Hydrophilic polymer foam and microsphere templates for fabrication of microcellular nickel and graphene foams with energy storage applications

Hydrophilic polymer foam and microsphere templates have attracted tremendous attentions in the past decade due to their applicability in numerous areas such as catalyst carriers and mini-reactors, filtration media, carbon foam fabrication templates, thermal and electrical insulators, and tissue engineering scaffolds. Hydrophilic polymer sphere and foam templates can be used to fabricate microcellular nickel foams and graphene foams that are finding unique opportunities in energy storage applications, including battery electrodes and matrices for solar energy storage. In this study open celled hydrophilic polymer foams and microsphere templates with controllable pore size and porosity were fabricated via solid state foaming and vacuum-assisted assembling methods. Hydrophilic polymer foams were fabricated with disulfonated poly(arylene ether sulfone) (BPS) and poly(ethylene glycol) (PEG) miscible blends. Polymer microsphere templates made with PMMA, paraffin, and EAA spheres were used as templates for fabricating bulk nickel foams, which were further used as a template to fabricate graphene foams. In order to achieve bulk microcellular nickel and graphene foams, a novel electro-polishing-assisted electroless nickel (Ni) deposition process was developed to mitigate the diffusion limitation problem. Fundamental mechanisms of the proposed process were studied using a finite difference model considering both ion diffusion and chemical reaction inside the porous media. The fabricated microcellular Ni foams exhibited sufficient thermal stability and were used to fabricate three dimensional (3D) few-layer-graphene (FLG) foams using a chemical vapor deposition (CVD) method. The resulting graphene foams had a pore size less than 100 μm, density of 0.0020 g·cm⁻³, and strut wall thickness of 5 nm. The surface-to-volume ratio of the foam was 2.5×10⁵ m²·m⁻³.Materials Science and Engineerin

Electroless Deposition of Nanolayered Metallic Coatings

Electroless metallic coating is referred as the deposition of a substrate material by the process of chemical or autocatalytic reduction of aqueous metal ions deposited to a substrate material without any external supply of power. Electroless nickel alloys are generally considered synonymous to the word “electroless coating” as ~90% of productions in industries are of this alloy coating. Rest of the electroless metallic coatings includes gold, copper, palladium, cobalt, silver, etc. These electroless metallic coatings (other than electroless nickel coatings) are also one of the vibrant areas in the field of materials properties and surface engineering research. From the year 2000 to till date, nearly 1000 SCI indexed research papers were published on this topic. However, no comprehensive studies about the recent progress on this topic were reported elsewhere so far. In this context, the present chapter aims to give a complete overview on various aspects of the rest of the electroless metallic nanocoatings/layer as a whole. More importance will be on the recent developments of the nanocharacteristics and future scopes

Fabrication and functionalization of PCB gold electrodes suitable for DNA-based electrochemical sensing

The request of high specificity and selectivity sensors suitable for mass production is a constant demand in medical research. For applications in point-of-care diagnostics and therapy, there is a high demand for low cost and rapid sensing platforms. This paper describes the fabrication and functionalization of gold electrodes arrays for the detection of deoxyribonucleic acid (DNA) in printed circuit board (PCB) technology. The process can be implemented to produce efficiently a large number of biosensors. We report an electrolytic plating procedure to fabricate low-density gold microarrays on PCB suitable for electrochemical DNA detection in research fields such as cancer diagnostics or pharmacogenetics, where biosensors are usually targeted to detect a small number of genes. PCB technology allows producing high precision, fast and low cost microelectrodes. The surface of the microarray is functionalized with self-assembled monolayers of mercaptoundodecanoic acid or thiolated DNA. The PCB microarray is tested by cyclic voltammetry in presence of 5 mM of the redox probe K3Fe(CN6) in 0.1 M KCl. The voltammograms prove the correct immobilization of both the alkanethiol systems. The sensor is tested for detecting relevant markers for breast cancer. Results for 5 nM of the target TACSTD1 against the complementary TACSTD1 and non-complementary GRP, MYC, SCGB2A1, SCGB2A2, TOP2A probes show a remarkable detection limit of 0.05 nM and a high specificity

Catastrophic vs Gradual Collapse of Thin-Walled Nanocrystalline Ni Hollow Cylinders As Building Blocks of Microlattice Structures

Lightweight yet stiff and strong lattice structures are attractive for various engineering applications, such as cores of sandwich shells and components designed for impact mitigation. Recent breakthroughs in manufacturing enable efficient fabrication of hierarchically architected microlattices, with dimensional control spanning seven orders of magnitude in length scale. These materials have the potential to exploit desirable nanoscale-size effects in a macroscopic structure, as long as their mechanical behavior at each appropriate scale – nano, micro, and macro levels – is properly understood. In this letter, we report the nanomechanical response of individual microlattice members. We show that hollow nanocrystalline Ni cylinders differing only in wall thicknesses, 500 and 150 nm, exhibit strikingly different collapse modes: the 500 nm sample collapses in a brittle manner, via a single strain burst, while the 150 nm sample shows a gradual collapse, via a series of small and discrete strain bursts. Further, compressive strength in 150 nm sample is 99.2% lower than predicted by shell buckling theory, likely due to localized buckling and fracture events observed during in situ compression experiments. We attribute this difference to the size-induced transition in deformation behavior, unique to nanoscale, and discuss it in the framework of “size effects” in crystalline strength

Advances in nanomaterials integration in CMOS-based electrochemical sensors: a review

