Stretchable and Lithography-Compatible Interconnects Enabled by Self-Assembled Nanofilms with Interlocking Interfaces.

Stretchable interconnects with miniature widths are vital for the high-density integration of deformable electronic components on a single substrate for targeted data logic or storage functions. However, it is still challenging to attain high-resolution patternability of stretchable conductors with robust circuit fabrication capability. Here, we report a self-assembled silver nanofilm firmly interlocked by an elastomeric nanodielectric that can be photolithographically patterned into microscale features while preserving high stretchability and conductivity. Both silver and dielectric nanofilms are fabricated by layer-by-layer assembly, ensuring wafer-scale uniformity and meticulous control of thicknesses. Without any thermal annealing, the as-fabricated nanofilms from silver nanoparticles (AgNPs) exhibit conductivity of 1.54 × 106 S m-1 and stretchability of ∼200%, which is due to the impeded crack propagation by the underlying PU nanodielectrics. Furthermore, it is revealed that AgNP microstrips defined by photolithography show higher stretchability when their widths are downscaled to 100 µm owing to confined cracks. However, further scaling restricts the stretchability, following the early development of cracks cutting across the strip. In addition, the resistance change of these silver interconnects can be decreased using serpentine architectures. As a demonstration, these self-assembled interconnects are used as stretchable circuit boards to power LEDs.

Predicting of tunneling resistivity between adjacent nanosheets in graphene-polymer systems.

In this work, the tunneling resistivity between neighboring nanosheets in grapheme-polymer nanocomposites is expressed by a simple equation as a function of the characteristics of graphene and tunnels. This expression is obtained by connecting two advanced models for the conductivity of graphene-filled materials reflecting tunneling role and interphase area. The predictions of the applied models are linked to the tested data of several samples. The impressions of all factors on the tunneling resistivity are evaluated and interpreted using the suggested equation. The calculations of tunneling resistivity for the studied examples by the model and suggested equation demonstrate the same levels, which confirm the presented methodology. The results indicate that the tunneling resistivity decreases by super-conductive graphene, small tunneling width, numerous contacts among nanosheets and short tunneling length.

Effect of contact number among graphene nanosheets on the conductivities of tunnels and polymer composites.

Simple equations are expressed for tunnel conductivity, tunnel resistance and conductivity of a graphene-filled composite by the number of contacts and interphase part. More specially, the active filler amount is suggested by interphase depth, which changes the contact number. The conductivity of nanocomposite is presented by filler content, filler dimensions, tunneling length and interphase depth. The innovative model is surveyed by the experimented conductivity of real examples. Too, the impacts of numerous issues on the tunnel resistance, tunnel conductivity and conductivity of nanocomposite are discussed to validate the novel equations. The estimates agree with the experimented data and the impacts of several terms on the tunnel resistance, tunnel conductivity and conductivity of system are sensible. Thin and big nanosheets positively affect the nanocomposite's conductivity, but thick nanosheets improve the tunnel conductivity. High conductivity is found at short tunnels, while the nanocomposite's conductivity directly depends on the tunneling length. The dissimilar effects of these features on the tunneling properties and conductivity are described.

Enhanced Mechanical and Thermal Properties of Chain-Extended Waterborne Polyurethane Coatings with Cellulose Acetate Butyrate.

A series of waterborne polyurethane (WPU) dispersions were prepared by chain-extending a prepolymer made of polyester diol, isophorone diisocyanate, and dimethylol propionic acid using cellulose acetate butyrate (CAB). The particle size and viscosity of the WPU dispersion were measured. In addition, we investigated the effects of CAB on the thermal, mechanical, and optical properties of WPU films. The use of CAB effectively improved the crosslinking degree of the WPUs, increasing the thermal stability and water resistance of the corresponding films. In particular, CAB increased the tensile strength of the WPU films up to 67%, while maintaining their elongation at break unchanged. In addition, CAB improved the optical transmittance by reducing the microphase separation between the soft and hard segments of PU. The rough surface structure of the WPU films formed by CAB led to improved matting properties.

From Hazardous Waste to Green Applications: Selective Surface Functionalization of Waste Cigarette Filters for High-Performance Robust Triboelectric Nanogenerators and CO2 Adsorbents.

