Research

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17 pages, 6228 KiB

Open AccessArticle

The Role of APTES as a Primer for Polystyrene Coated AA2024-T3

by John Halford IV and Cheng-fu Chen

Micromachines 2024, 15(1), 93; https://doi.org/10.3390/mi15010093 - 31 Dec 2023

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(3-Aminopropyl)triethoxysilane (APTES) silane possesses one terminal amine group and three ethoxy groups extending from each silicon atom, acting as a crucial interface between organic and inorganic materials. In this study, after APTES was deposited on the aluminum alloy AA2024-T3 as a primer for [...] Read more.

(3-Aminopropyl)triethoxysilane (APTES) silane possesses one terminal amine group and three ethoxy groups extending from each silicon atom, acting as a crucial interface between organic and inorganic materials. In this study, after APTES was deposited on the aluminum alloy AA2024-T3 as a primer for an optional top coating with polystyrene (PS), its role with regard to stability as a protection layer and interaction with the topcoat were studied via combinatorial experimentation. The aluminum alloy samples primed with APTES under various durations of concentrated vapor deposition (20, 40, or 60 min) with an optional post heat treatment and/or PS topcoat were comparatively characterized via electrochemical impedance spectroscopy (EIS) and surface energy. The samples top-coated with PS on an APTES layer primed for 40 min with a post heat treatment revealed excellent performance regarding corrosion impedance. A primed APTES surface with higher surface energy accounted for this higher corrosion impedance. Based on the SEM images and the surface energy calculated from the measured contact angles on the APTES-primed surfaces, four mechanisms are suggested to explain that the good protection performance of the APTES/PS coating system can be attributed to the enhanced wettability of PS on the cured APTES primer with higher surface energy. The results also suggest that, in the early stages of exposure to the corrosion solution, a thinner APTES primer (deposited for 20 min) enhances protection against corrosion, which can be attributed to the hydrolytic stability and hydrolyzation/condensation of the soaked APTES and the dissolution of the naturally formed aluminum oxide pre-existing in the bare samples. An APTES primer subjected to additional heat treatment will increase the impedance of the coating system significantly. APTES, and silanes, in general, used as adherent agents or surface modifiers, have a wide range of potential applications in micro devices, as projected in the Discussion section. Full article

(This article belongs to the Special Issue Nanomaterials for Micro/Nano Devices)

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18 pages, 3653 KiB

Open AccessArticle

Comparison of PDMS and NOA Microfluidic Chips: Deformation, Roughness, Hydrophilicity and Flow Performance

by Tatiana Turcitu, Curtis J. K. Armstrong, Niko Lee-Yow, Maya Salame, Andy Vinh Le and Marianne Fenech

Micromachines 2023, 14(11), 2033; https://doi.org/10.3390/mi14112033 - 31 Oct 2023

Viewed by 1060

Abstract

Microfluidic devices are frequently manufactured with polydimethylsiloxane (PDMS) due to its affordability, transparency, and simplicity. However, high-pressure flow through PDMS microfluidic channels lead to an increase in channel size due to the compliance of the material. As a result, longer response times are [...] Read more.

Microfluidic devices are frequently manufactured with polydimethylsiloxane (PDMS) due to its affordability, transparency, and simplicity. However, high-pressure flow through PDMS microfluidic channels lead to an increase in channel size due to the compliance of the material. As a result, longer response times are required to reach steady flow rates, which increases the overall time required to complete experiments when using a syringe pump. Due to its excellent optical properties and increased rigidity, Norland Optical Adhesive (NOA) has been proposed as a promising material candidate for microfluidic fabrication. This study compares the compliance and deformation properties of three different characteristic sized (width of parallel channels: 100, 40 and 20 µm) microfluidic devices made of PDMS and NOA. The comparison of the microfluidics devices is made based on the Young’s modulus, roughness, contact angle, channel width deformation, flow resistance and compliance. The experimental resistance is estimated through the measurement of the flow at a given pressure and a precision flow meter. The characteristic time of the system is extracted by fitting the two-element resistance-compliance (RC) hydraulic circuit model. The compliance of the microfluidics chips is estimated through the measurement of the characteristic time required for channels to achieve an output flow rate equivalent to that of the input flow rate using a syringe pump and a precision flow meter. The Young modulus was found to be 2 MPa for the PDMS and 1743 MPa for the NOA 63. The surface roughness was found to be higher for the NOA 63 than for the PDMS. The hydrophilicities of materials were found comparable with and without plasma treatment. The results show that NOA devices have lower compliance and deformation than PDMS devices. Full article

