Water Vapor Transmission Rate Values Research Articles

Organic/Inorganic Hybrid Materials for Organic Electronic Application

Organic/inorganic stacks were deposited on flexible polycarbonate substrate using inductively coupled plasma chemical vapor deposition (ICP-PECVD) for permeation barrier application. The effects of deposition temperature, RF power, gas flow ratio, deposition pressure on film properties of surface roughness, water vapor transmission rate (WVRT) were investigated. Energy dispersive spectrum (EDS), atomic force microscopy (AFM) and transmission electron microscopy (TEM) were used to characterize the film characteristics of the stack layers. It was found that the surface roughness Ra was as low as is 0.25 nm. The WVRT values of the optimum barriers structures were 10-2g/m2 day (1 pair of stacks) and 4.8 x 10-5g/m2 day (4 pair of stacks). This result indicated that the permeation barrier films prepared by ICP-PECVD could be a promising candidate for flexible electronic applications.

Preparation and Characterization of Exfoliated PHBV Nanocomposites to Enhance Water Vapor Barriers of Calendared Paper

The water vapor transmission rates (WVTRs) of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (PHBV) and PHBV/nanocomposite-coated papers were measured at various levels of relative humidity and temperature. The coating of PHBV on base paper was performed with two different methods, and the more effective one for lowering WVTR values was utilized for coating the PHBV/nanocomposites on the paper. Nanocomposites of PHBV were prepared with a commercial montmorillonite Cloisite30B (CS30B), and a novel modified clay was obtained via a solution-blending process. To prepare the series of modified clays, which were coined here as HPGC, MPGC, and LPGC, we intercalated β-butyrolactone in the Cloisite30B clay by a ring-opening polymerization. The morphology of the clay and nanocomposites was revealed by X-ray diffraction. Additionally, the dispersion and phase behavior of the clay in the PHBV matrix was observed using a transmission electron microscope. It was found that the coating method and clay exfoliation were the...

Cellulose/nanoclay composite films with high water vapor resistance and mechanical strength

Cellulose based films were fabricated by dissolving the micro-crystalline cellulose and cotton linter in a LiOH/urea aqueous system, followed by regeneration in acetone. The water vapor transmission rate (WVTR) values of the films were measured and the results indicated that regenerated micro-crystalline cellulose (RMCC) showed lower WTVR than regenerated cotton linter (RCL). WVTR values were proportional to the thickness of samples. The films also exhibited high oil resistance as no fat oil could pass through the RMCC and RCL films even after a week. The RMCC and RCL/natural-montmorillonite nanocomposites (Na-MMT) films were prepared and characterized. The effect of Na-MMT loading on the mechanical, crystallinity and water vapor transmission properties of the nanocomposites was further investigated. Na-MMT loading improved the mechanical properties and decreased the crystallinity of the nanocomposite films. The results indicated partially intercalated nano-layered structures with WVTR as low as 43 g/m2/day.

Low-Temperature Plasma-Assisted Atomic Layer Deposition of Silicon Nitride Moisture Permeation Barrier Layers.

Encapsulation of organic (opto-)electronic devices, such as organic light-emitting diodes (OLEDs), photovoltaic cells, and field-effect transistors, is required to minimize device degradation induced by moisture and oxygen ingress. SiNx moisture permeation barriers have been fabricated using a very recently developed low-temperature plasma-assisted atomic layer deposition (ALD) approach, consisting of half-reactions of the substrate with the precursor SiH2(NH(t)Bu)2 and with N2-fed plasma. The deposited films have been characterized in terms of their refractive index and chemical composition by spectroscopic ellipsometry (SE), X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared spectroscopy (FTIR). The SiNx thin-film refractive index ranges from 1.80 to 1.90 for films deposited at 80 °C up to 200 °C, respectively, and the C, O, and H impurity levels decrease when the deposition temperature increases. The relative open porosity content of the layers has been studied by means of multisolvent ellipsometric porosimetry (EP), adopting three solvents with different kinetic diameters: water (∼0.3 nm), ethanol (∼0.4 nm), and toluene (∼0.6 nm). Irrespective of the deposition temperature, and hence the impurity content in the SiNx films, no uptake of any adsorptive has been observed, pointing to the absence of open pores larger than 0.3 nm in diameter. Instead, multilayer development has been observed, leading to type II isotherms that, according to the IUPAC classification, are characteristic of nonporous layers. The calcium test has been performed in a climate chamber at 20 °C and 50% relative humidity to determine the intrinsic water vapor transmission rate (WVTR) of SiNx barriers deposited at 120 °C. Intrinsic WVTR values in the range of 10(-6) g/m2/day indicate excellent barrier properties for ALD SiNx layers as thin as 10 nm, competing with that of state-of-the-art plasma-enhanced chemical vapor-deposited SiNx layers of a few hundred nanometers in thickness.

