Low-density Polyethylene Substrate Research Articles

Temperature Dependence of Electrical Resistance in Graphite Films Deposited on Glass and Low-Density Polyethylene by Spray Technology

Graphite lacquer was simply sprayed on glass and low-density polyethylene (LDPE) substrates to obtain large area films. Scanning Electron Microscopy (SEM) images, Raman spectra, X Ray Diffraction (XRD) spectra and current-voltage characteristics show that at room temperature, the as-deposited films on different substrates have similar morphological, structural and electrical properties. The morphological characterization reveals that the films are made of overlapped graphite platelets (GP), each composed of nanoplatelets with average sizes of a few tens of nanometers and about forty graphene layers. The thermoresistive properties of the GP films deposited on the different substrates and investigated in the temperature range from 20 to 120 °C show very different behaviors. For glass substrate, the resistance of the film decreases monotonically as a function of temperature by 7%; for LDPE substrate, the film resistance firstly increases more than one order of magnitude in the 20–100 °C range, then suddenly decreases to a temperature between 105 and 115 °C. These trends are related to the thermal expansion properties of the substrates and, for LDPE, also to the phase transitions occurring in the investigated temperature range, as evidenced by differential scanning calorimetry measurements.

Evaluation of copper-doped TiO2 film supported on glass and LDPE with the design of a pilot-scale solar photoreactor

Synthesis of copper-doped TiO2 (Cu:TiO2) and undoped TiO2 were performed by the sol–gel method. These photocatalysts were characterized by Raman spectroscopy, XRD, and diffuse reflectance. The synthesized catalysts were fixed on glass by the Doctor Blade technique, and on low-density polyethylene (LDPE) by the liquid phase suspension method. The films were characterized by SEM-EDX. The use of doped and undoped photocatalysts fixed in two types of substrates was evaluated in a pilot scale photoreactor under solar radiation. The photoreactor consisted of a simple model designed based on the use of photocatalysts fixed on flat substrates. The adsorption, photodegradation and photolysis processes of methylene blue (MB) were evaluated separately in order to define the extent to which the photocatalyst degraded. The pilot scale system, with the method of fixing the catalyst on a glass substrate, degraded 72.8% of the dye in 6 h, studied under the Langmuir Hinshelwood pseudo-first-order mathematical model with a constant of 0.0024 min−1. With the method of fixing the catalyst on an LDPE substrate, it degraded 68.1% in 6 h, following the same mathematical model, with a constant of 0.0021 min−1.

Influence of the Thermomechanical Characteristics of Low-Density Polyethylene Substrates on the Thermoresistive Properties of Graphite Nanoplatelet Coatings

Morphological, structural, and thermoresistive properties of films deposited on low-density polyethylene (LDPE) substrates are investigated for possible application in flexible electronics. Scanning and transmission electron microscopy analyses, and X-ray diffraction measurements show that the films consist of overlapped graphite nanoplatelets (GNP) each composed on average of 41 graphene layers. Differential scanning calorimetry and dynamic-mechanical-thermal analysis indicate that irreversible phase transitions and large variations of mechanical parameters in the polymer substrates can be avoided by limiting the temperature variations between −40 and 40 °C. Electrical measurements performed in such temperature range reveal that the resistance of GNP films on LDPE substrates increases as a function of the temperature, unlike the behavior of graphite-based materials in which the temperature coefficient of resistance is negative. The explanation is given by the strong influence of the thermal expansion properties of the LDPE substrates on the thermo-resistive features of GNP coating films. The results show that, narrowing the temperature range from 20 to 40 °C, the GNP on LDPE samples can work as temperature sensors having linear temperature-resistance relationship, while keeping constant the temperature and applying mechanical strains in the 0–4.2 × 10−3 range, they can operate as strain gauges with a gauge factor of about 48.

