Micro

8 pages, 2622 KiB

Open AccessArticle

Spongy-Network-like Polyaniline Thin Films as Electrodes for a Supercapacitor

by P. M. Kharade, J. V. Thombare, S. S. Dhasade, S. S. Deokar, D. J. Salunkhe, Mohaseen S. Tamboli and Santosh S. Patil

Micro 2022, 2(3), 541-548; https://doi.org/10.3390/micro2030035 - 19 Sep 2022

Cited by 2 | Viewed by 1720

Abstract

An easy and cost-effective route is demonstrated to grow spongy-network-like polyaniline (SpN-PANI) thin films on stainless steel (SS) by galvanostatic electrodeposition. Through X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM) characterizations, the physicochemical properties of the SpN-PANI thin [...] Read more.

An easy and cost-effective route is demonstrated to grow spongy-network-like polyaniline (SpN-PANI) thin films on stainless steel (SS) by galvanostatic electrodeposition. Through X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM) characterizations, the physicochemical properties of the SpN-PANI thin films were fine-tuned for supercapacitor application. The hydrophilic nature of SpN-PANI thin films was examined by using contact angle measurements. Next, the capacitive behavior of the SpN-PANI thin film was assessed by using cyclic voltammetry (CV), galvanostatic charging-discharging (GCD), and electrochemical impedance spectroscopy (EIS). Specifically, these results show that SpN-PANI thin films can exhibit a maximum specific capacitance of 580 F.g⁻¹ at a scan rate of 5 mV.s⁻¹ in a 0.5 M Na₂SO₄ electrolyte solution, as well as superior cycling stability (84% capacity retention after 1000 cycles). Thus, the strategy presented here can be applicable to produce a SpN-PANI-based thin film which has prospects as an active electrode material for supercapacitor devices. Full article

(This article belongs to the Section Microscale Engineering)

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17 pages, 7905 KiB

Open AccessArticle

Rheological and Aesthetical Properties of Polyolefin Composites for Flame Retardant Cables with High Loading of Mineral Fillers

by Sara Haveriku, Michela Meucci, Marco Badalassi, Camillo Cardelli and Andrea Pucci

Micro 2022, 2(3), 524-540; https://doi.org/10.3390/micro2030034 - 02 Sep 2022

Viewed by 1820

Abstract

It was found that the use of natural magnesium hydroxide (n–MDH) as mineral filler in EVA based composites provided mechanical and rheological properties that did not completely comply with the halogen-free flame-retardant (HFFR) cables parameters. Moreover, the use of n–MDH mostly gave a [...] Read more.

It was found that the use of natural magnesium hydroxide (n–MDH) as mineral filler in EVA based composites provided mechanical and rheological properties that did not completely comply with the halogen-free flame-retardant (HFFR) cables parameters. Moreover, the use of n–MDH mostly gave a rough grey surface in the compound extruded by rheometry capillary. In contrast, with the use of synthetic material (s–MDH), a combination of better outcomes was observed. Mechanical and rheological properties were more aligned with the application, and the aesthetics were also improved, i.e., the surface was smooth and whiter. Therefore, with the aim of obtaining good aesthetical quality on the extrudate, we studied formulations by varying the type of polymer matrix and using a mixture of the natural magnesium hydroxide combined with other kind of fillers (in a 3:1 ratio using as main filler n–MDH). On this account, we found a synergistic effect in the mechanical, rheological, and aesthetic properties for the filler blend system containing n–MDH in combination with s–MDH or Böhmite AlO(OH), or using a secondary polymer belonging to the polybutene family combined with EVA. Full article

(This article belongs to the Special Issue State-of-the-Art Microscale and Nanoscale Researches in Italy)

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11 pages, 3236 KiB

Open AccessArticle

Experimental Characterization of Water Condensation Processes on Self-Assembled Monolayers Using a Quartz Crystal Microbalance with Energy Dissipation Monitoring

by Subin Song, Glenn Villena Latag, Evan Angelo Quimada Mondarte, Ryongsok Chang and Tomohiro Hayashi

Micro 2022, 2(3), 513-523; https://doi.org/10.3390/micro2030033 - 29 Aug 2022

Cited by 3 | Viewed by 1930

Abstract

Water condensation on solid surfaces is a universal phenomenon that plays an essential role in many interfacial phenomena, such as friction, corrosion, adsorption, etc. Thus far, the initial states of water condensation on surfaces with varying chemical properties have yet to be fully [...] Read more.

