the porous structure offers enough space to alleviate the volume changes and stress generated in the sodiation/desodiation process. Most importantly, the 3D porous Ni foam, as a support for NiSb nanoparticles, can effectively prevent the agglomeration of the NiSb and Na3Sb nanoparticles. Therefore, such a unique NiSb anode material may be of great significance in next‐generation energy storage devices.

Generation of Solid Foams with Controlled Polydispersity Using Microfluidics.

Many properties of solid foams depend on the distribution of the pore sizes and their organization in space. However, these two parameters are very difficult to control with most traditional foaming techniques. Here we show how microfluidics can be used to tune the polydispersity of the foams (mono- vs different polydispersities) and the spatial organization of the pores (ordered vs disordered). For this purpose, the microfluidic flow-focusing technique was modified such that the gas pressure oscillates periodically, which translates into periodically oscillating bubble sizes in the liquid foam template. The liquid foams were generated from chitosan solutions and then gelled via cross-linking with genipin before we freeze-dried them to obtain a solid foam with a specific structure. The study at hand fills two existing scientific gaps. On the one hand, we present a novel approach for the generation of foams with controlled polydispersity. On the other hand, we obtained a solid foam with a new structure for foam templating consisting of rhombic dodecahedra. The controlled variation of the foam's structure will allow studying systematically structure-property relations. Moreover, being fully biobased, this type of solid foam is a suitable candidate for applications in tissue engineering.

Preparation and thermal insulation analysis of SiCw-SiC foam with hollow skeletons via carbon foam template CVI method

SiCw-SiC foams with hollow skeleton were synthesized by a simple procedure that consisted of the chemical vapor infiltration (CVI) and oxidation process. Flexible carbon foam was employed as CVI template. A typical structure of SiCw-SiC foams consisting of SiC supporter with hollow skeleton structure accompanying numerous crooked SiC whiskers was obtained after burning out carbon skeleton of the carbon foam during oxidation process. SiCw-SiC foams have a density of 0.11≤ρ≤0.12g/cm3, porosity ≥96% and a thermal conductivity at room temperature between 0.040 and 0.075W/m·K. Thermal conductivity of the SiCw-SiC foams moderately increased with elevation of temperature, indicating that these foams with larger amount of whiskers exhibit excellent thermal insulation property at elevated temperature.

Me-ZSM-5 monolith foams for the NH3-SCR of NO

Self-supported ZSM-5 zeolite monolith foams (ZMFs) with different Si/Al ratios have been successfully prepared by hydrothermal synthesis with a polyurethane foam (PUF) template followed by calcination in air at 550 °C to harden. Cu or Mn have been introduced on preformed ZMF samples to obtain monolithic catalysts that have been fully characterized by morphological (XRD and SEM), textural (BET and pore size distribution), mechanical (compressive strength) and chemical (ICP-MS) analyses, and eventually tested in the Selective Catalytic Reduction of NO with NH3 in the temperature range 100–450 °C. The zeolite monolith foams are characterized by a well crystallized ZSM-5 structure, a BET surface area ca. 420 m2 g−1 and remarkable mechanical resistance even without any binder. Those structured catalysts show specific catalytic activity in line with powdered counterparts, but they can guarantee improved NO conversion due to the higher amount of catalyst per unit volume of reactor and to their superior mass transfer coefficients coupled to low internal diffusion limitations.

Fluoroalkyl-silane-modified 3D graphene foam with improved Joule-heating effects and high hydrophobicity-derived anti-icing properties

A fluoroalkyl-silane (FS)-modified three-dimensional (3D) graphene foam (GF) composite (FS-GF) with a hierarchical porous microstructure was fabricated via a nickel foam template chemical vapor deposition and followed modification. The 3D GF, as an electrically conductive framework and hydrophobic porous substrate, was grafted with FS to further improve the hydrophobicity due to its long non-polar molecular chains and numerous fluoric/silicon functional groups. Porous FS-GF with high electrical conductivity (~650 S/m) is functionalized as a Joule-heating mesh for airflow, which synchronously demonstrates rapid heating rates, high conversion efficiencies, and uniform temperature distributions. Moreover, FS-GF exhibits self-cleaning and anti-icing properties that are superior to metallic and inorganic coatings. The outstanding performances of FS-GF suggest the potential for functionalizing 3D graphene composites using hierarchical structures at the multi-scale and chemical modifications of functional molecular groups.

