Electromechanical behavior of fiber-reinforced dielectric elastomer membrane

Based on its large deformation, light weight, and high energy density, dielectric elastomer (DE) has been used as driven muscle in many areas. We design the fiber-reinforced DE membrane by adding fibers in the membrane. The deformation and driven force direction of the membrane can be tuned by changing the fiber arrangements. The actuation in the perpendicular direction of the DE membrane with long fibers first increases and then decreases by the increasing of the fiber spacing in the perpendicular direction. The horizontal actuation of the membrane decreases by decreasing the spacing of short fibers. In the membrane-inflating structure, the radially arranged fibers will break the axisymmetric behavior of the structure. The top area of the inflated balloon without fiber will buckle up when the voltage reaches a certain level. Finite element simulations based on nonlinear field theory are conducted to investigate the effects of fiber arrangement and verify the experimental results. This work can guide the design of fiber-reinforced DE.     

Formation and characterization of cast and biaxially stretched poly(butylene terephthalate) film

An experimental study of structure development in cast film exhibited only α-form crystallites and relatively low crystallinities (X_c = 3.5–14%), while biaxially stretched films showed a mixed character of both α- and β-form crystallites with crystallinities of 20–30%. Crystal perfection increases with uniaxial deformation. Biaxiality causes a decrease both in crystal perfection and crystallinity of the films. Annealing increases crystallinity. The orientation of the films has been determined by refractive indices and WAXS pole figures. Polymer chains orient rapidly to the machine direction (MD) with uniaxial stretching. Increasing biaxiality causes an increase in population of TD-oriented crystals. The planarity of the film increases with simultaneous transverse stretching. The phenyl rings orient into the plane of the film. Annealing further increased the orientation of the films.     

Mixed-ion linear actuation behaviour of polypyrrole

The linear actuation of polypyrrole (PPy) films polymerized at 0.85 V (versus Ag-wire) and −27 °C in propylene carbonate solutions of tetrabutylammonium trifluoromethanesulfonate (TBACF₃SO₃) was investigated in the same monomer-free electrolyte. The actuation properties were evaluated by electrochemomechanical deformation measurements (ECMD) during cyclic voltammetry and potential step experiments. The ECMD response revealed mixed-ion actuation behaviour for the film, namely the polymer film actuation was dominated by cation movement at potentials less than 0 V and anion movement at potentials greater than 0 V, with film lengthening seen at both potential extremes. It was found that the ratio of cathodic to anodic actuation can be modulated by the scan rate. Longer-term actuation (50 potential steps from −1 V to 0 V, or from 0 V to +1 V), indicated better film stability when cycled in the anodic region. Changing the electropolymerisation potential to a higher value of 1.2 V led to a modification in ECMD characteristics for the PPy/CF₃SO₃ films.     

Cost-effective disposable thiourea film modified copper electrode for capacitive immunosensor

Cost-effective disposable electrodes were fabricated from copper clad laminate, usually used for printed circuit board (PCB) in electronic industries, by using dry film photoresist. Electro-oxidation (anodisation) was employed to obtain a good formation of thiourea film on the electrode surface. The affinity binding pair of carcinoembryonic antigen (CEA) and anti-carcinoembryonic antigen (anti-CEA) was used as a model system. Anti-CEA was immobilized on thiourea film via covalent coupling. This modified electrode was incorporated with a capacitive system for CEA analysis. This capacitive immunosensor provided a linear range between 0.01 and 10 ng ml⁻¹ with a detection limit of 10 pg ml⁻¹. When applied to analyze CEA in serum samples, the results agreed well with the enzyme linked fluorescent assay (ELFA) technique (P > 0.05). The proposed strategy for the preparation of disposable modified copper electrode is very cost effective and simple. Moreover, it provides good reproducibility. This technique can easily be applied to immobilize other biological sensing elements for biosensors development.     