(This article belongs to the Special Issue Nanomaterials for Micro/Nano Devices)

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18 pages, 7106 KiB

Open AccessArticle

Commercially Accessible High-Performance Aluminum-Air Battery Cathodes through Electrodeposition of Mn and Ni Species on Fuel Cell Cathodes

by Paloma Almodóvar, Belén Sotillo, David Giraldo, Joaquín Chacón, Inmaculada Álvarez-Serrano and María Luisa López

Micromachines 2023, 14(10), 1930; https://doi.org/10.3390/mi14101930 - 14 Oct 2023

Viewed by 1143

Abstract

This study presents a cost-effective method for producing high-performance cathodes for aluminum-air batteries. Commercial fuel cell cathodes are modified through electrodeposition of nickel and manganese species. The optimal conditions for electrodeposition are determined using a combination of structural (Raman, SEM, TEM) and electrochemical [...] Read more.

This study presents a cost-effective method for producing high-performance cathodes for aluminum-air batteries. Commercial fuel cell cathodes are modified through electrodeposition of nickel and manganese species. The optimal conditions for electrodeposition are determined using a combination of structural (Raman, SEM, TEM) and electrochemical (LSV, EI, discharge curves) characterization techniques. The structural analysis confirms successful incorporation of nickel and manganese species onto the cathode surface. Electrochemical tests demonstrate enhanced electrochemical activity compared to unmodified cathodes. By combining the favorable properties of electrodeposited manganese species with nickel species, a high-performance cathode is obtained. The developed cathode exhibits capacities of 50 mA h cm⁻² in aluminum-air batteries across a wide range of current densities. The electrodeposition method proves effective in improving electrochemical performance. A key advantage of this method is its simplicity and cost-effectiveness. The use of commercially available materials and well-established electrodeposition techniques allows for easy scalability and commercialization. This makes it a viable option for large-scale production of high-performance cathodes for the next-generation energy storage devices. Full article

(This article belongs to the Special Issue Nanomaterials for Micro/Nano Devices)

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15 pages, 3302 KiB

Open AccessArticle

A Novel Approach for Identifying Nanoplastics by Assessing Deformation Behavior with Scanning Electron Microscopy

by Jared S. Stine, Nicolas Aziere, Bryan J. Harper and Stacey L. Harper

Micromachines 2023, 14(10), 1903; https://doi.org/10.3390/mi14101903 - 05 Oct 2023

Cited by 2 | Viewed by 1567

Abstract

As plastic production continues to increase globally, plastic waste accumulates and degrades into smaller plastic particles. Through chemical and biological processes, nanoscale plastic particles (nanoplastics) are formed and are expected to exist in quantities of several orders of magnitude greater than those found [...] Read more.

As plastic production continues to increase globally, plastic waste accumulates and degrades into smaller plastic particles. Through chemical and biological processes, nanoscale plastic particles (nanoplastics) are formed and are expected to exist in quantities of several orders of magnitude greater than those found for microplastics. Due to their small size and low mass, nanoplastics remain challenging to detect in the environment using most standard analytical methods. The goal of this research is to adapt existing tools to address the analytical challenges posed by the identification of nanoplastics. Given the unique and well-documented properties of anthropogenic plastics, we hypothesized that nanoplastics could be differentiated by polymer type using spatiotemporal deformation data collected through irradiation with scanning electron microscopy (SEM). We selected polyvinyl chloride (PVC), polyethylene terephthalate (PET), and high-density polyethylene (HDPE) to capture a range of thermodynamic properties and molecular structures encompassed by commercially available plastics. Pristine samples of each polymer type were chosen and individually milled to generate micro and nanoscale particles for SEM analysis. To test the hypothesis that polymers could be differentiated from other constituents in complex samples, the polymers were compared against proxy materials common in environmental media, i.e., algae, kaolinite clay, and nanocellulose. Samples for SEM analysis were prepared uncoated to enable observation of polymer deformation under set electron beam parameters. For each sample type, particles approximately 1 µm in diameter were chosen, and videos of particle deformation were recorded and studied. Blinded samples were also prepared with mixtures of the aforementioned materials to test the viability of this method for identifying near-nanoscale plastic particles in environmental media. Based on the evidence collected, deformation patterns between plastic particles and particles present in common environmental media show significant differences. A computer vision algorithm was also developed and tested against manual measurements to improve the usefulness and efficiency of this method further. Full article