Ni-Co nanoparticles immobilized on a 3D Ni foam template as a highly efficient catalyst for borohydride electrooxidation in alkaline medium

Proton exchange membrane (PEM) fuel cells have drawn a great deal of attention due to the rapidly growing energy consumption. Recently, Ni- and Co-based materials have been considered as promising electorcatalysts owing to their multi-functionality. In this work, Ni and Co nanoparticles are directly immobilized on a three-dimensional Ni foam substrate (Ni-Co/NF) without any conductive agents or polymer binder by a facile ion implantation method. The structure and morphology of the Ni-Co/NF electrode were characterized by scanning electron microscopy, powder X-ray diffraction, and X-ray photoelectron spectroscopy. The performance of the Ni-Co/NF electrode in the electrochemical oxidation of NaBH4 is investigated by cyclic voltammetry and chronoamperometry. The Ni-Co/NF electrode exhibited excellent electrocatalytic activity and good stability during electrochemical reactions. These properties are attributed to the 3D porous structure of the Ni foam and the synergistic effect of Ni and Co nanoparticles. The enhanced electrocatalytic performance in NaBH4 electrooxidation compared with either Ni or Co nanoparticles alone suggests that the Ni-Co/NF is promising for fuel cell applications.

Fabrication of 3D graphene foam for a highly conducting electrode

A large number of pitting pits were formed on the surface of Ni foam by immersion corrosion in NaCl solution. The graphene was deposited on Ni foam templates, then 3D graphene foams were obtained by removing Ni foam in the mixed solution of ferric chloride and hydrochloric acid. It was found that pitting pits on Ni foam facilitated to form fewer-layers graphene, however, pitting pits on Ni foam induced more defects on 3D graphene foam. The graphene with fewer-layers exhibited better electrical and mechanical properties for strain sensor devices. Moreover, fewer-layers graphene effectively inhibited degradation of resistance during cycling stability tests.

Well-Ordered Oxygen-Deficient CoMoO4 and Fe2O3 Nanoplate Arrays on 3D Graphene Foam: Toward Flexible Asymmetric Supercapacitors with Enhanced Capacitive Properties.

In this work, we report the development of well-ordered hydrogenated CoMoO4 (H-CoMoO4) and hydrogenated Fe2O3 (H-Fe2O3) nanoplate arrays on 3D graphene foam (GF) and explore their practice application as binder-free electrodes in assembling flexible all-solid-state asymmetric supercapacitor (ASC) devices. Our results show that the monolithic 3D porous GF prepared by solution casting method using Ni foam template possesses large surface area, superior electrical conductivity, and sufficient surface functional groups, which not only facilitate in situ growth of CoMoO4 and Fe2O3 nanoplates but also contribute the double-layer capacitance of the resultant supercapacitor. The well-ordered pseudocapacitive metal oxide nanoplate arrays standing up on 3D GF scaffold can provide efficient space and shorten the length for electrolyte diffusion from the outer to the inner region of the electrode material for Faradaic energy storage. Furthermore, one of our major findings is that the introduction of oxygen vacancies in CoMoO4 and Fe2O3 nanoplates by hydrogenation treatment can increase their electronic conductivity as well as improve their donor density and surface properties, which gives rise to a substantially improved electrochemical performance. Benefiting from the synergistic contributions of different components in the nanohybrid electrode, the resultant flexible ASC device with GF/H-CoMoO4 as the positive electrode and GF/H-Fe2O3 as the negative electrode achieves a wide operation voltage of 1.5 V and a maximum volumetric specific capacitance of 3.6 F cm-3, which is two times larger than that of the Ni/GF/CoMoO4//Ni/GF/Fe2O3 device (1.8 F cm-3), and the rate capability is up to 70% as the current density increases from 2 to 200 mA cm-3. Moreover, the Ni/GF/H-CoMoO4//Ni/GF/H-Fe2O3 device also exhibits a high energy density of 1.13 mWh cm-3 and a high power density of 150 mW cm-3, good mechanical flexibility with the decrease in capacitance of less than 4% after being bent inward to different angles and inward to 90° 200 times, and good cycling stability of 93.1% capacitance retention after 5000 cycles.

