Transport and dielectric properties of poly(ethylene terephthalate) as determined via electrochemical techniques

The electrochemical impedance spectroscopy (EIS) technique was used to evaluate the water transport (diffusion and equilibrium water uptake) and the dielectric properties of free-standing poly(ethylene terephthalate) (PET) membranes at 40°C. Permeability and diffusion coefficients were also obtained using the Payne cup method and the MacBain quartz spring balance to assess the reliability of the EIS method when compared to other techniques. In addition, an electromigration (dc) technique was used to estimate the NaCl diffusion coefficient across PET films. Results obtained indicate that PET is highly permeable to water and much less permeable to salt. The water diffusion coefficient, D, varies from 2.11× 10^?9 to 9.97× 10^?9 cm²s^?1 for thicknesses between 22 and 205μm, whereas the equilibrium water uptake, W, varies from 0.54 to 0.95 wt % for the same given range of thicknesses. The average calculated dielectric constant of the free-standing PET films is 3.6. An estimate of the NaCl diffusion coefficient, D_s, is 9.34× 10^?14 cm²s^?1. Transport properties results obtained via the electrochemical technique are in reasonable agreement with those obtained with the classical gravimetric method. © 1993 John Wiley & Sons, Inc.     

Improvement of wettability of hydrophobic films by impregnation of anthraquinone attached to polyoxyethylene glycol

Amphiphilic anthraquinone bearing polyoxyethylene moiety (PEG_MW‐AQ) was prepared and impregnated in polyethylene terephthalate (PET) and nylon 6 (ON) films. The uptake of PEG_MW‐AQ to PET film increased in proportion to the concentration of PEG_MW‐AQ in a bath, and the contact angle of water dropped on the film decreased with increase in the uptake. At a constant uptake of PEG_MW‐AQ, the contact angle decreased with an increase of molecular weight of PEG_MW attached to the anthraquinone, which indicates that polyoxyethylene moiety of PEG_MW‐AQ is effective on the wettability of the film. The decrement of water contact angle on PET film dyed with PEG_MW‐AQ was larger than that on ON film at the same dye uptake because of the higher dyeability of PET film than ON film with PEG_MW‐AQ. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 545–549, 2005     

Influence of the solution cation mobility on the water uptake estimation of PVC Plastisol freestanding films by EIS

In this work, the influence of the outer solution cation mobility on the electrochemical behaviour of PVC Plastisol freestanding films was studied. For that purpose, the paint films were immersed in 0.5 M and 0.05 M chloride solutions with different cations (Na⁺, K⁺, Cs⁺). The electrochemical impedance spectroscopy (EIS) was the technique chosen for this study and estimated values of film capacitance and resistance were calculated.For PVC Plastisol films, it was observed that the ion diffusion depends on the outer solution concentration. To explain such results different mechanisms for the ionic diffusion were considered. For higher concentration solutions the ions of the outer solution must diffuse into the film, while for lower concentration solutions the dissolution inside the film occurs followed by ionic diffusion from the film to the outer solution.The water uptake was determined by EIS and gravimetry techniques. The Brasher and Kingsbury (BK) and the low frequency solution (LF) models were used to estimate this parameter by the EIS technique. A direct dependency between water uptake and solution concentration was obtained by this technique, while by gravimetry an inverse relation was obtained. However, the LF model presented water uptake values better correlated with the gravimetric ones comparatively to the BK equation. For the more concentrated solutions, the cation mobility influenced the water uptake estimated by EIS, whereas, such dependency was not observed with the gravimetric technique.The results obtained in this work suggest that the outer solution resistivity and consequently the film resistance influence the water uptake measurements and should take part in any improved model used for water uptake determination.     