Water condensation on solid surfaces is a universal phenomenon that plays an essential role in many interfacial phenomena, such as friction, corrosion, adsorption, etc. Thus far, the initial states of water condensation on surfaces with varying chemical properties have yet to be fully explained at the nanoscale. In this study, we performed a real-time characterization of water condensation on self-assembled monolayers (SAMs) with different functional groups using quartz crystal microbalance with energy dissipation monitoring (QCM-D). We found that the kinetics of water condensatison is critically dependent on the head group chemistries. We discovered that the condensed water’s viscoelasticity cannot be predicted from macroscopic water contact angles, but they were shown to be consistent with the predictions of molecular simulations instead. In addition, we also found a highly viscous interfacial water layer on hydrophilic protein-resistant SAMs. In contrast, the interfacial water layer/droplet on either hydrophilic protein-adsorbing or hydrophobic SAMs exhibited lower viscosity. Combining our and previous findings, we discuss the influence of interfacial hydration on the viscoelasticity of condensed water. Full article

(This article belongs to the Special Issue Microsystem and Nanosystem Researches for Sensors, Actuators and Energy Conversion Devices)

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5 pages, 1993 KiB

Open AccessCommunication

Anisotropic and Isotropic Shrinking of Candle Droplets in Cold Water and Warm Water

by An-Xin Xie, Nicole Rendine and Hai-Feng Ji

Micro 2022, 2(3), 508-512; https://doi.org/10.3390/micro2030032 - 29 Aug 2022

Cited by 1 | Viewed by 1294

Abstract

The effects of temperature and surfactant on the shape of candle droplets that solidify at air-water interfaces were investigated. In pure water, triangular or quadrangular shaped candle droplets were formed when the temperature was ≤6 °C and round shape droplets were observed when [...] Read more.

The effects of temperature and surfactant on the shape of candle droplets that solidify at air-water interfaces were investigated. In pure water, triangular or quadrangular shaped candle droplets were formed when the temperature was ≤6 °C and round shape droplets were observed when the temperature was ≥10 °C. In SDS/water solutions ≥ 0.5 mM, oval or concave bowl-shaped candle droplets were formed when the temperature was ≤6 °C and round shape droplets were observed when the temperature was ≥10 °C. The formation mechanisms of the different shapes were explored and discussed. Full article

(This article belongs to the Section Microscale Biology and Medicines)

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13 pages, 2602 KiB

Open AccessArticle

Non-Destructive Characterization of Selected Types of Films and Other Layers via White Light Reflectance Spectroscopy (WLRS)

by Dimitrios Goustouridis, Ioannis Raptis, Theodora Mpatzaka, Savvina Fournari, Grigorios Zisis, Panagiota Petrou and Konstantinos G. Beltsios

Micro 2022, 2(3), 495-507; https://doi.org/10.3390/micro2030031 - 11 Aug 2022

Cited by 4 | Viewed by 2477

Abstract

In this work, we consider White Light Reflectance Spectroscopy (WLRS) as an optical methodology for the accurate, fast and non-destructive measurement of film thickness in the 1 nm to the 1 mm range and for applications that include microelectronics, photonics, bioanalysis and packaging. [...] Read more.

In this work, we consider White Light Reflectance Spectroscopy (WLRS) as an optical methodology for the accurate, fast and non-destructive measurement of film thickness in the 1 nm to the 1 mm range and for applications that include microelectronics, photonics, bioanalysis and packaging. Films to which WLRS is applicable can be either homogeneous or layered-composite ones, while thickness and composition might be fixed or varying with time; in the latter case, real-time monitoring of the kinetics of processes such as certain transitions, film dissolution and bioreactions is possible. We present the basic principles of WLRS and a selection of characteristic application examples of current interest, and we also briefly compare WLRS with alternative methods for film measurement. Full article

(This article belongs to the Section Analysis Methods and Instruments)

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7 pages, 1540 KiB

Open AccessArticle

Electrical Utilizations of Air Gap Region Formed on Superhydrophobic Silicone Rubber in NaCl Aqueous Solution

by Masayuki Okoshi

Micro 2022, 2(3), 488-494; https://doi.org/10.3390/micro2030030 - 10 Aug 2022

Cited by 3 | Viewed by 1364

Abstract

A uniform air gap was successfully formed on a superhydrophobic silicone rubber in water or NaCl aqueous solution. The main chain of Si–O bonds of a silicone rubber was photodissociated by a 193 nm ArF excimer laser to lower the molecular weight only [...] Read more.