Linear organodecaborane block copolymer as a single-source precursor for porous boron carbide ceramics

Boron carbide is one of the most widely used non-oxide ceramics as it possesses excellent physical and chemical properties. Much attention has been paid to prepare boron carbide ceramics via precursor derived method. In this work, poly(6-norbornenyldecaborane)-b-poly(6-cyclooctenyldecaborane) (PND-b-PCD) block copolymer was synthesized by the ruthenium-catalyzed ring-opening metathesis polymerization (ROMP) of 6-norbornenyldecaborane with 6-cyclooctenyldecaborane. The synthesized boron carbide preceramic polymer had good solubility and film-forming ability with a high ceramic yield of 75% at 850°C. TGA, XRD and TG-IR-GC–MS were used to investigate the ceramization process of the precursor. Boron carbide ceramic foams were prepared by the precursor via replicating polyurethane foam template. The component, crystalline and morphology were investigated in detail. The ceramic foams showed a good high temperature performance and could keep their structure even up to 1800°C.

Fabrication and characterization of ZrC foam by melt infiltration

A new ultra-high temperature ceramic foam was developed with carbon foam template and zirconium alloy by adopting melt infiltration in this work. The obtained ZrC foam was highly macro-porous with low density and open cell structure, in which the pore diameter ranged from 400 to 520 μm with a mean value of 465 μm. Microstructural formation mechanism of the ZrC foam by infiltration was analyzed. With an open porosity of 75.38% and a density of 1.35 g/cm3, the composite foam possessed a high compressive strength of 26.5 ± 6.28 MPa. Moreover, the thermal conductivity of ZrC foam ranged from 40.411 W m−1 K−1 to 9.102 W m−1 K−1 from ambient to 1200 °C.

Porous Materials with Tunable Structure and Mechanical Properties via Templated Layer-by-Layer Assembly.

The deposition of stiff and strong coatings onto porous templates offers a novel strategy for fabricating macroscale materials with controlled architectures at the micro- and nanoscale. Here, layer-by-layer assembly is utilized to fabricate nanocomposite-coated foams with highly customizable properties by depositing polymer-nanoclay coatings onto open-cell foam templates. The compressive mechanical behavior of these materials evolves in a predictable manner that is qualitatively captured by scaling laws for the mechanical properties of cellular materials. The observed and predicted properties span a remarkable range of density-stiffness space, extending from regions of very soft elastomer foams to very stiff, lightweight honeycomb and lattice materials.

Hydroxypropyl methylcellulose and methylcellulose structured oil as a replacement for shortening in sandwich cookie creams

The partial and full substitution of icing shortening with freeze dried hydroxypropyl methylcellulose (HPMC) and methylcellulose (MC) structured canola oil in sandwich cookie cream was investigated. The cellulose derivatives were prepared using a foam templating approach and incorporated as a shortening replacer in food applications. Treatments were formulated with a 40 wt% fat component and 60 wt% icing sugar, with icing shortening being replaced at 50, 75, and 100% with HPMC- or MC-structured canola oil. These treatments were compared to a 100% shortening control and commercial sandwich cookie cream as an industry benchmark. Shelf life of cookie creams was effectively improved with increasing level of shortening replacement; the amount of unbound oil decreased as a higher amount of oil adsorbed to the surface of added polymer sheets. It was found that the shortening control resulted in highly sticky and gummy creams, while shortening replacement at 50 and 75% gave similar large deformation textural properties as the commercial benchmark. Full replacement resulted in creams that were excessively hard. The storage modulus of creams were used as an interpretation of stiffness, and showed that shortening replacement increased stiffness to match the commercial benchmark. As a rheological fingerprint, nonlinear, large amplitude oscillatory shear Lissajous plots were used to show differences among samples at stresses beyond the linear regime. Based on these results, it was found that cookie creams with desirable functional behaviour can be made by replacing shortening with HPMC- and MC-structured canola oil at intermediate levels.

Osteoconductivity and Bioresorption of an Interconnecting Porous Carbonate Apatite with Enhanced Mechanical Strength

We have established a processing method to fabricate three - dimensional porous carbonate apatite (CO3Ap) with interconnected porous structure and improved mechanical strength. Briefly, porous CO3Ap materials were produced via phosphorization of porous calcite precursor in hydrothermal condition. In order to make porous calcite precursor, negative replication of modified polyurethane foam template was conducted. In this study, an in vivo behavior of that porous CO3Ap was evaluated. The interconnected porous CO3Ap material was implanted in the tibia of Japanese male rabbits and removed after a period of 6 months. Micro-computed tomography (μ-CT) scanner and histological analysis were used to characterize the bone formation response of the porous CO3Ap. The results suggest that porous CO3Ap with enhanced mechanical strength was not only osteoconductive but also bioresorbable therefore it could be used as bone substitute material.