Structure–property–processing relationships of single-wall carbon nanotube thin film piezoresistive sensors

In an investigation of structure–property–processing relationships for SWCNT thin film piezoresistive sensors, the gauge factor of the sensors for a small tensile deformation (less than 2% strain) was found to be close to unity and showed negligible dependence on the film thickness and SWCNT bundle length (L) and diameter (d). However, for a large tensile deformation (20–30% strain), the film thickness and the microstructure of SWCNTs had a compounding effect on the piezoresistive behavior. A gauge factor of ∼5 was obtained for the sensors fabricated with SWCNT bundles of short length and thin diameter (L = 549 nm and d = 3.7 nm) with thicker films. Furthermore, the gauge factor of the sensors was found inversely proportional to the excluded volume V_ex of SWCNT bundles (V_ex ∝ 1/L² d).     

Self-Strengthening Dielectric Elastomer of Triblock Copolymer with Significantly Improved Electromechanical Performance under Low Voltage

Dielectric elastomer actuators (DEAs) are promising soft electromechanical transducers for soft robotics. Fabricating a high-performance DEA actuated by sub-kV voltage remains challenging. Here, a facile method not only to fabricate ultrathin dielectric elastomer films of triblock copolymers but also to enhance the dielectric breakdown strength and thus enhance the electromechanical performance is reported. A thick thermoplastic elastomer film of poly(styrene-b-butyl acrylate-b-styrene) from solution blading is symmetrically pre-stretched and relaxed at 120 °C to fabricate a freestanding ultrathin DE film. Compared with the pristine DE film of the same thickness (12 µm), the thermally-relaxed DE film with equally biaxial pre-stretch ratio 3.5 × 3.5 exhibits increased electrical breakdown strength by a factor of 1.9 (from 43 to 82 V µm⁻¹), maximum actuation area strain by a factor of 1.9 (from 11.7% to 22.4%), and highest energy density by a factor of 5.7 (from 4.5 to 25.8 kJ m⁻³). The enhancement may be ascribed to the self-reinforcement of the dielectric breakdown strength due to the morphology change of polystyrene nanodomains from spheres to oblate spheroids. Thanks to the ultra-thinness, the high electromechanical performance is achieved within sub-kV driving voltage in all cases.     

Annealing a graphene oxide film to produce a free standing high conductive graphene film

A free-standing graphene oxide film (GOF) obtained by self-assembly at a liquid/air interface was annealed in a confined space between two stacked substrates to form a free-standing highly conductive graphene film. Characterization indicates that the oxygen-containing functional groups (e.g. epoxy, carboxyl, and carbonyl) were removed as small molecules (e.g. H₂O, CO₂, and CO) during the annealing, meanwhile the size of sp² domains in the film was decreased. When annealed between two stacked wafers, random interlayer expansion and fractional movement in the GOF were suppressed by the pressure-induced friction, which helps preserve the morphology of the film. The conjugation in the basal plane of graphene and π–π interactions between well stacked graphene sheets favor the transportation of charge carriers in the film, to produce a good electrical conductivity of the resulting free-standing reduced GOF (increased from 1.26 × 10^?5 to 272.3 S/cm).     

Functionalization of porous agarose film with single‐walled carbon nanotubes as excellent electrochemical interface materials

Three‐dimensional (3D) agarose gel network could be readily modified with single‐walled carbon nanotubes (SWNTs) through their noncovalent interactions. Because of the embedded SWNT network, the agarose‐SWNT film fabricated by the gel‐drying method well maintained its in‐plane shape and size. Compared with pure agarose film, the maximum strain at break and strength of agarose‐SWNT film could be increased by 67.2% and 24%, respectively. More importantly, modifying the bare glass carbon electrode (GCE) with agarose‐SWNT film, we observed 12 times increase in dopamine (DA) electrochemical peak current, and 2.6 times increase in the case of potassium ferricyanide (K₃Fe(CN)₆). The porous 3D agarose network interpenetrated with high‐conductivity SWNT network might contribute to the excellent electrochemical interface property. POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers     