A uniform air gap was successfully formed on a superhydrophobic silicone rubber in water or NaCl aqueous solution. The main chain of Si–O bonds of a silicone rubber was photodissociated by a 193 nm ArF excimer laser to lower the molecular weight only in the laser-irradiated microareas; due to the volume expansion, the microswelling structure was periodically fabricated on a silicone rubber, showing the superhydrophobic property. A pair of metal needles were inserted in the air gap formed on the superhydrophobic silicone rubber in a NaCl aqueous solution; an electrical insulation between two metal needles in the air gap was demonstrated. Additionally, a droplet of NaCl aqueous solution was confined in the air gap, after which the pair of metal needles contacted with the droplet through the air gap. As a result, an electrolysis of the droplet of NaCl aqueous solution occurred to produce hydrogen gas on the cathode in the air gap. Moreover, when Al and Cu wires were provided across the air gap and NaCl aqueous solution on the superhydrophobic silicone rubber, approximately 0.8–0.9 V of electric voltage was successfully generated between the two wires in the air gap based on the difference in electrochemical potential as an energy harvesting device in the sea. Full article

(This article belongs to the Section Microscale Physics)

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13 pages, 1699 KiB

Open AccessArticle

Electrochemical Characterization of Nanoporous Alumina-Based Membranes with Different Structure and Geometrical Parameters by Membrane Potential Analysis

by Virginia Romero and Juana Benavente

Micro 2022, 2(3), 475-487; https://doi.org/10.3390/micro2030029 - 27 Jul 2022

Viewed by 1348

Abstract

Electrochemical characterization of alumina-based membranes obtained by two different techniques, sinterization or anodization, is performed by analyzing membrane potential values. This analysis allows us the estimation of the effective concentration of fixed charge in the membrane (X_ef) and the transport number [...] Read more.

Electrochemical characterization of alumina-based membranes obtained by two different techniques, sinterization or anodization, is performed by analyzing membrane potential values. This analysis allows us the estimation of the effective concentration of fixed charge in the membrane (X_ef) and the transport number of the ions into the pores (t_i), as well as the determination of ionic permselectivity (P(i)) and their correlation with the different structures (supported, symmetrical or asymmetric), geometrical parameters (pore size and porosity) and surface materials (alumina-zirconia or alumina) of the studied membranes. From these results, the electropositive character of the membranes was stated, but also the significant reduction (70%) in X_ef value and around 30% in permselectivity when pore size increases from 25 nm to 100 nm, in the case of sinterized alumina-zirconia membranes with similar porosity (CRF samples), while the clear influence of pore size on the electrochemical behavior of the electrochemically synthesized alumina membranes (NPAM samples) was confirmed as well as the lower influence of membrane porosity. Moreover, the effect of protein (BSA) static fouling on electrochemical parameters for both CRF and NPAMs samples was also analyzed, and our results show a reduction in the electropositive character of both membranes, being this behavior opposite to that discussed for one of the NPAMs as a result of surface modification with a theophylline derivative (Theo 1). Full article

(This article belongs to the Special Issue Polymeric Micro/Nano Vectors for Drug Delivery)

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49 pages, 14121 KiB

Open AccessReview

Methods for the Synthesis of Phase Change Material Microcapsules with Enhanced Thermophysical Properties—A State-of-the-Art Review

by Refat Al-Shannaq, Mohammed M. Farid and Charles A. Ikutegbe

Micro 2022, 2(3), 426-474; https://doi.org/10.3390/micro2030028 - 09 Jul 2022

Cited by 5 | Viewed by 5222

Abstract

Thermal energy storage (TES) has been identified by many researchers as one of the cost-effective solutions for not only storing excess or/wasted energy, but also improving systems’ reliability and thermal efficiency. Among TES, phase change materials (PCMs) are gaining more attention due to [...] Read more.

