Flexible Polymeric Materials Research Articles

Self-assembly and energy storage potentials of biphasic phase change azobenzene liquid crystalline block copolymers

Flexible polymeric materials with potentials in energy storage have attracted extensive attention in today's sustainable society. Here, we reported a series of crystalline-liquid crystalline biphasic phase change block copolymers, poly(ethylene oxide)-b-poly(11-(4-(4-cyanophenylazo)phenoxy)undecane methacrylate) (PEO-b-PMAAzo), and studied the UV and Li+ ions coordination-mediated self-assembly for the potentials in phase change energy storage and solid electrolytes. The PEO-b-PMAAzo BCPs possess both the solid-liquid phase transition of PEO and the photo-chemical-thermal energy transition of PMAAzo block. Meanwhile, PEO has the capability to coordinate with the Li+ for the ionic conductivity. We explored the binary phase change behaviors and thermal energy density of the BCPs with different lithium ion concentrations before and after UV irradiation. The addition of LiTFSI salts increases the interaction parameters (χ) of the BCPs leading to phase transition of the self-assembled nanostructures. The phase diagram covering LAM, HEX, GYR, Fddd and HPL nanostructures facilitating ion transport was demonstrated. The PMAAzo block enabled the solid feature of the BCPs and ensured the high energy density and high conductivity. This work demonstrates that the combination of the functional polymers in one BCP not only provides multiple morphology tunabilities but also enables multiple functionalities from energy conversation and storage to ionic conductive electrolytes.

Highly Sensitive and Flexible Capacitive Pressure Sensors Combined with Porous Structure and Hole Array Using Sacrificial Templates and Laser Ablation.

Flexible, wearable pressure sensors offer numerous benefits, including superior sensing capabilities, a lightweight and compact design, and exceptional conformal properties, making them highly sought after in various applications including medical monitoring, human-computer interactions, and electronic skins. Because of their excellent characteristics, such as simple fabrication, low power consumption, and short response time, capacitive pressure sensors have received widespread attention. As a flexible polymer material, polydimethylsiloxane (PDMS) is widely used in the preparation of dielectric layers for capacitive pressure sensors. The Young's modulus of the flexible polymer can be effectively decreased through the synergistic application of sacrificial template and laser ablation techniques, thereby improving the functionality of capacitive pressure sensors. In this study, a novel sensor was introduced. Its dielectric layer was developed through a series of processes, including the use of a sacrificial template method using NaCl microparticles and subsequent CO2 laser ablation. This porous PDMS dielectric layer, featuring an array of holes, was then sandwiched between two flexible electrodes to create a capacitive pressure sensor. The sensor demonstrates a sensitivity of 0.694 kPa-1 within the pressure range of 0-1 kPa and can effectively detect pressures ranging from 3 Pa to 200 kPa. The sensor demonstrates stability for up to 500 cycles, with a rapid response time of 96 ms and a recovery time of 118 ms, coupled with a low hysteresis of 6.8%. Furthermore, our testing indicates that the sensor possesses limitless potential for use in detecting human physiological activities and delivering signals.

Self-Healing Transparent Poly(dimethyl)siloxane with Tunable Mechanical Properties: Toward Enhanced Aging Materials for Space Applications.

When exposed to the geostationary orbit, polymeric materials tend to degrade on their surface due to the appearance of cracks. Implementing the self-healing concept in polymers going to space is a new approach to enhancing the lifespan of materials that cannot be replaced once launched. In this study, the elaboration of autonomous self-healing transparent poly(dimethylsiloxane) (PDMS) materials resistant to proton particles is presented. The PDMS materials are functionalized with various compositions of urea and imine moieties, forming dynamic covalent and/or supramolecular networks. The hydrogen bonds induced by the urea ensure the formation of a supramolecular network, while the dynamic covalent imine bonds are capable of undergoing exchange reactions. Materials with a broad range of mechanical properties were obtained depending on the composition and structure of the PDMS networks. As coating applications in a spatial environment were mainly targeted, the surface properties of the polymer are essential. Thus, percentages of scratch recovery were determined by AFM. From these data, self-healing kinetics were extracted and rationalized based on the polymer structures. The obtained data were in good agreement with the relaxation times determined by rheology in stress relaxation experiments. Moreover, the accelerated aging of materials under proton irradiation, simulating a major part of the geostationary environment, revealed a strong limitation or disappearance of cracks while keeping the transparency of the PDMS. These promising results open routes to prepare new flexible autonomous polymeric materials for space applications.