Peening Effect of Glass Beads in the Cold Spray Deposition of Polymeric Powders

Cold spray is a green additive manufacturing method that accelerates micron-size particles to supersonic speeds. At these high speeds, the particles deposit upon impact with a desired surface. High-density polyethylene, polyurethane, polyamide-12, polystyrene, and ultra-high molecular weight polyethylene particles were cold-sprayed onto a low-density polyethylene substrate under different process conditions. Glass beads with diameters between 20 and 120 µm were added to each batch to study the effect of non-adhesive peening particles on the deposition efficiency and the quality of the final deposited layer of a series different polymeric powders. The successful deposition window was compared for the cold spray process with and without the addition of glass beads. Adding the glass beads to the polymer powders was found to widen the successful windows of deposition to both higher and lower impact velocities at a given temperature for all the polymer powder studied. In addition, adding peening particles were found to make deposition possible at lower particle temperatures where deposition had not been successful previously. This was especially important for ultra-high molecular weight polyethylene particles for which deposition in the absence of peening particles was not possible below 60 °C, but with peening particles was successful even at room temperature. Peening particles were found to increase deposition efficiency by as much as 50% for a given set of deposition conditions. The appropriate size of the added glass beads to maximize the deposition efficiency was found to be comparable to the size of the depositing particles. The addition of glass beads was also found to reduce the surface roughness of the deposited layer by more than 50%. Finally, for processing conditions with particle velocities below a Mach number of one, no glass beads were found to adhere to the resulting cold-sprayed substrates.

Thermoresistive Properties of Graphite Platelet Films Supported by Different Substrates.

Large-area graphitic films, produced by an advantageous technique based on spraying a graphite lacquer on glass and low-density polyethylene (LDPE) substrates were studied for their thermoresistive applications. The spray technique uniformly covered the surface of the substrate by graphite platelet (GP) unities, which have a tendency to align parallel to the interfacial plane. Transmission electron microscopy analysis showed that the deposited films were composed of overlapped graphite platelets of different thickness, ranging from a few tens to hundreds of graphene layers, and Raman measurements provided evidence for a good graphitic quality of the material. The GP films deposited on glass and LDPE substrates exhibited different thermoresistive properties during cooling–heating cycles in the −40 to +40 °C range. Indeed, negative values of the temperature coefficient of resistance, ranging from −4 × 10−4 to −7 × 10−4 °C−1 have been observed on glass substrates, while positive values varying between 4 × 10−3 and 8 × 10−3 °C−1 were measured when the films were supported by LDPE. These behaviors were attributed to the different thermal expansion coefficients of the substrates. The appreciable thermoresistive properties of the graphite platelet films on LDPE could be useful for plastic electronic applications.

Graphite platelet films deposited by spray technique on low density polyethylene substrates

Abstract An inexpensive technique based on spraying a graphite lacquer on low-density polyethylene (LDPE) substrate has been proposed to produce large area thermoresistive films. Scanning electron microscopy analysis shows that the coatings are composed of overlapped graphite platelets. Raman measurements reveal that the deposited films are made of a good quality graphitic material. Electrical measurements as a function of temperature of graphite platelet films on LDPE have been carried out between −40 and +40 °C and it has been found that the resistance of the films increases with increasing the temperature. This behaviour, opposite to that of graphite material, could be attributed to the thermal expansion effects of the substrate. Graphite platelet films deposited on LDPE are promising materials for thermoresistive applications in plastic electronics.

Tunable surface chemistry and wettability of octafluorocyclobutane and acrylic acid copolymer combined LDPE substrate by pulsed plasma polymerization

Octafluorocyclobutane and acrylic acid (C4F8-co-AA) are plasma copolymerized onto low-density polyethylene (LDPE) and glass slides under various pulsation periods of radio frequency pulsed plasma. The surface wettability of plasma polymer coating is traditionally considered as a substrate-independent property. The combined effect of ultrathin C4F8-co-AA coatings and LDPE substrate on surface wettability is presented. The high concentration of the carboxylic acid functional groups gives rise to hydrophilicity via lowering duty cycle, and substrate impact gives rise to hydrophobicity for ultrathin coatings. The X-ray photoelectron spectroscopy and coating thickness measurements confirmed that the sudden increase in water contact angle for the lower duty cycle is influenced by the hydrophobic substrate for ultrathin polymer coatings. It is highlighted that the precise control over the surface wettability is attained by tuning the plasma parameters. The substrate-dependent wettability for flat substrate persisted for longer than 8 weeks, which demonstrates wetting stability for ultrathin coatings.