Uniaxial orientation and tensile properties of poly(ethylene terephthalate)/poly(ethylene-2,6-naphthalate) blends

Amorphous films of poly(ethylene terephthalate)/poly(ethylene-2,6-naphthalate) (PET/PEN) blends with different blend ratios were uniaxially drawn by solid-state coextrusion and the structure development during solid state deformation was studied. As-prepared blends showed two T_gs. The lower T_g was ∼72 °C, independent of the blend ratio. In contrast, the higher T_g increased with increasing PEN content. Thus, the coextrusion was carried out around the higher T_g of the sample. At a given draw ratio of 5, which was close to the achievable maximum draw ratio, the tensile strength of the drawn samples from the initially amorphous state increased gradually with increasing PEN content. On the other hand, the tensile modulus was found to decrease initially, reaching a minimum at 40-60 wt% PEN, and then increased as the PEN content increased. The results indicate that we can get the drawn films with a moderate tensile modulus and a high tensile strength. The drawn samples from the blends containing 40-60 wt% of PEN showed a maximum elongation at break, and a maximum thermal shrinkage around 100 °C. Also, the degree of stress-induced crystallinity showed a broad minimum around the blend ratio of 50% of PEN. These morphological characteristics explained well the effects of blend ratio on the tensile modulus and strength of drawn PET/PEN blend films.     

Use of electrochemical impedance spectroscopy for the study of corrosion protection by polymer coatings

A discussion of the requirements for hardware and software necessary for collection and analysis of electrochemical impedance spectroscopy data for polymer coated metals is presented. Most authors agree that a simple model can describe the frequency dependence of impedance spectra for polymer coated metals exposed to corrosive environments. The water uptake of the coating can be estimated from the time dependence of the coating capacitance C _c, The pore resistance R _po depends both on the resistivity of the coating and the disbonded area A _d. The polarization resistance R _P of the corroding area under the coating and the corresponding capacitance C _dl both depend on A _d. The breakpoint frequency method is discussed in detail and the dependence of the breakpoint frequency f _b on and A _d is derived. In addition to f _b other parameters can be obtained which depend on the ratio A _d/ or only on A _d or . Since these parameters can be obtained at frequencies exceeding 1 Hz without the need for an analysis of the impedance spectra in the entire frequency region, this approach is considered especially useful for corrosion monitoring. The concepts proposed for the analysis and interpretation of EIS data for polymer coated metals are illustrated using data for Al alloys, Mg and steel exposed to NaCl. For an alkyd coating on cold rolled steel the time dependence of A _d and during exposure to 0.5 m NaCl has been determined qualitatively using the modified breakpoint frequency method.     

In situ AFM study of near‐surface crystallization in PET and PEN

The surface crystallization behavior of poly(ethylene terephthalate) (PET) and poly(ethylene 2,6‐naphthalate) (PEN) spin‐coated thin films was compared by means of atomic force microscopy (AFM) with an in situ heating stage. As the films were heated up stepwise, characteristic surface crystals appeared at a crystallization temperature (T_c) in the near‐surface region which is about 15 °C under the bulk T_c, and were replaced by bulk crystals when the temperature was increased to the bulk T_c. In the case of films whose thickness is less than 70 nm (PET) and 60 nm (PEN), significant increases in the bulk T_c were observed. Scanning force microscopy (SFM) force‐distance curve measurements showed that the glass transition temperature (T_g) of the near‐surface region of PET and PEN were 22.0 and 26.6 °C below their bulk T_g (obtained by DSC). After the onset of surface crystallization, edge‐on and flat‐on crystals appeared at the free surface of PET and PEN thin films, whose morphologies are very different to those of the bulk crystals. Although the same general behavior was observed for both polyesters, there are significant differences both the influence of the surface and substrate on the transition temperatures, and in morphology of the surface crystals. These phenomena are discussed in terms of the differences in the mobility of polymer chains near the surface. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44269.     

Evidencing antagonist effects of water uptake and leaching processes in marine organic coatings by gravimetry and EIS

Two distinct marine epoxy organic coatings were aged in a sodium chloride (30 g L⁻¹) solution at different temperatures. The water absorption was evaluated using gravimetric tests onto free films and EIS experiments were realized onto attached films. A strong leaching process was evidenced by gravimetry and the FT-IR analysis of the solution after ageing revealed the presence of extracted organic components. However, EIS results were not sensitive to this phenomenon and the water uptake values, obtained with a modified Brasher–Kingsbury equation, were found to be higher than gravimetric values. The comparison of the water volume fraction obtained by EIS with the apparent water mass fraction allowed following the species desorption with immersion time. It was proposed that this leaching process was related to a loss of the polymer density and the results showed that this phenomenon was thermally activated.     