Effect of argon ion energy on the performance of silicon nitride multilayer permeation barriers grown by hot-wire CVD on polymers

Permeation barriers for organic electronic devices on polymer flexible substrates were realized by combining stacked silicon nitride (SiNx) single layers (50nm thick) deposited by hot-wire chemical vapor deposition process at low-temperature (~100°°C) with a specific argon plasma treatment between two successive layers. Several plasma parameters (RF power density, pressure, treatment duration) as well as the number of single layers have been explored in order to improve the quality of permeation barriers deposited on polyethylene terephthalate. In this work, maximum ion energy was highlighted as the crucial parameter making it possible to minimize water vapor transmission rate (WVTR), as determined by the electrical calcium test method, all the other parameters being kept fixed. Thus fixing the plasma treatment duration at 8min for a stack of two SiNx single layers, a minimum WVTR of 5×10−4g/(m2day), measured at room temperature, was found for a maximum ion energy of ~30eV. This minimum WVTR value was reduced to 7×10−5g/(m2day) for a stack of five SiNx single layers. The reduction in the permeability is interpreted as due to the rearrangement of atoms at the interfaces when average transferred ion energy to target atoms exceeds threshold displacement energy.

Synergy Between Plasma‐Assisted ALD and Roll‐to‐Roll Atmospheric Pressure PE‐CVD Processing of Moisture Barrier Films on Polymers

The synergy between fast (1600 nm · min−1), roll‐to‐roll plasma‐enhanced chemical vapor deposited (PE‐CVD) SiO2 layers and plasma‐assisted atomic layer deposited (PA‐ALD) ultra‐thin Al2O3 films has been investigated in terms of moisture permeation barrier properties. The effective and intrinsic water vapor transmission rates (WVTR) were studied as a function of the number of ALD cycles. It was demonstrated that a synergistic combination of a silica buffer layer deposited on polymer with an ultra‐thin (≤ 2 nm) alumina barrier film can provide excellent intrinsic (10−5–10−6 g · m−2 · day−1) and good effective (∼10−3 g · m−2 · day−1) WVTR values, whereas both single layers individually exhibit poor barrier performances with effective WVTR values of ≥ 1.0 g · m−2 · day−1.

Analysis of Nanoporosity in Moisture Permeation Barrier Layers by Electrochemical Impedance Spectroscopy.

Water permeation in inorganic moisture permeation barriers occurs through macroscale defects/pinholes and nanopores, the latter with size approaching the water kinetic diameter (0.27 nm). Both permeation paths can be identified by the calcium test, i.e., a time-consuming and expensive optical method for determining the water vapor transmission rate (WVTR) through barrier layers. Recently, we have shown that ellipsometric porosimetry (i.e., a combination of spectroscopic ellipsometry and isothermal adsorption studies) is a valid method to classify and quantify the nanoporosity and correlate it with the WVTR values. Nevertheless, no information is obtained about the macroscale defects or the kinetics of water permeation through the barrier, both essential in assessing the quality of the barrier layer. In this study, electrochemical impedance spectroscopy (EIS) is shown as a sensitive and versatile method to obtain information on nanoporosity and macroscale defects, water permeation, and diffusivity of moisture barrier layers, complementing the barrier property characterization obtained by means of EP and calcium test. EIS is performed on thin SiO2 barrier layers deposited by plasma enhanced-CVD. It allows the determination of the relative water uptake in the SiO2 layers, found to be in agreement with the nanoporosity content inferred by EP. Furthermore, the kinetics of water permeation is followed by EIS, and the diffusivity (D) is determined and found to be in accordance with literature values. Moreover, differently from EP, EIS data are shown to be sensitive to the presence of local macrodefects, correlated with the barrier failure during the calcium test.

Low temperature temporal and spatial atomic layer deposition of TiO2 films

Titanium dioxide films were grown by atomic layer deposition (ALD) using titanium tetraisopropoxide as a titanium precursor and water, ozone, or oxygen plasma as coreactants. Low temperatures (80–120 °C) were used to grow moisture barrier TiO2 films on polyethylene naphthalate. The maximum growth per cycle for water, ozone, and oxygen plasma processes were 0.33, 0.12, and 0.56 Å/cycle, respectively. X-ray photoelectron spectrometry was used to evaluate the chemical composition of the layers and the origin of the carbon contamination was studied by deconvoluting carbon C1s peaks. In plasma-assisted ALD, the film properties were dependent on the energy dose supplied by the plasma. TiO2 films were also successfully deposited by using a spatial ALD (SALD) system based on the results from the temporal ALD. Similar properties were measured compared to the temporal ALD deposited TiO2, but the deposition time could be reduced using SALD. The TiO2 films deposited by plasma-assisted ALD showed better moisture barrier properties than the layers deposited by thermal processes. Water vapor transmission rate values lower than 5 × 10−4 g day−1 m−2 (38 °C and 90% RH) was measured for 20 nm of TiO2 film deposited by plasma-assisted ALD.