A comparison of cold spray technique to single particle micro-ballistic impacts for the deposition of polymer particles on polymer substrates

A laboratory-scale cold spray system with the capability of accelerating 10–100 μm polymer particles up to Mach 2 was used to deposit polystyrene and polyamide particles on a variety of different substrates for both cases of like-on-like deposition and deposition onto a melt-cast low-density polyethylene (LDPE) substrate. By systematically varying the particle temperature and impact velocity, the deposition window was developed for each particle and substrate combination in order to understand the cold spray processing conditions necessary to form coatings. The results were compared to those of the micro-ballistic single particle impact experiments. In the latter technique, an ablation laser pulse was used to accelerate a single polymer particle to over 400 m/s while being tracked during flight and rebound from the substrate using ultrafast laser photography. Single particle impact studies provide information about the particle impact dynamics including the plastic deformation of a successfully deposited particles and the coefficient of restitution of a rebounding particle that cannot be monitored during cold spray. Particles of both polyamide and polystyrene were found to deposit on a soft LDPE substrate at similar impact velocities using both deposition techniques. A number of differences between the two techniques were also observed. Like-on-like deposition was only found to be successful in cold spray. Additionally, when single particle impacts successfully deposited, the efficiency of deposition was close to 100%, while for the cold spray processes the deposition was <5%. These results suggest multiple particle impacts and/or surface roughness can play a major role in the effectiveness and efficiency of the cold spray deposition process for polymers.

Antimicrobial and improved barrier properties of natural phenolic compound-coated polymeric films for active packaging applications

Functional antimicrobial low-density polyethylene (LDPE) films with coatings containing different amounts of pyrogallol (PGL), a natural phenolic substance, and polyurethane were prepared. To examine the applicability of the prepared LDPE/PGL films in packaging, the films were characterized by scanning electron microscopy, Fourier transform infrared, thermogravimetric analysis, and X-ray diffraction. The role of the coating, the barrier and color properties, and the antimicrobial activity of the films were evaluated. The thermal stability of the LDPE/PGL films was affected by the PGL concentration. Coatings with pyrogallol caused the barrier properties for water, and oxygen was increased from 0.78–0.32 to 470 ± 23.2–273 ± 57.1 (g mm)/(m2 h kPa), respectively. These findings indicate that the barrier properties of the LDPE/PGL films were highly improved compared to those of neat LDPE. Moreover, the LDPE/PGL films exhibited acceptable antimicrobial activity against Staphylococcus aureus (Gram-positive) and Escherichia coli (Gram-negative), especially for S. aureus. Further studies are necessary to increase the thermal stability of the pyrogallol coatings with the LDPE substrate in order to improve their performance and extend their packaging applications.

Superhydrophobic Bilayer Coating Based on Annealed Electrospun Ultrathin Poly(ε-caprolactone) Fibers and Electrosprayed Nanostructured Silica Microparticles for Easy Emptying Packaging Applications