Synthesis and properties of phosphorus containing PET and PEN (I)

2-(6-Oxido-6H-dibenz 〈c,e〉〈1,2〉 oxaphosphorin-6-yl) dimethyl itaconate (ODOP-DI) was prepared by the addition reaction between 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and dimethyl itaconate while DOPO was synthesized through multistep reaction from o-phenylphenol and phosphorus trichloride. The compound (ODOP-DI) was used as a reactive flame retardant in polyethylene 1,4-terephthalate (PET) and polyethylene 2,6-naphthalate (PEN) for film, fiber, and electronic applications. The thermal properties of the resulted copolyesters were investigated by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). Owing to the incorporation of the rigid structure of DOPO and pendant P groups, the resulted phosphorus containing copolyesters exhibited better flame retardancy, higher char yield, and thermal stability than homopolymers of PET and PEN. UL 94-VO rating could be achieved with a phosphorus content of as low as 0.75% for PET, 0.5% for PEN, and no fume and toxic gas emission were observed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1959–1964, 1998     

Electrochemical impedance spectroscopy of poly[carbazole-co-N-p-tolylsulfonyl pyrrole] on carbon fiber microelectrodes,equivalent circuits for modelling

Polycarbazole (PCz) and copolymerization of carbazole (Cz) and N-p-tolylsulfonyl pyrrole (pTsp), P(Cz-co-pTsp), thin films have been cyclovoltammetrically coated onto carbon fiber electrodes as an active functionalized microelectrode in sodium perchlorate (NaClO₄)/acetonitrile (ACN) medium. The resulting thin films of homopolymer and copolymer were characterised by using Fourier transform infrared reflectance spectroscopy (ATR-FTIR), energy dispersive X-ray (EDX) point analysis, scanning electron microscopy (SEM) and atomic force microscopy (AFM). An electrical impedance study on the prepared electrodes is reported in the present paper under different feed ratios of [pTsp]₀/[Cz]₀ during electrochemical impedance spectroscopic (EIS) measurements. Specific capacitance (C_sp) were calculated, P(Cz-co-pTsp) in feed ratio of [pTsp]₀/[Cz]₀ = 200 has preserved more capacitive behavior especially at lower frequency (C_sp = ∼156 mF g⁻¹) than polycarbazole (C_sp = ∼2.1 mF g⁻¹. The electrochemical impedance data fitted to three different equivalent models were used to find out numerical values of the proposed components.     

The effect of compression on electron transport and recombination in plastic TiO2 photoanodes

The compression method was applied for the preparation of plastic TiO₂ porous films on a conductive indium–tin oxide (ITO)-coated polyethylene naphthalate (PEN) substrate at low temperature for the generation of high-efficiency plastic dye-sensitized solar cells (DSCs). The compression parameters, including pressure and time, were varied in order to determine their effect on the photovoltaic performance of the plastic DSCs. The results from electrochemical impedance spectroscopy (EIS) showed that charge transport resistance in the porous TiO₂ films (R_t) gradually decreased when the applied pressure was increased from 0 MPa to 150 MPa, which indicated a better connection between the TiO₂ nanoparticles and electron transport in the TiO₂ films. In addition, a longer press time led to an increased resistance of electron recombination (R_ct) and an increased charge-collection efficiency. After optimization of the compression parameters, the efficiency of energy conversion was increased by approximately 81.6%. In addition, the efficiency of energy conversion was increased by an additional 4.65% under AM1.5 illumination.     