Pushing the Limits of Heat Conduction in Covalent Organic Frameworks Through High-Throughput Screening of Their Thermal Conductivity.

Tailor-made materials featuring large tunability in their thermal transport properties are highly sought-after for diverse applications. However, achieving `user-defined' thermal transport in a single class of material system with tunability across a wide range of thermal conductivity values requires a thorough understanding of the structure-property relationships, which has proven to be challenging. Herein, large-scale computational screening of covalent organic frameworks (COFs) for thermal conductivity is performed, providing a comprehensive understanding of their structure-property relationships by leveraging systematic atomistic simulations of 10,750 COFs with 651 distinct organic linkers. Through the data-driven approach, it is shown that by strategic modulation of their chemical and structural features, the thermal conductivity can be tuned from ultralow (≈0.02 W m-1 K-1) to exceptionally high (≈50 W m-1 K-1) values. It is revealed that achieving high thermal conductivity in COFs requires their assembly through carbon-carbon linkages with densities greater than 500 kg m-3, nominal void fractions (in the range of ≈0.6-0.9) and highly aligned polymeric chains along the heat flow direction. Following these criteria, it is shown that these flexible polymeric materials can possess exceptionally high thermal conductivities, on par with several fully dense inorganic materials. As such, the work reveals that COFs mark a new regime of materials design that combines high thermal conductivities with lowdensities.

A review of microfabrication approaches for the development of thin, flattened heat pipes and vapor chambers for passive electronic cooling applications

With the rapid development of microelectronics and the telecommunication industry, a variety of high performance, portable and slim electronic devices have become available. Miniaturization of devices and increased packing density of electronics can generate “hot spots” i.e. a high heat flux on a small area. Thus, in such devices the heat management requirements go beyond the limits of typical approaches and the development of miniaturized, high-performance thermal management concepts to cool high-performance, compact electronic devices is urgently required. To this direction, micro and nanofabrication methods can provide solutions in both miniaturizing existing concepts of passive cooling as well as in improving their performance. In this review, we start by introducing the most commonly used metrics used to evaluate the performance of passive cooling devices (i.e. vapor chambers and flattened heat pipes) together with the most prominent performance limitations. Then, in the main part, we present state of the art examples of microfabricated, thin vapor chambers and flattened heat pipes on rigid substrates (i.e. using metals and silicon), but also vapor chambers on thin and flexible polymeric or composite materials. Finally, the main conclusions and the steps which should be followed to further enhance the performance of such devices are summarized in the conclusions and future perspectives section.

Bacterial Population Changes during the Degradation Process of a Lactate (LA)-Enriched Biodegradable Polymer in River Water: LA-Cluster Preferable Bacterial Consortium.

The lactate-based polyester poly[lactate (LA)-co-3-hydroxybutyrate (3HB)], termed LAHB, is a highly transparent and flexible bio-based polymeric material. There are many unknowns regarding its degradation process in riverine environments, especially the changes in bacterial flora that might result from its degradation and the identities of any LAHB-degrading bacteria. LAHB were immersed in the river water samples (A and B), and LAHB degradation was observed in terms of the weight change of the polymer and the microscopic changes on the polymer surfaces. A metagenomic analysis of microorganisms was conducted to determine the effect of LAHB degradation on the aquatic environment. The bacterial flora obtained from beta diversity analysis differed between the two river samples. The river A water sample showed the simultaneous degradation of LA and 3HB even though the copolymer was LA-enriched, suggesting preferable hydrolysis of the LA-enriched segments. In contrast, only 3HB degraded for the LAHB in the river B water sample. The linear discriminant analysis effect size (LEfSe) analysis revealed 14 bacteria that were significantly increased in the river A water sample during LAHB degradation, suggesting that these bacteria preferentially degraded and assimilated LA-clustering polymers. Our metagenomic analysis provides useful insights into the dynamic changes in microbial communities and LA-clustering polymer-degrading bacteria.

