Multilayer Polymer Structures Research Articles

Direct ink writing of polymer matrix composite with carbon for driving a flexible thermoelectric actuator of shape memory polymer

Carbon nanomaterials and polymer composites that possess excellent electrical and mechanical properties for soft robots have been investigated over decades in multidisciplinary research fields. As considering the incorporation of carbon into polymer composite, several major concerns include the electrical conductivity, elastic module, and manufacturing flexibility that can enable them to satisfy various functions such as actuation and sensing. In this paper, we report a comprehensive study on how to design and fabricate a soft gripper based on carbon polymer matrix composite and multilayer structure through multistep processes of 3D printing on paper. Using commercial conductive additives of graphene and carbon nanotube with polydimethylsiloxane (PDMS), a polymer matrix composite (PMC) was prepared for the ink of direct ink writing (DIW) with percolation conductivity. Additionally, a shape memory polymer (SMP) was utilized for fused deposition modeling (FDM) of a thermal actuator. Incorporating the DIW of PMC with the FDM of SMP on paper, a soft gripper with four fingers was designed and fabricated to show remarkable thermoelectrical actuation for grasping a 50 mm-diameter 10 g-weight spherical ball. In the future, it would provide an alternative approach for the fields of science and engineering, such as nanomaterials and nanotechnology, space applications, sustainable soft robots, and flexible autonomous systems.

High-throughput 3D printing of continuous carbon fiber–reinforced Polyamide 6/Maleic Anhydride-modified Polypropylene/polypropylene composite by a multifilament feeder

A multifilament feeder was developed to achieve the high-throughput 3D printing of continuous carbon fiber–reinforced thermoplastic composites. Four filaments were supplied to the feeder and simultaneously printed by controlling the feeding speeds to quadruple the manufacturing volume. A water-resistant filament was also developed by the polymer blending of polyamide 6 (PA6) and polypropylene (PP), which provided good adhesion to the carbon fibers and water resistance, respectively. The polymer structure in the continuous carbon fiber–reinforced thermoplastic composites was characterized by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The multilayer polymer structure was observed, which enhanced the water-resistant property. The bending test results revealed that the blending minimized the degradation of the flexural modulus of the 3D-printed unidirectional carbon fiber–reinforced thermoplastic composite under wet conditions.

Research on the mechanical clinching process for the metal–polymer multilayer structure

With the wide application of lightweight materials, the metal–polymer multilayer structure has become a research focus owing to the advantages of lower weight and higher vibration damping. In the current work, the mechanical clinching process of the metal–polymer multilayer structure between Al5052-H32 and polyoxymethylene was investigated. The effect of diverse plate configurations and different test specimen forms on the mechanical characteristics was analysed in terms of geometric parameters, static strength, failure modes and energy absorption. The results showed that the metal–polymer multilayer structure could be successfully connected utilizing the mechanical clinching process. The cross-tension load and lap-shear load of the joint were greatly affected by the plate configuration as well as the test specimen form.

Numerical analysis of two-layered isothermal calendering of viscoplastic and Newtonian fluids with different viscosity ratios

Co-extruded multi-layer plastic sheets and polymer structures formed by calendering process or by cold rolling are widely used in the packaging industry and thin-film transistor manufacturing. The different materials are extruded from separate extruders into the single sheet die which delivers a multi-layer sheet with uniform layer thickness at die exit. This multi-layer sheet is then stretched between counter-rotating rolls to obtain final uniform multi-layer sheet. There are many factors which can influence this process. In this article, calendering a single layer Newtonian or Non-Newtonian material has been extended to analyze a two-layer calendering process for an incompressible Viscoplastic and Newtonian fluids as upper and lower layers with different viscosity ratios. To simplify the equations of motion, the lubrication approximation theory is used. The expressions of non-dimensional pressure gradient, pressure and velocity distribution of both layers are obtained analytically by using proper no slip boundary conditions and dimensionless variables. The dimensionless detachment point is approximated by Regula-Falsi (false position) method. The important engineering factors including detachment point, calendered sheet thickness, roll separation force, power input by rolls, torque on each roll, and adiabatic temperature are all computed. In addition, how the viscosity ratios and viscoplastic casson parameter affect these factors have been investigated. Moreover all established results in literature for single layer calendering Newtonian fluids are also validated at casson parameter β tending towards infinity.