Oxygen and carbon dioxide transport through high barrier polyester blends

The transport of oxygen and carbon dioxide through a set of random copolymer films based on poly(ethylene terephthalate) (PET) and poly(ethylene 2,6‐naphthalate) (PEN) were explored. Diffusivity and permeability of both gases decreased with increasing PEN content. The oxygen and carbon dioxide diffusion coefficients decreased 74 and 82% from pure PET to pure PEN, respectively. The presence of stiffer PEN moieties had an effect on the glass transition temperature (T_g) of PET/PEN blends and gas barrier. In the complete range of tested blends, the differential scanner calorimeter analysis displayed a single value of thermal glass transition temperature. As the PEN content was increased, the fractional free volume (FFV) and the diffusion coefficients of the blends were decreased. The Doolittle equation provided the best fit for diffusivity and FFV and showed that the gas transport behavior was better understood when it was taken into consideration the cohesive energy of blends. As the PEN content in films was increased, their rigidity and the glass/rubber transition temperature were increased, and their capacity to be penetrated by small molecules like O₂ and CO₂ was decreased. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Study on the alcoholysis of aromatic polyesters and related esters using a high-pressure calorimeter

Summary The heat of base-catalyzed alcoholysis of poly(ethylene terephthalate) (PET) and poly(ethylene 2,6-naphthalenedicarboxylate) (PEN) as well as several related aromatic and aliphatic esters has been measured using a high-pressure calorimeter. The process is essentially thermoneutral, and heats of CH₃ONa-catalyzed methanolysis of PET and PEN are +1.8±0.6 and +9.3±0.2 kJ/mol-carboxyl group, respectively. Furthermore, the heats of Zn(OCOCH₃)₂-catalyzed alcoholysis of PET with ethylene glycol and benzyl alcohol are also calculated as +5.8±0.2 and +6.6±0.8 kJ/mol-carboxyl group, respectively. These values are comparable to those for ethyl esters of p-substituted benzoic acids and propionic acid. Received: 15 December 1998/Revised version: 22 January 1999/Accepted: 29 January 1999     

Glass‐transition and melting behavior of poly(ethylene terephthalate)/poly(ethylene 2,6‐naphthalate) blends

The glass‐transition temperatures and melting behaviors of poly(ethylene terephthalate)/poly(ethylene 2,6‐naphthalate) (PET/PEN) blends were studied. Two blend systems were used for this work, with PET and PEN of different grades. It was found that T_g increases almost linearly with blend composition. Both the Gibbs–DiMarzio equation and the Fox equation fit experimental data very well, indicating copolymer‐like behavior of the blend systems. Multiple melting peaks were observed for all blend samples as well as for PET and PEN. The equilibrium melting point was obtained using the Hoffman–Weeks method. The melting points of PET and PEN were depressed as a result of the formation of miscible blends and copolymers. The Flory–Huggins theory was used to study the melting‐point depression for the blend system, and the Nishi–Wang equation was used to calculate the interaction parameter (χ₁₂). The calculated χ₁₂ is a small negative number, indicating the formation of thermodynamically stable, miscible blends. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 11–22, 2001     

Studies of the impedance models and water transport behaviors of cathodically polarized coating

Cathodic protection (CP) is usually combined with organic coatings to protect metallic structures exposed to seawater. However, the application of CP would enhance coating failure, such as cathodic delamination. To date, there has been few works characterizing the impedance models and water transport behaviors of cathodically polarized coating. In the present article, the analyses of impedance models and water uptake processes of chlorinated rubber coating subjected to various levels of cathodic protection were studied during coatings aging process by electrochemical impedance spectroscopy (EIS).Four distinguished electrical equivalent circuits (EEC) were used to fit the EIS plots of coatings without CP, while only two were employed for samples with CP. Since no corrosion was expected to take place at the metal/coating interface for sample which was polarized cathodically. Coating capacitance was used to investigate the sorption characteristic of water in coating since the increase of C_c was associated with water penetration into the coating. Compared with the sample without CP, those coating systems under CP have a smaller water diffusion coefficient and a further water uptake process after the saturation period.     