A high-fidelity MEMS microphone with a polymer membrane that can detect infra-sounds

This study proposes a polymer MEMS microphone that operates through electromechanical amplitude modulation. We have developed a highly optimized MEMS structure with a flexible polymer material, resulting in a miniaturized and flexible device with excellent acoustic performance. The stiffness and damping characteristics of the polymer diaphragm are analyzed and it shows that the polymer material would be suitable for microphone applications. An equivalent circuit model is also developed for design purposes, so that the device could be properly designed using it and fabricated by in-house polymer thin film processes. The fabricated device is tested using a DC bias scheme to reach its signal-to-noise ratio (SNR) of 65 dBA within a bandwidth of 10 to 10,000 Hz, which is comparable to existing high-end commercial silicon MEMS microphones. We would then extend the frequency bands of linear detection down to the infrasound range by using electromechanical amplitude modulation. This operation scheme can also provide the microphone with no need for metal packaging. Its feasibility is confirmed theoretically by numerical simulations including electromechanical amplitude modulation and experimentally by implementing it at the PCB level. In addition, this approach enables the sensor stronger to the environmental noise so that metal shielding could be omitted.

In-situ constructing SiC frame in silicone rubber to fabricate novel flexible thermal protective polymeric materials with excellent ablation resistance

To meet the urgent need for thermal protection of high-temperature deformable mechanisms in the aerospace industry, a novel strategy for the preparation of ablation-resistant flexible composites is proposed. Ceramic precursor is selected and introduced to epoxy modified silicone rubber (SR) to in-situ build SiC frame at high temperature to fabricate flexible thermal protective polymeric materials with excellent ablation resistance. The static ablation and dynamic ablation behaviors of the SR composites are systematically and comparatively investigated in a tube furnace and oxyacetylene torch in an automatic ablation machine for the first time. The influence of polycarbonylsilane (PCS) content on the microstructure, strength and composition of char layer, and the ablation properties at different heat environments are discussed. When the addition of PCS reached 10 phr, for the static ablation, the maximum puncture strength of char and the residual weight increased 3233% and 48.48%, respectively. The same for dynamic ablation, with the introduction of PCS, each indicator was greatly improved. Moreover, the ablation enhancement mechanisms of PCS in different ablation environments are revealed. This work may provide a new perspective for the preparation of silicone rubber composites with excellent ablation performance, expected to be well used as a thermal protection coating for hypersonic spacecrafts.

Creating Quantitative Regulation Principles of the Heating Networks’ Parameters Based on the Life Cycle Analysis

Materials and Methods. The elaboration of the heating networks should be carried out in compliance with the currently enacted Code of Practices “Information modeling in construction. Rules for the objects’ information model creation at different stages of the life cycle». The life cycle can be divided into four stages. It is noted that each type of digital information model at each stage of the life cycle correlates with the certain level of elaboration, which envisages the minimum of geometric, spatial, quantitative and attributive data necessary to solve the task of information modeling at a specific stage of the object's life cycle.Results. 4th generation heating supply technologies allow reducing the temperature of the heat-carrying agent, hereby creating conditions for commencing the heating networks’ transit to the low temperature type of systems. As a result, reducing the heat carrying agent’s temperature, allows using more flexible polymer materials for the pipelines. In addition, application of the comprehensive approach to the heating networks innovative development is the important prerequisite for further development of the district heating infrastructure and technologies.Discussion and Conclusions. The main focus for improving the heating sector development should lie in the elaboration and implementation of the new technologies and digital information models, which will improve the quality of thermal energy generation, transportation and distribution.

P88: In vitro Nasopharyngeal Cavity Model for Comparative Performance Evaluation Between New Nasopharyngeal and Commercial Swabs in Viral Detection