This article reports a novel and rational approach to convert waste cigarette filters (CFs), one of the largest sources of ocean pollution, into high-performance triboelectric nanogenerators (TENGs) and efficient CO2-capturing adsorbents. CFs are plasticized cellulose acetate, which take several years to degrade. To revalorize these fibers, selective amine surface functionalization is performed (10PAL-20T-CFs). For the proof of concept, when the modified fibers are employed in a TENG, it could generate an output voltage (96.63 V) and current (9.37 µA) that are, respectively, 43 and 8 times higher than those obtained employing the pristine CFs for the nanogenerator. The proposed TENG displays an instantaneous peak power of 3.75 mW, which is higher than that of many recently reported TENGs made from cellulose materials. Moreover, the TENG displayed outstanding durability to humidity and high-performance stability when it is subjected to cyclic loading (i.e., 12,000 cycles of loading-unloading). A 9 cm2 TENG could effectively light up 100 or more colored light-emitting diodes when it is manually pressed. Finally, the modified filter fibers show an excellent CO2 adsorption capacity of 1.93 mmol/g, which is 9.2 times higher than that obtained using the pristine fibers. These results demonstrate that hazardous wastes such as CFs can be upcycled into valuable resources.

Effect of the High-Pressure Hydrogen Gas Exposure in the Silica-Filled EPDM Sealing Composites with Different Silica Content.

With the increasing interest in hydrogen energy, the stability of hydrogen storage facilities and components is emphasized. In this study, we analyzed the effect of high-pressure hydrogen gas treatment in silica-filled EPDM composites with different silica contents. In detail, cure characteristics, crosslink density, mechanical properties, and hydrogen permeation properties were investigated. Results showed that material volume, remaining hydrogen content, and mechanical properties were changed after 96.3 MPa hydrogen gas exposure. With an increase in the silica content, the crosslink density and mechanical properties increased, but hydrogen permeability was decreased. After treatment, high-silica-content composites showed lower volume change than low-silica-content composites. The crack damage due to the decompression caused a decrease in mechanical properties, but high silica content can inhibit the reduction in mechanical properties. In particular, EPDM/silica composites with a silica content of above 60 phr exhibited excellent resistance to hydrogen gas, as no change in their physical and mechanical properties was observed.

Capacitive biosensor based on vertically paired electrodes for the detection of SARS-CoV-2.

Vertically paired electrodes (VPEs) with multiple electrode pairs were developed for the enhancement of capacitive measurements by optimizing the electrode gap and number of electrode pairs. The electrode was fabricated using a conductive polymer layer of PEDOT:PSS instead of Ag and Pt metal electrodes to increase the VPE fabrication yield because the PEDOT:PSS layer could be effectively etched using a reactive dry etching process. In this study, sensitivity enhancement was realized by decreasing the electrode gap and increasing the number of VPE electrode pairs. Such an increase in sensitivity according to the electrode gap and the number of electrode pairs was estimated using a model analyte for an immunoassay. Additionally, a computer simulation was performed using VPEs with different electrode gaps and numbers of VPE electrode pairs. Finally, VPEs with multiple electrode pairs were applied for SARS-CoV-2 nucleoprotein (NP) detection. The capacitive biosensor based on the VPE with immobilized anti-SARS-CoV-2 NP was applied for the specific detection of SARS-CoV-2 in viral cultures. Using viral cultures of SARS-CoV-2, SARS-CoV, MERS-CoV, and CoV-strain 229E, the limit of detection (LOD) was estimated to satisfy the cutoff value (dilution factor of 1/800) for the medical diagnosis of COVID-19, and the assay results from the capacitive biosensor were compared with commercial rapid kit based on a lateral flow immunoassay.

Near-Infrared Light-Responsive Shape Memory Polymer Fabricated from Reactive Melt Blending of Semicrystalline Maleated Polyolefin Elastomer and Polyaniline.

A shape memory polymer was prepared by melt mixing a semicrystalline maleated polyolefin elastomer (mPOE) with a small amount of polyaniline (PANI) (up to 15 wt.%) in an internal mixer. Transmission electron microscopy (TEM), FTIR analysis, DMA, DSC, melt rheological analysis, and a tensile test were performed to characterize the structure and properties of the mPOE/PANI blends. The results revealed that the blends form a physically crosslinked network via the grafting of PANI onto the mPOE chains, and the PANI dispersed at the nanometer scale in the POE matrix served as a photo-thermal agent and provided increased crosslinking points. These structural features enabled the blends to exhibit a shape memory effect upon near-infrared (NIR) light irradiation. With increasing PANI content, the shape recovery rate of the blend under NIR stimulation was improved and reached 96% at 15 wt.% of PANI.

Elastomeric Nanodielectrics for Soft and Hysteresis-Free Electronics.