The monolithic integration of electrochemical sensors with instrumentation electronics on semiconductor technology is a promising approach to achieve sensor scalability, miniaturization and increased signal to noise ratio. Such an integration requires post-process modification of microchips (or wafers) fabricated in standard semiconductor technology (e.g. CMOS) to develop sensitive and selective sensing electrodes. This review focuses on the post-process fabrication techniques for addition of nanomaterials to the electrode surface, a key component in the construction of electrochemical sensors that has been widely used to achieve surface reactivity and sensitivity. Several CMOS-compatible techniques are summarized and discussed in this review for the deposition of nanomaterials such as gold, platinum, carbon nanotubes, polymers and metal oxide/nitride nanoparticles. These techniques include electroless deposition, electro-chemical deposition, lift-off, micro-spotting, dip-pen lithography, physical adsorption, self-assembly and hydrothermal methods. Finally, the review is concluded and summarized by stating the advantages and disadvantages of these deposition methods

Development of a Novel Electroless Plating Approach for Coating Aluminum (Al) on Multi-Walled Carbon Nanotubes (MWCNTs) and Investigating their Use in Reinforcing Cast and Powder Compacted Aluminum Composites

Due to their superior mechanical properties, Aluminum-Carbon Nanotube (Al-CNT) composites have been widely investigated by various researchers using several processing techniques. One of the most successful techniques in creating Al-CNT composites is the ball milling technique followed by hot compaction and hot extrusion for powder consolidation. However, this technique has some drawbacks including the limited design flexibility of the produced parts, the high initial cost of milling equipment, and the damage of CNTs during milling that has been reported to take place due to the harsh impact of milling balls on CNTs leading to the formation of brittle Al4C3 phases in the aluminum matrix with the increase of milling time. Therefore, researchers have investigated simple, cheap and flexible casting techniques in producing Al-CNT composites. However, it was found that CNTs are not wettable in molten aluminum due to the big difference in surface tension between them. Besides, CNTs have a lower condensed phase density than aluminum. Therefore, they tend to form segregations in the aluminum matrix that hinder the mechanical properties of the entire composite. Therefore, some researchers have experimented coating CNTs with metals by electroless plating to modify their surface characteristics and make them wettable with molten aluminum. However, these metallic coats were found to have a misleading alloying effect on the aluminum matrix that made the investigation of CNTs addition on aluminum not viable. In the current study, a novel aluminum electroless plating approach was developed and made it possible to cover CNTs with a nano-crystalline layer of pure aluminum at room temperature. The Al-coated CNTs are used as a reinforcement phase for pure aluminum without introducing any alloying elements. Previously, aluminum electroless plating in aqueous solutions represented an impossible challenge due to the high electrode potential of aluminum (-1.66 E(V)) that lies outside the electrochemical window (EW) of water. Therefore, limited number of trials have been made towards developing room temperature ionic liquids (RTILs) of a wide EW suitable for aluminum electroless plating. Researchers have focused on expensive RTILs such as AlCl3-EMIC that has a wide electrochemical window allowing aluminum to be deposited without decomposing the ionic compound. However, due to the high surface area to volume ratio of CNTs, they require a larger volume of the RTIL to be electroless plated. This could put Al-coated CNTs at a tremendously high cost of production. Therefore, the current study focused on finding an alternative cost effective RTIL for aluminum electroless plating by modifying AlCl3-Urea battery electrolyte. This modification was done by adjusting the molar ratio of AlCl3-Urea from 1.3:1 to 2:1 in addition to adding lithium aluminum hydride (LAH) as a reducing agent. The electrochemical window of the new electrolyte was measured against a standard Ag/Ag+ electrode and reported to be wider than the requirement of aluminum plating. This modified RTIL was used to coat MWCNTs (10 nm diameter) by aluminum in 3 steps starting by catalyzing CNTs using colloidal palladium-stannous (Pd-Sn) nanoparticles in a single step followed by an acceleration step in a group of acids to remove excess stannous hydroxide Sn(OH)2 from the surface of Pd-Sn particles. Finally, electroless plating of Al on CNTs was done in the developed RTIL. Electron microscopy imaging revealed that CNTs had up to 160 nm increase in their thickness after deposition indicating the formation of Al-coat on their surfaces. Energy dispersive X-ray (EDX) analysis along with the X-ray diffraction (XRD) pattern confirmed the presence of crystalline Al on the surface of CNTs. The Raman analysis revealed that CNTs did not undergo any damage during the chemical coating process as the D-band to the G-band intensity ratio of Al-coated CNTs did not differ from the one reported for the as-received CNTs. The prepared Al-CNT powders were used to reinforce pure aluminum using both the casting and hot compaction techniques such that the overall percent of CNTs in the final composite were 2% by weight in each sample. The XRD of bulk samples detected the presence of all the crystallographic planes of aluminum in addition to small spikes of Al4C3 in both cast and powder compacted samples. Raman analysis showed that a small increase in the D-band took place in both the cast and the hot compacted samples. However, the D-band was higher in the hot compacted sample than in the cast sample. Mechanical properties of the obtained Al-CNT composites were investigated for both the hot compacted-hot extruded samples and the cast samples. The coated layer of aluminum on CNTs resulted in excellent dispersion and wettability of CNTs in the cast sample reflected on the homogeneous mechanical properties obtained with a minimal standard error (SE) and on the SEM fractography imaging obtained for each sample. The mechanical testing showed an increase of 353.4 %, 338.7 %, and 266.1 % in the tensile strength, Vickers hardness, and nanoindentation hardness of the reinforced cast sample in addition to an increase of 164.8 %, 147.2 %, and 165.8 % of the same properties for the hot compacted-hot extruded reinforced samples respectively. These promising results will open the road for producing low cost, design flexible, and fast to produce Al-CNT composites with enhanced mechanical properties