Background: During SARS-CoV-2 pandemic, one of the challenges during the planning and execution of control strategies was the global shortage of supplies and personal protection elements (PPEs). For instance, nasopharyngeal swabs for the collection of mucosal samples were one of the scarcest. In Colombia, the limited capacity for characterization, evaluation, validation and the absence of clear regulatory pathways was a major obstacle for manufacturers. The aim of this study is to design, manufacture a bench testing platform as a nasal cavity to evaluate the performance of locally produced nasopharyngeal swabs for mucosal sample collection. Methods: Experimental nasopharyngeal swabs were designed and manufactured via a one-step injection in collaboration with Plastinovo S.A.S. (Bogota, COL). Commercial nasopharyngeal swabs were acquired from Nodford International Co., Ltd and HanChang Medic Co., Ltd. A 3D digital reconstruction of the nasopharyngeal cavity was generated from computed tomography images of an adult patient. An anatomical model of the soft tissues was 3D printed, using a flexible translucent polymeric material (Agilus30, Stratasys) while a rigid white material (VeroWhite, Stratasys) was employed for the bone. A mucous substitute made from egg albumin was loaded with a RNA based vaccine (Stamaril) and placed on the internal cavity of the 3D model. Swabs were introduced into the nasopharyngeal cavity to simulate the conventional sampling process and the sample was transferred to a viral transport medium for RNA extraction followed by RT-qPCR for viral RNA detection. Locally manufactured swabs were tested against commercial counterparts. Results: The 3D printed nasopharyngeal model accurately replicated the anatomy of cavities and the mechanical properties of soft and hard tissue structures. The collection of viral samples proceeded successfully with the mucosal substitute. The substitute exhibited appropriate viscoelastic properties and do not interfere with RT-qPCR. The released/collected sample percentage of injection and commercial swabs was 77.06±5.14% and 63.74±6.28%, respectively. The Plastinovo swabs provide a detection limit and viral load comparable to commercial swabs as demonstrating by Ct values close to the positive control of the vaccine alone (16.51). Conclusion: Nasopharyngeal cavity allows for the bench testing of nasopharyngeal swabs and could be tough for other medical devices. On the other hand, swabs developed by Plastinovo were validated and showed to be suitable for large-scale local production. The next steps will focus on devising the routes to complying with the regulatory schemes for local and international commercialization of nasopharyngeal swabs.

Supercritical CO2Foaming of Lightweight Polyolefin Elastomer/trans-Polyoctylene Rubber Composite Foams with Extra-Soft and Anti-Shrinkage Performance

Lightweight polyolefin elastomer (POE) foams are of great interest in numerous fields. However, POE is difficult to foaming and obtaining the ideal cellular structures before cross-linking. Herein, low-molecular-weight trans-polyoctylene rubber (TOR) with lots of double bonds and low molecular weight was introduced into the POE matrix to improve their vulcanizing and foaming process. Then, a series of lightweight POE/TOR composite foams with adjustable cellular structures and outstanding performance were prepared by supercritical CO2 foaming. It was worth noting that the gel content and foaming temperature windows were greatly improved under the action of TOR, and a record-breaking density as low as 0.036 g/cm3 for POE-based composite foams was harvested. In addition, the as-prepared elastomer foams exhibited rapid shrinkage but slow recovery feature due to the diffusivity difference of gas and cross-linking nature of materials, and its recovery ratio could reach 91.3%. More interestingly, the conversion law of the corresponding density change between hard and soft materials was discovered, and extra-soft POE-based composite foams (like Shore C below 10) were obtained, which could be twisted, folded, compressed, stretched, bent, and rolled with ease. Furthermore, the residual strain and hysteresis loss ratio of as-prepared elastomer foams were as low as 1.56 and 12.95%, respectively. These distinct advantages together with the green foaming process make the composite elastomer foams very promising toward high-performance flexible cellular polymeric materials.

Flexible Thermal Protection Polymeric Materials with Self-Sensing and Self-Adaptation Deformation Abilities

Based on the strategy of killing two birds with one stone, we introduce thermally expandable microspheres into a silicone rubber matrix to fabricate temperature-responsive controllable deformation materials, which exhibit intelligent deformation properties as well as enhanced thermal protection performance, for dynamic thermal protection in the next-generation morphing aircrafts. The formation of hollow structures endows the material with intelligent thermal management ability and makes the thermal conductivity controllable, meeting the requirements of rapid deformation and excellent thermal insulation. The dimensions of the material adaptively expand with increasing temperature, and a constant 50N force can be provided to ensure reliable sealing. Moreover, benefiting from the synergistic effect of the hollow structure and zinc borate in the ceramization process of the silicone rubber, the 10 mm thick material can reduce the temperature from 2000 to 63 °C, and the mass ablation rate is only 4.8 mg/s. To broaden the application of our material, a sensor with a sandwich structure composed of different functional layers is designed. It is pleasantly surprising to observe that the sensor can provide real-time remote warning of fire and overheating sites with a response time as short as 1 s. This synergistic strategy opens a new possibility to fabricate intelligent thermal protection materials.