A coating rendering superhydrophobic properties to low-density polyethylene (LDPE) films used in packaging applications was herein generated by means of the electrohydrodynamic processing (EHDP) technique. To this end, electrospun ultrathin poly(ε-caprolactone) (PCL) fibers, followed by electrosprayed nanostructured silica (SiO2) microparticles, were deposited on top of the LDPE film. Various electrospinning and electrospraying times were tested and optimized followed by a thermal post-treatment to provide physical adhesion between the bilayer coating and the LDPE substrate. The morphology, hydrophobicity, permeance to limonene, and thermal stability of the resultant nanostructured coatings were characterized. It was observed that by controlling both the deposition time of the electrospun ultrathin PCL fibers and the electrosprayed SiO2 microparticles, as well as the conditions of the thermal post-treatment, effective superhydrophobic coatings were developed onto the LDPE films. The resultant multilayer presented a hierarchical micro/nanostructured surface with an apparent contact angle of 157° and a sliding angle of 8°. The addition of silica reduced, to some extent, the limonene (aroma) barrier, likely due to the increased surface-to-volume ratio, which allowed permeant sorption to occur but improved the thermal stability of the LDPE/PCL film. As a result, the developed multilayer system of LDPE/PCL/SiO2 has significant potential for use in easy-to-empty packaging applications of high water activity products.

Physicochemical and Biological Activity Analysis of Low-Density Polyethylene Substrate Modified by Multi-Layer Coatings Based on DLC Structures, Obtained Using RF CVD Method

In this paper, the surface properties and selected mechanical and biological properties of various multi-layer systems based on diamond-like carbon structure deposited on low-density polyethylene (LDPE) substrate were studied. Plasma etching and layers deposition (incl. DLC, N-DLC, Si-DLC) were carried out using the RF CVD (radio frequency chemical vapor deposition) method. In particular, polyethylene with deposited N-DLC and DLC layers in one process was characterized by a surface hardness ca. seven times (up to ca. 2.3 GPa) higher than the unmodified substrate. Additionally, its surface roughness was determined to be almost two times higher than the respective plasma-untreated polymer. It is noteworthy that plasma-modified LDPE showed no significant cytotoxicity in vitro. Thus, based on the current research results, it is concluded that a multilayer system (based on DLC coatings) obtained using plasma treatment of the LDPE surface can be proposed as a prospective solution for improving mechanical properties while maintaining biocompatibility.

Development of a Flexible Strain Sensor Based on PEDOT:PSS for Thin Film Structures.

The aim of this study was to develop and optimize a reproducible flexible sensor adapted to thin low-density polyethylene (LDPE) films and/or structures to enable their deformation measurements. As these deformations are suspected to be weak (less than 10%), the developed sensor needs to be particularly sensitive. Moreover, it is of prime importance that sensor integration and usability do not modify the mechanical behavior of its LDPE substrate. The literature review allowed several materials to be investigated and an elastomer/intrinsically conductive polymer PEDOT:PSS (CleviosTM) filled composite was selected to simultaneously combine mechanical properties and electrical conductivity. This composite (made of PEDOT:PSS and silicone Bluesil®) presented satisfying compatibilities with piezoresistive effects, negative temperature performances (in a range from −60 °C to 20 °C), as well as elongation properties (until the elastic limit of the substrate was reached). The method used for creating the sensor is fully described, as are the optimization of the sensor manufacture in terms of used materials, the used amount of materials where the percolation theory aspects must be considered, the adhesion to the substrate, and the manufacturing protocol. Electromechanical characterization was performed to assess the gauge factor (K) of the sensor on its substrate.

A new micromechanical approach for the preparation of graphene nanoplatelets deposited on polyethylene

An advantageous micromechanical technique to deposit large area graphene nanoplatelet (GNP) thin films on a low-density polyethylene substrate is proposed. This method is based on the application of shear-stress and friction forces to a graphite platelets/ethanol paste on the surface of a polymeric substrate; it allows us to obtain a continuous film of superimposed nanoplatelets mainly made of 13–30 graphene layers. X-ray diffraction (XRD), atomic force and transmission electron microscopy (TEM) measurements support the occurrence of a partial exfoliation of the graphite platelets due to shear-stress and friction forces applied during film formation. Scanning electron microscopy (SEM) observations point out that the surface of the polymer is uniformly coated by the overlap of GNPs, and TEM analysis reveals the tendency of the nanoplatelets to align parallel to the interface plane. It has been found that the deposited samples, under white light illumination, exhibit a negative photoconductivity and a linear photoresponse as a function of the applied voltage and the optical power density in the −120 ÷ 120 mV and 20.9 ÷ 286.2 mW cm−2 ranges, respectively.