The deformation behavior of polypropylene film under high strain rates

The relationship between stress and strain for polypropylene film was studied under strain rates from 0.13 to 5.21 s^?1 in order to study the deformation behavior of film under higher strain rates than previous studies. Uniform thickness was obtained in the strain rates from 2.08 to 5.21 s^?1 at 435 K, or from 2.08 to 3.13 s^?1 at 437 K. The temperature rise of film due to the generation of heat from plastic strain influenced the relationship between stress and strain, in particular, at high strain rates and low temperature. Material constants for the constitutive equation of film were determined using the measurements from 2.08 to 5.21 s^?1 at 435 K and from 2.08 to 3.13 s^?1 at 437 K. Film thicknesses during and after transverse direction stretching were successfully predicted by applying the material constants obtained. The authors concluded that the material constants should be determined by applying the stretching conditions, under which there is little or no effect from heat generation and under which film can be stretched uniformly in thickness. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Process for the formation of biaxially oriented films of poly(p-phenylene terephthalamide) from liquid crystalline solutions

A new process for making equal biaxially oriented films from liquid crystalline solutions of poly(p-phenylene terephthalamide) (PPD-T) is described. The process involves extruding solutions of PPD-T/H₂SO₄ through an annular die and over an oil-coated mandrel into a coagulation bath. The films were studied using wide angle X-ray diffraction (WAXS) and scanning electron microscopy (SEM). Tensile stress–strain properties were obtained on samples cut at various directions in the plane of the film. Biaxially oriented films which possess equal properties in the various directions in the plane of the film were produced. Moduli of 2.3 × 10⁹ Pa and tensile strengths of 9.6 × 10⁷ Pa were obtained in the plane of the film. Films with unequal biaxial orientation were also produced. These tend to have higher modulus/tensile strength in the direction of major orientation, the machine direction (up to 8.3 × 10⁹ Pa/2.5 × 10⁸ Pa), but become brittle in the transverse direction.     

Strain rate dependence of the work of fracture response of an amorphous poly(ethylene‐naphthalate) (PEN) film

The essential work of fracture (EWF) response of an amorphous film of high molecular weight poly(ethylene‐2, 6‐naphthalate) (PEN) was determined on tensileloaded deeply double‐edge notched (DDEN‐T) specimens at various deformation rates (v=1, 10 and 100 mm/min) at ambient temperature. The DDEN‐T specimens showed full ligament yielding (marked by a load drop in the force‐displacement curves) based on which the yielding was separated from the subsequent necking. The yielding related specific essential work of fracture (W_e,y) changed parallel with the yield strength (σ_y), whereas the critical crack tip opening displacement (?_y, 0) remained practically constant in the v range studied. As a consequence, W_e,y(v) could well be estimated by the product of σ_y(v).?_y,0. Necking occurred by cold drawing superimposed by some strain‐induced crystallization at the highest deformation rate. The necking‐related EWF terms strongly depended on the deformation (strain) rate. Based on previous results on amorphous PENs of various molecular weight (MW), it was argued that increasing deformation rate corresponds to decreasing MW and vice versa. This was reasoned by assuming that only a part of the entangled molecular chain participates in the load distribution under high strain rate conditions.     

Material properties of ZnS nanoparticles incorporated soy protein isolate biopolymeric film

ABSTRACT

Glycerol plasticised soy protein isolate (SPI) films at different contents (1 to 5% w/w w.r.t SPI) of zinc sulphide (ZnS) nanoparticles were fabricated. Before the film formation, the ZnS nanoparticles incorporated SPI suspensions were subjected to molecular mass studies by SDS-PAGE and specific conductivity studies. SPI films and ZnS nanoparticles incorporated SPI films were structurally and mechanically characterised by Fourier transform infrared spectroscopy (FT-IR) and mechanical properties, respectively. Transmittance and water uptake studies were also carried out for ZnS nanoparticles incorporated SPI films. The results from transmittance, water uptake and FT-IR studies indicated a good compatibility between the ZnS nanoparticles and the SPI. With the increase in the contents of ZnS nanoparticles from 0 to 4%, the tensile modulus increased from 87.4 to 99?MPa. The water uptake decreased significantly from 159 to 10.76%. However, the results showed the absence of antibacterial effect in ZnS nanoparticles incorporated SPI film.     