Avian‐Inspired Perching Mechanism for Jumping Robots

The integration of multiple locomotion strategies and behaviors allows robots to extend the working environment and enhance the performance of each motion. This work integrates perching to a jumping robot to improve the jumping performance. The developed avian‐inspired perching device has a shock‐absorbing mechanism, which consist of a 3D printable flexible polymer material that absorbs the perching impact. This work characterizes the shock‐absorbing performance of the viscoelastic material as a function of hardness and thickness of the material, initial angles of a mechanism, mechanism length, perching speed, and perching angle. This work also characterizes the performance of mechanical interlocking and penetration as the engagement strategies for vertical surfaces. The performance of perching mechanism as a function of hardness of the target surface, contact angle of the claw, and performance of the shock absorption is observed. Finally, demonstrations to evaluate the perching mechanism's performance on the complete system are conducted, and the robot's performance enhancement with an integrated perching motion is shown. This work provides a design methodology to develop and integrate a perching mechanism into jumping robots.

Triboelectric Nanogenerators (TENGs) Based on Various Flexible Polymeric Materials Along With Printed and Non-Printed Electrodes

Four designs (D1-D4) of flexible triboelectric nanogenerators (TENGs) were successfully fabricated in three different configurations for energy harvesting applications. Typically, TENG consists of anode layer, cathode layer, and electrodes. Combination of materials were investigated in this study using polyethylene terephthalate (PET), thermoplastic polyurethane (TPU) and a flexible fabric as top triboelectric (cathode) layers; Kapton and polydimethylsiloxane (PDMS) as bottom triboelectric (anode) layers. Copper (Cu) tape and screen-printed silver (Ag) were used as electrodes. Each of these designs (D1-D4) has three configurations C1, C2 and C3 in which the top substrate (cathode layer) was different from one configuration to other. In order to determine the best material combination that would provide better TENG performance, different configurations were considered. The capability of the TENGs in terms of open circuit voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</sub> ) and short circuit current (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sc</sub> ) were demonstrated by subjecting them to ~5 to 6 N force at 10 Hz operating frequency. A maximum V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</sub> of 21.61 ± 2.27 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</sub> , 35.32 ± 0.89 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</sub> , 31.21 ± 1.43 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</sub> and 45.75 ± 5.09 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</sub> resulted in a power density of 0.29 μW/cm², 1.12 μW/cm², 0.47 μW/cm² and 0.91 μW/cm² from the D1, D2, D3 and D4 designs, respectively. The TENG fabricated using screen printed Ag flake on PDMS and fabric (D4) exhibited the highest open circuit output and a good repeatability after six months of re-testing with a maximum difference of ~ 7.39 % change(ΔV/V) in the output signal. In addition, a cyclic test was performed on D4, the results obtained demonstrate a good durability of the TENG sensor over 1000 cycles. The fabricated TENG device has a simple design, compact size, and demonstrated a better performance in comparison with some of the other works in terms of output voltage.

Control of the pore chemistry in metal-organic frameworks for efficient adsorption of benzene and separation of benzene/cyclohexane

Control of the pore chemistry in metal-organic frameworks for efficient adsorption of benzene and separation of benzene/cyclohexane

Evaluation of Mechanical Properties of 3D-Printed Polymeric Materials for Possible Application in Mouthguards.

Custom mouthguards are used in various sports disciplines as a protection for teeth, temporomandibular joints, and soft tissues of the oral cavity from impact forces. The purpose of this research was to evaluate the mechanical properties of flexible polymeric 3D-printable materials and to select a material with the most favourable physical properties for making intraoral protectors. Four 3D-printable polymeric materials were selected for the evaluation: IMPRIMO LC IBT (Scheu-Dental, Iserlohn, Germany), Keyortho IBT (EnvisionTEC, Gladbeck, Germany), IBT (Formlabs, Somerville, MA, USA), and Ortho IBT (NextDent, Utrecht, Netherlands). A total of 176 samples (44 from each material) was 3D-printed using the stereolitography (SLA) technique. Tensile strength, flexural strength, notch-toughness, Shore hardness, sorption, and solubility tests were conducted. The materials were compared using a series of analyses of variance (one-way ANOVA) with Bonferroni post hoc tests. Statistical analyses were performed with the use of IBM SPSS Statistics 28.0.0 software (IBM, New York, NY, USA). Each material was assigned a score from 1 to 4 depending on the individual test results, and tests were given indexes according to the significance of the parameter in the mouthguard protective function. The number of points obtained by each material in each test was then multiplied by the test index, and the results were tabulated. The material with the highest result among the ones studied-most suitable for the application in mouthguard fabrication-was Keyortho IBT from EnvisionTEC.