Elastomeric dielectrics are crucial for reliably governing the carrier densities in semiconducting channels during deformation in soft/stretchable field-effect transistors (FETs). Uncontrolled stacking of polymeric chains renders elastomeric dielectrics poorly insulated at nanoscale thicknesses, thereby thick films are usually required, leading to high voltage or power consumption for on/off operations of FETs. Here, layer-by-layer assembly is exploited to build 15-nm-thick elastomeric nanodielectrics through alternative adsorption of oppositely charged polyurethanes (PUs) for soft and hysteresis-free FETs. After mild thermal annealing to heal pinholes, such PU multilayers offer high areal capacitances of 237 nF cm-2 and low leakage current densities of 3.2 × 10-8 A cm-2 at 2 V. Owing to the intrinsic ductility of the elastomeric PUs, the nanofilms possess excellent dielectric properties at a strain of 5% or a bending radius of 1.5 mm, while the wrinkled counterparts show mechanical stability with negligible changes of leakage currents after repeated stretching to a strain of 50%. Besides, these nanodielectrics are immune to high humidity and conserve their properties when immersed into water, despite their assembly occurs aqueously. Furthermore, the PU dielectrics are implemented in carbon nanotube FETs, demonstrating low-voltage operations (< 1.5 V) and negligible hysteresis without any encapsulations.

Morphology, Mechanical Properties and Shape Memory Effects of Polyamide12/Polyolefin Elastomer Blends Compatibilized by Glycidylisobutyl POSS.

Small amounts of glycidylisobutyl polyhedral oligomericsilsesquioxane (G-POSS) (up to 10 phr) were added into a immiscible polyamide12 (PA12)/polyolefin elastomer (POE) blend (70 wt%/30 wt%) by simple melt mixing. The effects of the G-POSS on phase morphology and mechanical properties were investigated by FE-SEM, tensile testing, Izod impact test and dynamic mechanical analysis. FE-SEM analysis revealed that domain size of the dispersed POE phase in matrix PA12 is decreased significantly by adding the G-POSS, indicating a compatibilization effect of the G-POSS for the immiscible PA12/POE blend. The PA12/POE blend compatibilized with POSS showed simultaneous enhancement in mechanical properties including tensile modulus, strength and toughness. Further, thermally triggered shape memory effect was observed in this compatibilized blend.

In Vitro and In Vivo Biosafety Analysis of Resorbable Polyglycolic Acid-Polylactic Acid Block Copolymer Composites for Spinal Fixation.

Herein, spinal fixation implants were constructed using degradable polymeric materials such as PGA-PLA block copolymers (poly(glycolic acid-b-lactic acid)). These materials were reinforced by blending with HA-g-PLA (hydroxyapatite-graft-poly lactic acid) and PGA fiber before being tested to confirm its biocompatibility via in vitro (MTT assay) and in vivo animal experiments (i.e., skin sensitization, intradermal intracutaneous reaction, and in vivo degradation tests). Every specimen exhibited suitable biocompatibility and biodegradability for use as resorbable spinal fixation materials.

Highly sensitive in situ-synthesized cadmium sulfide (CdS) nanowire photosensor for chemiluminescent immunoassays.

Highly sensitive in situ-synthesized cadmium sulfide (CdS) nanowires (NWs) for the detection of chemiluminescence in immunoassays with a photoresist (PR) layer to stabilize the CdS NWs before and after coating with a parylene film were developed. The thickness of the PR layer was controlled by adjusting the viscosity of the PR solution used for spin-coating. PR2005 was the optimal PR for passivation of the NW surface. After the addition of a parylene coating on the CdS NWs, the photocurrent increased by as much as 50% over a broad range of light intensities, and the additional PR layer increased the photoresponse over the whole range of light intensities. When the photoresponses of the CdS NWs with and without the parylene film were compared after the addition of a PR layer, significant differences were observed in the photocurrent behavior after the incident light was turned off. For the CdS NWs with a parylene film and PR layer, the photocurrent reached the baseline within milliseconds of the incident light being turned off. However, the CdS NWs without a parylene film but with a PR layer required >60 s to reach the baseline level. This difference was due to the capacitance arising from the contact between the NWs. The in situ-synthesized CdS NW photosensor passivated by the parylene film and a PR layer was used in a chemiluminescence-based immunoassay. Finally, the detection of human immunodeficiency virus antibodies was demonstrated via a chemiluminescent enzyme-linked immunosorbent assay based on the CdS NW photosensor in comparison with the optical-density measurement for the chromogenic reaction of TMB(3,3',5,5'-Tetramethylbenzidine).

Study on the Synthetic Characteristics of Biomass-Derived Isosorbide-Based Poly(arylene ether ketone)s for Sustainable Super Engineering Plastic.