Protecting an atomic layer deposited aluminum oxide barrier coating on a flexible polymer substrate

Atomic layer deposited (ALD) inorganic thin film coatings can produce high barrier properties against moisture and gas. However, if an ALD film is exposed to mechanical stress, it may lose these properties. In this study, a 40-nm thick aluminum oxide (Al2O3) ALD barrier layer turned out fragile on a low density polyethylene (LDPE) coated paper substrate during web handling. In such handling, the processing steps, such as bending, roll contacts, and friction, weakened the structure of the barrier. However, when the Al2O3 layer was deposited on polyethylene terephthalate coated paper, no loss of barrier properties was observed after web handling. We show here that an Al2O3 ALD barrier layer can be protected on an LDPE substrate against mechanical stress by adding a shielding polyethylene layer on top of the ALD coating. After this addition, oxygen permeation through the protected surface remained unchanged during web handling. The results of this study demonstrate that the protective layer was necessary to maintain the excellent barrier properties and intactness of the ALD layer on an LDPE substrate.

Design and Development of Expanded Graphite-Based Non-metallic and Flexible Metamaterial Absorber for X-band Applications

The possibility of using expanded graphite instead of a metallic layer as unit cells and ground planes for metamaterial absorbers in X-band is investigated. A metamaterial absorber was fabricated on a flexible linear low-density polyethylene substrate using an expanded graphite-based circular ring as the unit cell structure. The unit cell was simulated and optimized for which the metamaterial absorber exhibited 98.9% absorption at 11.22 GHz. The fabricated expanded graphite-based absorber showed a reflection loss of −24.51 dB at 11.56 GHz with −10 dB bandwidth of 0.39 GHz (3.37%). The performance of the same structure with copper was also measured. The expanded graphite-based metamaterial absorber showed enhanced performance as compared to the copper-based metamaterial absorber. The width of the ring was varied to tune the reflection loss. The proposed expanded graphite-based metamaterial absorber possesses the advantages of being ultra-thin, flexible and non-corrosive.

Facile preparation of superhydrophobic candle soot coating and its wettability under condensation

A facile method was developed to prepare a superhydrophobic candle soot coating by burning candle and simple deposition on a low-density polyethylene substrate. The water contact angle and sliding angle of the as-prepared superhydrophobic candle soot coating were, respectively, 160 ± 2° and 1° under common condition. ESEM images showed that the superhydrophobic candle soot coating was comprised of many nanoparticles with the size range of about 30–50 nm. After condensation for 30 min, the average contact angle of the condensed water droplets was 150° ± 2°, showing excellent superhydrophobicity under condensation. The mechanism of the candle soot coating remaining superhydrophobicity under condensation was analyzed. This work is helpful for the design and preparation of superhydrophobic surface which can remain superhydrophobicity in future.

Precise Actuation of Bilayer Photomechanical Films Coated with Molecular Azobenzene Chromophores.

Bilayer photomechanical films are fabricated by depositing one layer of molecular azobenzene chromophores onto flexible low-density polyethylene substrates. The photoinduced bending and unbending behavior of five azobenzene derivatives including azobenzene, 4-hydroxy-azobenzene, 4-((4-hydroxyphenyl)diazenyl)bezoitrile, 4-((4-methoxyph-enyl)diazenyl)phenol, and 4-(phenyldiazenyl)phenol is systematically studied by considering the incident light intensity and the thickness of the coated chromophore layers. Precise control of photoinduced curling of the bilayer film is successfully achieved upon irradiation with two beams of UV light, and the curled films can be recovered by thermal relaxation in the dark. The easily fabricated bilayer films show fast photomechanical response, strong photoinduced stress, and stability similar to crosslinked polymeric films.