Thermal energy storage (TES) has been identified by many researchers as one of the cost-effective solutions for not only storing excess or/wasted energy, but also improving systems’ reliability and thermal efficiency. Among TES, phase change materials (PCMs) are gaining more attention due to their ability to store a reasonably large quantity of heat within small temperature differences. Encapsulation is the cornerstone in expanding the applicability of the PCMs. Microencapsulation is a proven, viable method for containment and retention of PCMs in tiny shells. Currently, there are numerous methods available for synthesis of mPCMs, each of which has its own advantages and limitations. This review aims to discuss, up to date, the different manufacturing approaches to preparing PCM microcapsules (mPCMs). The review also highlights the different potential approaches used for the enhancement of their thermophysical properties, including heat transfer enhancement, supercooling suppression, and shell mechanical strength. This article will help researchers and end users to better understand the current microencapsulation technologies and provide critical guidance for selecting the proper synthesis method and materials based on the required final product specifications. Full article

(This article belongs to the Special Issue State-of-the-Art Microscale and Nanoscale Researches in Italy)

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16 pages, 3095 KiB

Open AccessArticle

Fluoroquinolone Metalloantibiotics: Fighting Staphylococcus aureus Biofilms

by Mariana Ferreira, Bruno Ribeiro, Catarina Leal Seabra, Ana Rita Ferreira and Paula Gameiro

Micro 2022, 2(3), 410-425; https://doi.org/10.3390/micro2030027 - 08 Jul 2022

Viewed by 1604

Abstract

Antimicrobial resistance (AMR) is one of the biggest public health challenges of this century. The misuse and/or overuse of antibiotics has triggered the rapid development of AMR mechanisms. Fluoroquinolones (FQs) are a broad-spectrum family of antibiotics, widely used in clinical practice. However, several [...] Read more.

Antimicrobial resistance (AMR) is one of the biggest public health challenges of this century. The misuse and/or overuse of antibiotics has triggered the rapid development of AMR mechanisms. Fluoroquinolones (FQs) are a broad-spectrum family of antibiotics, widely used in clinical practice. However, several AMR mechanisms against this family have been described. Our strategy to bypass this problem is their complexation with copper and 1,10-phenanthroline (phen). These stable complexes, known as CuFQphen metalloantibiotics, previously proved to be especially effective against methicillin-resistant Staphylococcus aureus (MRSA). This work aimed to characterize the interaction of CuFQphen metalloantibiotics with S. aureus membranes and to explore their antibiofilm activity with a combination of biophysical and microbiological approaches. Partition constants were assessed for metalloantibiotics in different mimetic systems of S. aureus membranes. The thermotropic profiles of the mimetic systems were studied in the absence and presence of the compounds. The antibiofilm activity of the metalloantibiotics was evaluated. The effects of the compounds on the membrane fluidity of MRSA clinical isolates were also investigated. Metalloantibiotics revealed a strong interaction with the lipidic component of the bacterial membranes, preferring cardiolipin-enriched domains. These complexes exhibited antibiofilm activity, and their presence proved to reduce the membrane fluidity of MRSA clinical isolates. Full article

(This article belongs to the Section Microscale Biology and Medicines)

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20 pages, 827 KiB

Open AccessArticle

Multifunctional Carbon-Based Hybrid Foams for Shape-Stabilization of Phase Change Materials, Thermal Energy Storage, and Electromagnetic Interference Shielding Functions

by Christina Gioti, Anastasios Karakassides, Georgios Asimakopoulos, Maria Baikousi, Constantinos E. Salmas, Zacharias Viskadourakis, George Kenanakis and Michael A. Karakassides

Micro 2022, 2(3), 390-409; https://doi.org/10.3390/micro2030026 - 05 Jul 2022

Cited by 2 | Viewed by 2043

Abstract

Carbon-red mud foam/paraffin hybrid materials were prepared and studied for their thermal energy storage and electromagnetic interference (EMI) shielding properties. The host matrices were prepared utilizing the polymeric foam replication method, with a polyurethane sponge as a template, resin as a carbon source, [...] Read more.