Crazelike features in deformation of hard elastic poly(4-methyl-1-pentene) film

A hard elastic film of poly(4-methyl-1-pentene) was investigated by using wide-angle X-ray diffraction, small-angle X-ray scattering (SAXS), and stress–strain measurements. The film showed somewhat hard elasticity above the glass transition temperature (T_g), while it showed a brittle nature below T_g. In the former case, the SAXS pattern of the stretched film was very analogous to that of usual crazed materials (crazelike feature), namely void scattering on the meridian and interference scattering due to microfibrils on the equator. The fibrillation was discussed in terms of deformability of the lamellae and, further, that of the hellcal chain. Our results were also compared with the model of ?a?kovi? and Hosemann for deformation of hard elastic crystalline materials.     

Color change of an iodinated poly(vinyl alcohol) film by physical deformation

The color change of an iodinated poly(vinyl alcohol) (PVA) film caused by physical deformation was investigated in this study. The color of a PVA film soaked in an aqueous potassium iodide (KI)/I₂ solution was light yellow, but it turned light blue when the film was physically deformed. The ultraviolet–visible absorption spectrum of the iodinated PVA film extended uniaxially in air was measured at various extension levels. Without deformation, the film showed UV absorption bands at 210, 290, and 360 nm. However, under deformation, the film showed new visible light absorption bands at 440 and 620 nm. From the UV–vis absorption spectra of several iodinated solutions, we found that the absorption wavelength of iodine was affected by the cohesive energy of the solvents. The KI/I₂ diethyl ether solution showed an absorption band at 460 nm, and this provided a clue to understanding the color change of the PVA–iodine complexes caused by physical deformation. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43036.     

A study of film thickness and hydrodynamic entrance length in liquid laminar film flow along a vertical tube

The liquid film thickness and hydrodynamic entrance length in a vertical tube was studied experimentally and numerically. Measurements using distilled water, 30 wt % MEA and 40 wt % sugar solutions were carried out to investigate the effects of liquid flow rate on the formation of the liquid film. The experimental results validate the new Navier‐Stokes based equation in cylindrical coordinates (Eq. 16) and the volume of fluid (VOF) model giving a competitively high prediction of the liquid film thickness especially in the low Reynolds number region. In addition, a new empirical model and an improved minimal surface model have been first proposed for calculation of the hydrodynamic entrance length, with a relatively reasonable average absolute relative deviation (AARD) of 3.03% and 6.83%, respectively. Furthermore, the effects of the hydrodynamic entry length on the gas–liquid interfacial area calculated by the improved minimal surface model were comprehensively studied, and can be ignored if the ratio of the liquid film length (y) and the hydrodynamic entrance length (λ_E) is lower than 10. However, it should be noted that the hydrodynamic entrance length cannot be ignored in packed columns in which the liquid flow is very complex due to the packings with different structures and materials. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2078–2088, 2018     

Real-time in situ light scattering and X-ray scattering studies of polyethylene blown film deformation

A series of linear low-density polyethylene blown films were studied using the techniques of time-resolved, small-angle X-ray scattering (SAXS) using a synchrotron source and a time-resolved, small-angle light scattering. Scattering patterns and the load-extension curve were obtained simultaneously during deformation. It was found that the initial orientation of the film, with respect to the tensile axis, was important in determining the operative elastic deformation modes. Films drawn parallel to the machine direction (MD) showed evidence for lamellar separation, whereas interlamellar shear occurred in films drawn parallel to the transverse direction. In films drawn at 45° to MD, lamellar stack rotation was observed via SAXS. In all cases, the yield point corresponded to the activation of crystallographic deformation and the onset of the disruption of crystalline lamellae. In films drawn parallel to MD, the SAXS showed a distinct 4-point pattern upon macroscopic yield, indicating lamellar corrugation. Regardless of the initial orientation, a fibrillar morphology was achieved at some strain after yield that coexisted with the fragmenting lamellar morphology. Comparison of results from deformed spherulitic bulk samples showed that the study of oriented blown film containing a stacked lamellar morphology may be used, to a first approximation, as a model for the deformation of different regions of spherulites in unoriented spherulitic samples. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 321–339, 1998     