Polyelectrolyte Multilayer Films Based on Natural Polymers: From Fundamentals to Bio-Applications.

Natural polymers are of great interest in the biomedical field due to their intrinsic properties such as biodegradability, biocompatibility, and non-toxicity. Layer-by-layer (LbL) assembly of natural polymers is a versatile, simple, efficient, reproducible, and flexible bottom-up technique for the development of nanostructured materials in a controlled manner. The multiple morphological and structural advantages of LbL compared to traditional coating methods (i.e., precise control over the thickness and compositions at the nanoscale, simplicity, versatility, suitability, and flexibility to coat surfaces with irregular shapes and sizes), make LbL one of the most useful techniques for building up advanced multilayer polymer structures for application in several fields, e.g., biomedicine, energy, and optics. This review article collects the main advances concerning multilayer assembly of natural polymers employing the most used LbL techniques (i.e., dipping, spray, and spin coating) leading to multilayer polymer structures and the influence of several variables (i.e., pH, molar mass, and method of preparation) in this LbL assembly process. Finally, the employment of these multilayer biopolymer films as platforms for tissue engineering, drug delivery, and thermal therapies will be discussed.

Ultrasonic Transducer From Piezoelectric Polymer Multilayer Through Electrophoretic Deposition for Photoacoustic Imaging.

Emerging ultrasound imaging modality based on optical-generated acoustic waves, such as photoacoustic (PA) imaging, has enabled novel functional imaging on biological samples. The performance of the ultrasonic transducer plays a critical role in producing higher quality PA images. However, the high electrical impedance of the small piezoelectric elements in the transducer array causes an electrical mismatch with external circuitry and results in degraded sensitivity. One effective method for reducing the electrical impedance is to implement a piezoelectric multilayer configuration instead of the conventional single layer for the transducer. In this work, we introduced an ultrasonic transducer comprising a piezoelectric polymer multilayer structure produced by an innovative multicycle powder-based electrophoretic deposition, using a suspension of polymer nanoparticles. The multicycle electrophoretic deposition overcomes the redissolution issue in solution-based methods. The ultrasonic transducer comprising the piezoelectric polymer multilayer exhibits significantly enhanced receiving sensitivity as compared to the ultrasonic transducer using a single layer. Ultrasonic transducer with multielement array configuration is obtained using the piezoelectric polymer multilayer, and PA imaging with improved resolution is demonstrated. Theoretical analysis shows that the enhanced transducer performance is mainly attributed to the improved electrical impedance match between the piezoelectric polymer element in the transducer and external receiving circuit.

Organic–Inorganic Hybrid Structure as a Conductive and Transparent Layer for Energy and Optoelectronic Applications

In the era of hybrid organic devices, solution-processed metal-embedded polymer multilayer structures are potential candidates for transparent electrode applications. Here, an organic–inorganic–organic (OIO) layered structure has been fabricated as a metal oxide-free transparent conducting electrode, where a thin metal layer (Ag) was sandwiched between two organic polymer (polystyrene) layers. The metal layer was deposited by the DC sputtering technique, and the polymer layers were deposited by an easy and efficient dip coating technique with good thickness control. The thickness of the middle Ag film was varied from 4 to 30 nm to investigate its effect on the transparency and conductivity of the multilayered structure. The morphological behavior shows that a higher thickness of Ag gives a continuous layer formation and a smooth top surface of the layered structure, which is a vital feature of a good electrode. The results of various investigations of the OIO structure show promising optoelectrical performance for its applicability in transparent and flexible optoelectronics. Depth profiling in X-ray photoelectron spectroscopy (XPS) revealed that the Ag layer retains its metallic form mostly and only a small amount gets oxidized when exposed to the environment. In spite of the formation of silver oxide, an electrical resistivity of 1.1 × 10–4 Ω cm with an optical transparency of ∼75% was obtained in the OIO structure for an 8 nm thickness of the Ag layer. The key findings of the present investigations demonstrate a facile, low-cost, and effective method with a rational design for the fabrication and application of a transparent conducting electrode, which can be an alternative to indium tin oxide (ITO).

