Polyethylene Substrate Research Articles

Imidazolium-Based Anion Exchange Membranes for Electrochemically Converted Liquid Organic Hydrogen Carrier

Liquid organic hydrogen carrier (LOHC) is a technology that uses renewable energy for hydrogen transportation, storage and utilization. LOHC have advantages that can store and utilize hydrogen rapidly in the lack of transportation infrastructure. A membrane-based LOHC system is a promising technology due to the dynamic operation using electrochemistry. Anion exchange membranes are widely used as electrolyte for electrochemical devices. The performance of LOHC could be determined by the properties of anion exchange membranes. Thus, high anion conducting ionomers must be developed for the superior conversion rates on the electrochemical reduction of liquid toluene to methylcyclohexane. In this study, anion exchangeable polymers containing imidazolium salt as anion-conducting group were synthesized to achieve good conduction of hydroxide ions and their chemical stability. Anion exchange membranes were prepared by a pore-filling method using porous polyethylene substrate. The pore-filling anion exchange membranes were characterized in terms of ion conductivity, areal resistance, ion exchange capacity, water uptake, swelling ratio and mechanical strength. Acknowledgment This research was supported in part by the Korea Institute of Science and Technology (No. 2E31871) and by 2021 Green Convergence Professional Manpower Training Program of the Korea Environmental Industry and Technology Institute funded by the Ministry of Environment.

Alkaline-Stable Anion Conducting Ionomers for Anion Exchange Membrane Water Electrolyzers

Water electrolysis is a process that uses renewable energy to decompose water into oxygen and hydrogen. It is one of the most promising alternatives to produce and store new energy from renewable energy resources. In this study, pore-filled anion exchange membranes (PFAEMs) were prepared by using quaternary ammonia groups along with various cross-linker groups with different chain lengths and using porous polyethylene substrates which were pretreated from hydrophobic into hydrophilic using surfactants. The conductivity of the anion exchange membranes was measured by the in-plane cell and through-plane at room temperature or 60 ℃. In addition, the characterizations of anion exchange membranes such as water uptake, swelling ratio, mechanical strength, contact angle and TGA were carried out. As a result, the PFAEM exhibited remarkably high ion conductivity at extremely low areal swelling ratio and excellent chemical stability in a NaOH solution for 500 h. As an essential component of anion exchange membrane water electrolyzers, catalyst layers prepared by the catalyst inks comprising of ionomer binder and electrocatalysts are sandwiched between the anion exchange membrane to form a membrane electrode assembly in order to evaluate its impedance and I-V polarization curves. Acknowledgment This research was supported in part by the New and Renewable Energy of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) granted financial resource from the Ministry of Trade, Industry & Energy, Republic of Korea (No. 20213030040520) and by 2021 Green Convergence Professional Manpower Training Program of the Korea Environmental Industry and Technology Institute funded by the Ministry of Environment.

Dopamine-Based Copolymer Bottlebrushes for Functional Adhesives: Synthesis, Characterization, and Applications in Surface Engineering of Antifouling Polyethylene.

Nonpolar materials like polyolefins are notoriously challenging substrates for surface modification. However, this challenge is not observed in nature. Barnacle shells and mussels, for example, utilize catechol-based chemistry to fasten themselves onto all kinds of materials, such as boat hulls or plastic waste. Here, a design is proposed, synthesized, and demonstrated for a class of catechol-containing copolymers (terpolymers) for surface functionalization of polyolefins. Dopamine methacrylamide (DOMA), a catechol-containing monomer, is incorporated into a polymer chain together with methyl methacrylate (MMA) and 2-(2-bromoisobutyryloxy)ethyl methacrylate (BIEM). DOMA serves as adhesion points, BIEM provides functional sites for subsequent "grafting from" reactions, and MMA provides the possibility for concentration and conformation adjustment. First, the adhesive capabilities of DOMA are demonstrated by varying its content in the copolymer. Then, terpolymers are spin-coated on model Si substrates. Subsequently, the atom transfer initiator (ATRP) initiating group is used to graft a poly(methyl methacrylate) (PMMA) layer from the copolymers, with 40% DOMA content providing a coherent PMMA film. To demonstrate functionalization on a polyolefin substrate, the copolymer is spin-coated on high-density polyethylene (HDPE) substrates. A POEGMA layer is grafted from the ATRP initiator sites on the terpolymer chain on the HDPE films to provide antifouling characteristics. Static contact angle values and Fourier transform infrared (FTIR) spectra confirm the presence of POEGMA on the HDPE substrate. Finally, the anticipated antifouling functionality of grafted POEGMA is demonstrated by observing the inhibition of nonspecific adsorption of the fluorescein-modified bovine serum albumin (BSA) protein. The poly(oligoethylene glycol methacrylate) POEGMA layers grafted on 30% DOMA-containing copolymers on HDPE show optimal antifouling performance exhibiting a 95% reduction of BSA fluorescence compared to nonfunctionalized and surface-fouled polyethylene. These results demonstrate the successful utilization of catechol-based materials for functionalizing polyolefin surfaces.