Charge-induced asymmetrical displacement of an aligned carbon nanotube buckypaper actuator

Randomly dispersed carbon nanotube buckypaper (BP) actuation in open air, ambient conditions was shown to correlates well with the carbon-carbon bond length changes due to charge and discharge. The displacement of magnetically aligned BP actuators applied with a positive voltage was 450% higher than that for an applied negative voltage, which verifies the asymmetrical deformation characteristics of nanotube actuation. Charge-injected actuation of aligned BP can produce a 0.22% strain by applying a high voltage (1100 V). The aligned BP actuators exhibited a higher strain than did randomly dispersed BP actuators. The aligned BP actuators showed stable and fast responses under ambient, open air conditions without electrolytes, which offers direct experimental verification that BP actuation comes directly from carbon-carbon bond deformation due to charge and discharge processes. The nanotube BP actuators demonstrated a much faster response compared to other polymer-based actuators.     

Strain history of the melt in film blowing

Techniques have been developed for measuring the strain and thermal histories of fluid elements as they move from the die lips to the freeze line. Motion pictures were analyzed to determine the rates of extension in the machine and transverse directions. A radiation pyrometer was used to measure the temperature of the film. These techniques were used to study the film blowing of polyethylene; a 2.5-in. diameter die was used, and blow-up ratios in the range of 1.8 to 3.4 were employed. Film thickness ranged from 2 to 4 mils. The maximum measured extensional strain rates in both the transverse and machine direction were in the range of 0.15 to 0.6 sec^?1. Standard shrinkage and impact tests were performed on the finished films, and an attempt was made to correlate the results with several simple empirical norms of the strain history. No correlation could be discerned. The results of this study are inconsistent with some popular ideas about the origin of orientation in blow films, but they are consistent with some recently published data on the influence of deformation on orientation in melt-drawn capillary extrudate.     

Thickness-dependent microstructural and electromechanical properties in polyurethane films obtained by polymer solution casting

Electroactive polymers (EAPs) are promising materials for actuation and energy harvesting applications. Among the EAPs, polyurethane (PU) material is of considerable interest given its high values of deformation under an electric field. The electromechanical properties were found to be dependent on the processing technique and the thickness of the film. To understand this relationship, a comprehensive study was carried out on polyether-based thermoplastic PU elastomer films elaborated by solution casting with thicknesses between 12 and 220 μm. Microstructural, dielectric, mechanical, and electrostriction studies were conducted. Thin films present a lower strain for a given electric field compared to thick films. The films exhibit a structural gradient along the thickness direction: a fast evaporation in the upper part of the film close to the interface with air inhibits the phase separation but a more favored one in the lower part. This is consistent with the modeling based on the gradient of dielectric constant and the experimental, mechanical, and dielectric characterizations. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46981.     

Electrochemical actuation properties of a novel solution-processable polythiophene

A solution-processable polythiophene, poly((E)-4,4″-didecoxy-3′-styryl[2,2′:5′,2′′]terthiophene) demonstrated large electrochemically induced strain up to 11.5%. Free-standing polymer films were characterised using four-point probe conductivity measurements, cyclic voltammetry and electrochemical actuation measurements. Conductivities of ∼6 × 10⁻⁵ S/cm (reduced state) or ∼1-2 S/cm (oxidised state) were measured. Well-defined polymer oxidation-reduction responses were observed in both the propylene carbonate and acetonitrile electrolytes, with electrochemical efficiency of >80% observed under ideal conditions. Results obtained suggested that the actuation strain approximately correlates with the size of the anion (i.e. TFSI > PF₆⁻ > ClO₄⁻) used in the electrolyte. The largest strain ∼11.5% was obtained in an electrolyte solution consisting of 0.1 M Li.TFSI in acetonitrile. The maximum strain attainable increased with an increase in the anodic potential applied and decreased with an increase in stimulation frequency or increasing mechanical load. Such functionalised polythiophene material has the combined advantage of solution processability and the ability to produce large strain.