(This article belongs to the Special Issue Nanomaterials for Micro/Nano Devices)

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14 pages, 5064 KiB

Open AccessArticle

Fabrication and Characterization of Dielectric ZnCr₂O₄ Nanopowders and Thin Films for Parallel-Plate Capacitor Applications

by Vasyl Mykhailovych, Gabriel Caruntu, Adrian Graur, Mariia Mykhailovych, Petro Fochuk, Igor Fodchuk, Gelu-Marius Rotaru and Aurelian Rotaru

Micromachines 2023, 14(9), 1759; https://doi.org/10.3390/mi14091759 - 12 Sep 2023

Viewed by 834

Abstract

We report here the successful shape-controlled synthesis of dielectric spinel-type ZnCr₂O₄ nanoparticles by using a simple sol-gel auto-combustion method followed by successive heat treatment steps of the resulting powders at temperatures from 500 to 900 °C and from 5 to [...] Read more.

We report here the successful shape-controlled synthesis of dielectric spinel-type ZnCr₂O₄ nanoparticles by using a simple sol-gel auto-combustion method followed by successive heat treatment steps of the resulting powders at temperatures from 500 to 900 °C and from 5 to 11 h, in air. A systematic study of the dependence of the morphology of the nanoparticles on the annealing time and temperature was performed by using field effect scanning electron microscopy (FE-SEM), powder X-ray diffraction (PXRD) and structure refinement by the Rietveld method, dynamic lattice analysis and broadband dielectric spectrometry, respectively. It was observed for the first time that when the aerobic post-synthesis heat treatment temperature increases progressively from 500 to 900 °C, the ZnCr₂O₄ nanoparticles: (i) increase in size from 10 to 350 nm and (ii) develop well-defined facets, changing their shape from shapeless to truncated octahedrons and eventually pseudo-octahedra. The samples were found to exhibit high dielectric constant values and low dielectric losses with the best dielectric performance characteristics displayed by the 350 nm pseudo-octahedral nanoparticles whose permittivity reaches a value of ε = 1500 and a dielectric loss tan δ = 5 × 10⁻⁴ at a frequency of 1 Hz. Nanoparticulate ZnCr₂O₄-based thin films with a thickness varying from 0.5 to 2 μm were fabricated by the drop-casting method and subsequently incorporated into planar capacitors whose dielectric performance was characterized. This study undoubtedly shows that the dielectric properties of nanostructured zinc chromite powders can be engineered by the rational control of their morphology upon the variation of the post-synthesis heat treatment process. Full article

(This article belongs to the Special Issue Nanomaterials for Micro/Nano Devices)

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15 pages, 4732 KiB

Open AccessArticle

A Highly Efficient Electromagnetic Wave Absorption System with Graphene Embedded in Hybrid Perovskite

by Haitao Yu, Hui Liu, Yao Yao, Ziming Xiong, Lei Gao, Zhiqian Yang, Wenke Zhou and Zhi Zhang

Micromachines 2023, 14(8), 1611; https://doi.org/10.3390/mi14081611 - 16 Aug 2023

Cited by 6 | Viewed by 836

Abstract

To cope with the explosive increase in electromagnetic radiation intensity caused by the widespread use of electronic information equipment, high-performance electromagnetic wave (EMW)-absorbing materials that can adapt to various frequency bands of EMW are also facing great demand. In this paper, CH₃ [...] Read more.