Polyethyleneimine (PEI) based positively charged thin film composite polyamide (TFC-PA) nanofiltration (NF) membranes for effective Mg2+/Li+ separation

To effectively separate Mg2+ and Li+ from high Mg2+/Li+ ratio salt lake brine, positively charged thin film composite polyamide (TFC-PA) nanofiltration (NF) membranes were prepared by the interface polymerization involving polyethyleneimine (PEI) with benzenetricarbonyl chloride (TMC). In this work, the structures and performances of PEI based TFC-PA NF membrane prepared on polysulfone (PSF) ultrafiltration substrates from the normal interface polymerization process PSF(NIP), was compared with those on the same substrates from the reverse-phase interface polymerization (RIP) process PSF(RIP), and those on polyethylene substrates from RIP process PE(RIP). Results showed that PSF(RIP) showed improved Mg2+/Li+ separation factor SLi/Mg from PSF(NIP) with an increased surface positive charge, but with greatly reduced water flux values due to reduced surface roughness, increased surface hydrophobicity, and decreased MWCO Stokes pore radius. PE(RIP) NF membrane showed not only higher Mg2+/Li+ separation factor SLi/Mg, but also higher water flux values due to increased surface roughness, decreased PA cross-linking degree, reduced PA separation layer thickness, and increased MWCO Stokes pore radius. PE(RIP) NF membrane also showed high rejection rates to a variety of divalent metal salts with high separation factors SLi/Mg of 40–49, high brine permeability values of 10.5 L·m−2·h−1·bar−1, and excellent chemical and operational stability.

A benzimidazole-linked polymer membrane in alkaline water electrolysis

Advanced alkaline water electrolysis for hydrogen production necessitates the development of new membranes with high ionic conductivity, gas-tightness, and structural robustness in the alkaline environment. To this end, a benzimidazole-linked polymer (BILP) based composite membrane is prepared by forming a BILP-101 dense layer via interfacial polymerization (IP) on top of a commercial porous polyethylene (PE) substrate membrane. The density and thickness of the dense layer are easily adjustable by changing the acid content in the aqueous phase and the IP time, respectively. The BILP-PE composite membranes exhibit an area resistance of only ∼75 mΩ cm2 at 30 °C and <30 mΩ cm2 at 80 °C in 1 M KOH. While their H2 gas crossover rate is ∼4 × 10−14 mol cm s−1 cm−2 kPa−1, nearly two orders of magnitude lower than that of commercial Zirfon UTP-500 diaphragm. The BILP-PE membranes also show a very low swelling ratio of ∼4% and high tensile strength of >100 MPa. Soaking in 30 wt% KOH solution at 60 °C, the BILP dense layers would lose their weight at an ever-decreased speed and come to a halt after ∼24 d of soak, with a total loss of <10% of their original weight. The BILP-PE composite membrane looks very promising in advanced alkaline water electrolysis.

Intense green upconversion in core-shell structured NaYF4:Er,Yb@SiO2 microparticles for anti-counterfeiting printing