Carbon-red mud foam/paraffin hybrid materials were prepared and studied for their thermal energy storage and electromagnetic interference (EMI) shielding properties. The host matrices were prepared utilizing the polymeric foam replication method, with a polyurethane sponge as a template, resin as a carbon source, and red mud as a filler. The paraffins, n-octadecane (OD) and the commercial RT18HC, were used as organic encapsulant phase change materials (PCMs) into the open pore structure of the foams. The foams’ morphological and structural study revealed a highly porous structure (bulk density, apparent porosity P > 65%), which exhibits elliptical and spherical pores, sized from 50 up to 500 μm, and cell walls composed of partially graphitized carbon and various oxide phases. The hybrid foams showed a remarkable encapsulation efficiency as shape stabilizers for paraffins: 48.8% (OD), 37.8% (RT18HC), while their melting enthalpies (ΔH_m) were found to be 126.9 J/g and 115.5 J/g, respectively. The investigated hybrids showed efficient electromagnetic shielding performance in frequency range of 3.5–9.0 GHz reaching the entry-level value of ~20 dB required for commercial applications, when filled with PCMs. Their excellent thermal and EMI shielding performance places the as-prepared samples as promising candidates for use in thermal management and EMI shielding of electronic devices as well. Full article

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21 pages, 1063 KiB

Open AccessArticle

Efficient and Accurate Modeling of the Surface Deflection of Thin Layers on Composite Substrates with Applications to Piezoelectric Parameter Measurements

by Thomas Voglhuber-Brunnmaier, Roman Beigelbeck, Ulrich Schmid, Thilo Sauter, Tiangui You, Xin Ou and Bernhard Jakoby

Micro 2022, 2(3), 369-389; https://doi.org/10.3390/micro2030025 - 29 Jun 2022

Viewed by 1625

Abstract

The electrical and mechanical response of multilayered structures involving a piezoelectric layer and bull’s eye shaped electrodes is investigated. A boundary element method is employed based on spectral domain Green’s functions. With this method, the electric field distribution is determined first, and the [...] Read more.

The electrical and mechanical response of multilayered structures involving a piezoelectric layer and bull’s eye shaped electrodes is investigated. A boundary element method is employed based on spectral domain Green’s functions. With this method, the electric field distribution is determined first, and the local mechanical displacement in a second step. As will be shown, this allows us to exploit cylindrical symmetry for the electric surface charge distribution, but not for the vertical surface displacements. The effect of substrate bending due to in plane-stress, introduced by the piezoelectric constant

d_{31}

, and the benefits of using bull’s eye electrode geometries with thick metallic backplates intended to reduce this effect are studied. A rigorous analysis and a largely simplified, but accurate approximation are compared. The application of this technique is demonstrated on a practical example for highly efficient and accurate determination of selected piezoelectric coefficients from surface topography measurements on such structures. Full article

(This article belongs to the Special Issue Microsystem and Nanosystem Researches for Sensors, Actuators and Energy Conversion Devices)

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8 pages, 974 KiB

Open AccessArticle

Molecular-Scale Hardware Encryption Using Tunable Self-Assembled Nanoelectronic Networks

by Anusha Venkataraman, Eberechukwu Amadi and Chris Papadopoulos

Micro 2022, 2(3), 361-368; https://doi.org/10.3390/micro2030024 - 21 Jun 2022

Viewed by 1555

Abstract

Nanomaterials are promising alternatives for creating hardware security primitives that are considered more robust and less susceptible to physical attacks compared to standard CMOS-based approaches. Here, nanoscale electronic circuits composed of tunable ratios of molecules and colloidal nanoparticles formed via self-assembly on silicon [...] Read more.

Nanomaterials are promising alternatives for creating hardware security primitives that are considered more robust and less susceptible to physical attacks compared to standard CMOS-based approaches. Here, nanoscale electronic circuits composed of tunable ratios of molecules and colloidal nanoparticles formed via self-assembly on silicon wafers are investigated for information and hardware security by utilizing device-level physical variations induced during fabrication. Two-terminal electronic transport measurements show variations in current through different parts of the nanoscale network, which are used to define electronic physically unclonable functions. By comparing different current paths, arrays of binary bits are generated that can be used as encryption keys. Evaluation of the keys using Hamming inter-distance values indicates that performance is improved by varying the ratio of molecules to nanoparticles in the network, which demonstrates self-assembly as a potential path toward implementing molecular-scale hardware security primitives. These nanoelectronic networks thus combine facile fabrication with a large variety of possible network building blocks, enabling their utilization for hardware security with additional degrees of freedom that is difficult to achieve using conventional systems. Full article

(This article belongs to the Section Microscale Engineering)

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Micro, Volume 2, Issue 3 (September 2022) – 12 articles

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