To cope with the explosive increase in electromagnetic radiation intensity caused by the widespread use of electronic information equipment, high-performance electromagnetic wave (EMW)-absorbing materials that can adapt to various frequency bands of EMW are also facing great demand. In this paper, CH₃NH₃PbI₃/graphene (MG) high-performance EMW-absorbing materials were innovatively synthesized by taking organic–inorganic hybrid perovskite (OIHP) with high equilibrium holes, electron mobility, and accessible synthesis as the main body, graphene as the intergranular component, and adjusting the component ratio. When the component ratio was 16:1, the thickness of the absorber was 1.87 mm, and MG’s effective EMW absorption width reached 6.04 GHz (11.96–18.00 GHz), achieving complete coverage of the Ku frequency band. As the main body of the composite, CH₃NH₃PbI₃ played the role of the polarization density center, and the defects and vacancies in the crystal significantly increased the polarization loss intensity; graphene, as a typical two-dimensional material distributed in the crystal gap, built an efficient electron transfer channel, which significantly improved the electrical conductivity loss strength. This work effectively broadened the EMW absorption frequency band of OIHP and promoted the research process of new EMW-absorbing materials based on OIPH. Full article

(This article belongs to the Special Issue Nanomaterials for Micro/Nano Devices)

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9 pages, 2294 KiB

Open AccessCommunication

A Flexible Supercapacitor Based on Niobium Carbide MXene and Sodium Anthraquinone-2-Sulfonate Composite Electrode

by Guixia Wang, Zhuo Yang, Xinyue Nie, Min Wang and Xianming Liu

Micromachines 2023, 14(8), 1515; https://doi.org/10.3390/mi14081515 - 28 Jul 2023

Viewed by 915

Abstract

MXene-based composites have been widely used in electric energy storage device. As a member of MXene, niobium carbide (Nb₂C) is a good electrode candidate for energy storage because of its high specific surface area and electronic conductivity. However, a pure Nb [...] Read more.

MXene-based composites have been widely used in electric energy storage device. As a member of MXene, niobium carbide (Nb₂C) is a good electrode candidate for energy storage because of its high specific surface area and electronic conductivity. However, a pure Nb₂C MXene electrode exhibits limited supercapacitive performance due to its easy stacking. Herein, sodium anthraquinone-2-sulfonate (AQS) with high redox reactivity was employed as a tailor to enhance the accessibility of ions and electrolyte and enhance the capacitance performance of Nb₂C MXene. The resulting Nb₂C–AQS composite had three-dimensional porous layered structures. The supercapacitors (SCs) based on the Nb₂C–AQS composite exhibited a considerably higher electrochemical capacitance (36.3 mF cm⁻²) than the pure Nb₂C electrode (16.8 mF cm⁻²) at a scan rate of 20 mV s⁻¹. The SCs also exhibited excellent flexibility as deduced from the almost unchanged capacitance values after being subjected to bending. A capacitance retention of 99.5% after 600 cycles was observed for the resulting SCs, indicating their good cycling stability. This work proposes a surface modification method for Nb₂C MXene and facilitates the development of high-performance SCs. Full article

(This article belongs to the Special Issue Nanomaterials for Micro/Nano Devices)

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Review

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30 pages, 6046 KiB

Open AccessReview

Recent Achievements for Flexible Encapsulation Films Based on Atomic/Molecular Layer Deposition

by Buyue Zhang, Zhenyu Wang, Jintao Wang and Xinyu Chen

Micromachines 2024, 15(4), 478; https://doi.org/10.3390/mi15040478 - 30 Mar 2024

Viewed by 562

Abstract

The purpose of this paper is to review the research progress in the realization of the organic–inorganic hybrid thin-film packaging of flexible organic electroluminescent devices using the PEALD (plasma-enhanced atomic layer deposition) and MLD (molecular layer deposition) techniques. Firstly, the importance and application [...] Read more.

The purpose of this paper is to review the research progress in the realization of the organic–inorganic hybrid thin-film packaging of flexible organic electroluminescent devices using the PEALD (plasma-enhanced atomic layer deposition) and MLD (molecular layer deposition) techniques. Firstly, the importance and application prospect of organic electroluminescent devices in the field of flexible electronics are introduced. Subsequently, the principles, characteristics and applications of PEALD and MLD technologies in device packaging are described in detail. Then, the methods and process optimization strategies for the preparation of organic–inorganic hybrid thin-film encapsulation layers using PEALD and MLD technologies are reviewed. Further, the research results on the encapsulation effect, stability and reliability of organic–inorganic hybrid thin-film encapsulation layers in flexible organic electroluminescent devices are discussed. Finally, the current research progress is summarized, and the future research directions and development trends are prospected. Full article

(This article belongs to the Special Issue Nanomaterials for Micro/Nano Devices)