Rare-earth-doped NaYF4 nanoparticles are considered crucial upconversion luminescent materials with many applications, including anti-counterfeiting printing, biological imaging, and optical information storage. This work presents progress in obtaining hydrophilic pigments based on NaYF4:Er,Yb@SiO2 nanoparticles, and their utilization in water-based ink printing for anti-counterfeiting applications. Coating NaYF4:Yb/Er microparticles with SiO2 shells can provide several benefits for printing purposes, such as improved stability, dispersion, and ease of printing. The hydrophilic core-shell structured β-NaYF4:Er, Yb@SiO2 microparticles were successfully prepared using the hydrothermal synthesis and sol-gel Stober method. The obtained microparticles were characterized by Scanning Electron Microscopy, X-ray diffraction, and Energy-dispersive X-ray spectroscopy. Such characterizations confirm that the Er3+ and Yb3+ ions are incorporated in NaYF4 cores, the NaYF4:Er, Yb cores are in hundreds of nanometer sizes, and the NaYF4:Er, Yb microparticles are coated by a silica layer of 50 nm thick. Both NaYF4:Er, Yb and NaYF4:Er, Yb@SiO2 behave as up-conversion luminescent microparticles for both green and red emissions. The CIE chromaticity coordinates indicate that both the nanoparticles have their greenish color under excitation at 980 nm. Although decorating the NaYF4:Er, Yb nanoparticles with the SiO2 shell decreases luminescent intensity (by a factor of 2), this step is still necessary to achieve hydrophilic surfaces for preparing water-based printing inks. Using the synthesized NaYF4:Er, Yb@SiO2 as a pigment, a new water-based ink formula was created based on Polyamide as a polymer matrix. The obtained ink is printable on paper and on transparent and flexible Polyethylene substrate. The printed patterns with a height of 2 cm and a width of 2.5 cm were observed clearly under the irradiation of a 980 nm LED. Their durability in terms of sharpness and color was also assessed after six months.

Facile hydrophilization of polyethylene substrate by in situ polymerization of m-phenylenediamine for preparing high-performance polyamide reverse osmosis membrane

Polyethylene (PE) microporous membrane-supported thin-film composite (TFC) polyamide membranes have received growing attention owing to their low cost, superior separation performance, and excellent chemical robustness. Developing facile and cost-effective methods to hydrophilize PE membranes is essential for the scale-up of PE-supported TFC membranes. Here, a facile approach of in situ polymerization of m-phenylenediamine (MPD) was employed to hydrophilize the PE membranes for the first time. Characterizations showed that both the outer surface and the interior of the PE membrane were homogeneously coated with poly(m-phenylenediamine) (PMPD). The hydrophilicity of the modified PE membrane was dramatically enhanced with the water contact angle decreasing from ∼120° to ∼72° and water flux at 2 bar increasing from 0 to ∼640 L m−2 h−1. The high surface porosity and appropriate surface hydrophilicity of the MPD-modified PE membrane together with the excellent coating uniformity favor the formation of a highly permselective polyamide active layer. The outstanding coating stability was demonstrated through different tests. The cost of the MPD-modified PE membrane is estimated to be less than 1% of that of the conventional substrates. Furthermore, high-performance and low-cost reverse osmosis (RO) membranes were prepared via interfacial polymerization on the MPD-modified PE substrates. The PE-supported RO membrane exhibited an excellent separation performance with NaCl rejection of 99.3%, pure water permeance of 1.3 L m−2 h−1 bar−1, and long-term operating stability. The proposed hydrophilization strategy of PE membrane is facile, low-cost, environmentally friendly, and reliable, and thus has a brilliant prospect for industrialization.

One Stone, Two Birds: Spidroin‐Inspired Nanogels for High‐Performance Fibers and Photothermal Actuators

AbstractThe exciting development of hydrogels makes it a promising candidate to be applied in various fields. However, it remains a great challenge to store the precursors of hydrogels and to process them after gelation, like synthetic polymer materials. Herein, spidroin‐inspired novel nanogels with extraordinary processability, which can be spun into fibers via direct drawing and fabricated into thermal actuators easily after gelation are prepared. These soluble and spinnable nanogels are composed of a liquid metal core and a poly (acrylic acid) (PAA) shell and are entangled with each other. The as fabricated nanogels and diluted dope solution can be stored &gt;1 month. The as‐spun nanogel fibers with hierarchical structures achiev extraordinary mechanical properties (tensile stress of 575 MPa, toughness of 381 MJ m−3) and supercontraction at 60% RH. Besides, a photothermal actuator is prepared by coating the nanogels on a polyethylene substrate with a commercial shading ink, and the as‐prepared actuator shows a rapid response to near‐infrared light as well as a fast recovery. Molecular dynamics simulation reveals a possible working mechanism of the actuator. This study provides a new strategy to prepare processable nanogels with broad application prospects for smart textiles and soft robots.