Demand for the development of novel polymers derived from biomass that can replace petroleum resources has been increasing. In this study, biomass-derived isosorbide was used as a monomer in the polymerization of poly(arylene ether ketone)s, and its synthetic characteristics were investigated. As a phase-transfer catalyst, crown ether has increased the weight-average molecular weight of polymers over 100 kg/mol by improving the reaction efficiency of isosorbide and minimizing the effect of moisture. By controlling the experimental parameters such as halogen monomer, polymerization solvent, time, and temperature, the optimal conditions were found to be fluorine-type monomer, dimethyl sulfoxide, 24 h, and 155 °C, respectively. Biomass contents from isosorbide-based polymers were determined by nuclear magnetic resonance and accelerator mass spectroscopy. The synthesized polymer resulted in a high molecular weight that enabled the preparation of transparent polymer films by the solution casting method despite its weak thermal degradation stability compared to aromatic polysulfone. The melt injection molding process was enabled by the addition of plasticizer. The tensile properties were comparable or superior to those of commercial petrochemical specimens of similar molecular weight. Interestingly, the prepared specimens exhibited a significantly lower coefficient of thermal expansion at high temperatures over 150 °C compared to polysulfone.

Layer-by-layer assembled multilayers of charged polyurethane and graphene oxide platelets for flexible and stretchable gas barrier films.

With the advent of the era of consumer-oriented displays and mobile devices, the importance of barrier film coatings for securing devices from oxygen or moisture penetration has become more salient. Recently developed approaches to generate gas barrier films in a combination of polyelectrolyte multilayer matrices and incorporated inorganic nanosheets have shown great potential in outperforming conventional gas barrier films. However, these films have the intrinsic drawback of vulnerability to brittleness and inability to stretch for flexible device applications. To overcome this issue, we present a method in which we prepare multilayered films of complementarily charged polyurethane and graphene oxide platelets using spin-assisted, layer-by-layer self-assembly to obtain well-stacked film structures. As a result, the multilayered, thin films deposited on a poly(ethylene terephthalate) (PET) substrate can exhibit significantly reduced oxygen penetration properties (∼30 cc m-2 day-1 for the oxygen transmission rate) while still demonstrating large bending or stretching deformations. Therefore, the proposed approach in this study is anticipated to be extensively utilized for surface coating and protection of flexible and stretchable devices under various operating conditions.

Hollow Pt-Functionalized SnO2 Hemipill Network Formation Using a Bacterial Skeleton for the Noninvasive Diagnosis of Diabetes.

Hollow-structured nanomaterials are presented as an outstanding sensing platform because of their unique combination of high porosity in both the micro- and nanoscale, their biocompatibility, and flexible template applicability. Herein, we introduce a bacterial skeleton method allowing for cost-effective fabrication with nanoscale precision. As a proof-of-concept, we fabricated a hollow SnO2 hemipill network (HSHN) and a hollow Pt-functionalized SnO2 hemipill network (HPN). A superior detecting capability of HPN toward acetone, a diabetes biomarker, was demonstrated at low concentration (200 ppb) under high humidity (RH 80%). The detection limit reaches 3.6 ppb, a level satisfying the minimum requirement for diabetes breath diagnosis. High selectivity of the HPN sensor against C6H6, C7H8, CO, and NO vapors is demonstrated using principal component analysis (PCA), suggesting new applications of HPN for human-activity monitoring and a personal healthcare tool for diagnosing diabetes. The skeleton method can be further employed to mimic nanostructures of biomaterials with unique functionality for broad applications.

Chronoamperometry-Based Redox Cycling for Application to Immunoassays.

In this work, the chronoamperometry-based redox cycling of 3,3',5,5'-tetramethylbenzidine (TMB) was performed by using interdigitated electrode (IDE). The signal was obtained from two sequential chronoamperometric profiles: (1) with the generator at the oxidative potential of TMB and the collector at the reductive potential of TMB, and (2) with the generator at the reductive potential of TMB and the collector at the oxidative potential of TMB. The chronoamperometry-based redox cycling (dual mode) showed a sensitivity of 1.49 µA/OD, and the redox cycling efficiency was estimated to be 94% (n = 10). The sensitivities of conventional redox cycling with the same interdigitated electrode and chronoamperometry using a single working electrode (single mode) were estimated to be 0.67 µA/OD and 0.18 µA/OD, respectively. These results showed that the chronoamperometry-based redox cycling (dual mode) could be more effectively used to quantify the oxidized TMB than other amperometric methods. The chronoamperometry-based redox cycling (dual mode) was applied to immunoassays using a commercial ELISA kit for medical diagnosis of the human hepatitis B virus surface antigen (hHBsAg). Finally, the chronoamperometry-based redox cycling (dual mode) provided more than a 10-fold higher sensitivity than conventional chronoamperometry using a single working electrode (single mode) when applied to a commercial ELISA kit for medical diagnosis of hHBsAg.