Performance Enhancement of Flexible Polymer Triboelectric Generator through Polarization of the Embedded Ferroelectric Polymer Layer

In this work, we report on a flexible triboelectric generator (TEG) with a multilayer polymer structure, consisting of a poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) layer sandwiched by polydimethylsiloxane (PDMS) layers for the performance enhancement of TEGs. We confirmed that the output performance of the TEG is closely dependent on the structure and polarization direction of the PVDF-TrFE layer. In addition, the PDMS layer serves as the electron trapping layer and suppresses the discharging of the surface charges, boosting the output performance. Furthermore, the polarized PVDF-TrFE layer in the preferred direction contributes to increasing the surface potential during the contact–separation motion. The interaction between these two polymer layers synergistically leads to the boosted output performance of TEGs. Specifically, the maximum peak-to-peak output voltage and current density of 420 V and 50 μA/cm2 generated by the proposed architecture, representing approximately a fivefold improvement compared with the TEG with a single layer, even though the same friction layers were used for contact electrification.

Design of multi-passband polymer multilayer film and its application in photovoltaic agriculture

To solve the issue of the contradiction between photovoltaic power generation and plant photosynthesis for sunlight demand, we propose a design method of multi-passband polymer multilayer optical structure. Using polycarbonate (PC) and polymethyl methacrylate (PMMA), two polymer materials with different refractive indices, the passband position and passband bandwidth are calculated and adjusted by the transmission matrix method and TFCalc software. A 450 nm, 660 nm, and 730 nm three-passband filter was realized by superimposing stacks of different band positions. The feasibility of the photovoltaic agriculture was confirmed by the power generation efficiency and the actual plant growth.

Nanocomposites for Food Packaging Applications: An Overview.

There is a strong drive in industry for packaging solutions that contribute to sustainable development by targeting a circular economy, which pivots around the recyclability of the packaging materials. The aim is to reduce traditional plastic consumption and achieve high recycling efficiency while maintaining the desired barrier and mechanical properties. In this domain, packaging materials in the form of polymer nanocomposites (PNCs) can offer the desired functionalities and can be a potential replacement for complex multilayered polymer structures. There has been an increasing interest in nanocomposites for food packaging applications, with a five-fold rise in the number of published articles during the period 2010–2019. The barrier, mechanical, and thermal properties of the polymers can be significantly improved by incorporating low concentrations of nanofillers. Furthermore, antimicrobial and antioxidant properties can be introduced, which are very relevant for food packaging applications. In this review, we will present an overview of the nanocomposite materials for food packaging applications. We will briefly discuss different nanofillers, methods to incorporate them in the polymer matrix, and surface treatments, with a special focus on the barrier, antimicrobial, and antioxidant properties. On the practical side migration issues, consumer acceptability, recyclability, and toxicity aspects will also be discussed.

Flexible Al2O3/plasma polymer multilayer moisture barrier films deposited by a spatial atomic layer deposition process

Al2O3/plasma polymer multilayers were developed and characterized for the moisture barrier films of flexible organic devices. The inorganic Al2O3 thin films were deposited by a spatial atomic layer deposition process and the organic layers were deposited by plasma polymerization in the same chamber using CHF3, benzene, and cyclohexane precursors. The deposition rate, light transmittance, and surface roughness of the plasma polymer films obtained from the three precursors were investigated. The three plasma polymer layers were introduced between Al2O3 layers and their effect on the water permeability and flexibility of each Al2O3/plasma polymer multilayer structure was evaluated. The multilayer structure with hydrocarbon from cyclohexane shows better flexibility than that with fluorocarbon by CHF3 and hydrocarbon by benzene. Polymer interlayers with plasma thicker than 20 nm are necessary for reasonable flexibility. The authors increased the number of layers up to 21 to improve the water permeability and flexibility. The water vapor transmission rate (WVTR) of a 100 nm-thick Al2O3/plasma polymer was reduced to 8.5 × 10−5 g/m2 day with the 21-layer structure. This WVTR value is 58% lower than that of the 100 nm-thick single-layer Al2O3. The WVTR of a 100 nm-thick single-layer Al2O3 increased by 900% when it was bent 1000 times with a bending radius of 1 cm due to film cracks, while, under the same conditions, the 21-layer structure showed only a 32% increase in the WVTR. These results indicate that the nanometer-scale-thick plasma polymer can be an effective solution for multilayer moisture barrier films.

Determination of rational process-dependent parameters of manufacturing multilayer polymer structures by physical modeling

Abstract The paper researches a very important issue of improving coextrusion technology of secondary polymer materials processing. The paper also presents the results of the research by physical modeling of such process-dependent parameters as preform cooling temperature in the mold and preform secondary deformation pressure, which were not studied enough earlier. Research was carried out using the physical modeling methods. The rational cooling time of the preform in the mold, which ensures its stability of shape, is determined. The rational blowing pressures of tubular preform in the press mold, ensuring the integrity of the end product, are determined.