Monolithic porous carbon materials prepared from polyurethane foam templates

Monolithic carbon foams with hierarchical porosity were prepared from polyurethane templates and resol precursors. Mesoporosity was achieved through the use of soft templating with surfactant Pluronic F127, and macroporosity from the polyurethane foams was retained. Conditions to obtain high porosity materials were optimized. The best materials have high specific surface areas (380 and 582 m2 g–1, respectively) and high electrical conductivity, which make them good candidates for supports in sensors. These materials showed an almost linear dependence between the potential and the pH of aqueous solutions.

Tailoring properties of reticulated vitreous carbon foams with tunable density

Reticulated vitreous carbon (RVC) foams were manufactured by multiple replications of a polyurethane foam template structure using ethanolic solutions of phenolic resin. The aims were to create an algorithm of fine tuning the precursor foam density and ensure an open-cell reticulated porous structure in a wide density range. The precursor foams were pyrolyzed in inert atmospheres at 700°C, 1100°C and 2000°C, and RVC foams with fully open cells and tunable bulk densities within 0.09–0.42 g/cm3 were synthesized. The foams were characterized in terms of porous structure, carbon lattice parameters, mechanical properties, thermal conductivity, electric conductivity, and corrosive resistance. The reported manufacturing approach is suitable for designing the foam microstructure, including the strut design with a graded microstructure.

Correlation between porous texture and cell seeding efficiency of gas foaming and microfluidic foaming scaffolds

In the design of scaffolds for tissue engineering applications, morphological parameters such as pore size, shape, and interconnectivity, as well as transport properties, should always be tailored in view of their clinical application. In this work, we demonstrate that a regular and ordered porous texture is fundamental to achieve an even cell distribution within the scaffold under perfusion seeding. To prove our hypothesis, two sets of alginate scaffolds were fabricated using two different technological approaches of the same method: gas-in-liquid foam templating. In the first one, foam was obtained by insufflating argon in a solution of alginate and a surfactant under stirring. In the second one, foam was generated inside a flow-focusing microfluidic device under highly controlled and reproducible conditions. As a result, in the former case the derived scaffold (GF) was characterized by polydispersed pores and interconnects, while in the latter (μFL), the porous structure was highly regular both with respect to the spatial arrangement of pores and interconnects and their monodispersity. Cell seeding within perfusion bioreactors of the two scaffolds revealed that cell population inside μFL scaffolds was quantitatively higher than in GF. Furthermore, seeding efficiency data for μFL samples were characterized by a lower standard deviation, indicating higher reproducibility among replicates. Finally, these results were validated by simulation of local flow velocity (CFD) inside the scaffolds proving that μFL was around one order of magnitude more permeable than GF.

Effect of Using Different Compositions and PU Foam Template to Produce Cobalt Chromium Molybdenum (CoCrMo) Foams

Slurry dipping is a simple and popular method of producing porous and interconnected foams using a metallic slurry. The advantage of the network-like metal foams is it exhibits a natural bone-like structure which enables ingrowth of bone cells and blood vessels. The aim of the present study was to investigate the effect of using difference composition and scaffold to produce Cobalt Chromium Molybdenum (CoCrMo) foams. The CoCrMo slurry was prepared by using different composition of CoCrMo powder which was 60wt%, 65wt% and 70wt%. Also two different types of scaffold were used in this study. The CoCrMo slurry was produced by mixing CoCrMo powder with Polyethylene Glycol (PEG), Carboxyl Methyl Cellulose (CMC) and distilled water. Then, polyurathane foam template was dipped in CoCrMo slurry and dried at room temperature. Sintering process was running by vacuum furnace at high temperature, 1200°C. The CoCrMo foam was characterized by using a Scanning Electron Microscopy (SEM) analysis. The physical properties of CoCrMo foam was analyzed by porosity and bulk density test that was Archimedes method. From the study it was expected that the composition of metallic slurry play important roles to produce a CoCrMo foam. In order to orthopaedics application to apply in cancellous bone, highest value of porosity from PU foams type (a) was most suitable result to use. This is due to the value of porosity that generate that was 65.2%.