Redox cycling-based immunoassay for detection of carcinogenic embryonic antigen.

Redox cycling based on an interdigitated electrode (IDE) was used as a highly sensitive immunoassay for carcinogenic embryonic antigen (CEA) through the quantification of 3,3',5,5'-tetramethylbenzidine (TMB). For the redox cycling process, one pair of interdigitated finger electrodes was used as the first working electrode (generator) for cyclic voltammetry of TMB, and another pair of interdigitated finger electrodes was used as the second working electrode (collector) for sequential application of potentials for reduction and oxidation of TMB. The reduction (and oxidation) products of TMB at the collector were supplied to the generator, and following sequential oxidization (and reduction) at the generator, again supplied to the collector. Such redox recycling processes between the generator and collector allowed signal amplification. In this work, the influences of the following factors on the redox cycling of TMB were analyzed: (1) the redox potential at the collector, (2) the gap between the interdigitated finger electrodes, and (3) the scan rate of the generator. The redox potential and electrode gap influences were simulated with COMSOL software and compared with empirical results. At the optimum redox potentials and electrode gap, redox cycling was estimated to be five-fold more sensitive for the quantification of TMB than conventional cyclic voltammetry using one pair of interdigitated finger electrodes as the working electrode. Finally, redox cycling was applied to a commercial immunoassay for CEA, and the sensitivity of redox cycling was three-fold higher than that of conventional cyclic voltammetry using a single set of interdigitated finger electrodes as the working electrode.

In situ-synthesized cadmium sulfide nanowire photosensor with a parylene passivation layer for chemiluminescent immunoassays.

The direct in situ synthesis of cadmium sulfide (CdS) nanowires (NWs) was presented by direct synthesis of CdS NWs on the gold surface of an interdigitated electrode (IDE). In this work, we investigated the effect of a strong oxidant on the surfaces of the CdS NWs using X-ray photoelectron spectroscopy, transmission electron microscopy, and time-of-flight secondary ion mass spectrometry. We also fabricated a parylene-C film as a surface passivation layer for in situ-synthesized CdS NW photosensors and investigated the influence of the parylene-C passivation layer on the photoresponse during the coating of parylene-C under vacuum using a quartz crystal microbalance and a photoanalyzer. Finally, we used the in situ-synthesized CdS NW photosensor with the parylene-C passivation layer to detect the chemiluminescence of horseradish peroxidase and luminol and applied it to medical detection of carcinoembryonic antigen.

A magnetite suspension-based washing method for immunoassays using Escherichia coli cells with autodisplayed Z-domains.

Escherichia coli cells with autodisplayed Z-domains have been used for immunoassays of specific target analytes. In this study, a magnetite suspension was used for the washing step in immunoassays of E. coli cells with autodisplayed Z-domains. This approach enhanced the washing conditions for these immunoassays by determining (1) the optimal concentration of the magnetite suspension, (2) the capacity of the magnetite suspension-based washing method to recover E. coli cells, and (3) the level at which the activity of autodisplayed Z-domains is maintained. In immunoassays of C-reactive protein (CRP), the immunoassay incorporating the magnetite suspension-based washing method showed a sensitivity and limit of detection considerably higher than those of the conventional centrifugation-based washing method. The results indicated that immunoassays incorporating the magnetite suspension-based washing method are effective for medical diagnoses based on CRP assay.

Band-type microelectrodes for amperometric immunoassays.

A band-type microelectrode was made using a parylene-N film as a passivation layer. A circular-type, mm-scale electrode with the same diameter as the band-type microelectrode was also made with an electrode area that was 5000 times larger than the band-type microelectrode. By comparing the amperometric signals of 3,5,3',5'-tetramethylbenzidine (TMB) samples at different optical density (OD) values, the band-type microelectrode was determined to be 9 times more sensitive than the circular-type electrode. The properties of the circular-type and the band-type electrodes (e.g., the shape of their cyclic voltammograms, the type of diffusion layer used, and the diffusion layer thickness per unit electrode area) were characterized according to their electrode area using the COMSOL Multiphysics software. From these simulations, the band-type electrode was estimated to have the conventional microelectrode properties, even when the electrode area was 100 times larger than a conventional circular-type electrode. These results show that both the geometry and the area of an electrode can influence the properties of the electrode. Finally, amperometric analysis based on a band-type electrode was applied to commercial ELISA kits to analyze human hepatitis B surface antigen (hHBsAg) and human immunodeficiency virus (HIV) antibodies.