Mechanical and tribological characterisations of PEG-based hydrogel coatings on XLPE surfaces

Hydrophilic hydrogel coatings can impart enhanced tribological and antifouling properties to biomedical device surfaces. The influence of crosslinking on the elastic moduli of poly (ethylene glycol) (PEG) hydrogels is well established, however, the effect of crosslinking on the ability of the hydrogels to form coatings on crosslinked polyethylene (XLPE) substrates is not fully understood, nor are the mechanics and tribological performance of the resultant hydrogel coated substrates. PEG hydrogels of four different crosslinking levels (5, 7.5, 10 and 12.5% crosslinker concentrations) were deposited onto XLPE substrates. Crosslinked matched hydrogel plugs were also manufactured for mechanical analysis. The wear performance and friction evolution of coated pins were assessed against sterilised cobalt chromium discs at a contact pressure of 0.08 MPa under an elliptical orbital motion. The indentation results showed an increase in the elastic modulus with increasing crosslinker concentration, which was augmented further by gamma sterilisation treatment. Hydrogel coated pins exhibited reduced friction levels compared to uncoated pins, and confocal imaging in conjuction with the roughness monitoring indicated that the coatings protected the asperities from being removed. The friction values increased as the tests progressed, in line with the coverage of the hydrogel coating decreasing and forming a hybrid XLPE/gel vs CoCr contact. The 10% cross-linker hydrogel coating produced the lowest friction and wear of all the coatings tested.

An Economical Composite Membrane with High Ion Selectivity for Vanadium Flow Batteries.

The ion exchange membrane of the Nafion series widely used in vanadium flow batteries (VFBs) is characterized by its high cost and high vanadium permeability, which limit the further commercialization of VFBs. Herein, a thin composite membrane enabled by a low-cost microporous polyethylene (PE) substrate and perfluorosulfonic acid (PFSA) resin is proposed to reduce the cost of the membrane. Meanwhile, the rigid PE substrate limits the swelling of the composite membrane, which effectively reduces the penetration of vanadium ions and improves the ion selectivity of the composite membrane. Benefiting from such a rational design, a VFB assembled with the PE/PFSA composite membrane exhibited a higher coulombic efficiency (CE ≈ 96.8%) compared with commercial Nafion212 at 200 mA cm-2. Significantly, the energy efficiency maintained stability within 200 cycles with a slow decay rate. In practical terms, the thin PE/PFSA composite membrane with low cost and high ion selectivity can make an ideal membrane candidate in VFBs.

Integrated techno-economic and life cycle assessment of a novel algae-based coating for direct air carbon capture and sequestration

Direct air carbon capture and storage (DACCS) systems are expected to play an important role in fighting global warming. While existing DACCS technologies have demonstrated CO2 removal rates at or below the kiloton scale, high capital costs and significant energy demands represent hurdles in achieving large scale deployment. This study evaluates a novel biomimetic coating primarily consisting of a hydrogel seeded with microalgae biomass printed on a polyethylene substrate. The coating has been developed to exploit the high photosynthetic rates of microalgae to fix atmospheric CO2 into cellulose using incident solar energy. The carbon embodied in the cellulose material is converted to biochar through pyrolysis to ensure durable carbon sequestration without the need for underground storage. The proposed system offers many advantages including modularity and scalability, the potential for high water retention rates, and long periods of operation with minimal maintenance and management. Three scenarios were evaluated using conservative, baseline, and optimistic assumptions to capture the true range in performance of the system. Results from the modeling work show a carbon removal efficiency ranging from 51% to 73% and carbon capture and sequestration costs of $702–$1585 per tonne CO2 sequestered. Furthermore, the modular design of the coated substrate system and utilization of solar energy supports the rapid upscaling necessary to meet mid-century carbon removal goals. Discussion focuses on the key performance drivers of the system and the challenges and feasibility of meeting target metrics to support economic and environmental sustainability.

Anion Exchange Membrane Reinforced with Polyethylene Substrate for Alkaline Fuel Cell Applications

Anion Exchange Membrane Reinforced with Polyethylene Substrate for Alkaline Fuel Cell Applications

Reinforcement effect in tandemly sulfonated, partially fluorinated polyphenylene PEMs for fuel cells.

The mechanical and chemical durability is one of the most crucial properties for proton exchange membranes in practical fuel cell applications. In the present paper, we report the physical reinforcement of chemically stable, highly proton conductive tandemly sulfonated, partially fluorinated polyphenylenes using porous polyethylene (PE). With the PE pores completely and homogeneously filled by ionomers through a push coating approach, the resulting reinforced membranes were more proton conductive (183.1-389.2 mS cm-1) than the commercial perfluorinated ionomer (Nafion: 120.6-187.2 mS cm-1) membrane at high humidity (80-95% RH). Benefiting from the tough PE supporting layer, the reinforced membranes outperformed the parent ionomer membranes in stretchability with maximum strain up to 453%. The combination of intrinsic chemical stability of partially fluorinated polyphenylene ionomers and physical reinforcement with PE substrates contributed for the reinforced membranes to achieving superior durability to survive more than 20 000 cycles in severe accelerated durability test combining OCV hold and wet/dry frequent cycling.