Effects of surface wettability and contact time on protein adhesion to biomaterial surfaces

Atomic force microscopy (AFM) was used to directly measure the adhesion forces between three test proteins and low density polyethylene (LDPE) surfaces treated by glow discharge plasma to yield various levels of water wettability. The adhesion of proteins to the LDPE substrates showed a step dependence on the wettability of surfaces as measured by the water contact angle ( θ). For LDPE surfaces with θ>∼60–65°, stronger adhesion forces were observed for bovine serum albumin, fibrinogen and human FXII than for the surfaces with θ<60°. Smaller adhesion forces were observed for FXII than for the other two proteins on all surfaces although trends were identical. Increasing the contact time from 0 to 50 s for each protein–surface combination increased the adhesion force regardless of surface wettability. Time varying adhesion data was fit to an exponential model and free energies of protein unfolding were calculated. This data, viewed in light of previously published studies, suggests a 2-step model of protein denaturation, an early stage on the order of seconds to minutes where the outer surface of the protein interacts with the substrate and a second stage involving movement of hydrophobic amino acids from the protein core to the protein/surface interface. Impact statement: The work described in this manuscript shows a stark transition between protein adherent and protein non-adherent materials in the range of water contact angles 60–65°, consistent with known changes in protein adsorption and activity. Time-dependent changes in adhesion force were used to calculate unfolding energies relating to protein–surface interactions. This analysis provides justification for a 2-step model of protein denaturation on surfaces.

Electroactive polymer patterns with metal incorporation on a polymeric substrate

AbstractElectroactive polymer patterns on a polymeric substrate were fabricated using either a UV lithographic approach or plasma polymerization method. For the lithographic patterning technique, photosensitive thin films comprising polyaniline (PANI) coatings on viologen‐grafted low‐density polyethylene (LDPE) substrates were first prepared. The composite film was subsequently exposed to UV irradiation through a mask. Under UV irradiation, reactions between PANI and viologen occurred, resulting in the conversion of the PANI to a doped state. The PANI micropatterns were developed by using N‐methylpyrrolidinone (NMP) to dissolve the soluble‐unexposed (and hence undoped) parts. The use of Ar plasma treatment of the composite film instead of UV irradiation was not successful in inducing the doping reaction between PANI and viologen. On the other hand, plasma polymerization was shown to be another convenient way for the selective surface deposition of aniline polymer on the surface of the LDPE substrate through a mask. The further incorporation of metal/metal ions in both the PANI‐viologen and plasma polymerized aniline system was successfully carried out on the micropatterns. Polym. Eng. Sci. 44:2061–2069, 2004. © 2004 Society of Plastics Engineers.

Comparative study of chemically synthesized and plasma polymerized pyrrole and thiophene thin films

Pyrrole and thiophene polymers prepared via chemical means or plasma polymerization at different radio frequency (RF) power input on different substrates were compared using X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy and UV–visible absorption spectroscopy. These polymers were deposited as thin films on either low-density polyethylene (LDPE) or LDPE surface graft copolymerized with acrylic acid (AAc). The results indicate that the structures of plasma polymerized pyrrole and thiophene are rather different from those of polymers synthesized by conventional chemical methods, due to a higher degree of crosslinking and branching reactions in plasma polymerization. A higher and more stable conductivity can be obtained with chemically synthesized polypyrrole and polythiophene, but the thin films generated from the plasma polymerization process are much smoother and more uniform. The lack of stability in the plasma polymerized samples’ conductivity may be due to the unstable nature of the charge transfer complex with the dopant (iodine) resulting in a greater ease of diffusion of the iodine from the film. Under the conditions tested, the thickness of plasma polymerized pyrrole and thiophene thin layers increases almost linearly with the RF power. The modification of the LDPE substrates using AAc-graft copolymerization can enhance the growth and adhesion of the thin film and its conductivity.