Poly(o-phenylenediamine)/ poly(butylene succinate-co-butylene adipate) blend as electroactive material for actuator application

Flexible and efficient electroactive polymeric materials that can convert electrical energy into mechanical work are potential be used as artificial muscles in soft robots, sensors and wearable technology. This work reports on the development of flexible electroactive material based on poly(butylene succinate-co-butylene adipate) (PBSA) as a matrix and poly(o-phenylenediamine) (PoPD) as a conductive filler. The PBSA film flexibility was modified by using dibutyl phthalate (DBP) as a plasticizer. The doped PoPD (dPoPD) particles with the polar free = NH substitution were synthesized and doped with perchloric acid. The prepared dPoPD/PBSA blends possess the enhanced mechanical and electrical properties compared to the pristine PBSA film. The dPoPD/PBSA blend with the dPoPD loading of 0.05%v/v provided the highest storage modulus (2.2 × 106 Pa) at 100 rad/s, the dielectric constant (28) at 40 Hz, and the electrical conductivity (2.67 × 10−9 S/cm). On the other hands, the 0.01%v/v dPoPD/PBSA blend showed the highest deflection distance of 9.71 mm, whereas the highest dielectrophoresis force density was obtained from the 0.05%v/v dPoPD/PBSA blend at 70 V/mm. This work presents the new biobased/conductive polymer blends and demonstrates that the bending response and the required dielectrophoresis force are not inclusively related and each can be individually tailored to meet the soft robot requirements.

Methyl Methacrylate-Based Copolymers: Recent Developments in the Areas of Transparent and Stretchable Active Matrices.

The recent advancements of poly(methyl methacrylate) (PMMA) as a transparent flexible polymer material have been utilized in numerous areas of engineering and materials science. PMMA-based copolymers demonstrate outstanding mechanical and optical properties owing to high transparency, lightweight nature, high impact resistance, and stress relaxation across glass transition temperature. These copolymers have unique characteristics of retaining optical and microstructural integrities during successive bending or elongations which make them an attractive choice for materials of stretchable electronics. In particular, there has been an escalated rise in the use of methyl methacrylate (MMA)-based transparent and stretchable copolymer films during the recent decades. Therefore, we have highlighted these recent developments into a comprehensive review in order to aid the future progress in these diverse fields. Herein, we have highlighted the scope of MMA as an important building block for the synthesis of highly transparent and flexible materials. The synthetic pathways of these copolymer materials and the resulting mechanical properties have been discussed. Moreover, the immense scope of these copolymer films has been highlighted by virtue of their applications in various industries.

Synthesis and Characterization of a Transparent PMMA Based Triboelectric Nanogenerator for Wearable Electronic Applications