New Pressure-Sensitive Acrylic Adhesives for Low Energy Substrates Prepared via UV-Induced Telomerization with a Fluorine-Based Telogen

Novel pressure-sensitive adhesives (PSA) for low energy substrates were prepared by a solvent-free UV-initiated telomerization process using n-butyl acrylate, butyl methacrylate, and lauryl methacrylate (LMA), with trifluoroethanol (TFEtOH) as a telogen, and acylphosphine oxide (APO) as a radical photoinitiator. A crosslinking monomer (an aliphatic urethane acrylate, L9033) and a radical UV-photoinitiator (α-hydroxyalkylphenone) were also tested as components of the adhesive compositions. The influence of LMA and TFEtOH on the UV-phototelomerization process kinetics and the physicochemical features of the obtained fluorotelomers, as well as the concentration of L9033 on the PSA adhesion to a polyethylene surface, were investigated. FT-IR results indicated that the fluorine groups were successfully introduced into the telomer structure. The highest adhesion relative to a polyethylene substrate (12.3 N/25 mm), and the highest hydrophobicity (with a contact angle of 95° for a water/PSA system) were observed for adhesives based on a telomer syrup containing 5 wt. parts of TFEtOH and 30 wt. parts of LMA (per 100 wt. parts of the monomer mixture). Additionally, it was revealed that a higher aliphatic urethane acrylate content and a higher UV dose increased the adhesion feature.

Tuning the Hydrophobic Component in Reinforced Poly(arylimidazolium)-Based Anion Exchange Membranes for Alkaline Fuel Cells

A series of imidazolium-based aromatic copolymers were synthesized using fluorinated and non-fluorinated hydrophobic monomers. The quaternized copolymers were reinforced with the plasma-treated porous polyethylene substrate to provide flexible, homogeneous membranes. Cross-sectional SEM images revealed a triple-layer structure. The reinforced membranes exhibited phase-separated morphology as confirmed through TEM images. Among the membranes, QQP-MEIm-PE-containing quinquephenylene hydrophobic groups exhibited the most balanced properties (ion conductivity, mechanical strength, and alkaline stability). In particular, QQP-MEIm-PE exhibited excellent elongation properties with 24 MPa maximum stress and 205% elongation at break. A single H2/O2 fuel cell using the QQP-MEIm-PE membrane (1.26 meq g–1) and non-PGM-(Fe–N–C) cathode achieved 222 mW cm–2, which accounted for 888 mW mg–1Pt at 560 mA cm–2. Reasonable durability was confirmed with the membrane in the operating fuel cell.

A reinforced composite membrane of two-layered asymmetric structure with Nafion ionomer and polyethylene substrate for improving proton exchange membrane fuel cell performance

The reinforced composite membrane with a two-layered asymmetric structure was fabricated by impregnating the Nafion on a porous polyethylene (PE) substrate to reduce the cost of the membrane used in proton exchange membrane fuel cells (PEMFCs) as well as to enhance the performance of the cell. The ion conductivity of the reinforced composite membrane annealed at 150 °C increases owing to the high crystallinity of the Nafion ionomer, and the mechanical strength is improved by the strong interaction between PE substrate and Nafion ionomer. The immiscibility between them was observed to intensify the interfacial resistance in the three-layered symmetric structure. On the other hand, the reduction of the interfacial resistance of the two-layered asymmetric structure membrane leads to similar results to the performance of traditional PEMFC using Nafion XL with a polytetrafluoroethylene (PTFE) substrate similar to a backbone of Nafion ionomer. Its high mechanical strength, low cost, and reliable ion conductivity make it a suitable substitute for PTFE-based membranes used in PEMFCs although the immiscibility with the ionomer in the membrane comprising a PE substrate is higher than that in the membrane with a PTFE substrate.