Processing characteristics,structure development,and properties of uni and biaxially stretched poly(ethylene 2,6 naphthalate) (PEN) films

Poly(ethylene 2,6, naphthalene dicarboxilate), PEN, is very similar to poly(ethylene terephthalate), PET, in its chemical structure and was, therefore, expected to exhibit similar processing characteristics. We, however, observed a few problems during stretching of PEN, the most important of which was necking behavior at 145°C, which is between T_g (117°C) and T^cc (195°C). This is usually observed in PET only when it is stretched close to or below T_g. At temperatures between T_g and T_cc (cold crystallization temperature) PET stretches rather uniformly. The temperature window for film stretching appears to be rather wide, but our results indicate that this is not the case. Films stretched to high stretch ratios become uniform due to propagation and final disappearance of necks as a result of stress hardening. Our attempts at stretching these films at higher temperatures indicated that necking is eliminated, but so is stress induced crystallization, which causes stress hardening (unless high stretching rates are employed). The presence of stress hardening is essential for obtaining high quality, uniform films of these polymers. In addition, at high temperatures thermally activated crystallization which starts dominating the structure development, detrimentally affects the general appearance of the films. In brief, the PEN films we investigated have a narrower processing window than was anticipated based on their thermal behavior alone. At elevated temperatures the films are sensitive to the rate of stretching even more than typical PET processed at comparable conditions. The uniformity of the films depends on the stretch ratio, stretching mode, ratio(s) and rates and temperature. WAXS studies on the films indicate that the macromolecules packed into the low temperature crystal modification. In addition, WAXS pole figure studies suggest that naphthalene planes preferentially orient parallel to the film surface during biaxial stretching. The biaxially stretched films were observed to exhibit a bimodal chain orientation as evidenced by pole figure analysis of the (010) planes.     

Correlation of morphology and barrier properties of thin microwave plasma polymer films on metal substrate

The barrier properties of thin model organosilicon plasma polymers layers on iron are characterised by means of electrochemical impedance spectroscopy (EIS). Tailored thin plasma polymers of controlled morphology and chemical composition were deposited from a microwave discharge. By the analysis of the obtained impedance diagrams, the evolution of the water uptake ?, coating resistance and polymer capacitance with immersion time were monitored and the diffusion coefficients of the water through the films were calculated. The impedance data correlated well with the chemical structure and morphology of the plasma polymer films with a thickness of less than 100 nm. The composition of the films were determined by means of infrared reflection absorption spectroscopy (IRRAS), X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The morphology of the plasma polymer surface and the interface between the plasma polymer and the metal were characterised using atomic force microscopy (AFM). It could be shown that, at higher pressure, the film roughness increases which is probably due to the adsorption of plasma polymer nanoparticles formed in the plasma bulk and the faster film growth. This leads to voids with a size of a few tens of nanometers at the polymer/metal interface. The film roughness increases from the interface to the outer surface of the film. By lowering the pressure and thereby slowing the deposition rate, the plasma polymers perfectly imitate the substrate topography and lead to an excellent blocking of the metal surface. Moreover, the ratio of siloxane bonds to methyl-silyl groups increases which implies that the crosslink density is higher at lower deposition rate. The EIS data consistently showed higher coating resistance as well as lower interfacial capacitance values and a better stability over time for the film deposited at slower pressure. The diffusion coefficient of water in thin and ultra-thin plasma polymer films could be quantified for the smooth films. The measurements show that the quantitative evaluation of the electrochemical impedance data requires a detailed understanding of the film morphology and chemical composition. In addition, the measured diffusion coefficient of about 1.5×10⁻¹⁴ cm² s⁻¹ shows that plasma polymers can act as corrosion resistant barrier layers at polymer/metal interfaces.     

Importance of Time-Dependent Wetting Behavior of Gas-Diffusion Electrodes for Reactivity Determination

Tin foil and SnO_x/C gas-diffusions electrodes (GDEs) were investigated via electrochemical impedance spectroscopy (EIS) to extract the differential double-layer capacitance (C_dl) as a measure of the wetted surface area. Time-dependent C_dl values revealed an immediate stationary wetting for tin foil electrodes while a distinct increase of C_dl – which becomes stationary with time – was observed for GDEs. The time-dependent wetting behavior of the GDEs was substantiated by physical post-mortem characterization. Since the wetted surface area determines the number of reachable active sites the performance of GDEs should be normalized to the wetted surface area for evaluation of reactivity.     