With the increase in energy consumption with unprecedented rate, there is an urgent need for the development of independent, efficient and maintenance free power sources. With the growing emergence of flexible, wearable electronic devices in the current market, the requirement for portable and highly flexible power sources has also increased many folds. The electronic devices such as stretchable circuits [1], e-papers [2], bendable displays [3], e-skins [4], wearable electronic devices [5], etc. are receiving wide attention due to their applications in robotics, medical science, human machine interface, fitness trackers, smart watches and many more. The waste mechanical energy in the environment such as vibration, wind and human body motions can be converted into electricity by triboelectric energy harvesting technologies [6]. Energy is one of the essential requirements of the society and it is necessary to search newly and highly efficient technologies that harvest many forms of energy from the environment which is generally wasted. For the last two decades, the scientists and researchers have been focused on the synthesis and characterization of novel source of energy harvesting and self-powered devices useful for numerous energy applications without external inputs.In this paper, a novel triboelectric nanogenerator (TENG) based on Polymethyl methacrylate (PMMA) as transparent and flexible polymer materials with gold nanoparticles (AuNPs) has been synthesized and characterized. The SEM image clearly reveals the spherical shape of the synthesized AuNPs. The XRD pattern of the prepared material shows accurate diffraction peaks at 2theta values indicate the presence of mixed phases of fluorine tin oxide (SnO2), AuNPs, and metallic copper (Cu) which are in excellent agreement with the previously mentioned 2theta values in the literature. Further, the EDS analysis confirms the presence of Sn, Au, O, and Cu within the synthesized TENG. Finally, the proposed synthesize PMMA-based TENG produces maximum AC output voltage and current signal up to 5V and 10 μA, respectively with very high transmittance of 100 %. The electric energy in terms of AC voltage produced by synthesized PMMA-based TENG is further converted into DC voltage which is used to light up light - emitting diodes in future.The synthesized TENG consists of two parts such as lower part and upper part. The spacer (sponge or spring) is placed between the upper part as well as the lower part. The synthesized lower part of TENG consists of three layers such as (a) fluorine tin oxide (FTO), (b) copper (Cu), and (c) gold nanoparticles (AuNPs) whereas the upper part of the synthesized TENG consists of two layers such as (a) aluminum (Al) and (b) polymethyl methacrylate (PMMA) transparent and flexible polymer. By taking FTO substrate, we first deposit the copper layer with micrometer range of thickness on the top of FTO with the help of Magnetron Sputtering technique at 5.8 X 10-2 m bar base working pressure, 60 sccm gas-flow, 200 W power, 200˚C temperature for 5 minutes. Next, the freshly prepared AuNPs are prepared by using the following steps: (A) Seed solution preparation; (B) Growth solution preparation; and (C) Washing the gold nanoparticles:- By centrifugation process, only the gold nanoparticles remains and the other byproducts in the form of liquid is removed.The spherical shape of the synthesized AuNPs has been observed within the SEM image. The XRD pattern of the prepared sample indicates the diffraction peaks of SnO2, AuNPs, and metallic Cu at different 2theta values. The EDS analysis further confirms the presence of Sn, Au, O, and Cu materials within the synthesized lower part of TENG while the UV-Visible spectroscopy analysis clearly shows 100 % light transmission and ~0 % light absorption of transparent and flexible PMMA polymer material used for synthesis of TENG. References Hu, H. S. Kim, J. Y. Lee, P. Peumans, Y. Cui, ACS Nano 4 (2010) 2955-2963. Chen, J. Au, P. Kazlas, A. Ritenour, H. Gates, M. McCreary, Nature 423 (2003) 136-136. Yoon, D.Y Ham, O. Yarimaga, H. An, C.W. Lee, J.M. Kim, Advanced Materials 23 (2011) 5492-5497. Hu, R. Xiong, H. Guo, R. Ma, S. Zhang, Z. L. Wang, V. V. Tsukruk, Advanced Materials 28 (2016) 3549-3556. S. Rim, S. H. Bae, H. Chen, J. L. Yang, J. Kim, A. M. Andrews, P. S. Weiss, Y. Yang, H. R. Tseng, ACS Nano 9 (2015) 12174-12181.W. Kim, J. H. Lee, J. K. Kim, U. Jeong, NPG Asia Materials 12 (2020) 6. Figure 1

Mechanical Behavior of Alkasite Posterior Restorations in Comparison to Polymeric Materials: A 3D-FEA Study.

The present investigation evaluated the effect of the combination of different dental filling materials in Class I cavities under occlusal loading using three-dimensional finite elements analysis (FEA). Six computer-generated and restored models of a lower molar were created in the CAD software and compared according to the biomechanical response during chewing load condition. Two adhesively bonded bulk restorative materials [bulk-fill resin composite (BF) or Alkasite (Alk)] were evaluated with or without the presence of a base material below (flowable resin composite or glass ionomer cement). A food bolus was placed on the occlusal surface mimicking the compressive occlusal load (600 N) during the static linear analysis. The maximum principal stress (tensile) was calculated as stress criteria in enamel, dentin and restoration. All models showed high stresses along the enamel/restoration margin with a similar stress trend for models restored with the same upper-layer material. Stress values up to 12.04 MPa (Alk) or up to 11.12 MPa (BF) were recorded at the enamel margins. The use of flexible polymeric or ionic base material in combination with bulk-fill resin composite or Alk did not reduce the stress magnitude in dentine and enamel. Class I cavities adhesively restored with bulk-fill resin composite showed lighter stress concentration as well as Alk. Therefore, adhesively bonded Alk restoration showed a promising mechanical behavior when used with different base materials or as a bulk restoration for posterior Class I cavity.