Carboxylated multiwalled carbon nanotubes effect on dynamic mechanical behavior of soft films composed of multilayer polymer structure

Dynamic mechanical properties due to incorporation of carboxylated multiwalled carbon nanotubes into three-layer polymer structure, with high damping property, via in situ emulsion polymerization and also blending are studied in detail. Using of storage modulus, loss modulus and damping behavior obtained from the DMA was investigated the manner of carboxylated MWCNTs into and onto the three-layer polymer structure. It was observed that different morphology and topology were formed using these two manufacturing methods. Also, it was observed that dynamic mechanical and damping properties are due to complex and multifunctional parameters such as adhesion, constrained chains, molecular optimum mobility between polymer and nanotubes.

Physical coloring of multilayered polymeric structures

Multilayered polymer structures made of two transparent, hyperelastic thermoplastic polyurethanes (TPUs) have been studied. The sheets, made by co‐extrusion and layer multiplication techniques, exhibited “physical coloring”, where a preferred wavelength range was reflected and visualized, due to the refractive index difference and nanometric thicknesses of the alternating layers. The extrusion system comprises two extruders and a series of multiplying units, each doubling the number of layers, such that 12 multiplying units render 212 + 1+1 (= 8,193) layers. For a 0.8 mm‐thick die, the resulting layers after die swell are ∼ 150 nm thick. The extrusion temperatures of both grades were adjusted to equilibrate the viscosities and thus stabilize the layers. TPUs are highly elastic, and large stretching ratios allow for significant reduction in thickness. Physical coloring developed in a controlled, reversible manner. The visual color correlates with elongation, and can be offset by choice of initial thickness. Both reflected and transmitted wavelengths change throughout the whole visible range. A model was developed to fit the reflectance data, by introducing a “stress–volume coefficient” due to volume changes during stretch. This model fits the data very well. Characterization by AFM and TEM showed few discontinuous layers and some defects in the structure, nevertheless the multilayer structure is demonstrated. POLYM. ENG. SCI., 59:112–119, 2019. © 2018 Society of Plastics Engineers

Graphene patterns supported terahertz tunable plasmon induced transparency.

The tunable plasmonic induced transparency has been theoretically investigated based on graphene patterns/SiO2/Si/polymer multilayer structure in the terahertz regime, including the effects of graphene Fermi level, structural parameters and operation frequency. The results manifest that obvious Fano peak can be observed and efficiently modulated because of the strong coupling between incident light and graphene pattern structures. As Fermi level increases, the peak amplitude of Fano resonance increases, and the resonant peak position shifts to high frequency. The amplitude modulation depth of Fano curves is about 40% on condition that the Fermi level changes in the scope of 0.2-1.0 eV. With the distance between cut wire and double semi-circular patterns increases, the peak amplitude and figure of merit increases. The results are very helpful to develop novel graphene plasmonic devices (e.g. sensors, modulators, and antenna) and find potential applications in the fields of biomedical sensing and wireless communications.

Inkjet-printed Polyvinyl Alcohol Multilayers.

Inkjet printing is a modern method for polymer processing, and in this work, we demonstrate that this technology is capable of producing polyvinyl alcohol (PVOH) multilayer structures. A polyvinyl alcohol aqueous solution was formulated. The intrinsic properties of the ink, such as surface tension, viscosity, pH, and time stability, were investigated. The PVOH-based ink was a neutral solution (pH 6.7) with a surface tension of 39.3 mN/m and a viscosity of 7.5 cP. The ink displayed pseudoplastic (non-Newtonian shear thinning) behavior at low shear rates, and overall, it demonstrated good time stability. The wettability of the ink on different substrates was investigated, and glass was identified as the most suitable substrate in this particular case. A proprietary 3D inkjet printer was employed to manufacture polymer multilayer structures. The morphology, surface profile, and thickness uniformity of inkjet-printed multilayers were evaluated via optical microscopy.