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57 pages, 16061 KiB

Open AccessReview

Nature-Inspired Superhydrophobic Coating Materials: Drawing Inspiration from Nature for Enhanced Functionality

by Subodh Barthwal, Surbhi Uniyal and Sumit Barthwal

Micromachines 2024, 15(3), 391; https://doi.org/10.3390/mi15030391 - 13 Mar 2024

Viewed by 1314

Abstract

Superhydrophobic surfaces, characterized by exceptional water repellency and self-cleaning properties, have gained significant attention for their diverse applications across industries. This review paper comprehensively explores the theoretical foundations, various fabrication methods, applications, and associated challenges of superhydrophobic surfaces. The theoretical section investigates the [...] Read more.

Superhydrophobic surfaces, characterized by exceptional water repellency and self-cleaning properties, have gained significant attention for their diverse applications across industries. This review paper comprehensively explores the theoretical foundations, various fabrication methods, applications, and associated challenges of superhydrophobic surfaces. The theoretical section investigates the underlying principles, focusing on models such as Young’s equation, Wenzel and Cassie–Baxter states, and the dynamics of wetting. Various fabrication methods are explored, ranging from microstructuring and nanostructuring techniques to advanced material coatings, shedding light on the evolution of surface engineering. The extensive applications of superhydrophobic surfaces, spanning from self-cleaning technologies to oil–water separation, are systematically discussed, emphasizing their potential contributions to diverse fields such as healthcare, energy, and environmental protection. Despite their promising attributes, superhydrophobic surfaces also face significant challenges, including durability and scalability issues, environmental concerns, and limitations in achieving multifunctionality, which are discussed in this paper. By providing a comprehensive overview of the current state of superhydrophobic research, this review aims to guide future investigations and inspire innovations in the development and utilization of these fascinating surfaces. Full article

(This article belongs to the Special Issue Nanomaterials for Micro/Nano Devices)

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93 pages, 12590 KiB

Open AccessReview

Bio-Inspired Nanomaterials for Micro/Nanodevices: A New Era in Biomedical Applications

by Mohammad Harun-Ur-Rashid, Israt Jahan, Tahmina Foyez and Abu Bin Imran

Micromachines 2023, 14(9), 1786; https://doi.org/10.3390/mi14091786 - 18 Sep 2023

Cited by 5 | Viewed by 4950

Abstract

Exploring bio-inspired nanomaterials (BINMs) and incorporating them into micro/nanodevices represent a significant development in biomedical applications. Nanomaterials, engineered to imitate biological structures and processes, exhibit distinctive attributes such as exceptional biocompatibility, multifunctionality, and unparalleled versatility. The utilization of BINMs demonstrates significant potential in [...] Read more.

Exploring bio-inspired nanomaterials (BINMs) and incorporating them into micro/nanodevices represent a significant development in biomedical applications. Nanomaterials, engineered to imitate biological structures and processes, exhibit distinctive attributes such as exceptional biocompatibility, multifunctionality, and unparalleled versatility. The utilization of BINMs demonstrates significant potential in diverse domains of biomedical micro/nanodevices, encompassing biosensors, targeted drug delivery systems, and advanced tissue engineering constructs. This article thoroughly examines the development and distinctive attributes of various BINMs, including those originating from proteins, DNA, and biomimetic polymers. Significant attention is directed toward incorporating these entities into micro/nanodevices and the subsequent biomedical ramifications that arise. This review explores biomimicry’s structure–function correlations. Synthesis mosaics include bioprocesses, biomolecules, and natural structures. These nanomaterials’ interfaces use biomimetic functionalization and geometric adaptations, transforming drug delivery, nanobiosensing, bio-inspired organ-on-chip systems, cancer-on-chip models, wound healing dressing mats, and antimicrobial surfaces. It provides an in-depth analysis of the existing challenges and proposes prospective strategies to improve the efficiency, performance, and reliability of these devices. Furthermore, this study offers a forward-thinking viewpoint highlighting potential avenues for future exploration and advancement. The objective is to effectively utilize and maximize the application of BINMs in the progression of biomedical micro/nanodevices, thereby propelling this rapidly developing field toward its promising future. Full article

(This article belongs to the Special Issue Nanomaterials for Micro/Nano Devices)

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