Development of Pore-Filling Anion Exchange Membranes for Anion Exchange Membrane Water Electrolysis: Enhancement of Alkaline Stability

Water electrolysis is a process that uses electricity to decompose water into oxygen and hydrogen. There are several types of ion exchange membrane can be used, anion exchange membrane, proton exchange membrane and bipolar membrane for water electrolysis. Alkaline based water electrolysis has several advantages to use non-precious electrocatalysts. However, the development of low resistance and durable anion-exchange membranes is of importance. In this study, several anion-exchange membranes were developed to enhance alkaline stability. Pore-filling anion exchange composite membranes with different contents of cross-linkers were prepared by mixing an electrolyte having good anion conducting ability. The mixture of monomers into a porous polyethylene (PE) substrate were polymerized by UV curing. The pore-filling reinforced composite membranes have been investigated in terms of good chemical stability properties, in particular, the variation of conductivity and mechanical strength in 1 M KOH at 60 oC. Characterization in terms of ion exchange capacity, water uptake, swelling ratio, and mechanical strength were also investigated. Acknowledgments This research was supported in part by "Cooperative Research Program for Agriculture Science and Technology Development (Project No. PJ016253)" Rural Development Administration, Republic of Korea, by the New and Renewable Energy of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) granted financial resource from the Ministry of Trade, Industry & Energy, Republic of Korea (No. 20213030040520) and by 2022 Green Convergence Professional Manpower Training Program of the Korea Environmental Industry and Technology Institute funded by the Ministry of Environment.

Development of Pore-Filling Anion Exchange Membranes for Anion Exchange Membrane Water Electrolysis: Enhancement of Resistance

Water electrolysis is a process that uses electricity to decompose water into oxygen and hydrogen. There are several types of ion exchange membrane can be used, anion exchange membrane, proton exchange membrane and bipolar membrane for water electrolysis. Alkaline based water electrolysis has several advantages to use non-precious electrocatalysts. However, the development of low resistance and durable anion-exchange membranes is of importance. In this study, several anion-exchange membranes were developed to enhance areal resistance, in other words, to minimize areal resistance. Pore-filling anion exchange composite membranes with different contents of cross-linkers were prepared by mixing an electrolyte having good anion conducting ability. The mixture of monomers into a porous polyethylene (PE) substrate were polymerized by UV curing. The pore-filling reinforced composite membranes have been investigated in terms of good electrochemical properties, in particular, areal resistance. The conductivity and areal specific resistance were measured in both in-plane cell and through-plane cell at 80 ℃ and at room temperature, respectively. Characterization in terms of ion exchange capacity, water uptake, swelling ratio, and mechanical strength were also investigated. Acknowledgments This research was supported in part by "Cooperative Research Program for Agriculture Science and Technology Development (Project No. PJ016253)" Rural Development Administration, Republic of Korea, by the New and Renewable Energy of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) granted financial resource from the Ministry of Trade, Industry & Energy, Republic of Korea (No. 20213030040520) and by 2022 Green Convergence Professional Manpower Training Program of the Korea Environmental Industry and Technology Institute funded by the Ministry of Environment.

ШИРИНА ЗАБОРОНЕНОЇ ЗОНИ ТА ПОКАЗНИК ЗАЛОМЛЕННЯ ПОЛІАНІЛІНУ

e-mail: yuliia.stetsiv@lnu.edu.ua Polyaniline (PAn) films, doped with citric acid, were synthesized on a polyethylene substrate by chemical oxidative polymerization using ammonium peroxydisulfate as an oxidant. The influence of monomer concentration on the optical properties of PAn films was investigated. Optical band gap, absorption coefficient, extinction coefficient, refractive index were calculated as a function of wavelength. Different methods for determining the energy of the energy gap (Tauc method and absorption spectrum fitting) were considered. It was found that the optical band gap for all thin PAn films is due to the direct allowed optical transitions. It was found that the band gap of PAn films decreases with increasing thickness of deposited PAn films. It is established that the optical energies of the band gap of PAn films of different thickness, estimated by the results of optical absorption measurements using Tauc methods and absorption spectrum fitting, are practically commensurate and are in the range of 3.13–2.36 eV for film thicknesses equal to 18.7–137.4 nm, respectively. Based on the correlations between the optical energy of the band gap and the refractive index of semiconductors using Moss, Ravindra, Ravindra-Gupta, Reddy-Ahammed, Gerve-Vandamme, Kumar-Singh, Annani and Duffy-Reddy ratios, the value of the refractive index of PAn films was calculated and these results were compared with the values obtained from the experimental results. From the obtained results it is seen that the refractive index of PAn films increases with increasing polyaniline film thickness on a polyethylene substrate. The values obtained from the Ravindra and Ravindra-Gupta relations are the closest to the experimental ones. Therefore, the synthesized PE/PAn films can be an available material for the production of optoelectronic devices, for example, for organic field transistors and LEDs.

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.