Corrosion stability of polyester coatings on steel pretreated with different iron–phosphate coatings

The influence of steel surface pretreatment with different types of iron–phosphate coatings on the corrosion stability and adhesion characteristics of polyester coatings on steel was investigated. The phosphate coating was chemically deposited either from the simple novel plating bath, or with the addition of NaNO₂, as an accelerator in the plating bath. The morphology of phosphate coatings was investigated using atomic force microscopy (AFM). The corrosion stability of polyester coatings on steel pretreated by iron–phosphate coatings was investigated by electrochemical impedance spectroscopy (EIS) in 3% NaCl solution, while “dry” and “wet” adhesion were measured by a direct pull-off standardized procedure. It was shown that greater values of pore resistance, R_p, and smaller values of coating capacitance of polyester coating, C_c, on steel pretreated with iron–phosphate coating were obtained, as compared to polyester coating on steel phosphated with accelerator, and on the bare steel. The surface roughness of phosphate coating deposited on steel from the bath without accelerator is favorable in forming stronger bonds with polyester coating. Namely, the dry and wet adhesion measurements are in accordance with EIS measurements in 3% NaCl solution, i.e. lower adhesion values were obtained for polyester coating on steel phosphated with accelerator and on the bare steel, while the iron–phosphate pretreatment from the novel bath enhanced the adhesion of polyester coating on steel.     

Stability of spontaneous passive films on high strength Mo-containing stainless steels in aqueous solutions

The stability of naturally grown passive films on some Mo-containing stainless steel specimens was examined in aerated and deaerated universal buffer solutions with different pH (2–12) as well as in sulphate and chloride solutions. Open circuit potential (E _oc) and electrochemical impedance spectroscopy (EIS) were used as measuring techniques. In all cases, E _oc shifts towards less negative values with time until the potential reaches its steady-state (E _ss) value. The E _ss value is found to be more positive with decrease in solution pH or increase in Mo content in the alloy and becomes less positive in deaerated buffer solutions. Also, the thickening rate of the outer layer for the duplex passive film increases with increasing extent of Mo in the steel substrate or pH of the test solution. For a given alloy, E _ss decreases linearly with the anion concentration (C), and is always more positive in Cl⁻ than in SO₄²⁻ media for C ≥ 0.05 M. Analysis of the EIS data showed that the total resistance (R _T) of the passive film has higher values in aerated solutions, and is generally lower in basic solutions. This indicates that lower solution pH favours the formation of oxide films offering better protection. Furthermore, the higher values of R _T in Na₂SO₄ solutions suggest the formation of more stable passive films in sulphate than in chloride solutions. This is discussed on the basis of the relative degree of anion incorporation into the passive films.     

Evaluation of biocompatibility of the surface of polyethylene films modified with various water soluble polymers using Ar plasma‐post polymerization technique

Surface modified polyethylene (g‐PE), PMPC‐g‐PE, PGEMA‐g‐PE, PNIPAAm‐g‐PE and PHPMA‐g‐PE films with the water soluble polymers such as poly[2‐(methacryloyloxy)ethyl phosphorylcholine] (PMPC), poly[2‐(glucosyloxy)ethyl methacrylate] (PGEMA), poly(N‐isopropylacrylamide) (PNIPAAm) and poly[N‐(2‐hydroxypropyl) methacrylamide] (PHPMA) were prepared by graft copolymerization using an Ar plasma‐post polymerization technique. The surface of the g‐PE films was characterized by means of X‐ray photoelectron spectroscopy and the grafting percentage of PMPC, PNIPAAm and PHPMA was found to be 5.31, 2.83, and 3.40% for the corresponding g‐PE film. Biocompatibility of the g‐PE films was evaluated by the adsorption of serum proteins and the Michaelis constant (K_m) for the enzymatic reaction of thrombin with synthetic substrate S‐2238 in the presence of g‐PE film. The biocompatibility of water soluble polymers such as PMPC, polyoxyethylene (POE), PGEMA, PNIPAAm and PHPMA was also evaluated by the same enzymatic reaction of thrombin with S‐2238 in their polymer solutions. The K_m values in the presence of water soluble polymers was found to decrease in the order PMPC > POE > PGEMA > PNIPAAm > PHPMA. As a conclusion, PMPC‐g‐PE film exhibited the most biocompatibility among g‐PE films because its surface adsorbed less protein than those of the untreated PE and other g‐PE films and it showed the largest K_m for the enzymatic reaction.