Cold sintering and co‐firing of a multilayer device with thermoelectric materials

AbstractCold‐sintered ZnO and Ca3Co4O9 polycrystalline materials were shown to have thermoelectric properties comparable to those of conventionally sintered ceramics. Extending these processing conditions into a cold sintering co‐fired ceramic (CSCC) technology, we integrated n‐type and p‐type thermoelectric oxides and a separating insulating layer to demonstrate functional multilayer thermoelectric generator devices. A co‐fired structure with an insulating 8 mol% yttria‐stabilized zirconia (8YSZ) layer enabled multilayer thermoelectric generators (TEG) to be fabricated with a 5 n‐p junction device (20 layers). A transmission electron microscopy analysis of the interfaces between the various materials under the co‐firing cold sintering showed some interdiffusion of chemical constitutes in a 2.0 μm interface region between the respective ceramic phases. The co‐firing of multilayer ceramic and polymer structures were also shown to be possible using insulation layers of polytetrafluoroethylene (PTFE) thermoplastic layers. This demonstrated the feasibility of a single‐step process for new structures with both ceramics and polymers, opening up new directions for many new device designs.

Sensitivity analysis of multilayer microporous polymer structures for terahertz volatile gas sensing.

The sensitivity of multilayer microporous polymer structures (MPSs) for in situ and label-free organic vapor sensing is investigated in terahertz frequency. The porous structure provides a large hydrophilic surface area and numerous micropores to adsorb or fill polar vapors, thereby leading to greatly enhanced wave-analyte interaction with an apparent terahertz signal change. Different configurations of MPS with distinct geometric parameters are fabricated to study the structure-dependent sensitivity. The signal responses from the acetone-vapor-filled MPS, represented as effective absorption coefficient and refractive index variation, are proportional to the amounts of vaporized molecules. The responsivity is independent of MPS stacking configuration but can be significantly improved by decreasing the micropore volume. The linear responsivity range for the acetone vapor concentration is as wide as 200 ppm, and the detection limit can be as low as 1 ppm corresponding to the molecular density of 31 pmol/mm3. Different concentrations of toxic methanol adulterated in alcoholic aqueous solutions are successfully identified in their vapor phase by using the MPS-based terahertz sensor with an optimal sensitivity.

Growth of ZnO nanowires on multi-layered polymer structures fabricated by UV liquid transfer imprint lithography

Among various growth processes, hydrothermal synthesis has been widely employed to produce ZnO nanowires because of its simplicity and cost effectiveness. However, the successful hydrothermal synthesis of ZnO nanowires on multi-layered polymer structures has been limited due to growth inhibitors in the polymer. For example, alpha-hydroxy ketone resolved in a UV-curable polyurethane acrylate (PUA) resin forms carboxyl groups (COOH) consisting of hydroxyl groups (OH) on the α-position of a carbonyl group (CO) during the UV-curing process. The carboxyl groups suppress the nucleation and growth of ZnO nanowires. In this paper, multi-layered polymer structures were fabricated by liquid transfer imprint lithography (LTIL), and the enriched carboxyl groups on the UV-cured PUA structures were pre-treated with hexamethylenetetramine (HMTA) solution to reduce the inhibitive influence of the carboxyl groups. The HMTA pre-treatment enabled ZnO nanowires to grow hydrothermally on multi-layered PUA structures despite the initial presence of carboxyl groups.

Relaxation dynamics of multilayer triangular Husimi cacti.

We focus on the relaxation dynamics of multilayer polymer structures having, as underlying topology, the Husimi cactus. The relaxation dynamics of the multilayer structures is investigated in the framework of generalized Gaussian structures model using both Rouse and Zimm approaches. In the Rouse type-approach, we determine analytically the complete eigenvalues spectrum and based on it we calculate the mechanical relaxation moduli (storage and loss modulus) and the average monomer displacement. First, we monitor these physical quantities for structures with a fixed generation number and we increase the number of layers, such that the linear topology will smoothly come into play. Second, we keep constant the size of the structures, varying simultaneously two parameters: the generation number of the main layer, G, and the number of layers, c. This fact allows us to study in detail the crossover from a pure Husimi cactus behavior to a predominately linear chain behavior. The most interesting situation is found when the two limiting topologies cancel each other. For this case, we encounter in the intermediate frequency/time domain regions of constant slope for different values of the parameter set (G, c) and we show that the number of layers follows an exponential-law of G. In the Zimm-type approach, which includes the hydrodynamic interactions, the quantities that describe the mechanical relaxation dynamics do not show scaling behavior as in the Rouse model, except the limiting case, namely, a very high number of layers and low generation number.