Moisture barrier evaluation of SiOx/SiNx stacks on polyimide substrates using electrical calcium test

Electrical calcium (Ca) test was used to measure water vapor transmission rate (WVTR) through polyimide (PI) substrate with barrier films. The WVTR was obtained by measuring the resistance of the Ca as a function of time. Barrier films consisted of silicon oxide (SiOx)/silicon nitride (SiNx) stacks were consecutively deposited onto the PI substrate at 350°C by plasma-enhanced chemical vapor deposition. SiNx and SiOx films show great moisture impermeability while the SiNx film presented higher moisture resistance than the SiOx film. The sample of PI coated with SiOx/SiNx stacks was kept flat by stress compensation of SiNx film and SiOx film. The WVTR value of the optimum barrier structure (5 pairs of SiOx/SiNx) is 5.58×10−6g/(m2day) under an electrical Ca test (25°C, 40% relative humidity). After 500 times cyclic bending in a compressive mode, WVTR value keeps below 4.32×10−5g/(m2day). The SiOx/SiNx barrier stacks presented on PI have a great potential for flexible electronics applications.

Development of flexible organic light-emitting diode on barrier film and roll-to-roll manufacturing

To come out with a successful organic light-emitting diode (OLED) lighting business, it is very important to have clear differentiation of OLED from LEDs. Flexible OLED has merits, such as capability to be mounted on the curved wall, which is not easy for LEDs to achieve the feature. There are several approaches to make flexible OLEDs especially among those plastic barrier films that can bring high level of flexibility, which could not be achieved by any conventional lighting method. In this paper, barrier films with various water vapor transmission rate values, including 10− 6 order, are applied, and the conditions to have almost no dark spot growth under 85 °C and 85% high temperature/humidity test are shown. Flexible OLED panels are manufactured with the world's first roll-to-roll equipment using plastic barrier film.

Hydrophobic-modified nano-cellulose fiber/PLA biodegradable composites for lowering water vapor transmission rate (WVTR) of paper

New biodegradable nanocomposites have been successfully prepared by incorporating modified nano-cellulose fibers (NCF) in a biodegradable polylactic acid (PLA) matrix in this work. The hydrophobic-modified NCF was obtained by grafting hydrophobic monomers on NCF to improve the compatibility between NCF and PLA during blending. The resulting NCF/PLA composites were then applied on paper surface via a cast-coating process in an attempt to reduce the water vapor transmission rate (WVTR) of paper. The WVTR tests, conducted under various testing conditions and with different coating weights, demonstrated that the modified NCF/PLA composites coating played a critical role in lowering WVTR of paper. The lowest WVTR value was 34g/m2/d, which was obtained with an addition of 1% of modified NCF to PLA and the composites coating weight at 40g/m2 and substantially lower than the control value at 1315g/m2/d. The paper coated with the modified biodegradable composite is promising as green-based packaging materials.

On the role of nanoporosity in controlling the performance of moisture permeation barrier layers

Satisfactory results in term of moisture permeation barrier performance have been achieved for the encapsulation of organic electronic devices. However, further insight into the correlation between barrier performances and moisture permeation pathways are sought. This contribution focuses on the residual nanoporosity in the inorganic layer and its role in controlling the barrier performance. Inorganic barrier layers (i.e. Al2O3 and SiO2) prepared by plasma-enhanced atomic layer deposition (PE-ALD) and plasma-enhanced chemical vapor deposition (PE-CVD) have been extensively analyzed by means of IR spectroscopy, spectroscopic ellipsometry, Rutherford backscattering spectroscopy, elastic recoil detection and X-ray photoelectron spectroscopy. The calcium test has been performed to determine the intrinsic water vapor transmission rate (WVTR), as well as the effective WVTR values. Ellipsometric porosimetry (EP) has been adopted to determine the open porosity and pore size range in the structure of the layer. Trivinyltrimethyl cyclotrisiloxane (dV3D3=1nm) and water (dH2O=0.3nm) have been chosen as probe molecules. A correlation between the residual nanoporosity and the intrinsic barrier properties has been found, regardless of the chemistry of the layer and deposition method used. Pores larger than 1nm with a relative content above 1% have been found responsible for mediocre barrier layers characterized by a WVTR in the range of 10−2 to 10−3gm−2day−1. Furthermore, the pore size range of 0.3–1nm and its relative content have been found to control the transition in WVTR between the 10−4gm−2day−1 and the 10−6gm−2day−1 regime, highlighting the role of residual nanoporosity in controlling the intrinsic barrier properties.

Permeation barrier properties of an Al2O3/ZrO2 multilayer deposited by remote plasma atomic layer deposition

We report the permeation barrier properties of Al2O3/ZrO2 multi-layers deposited by remote plasma atomic layer deposition. Electrical Ca degradation tests were performed to derive the water vapor transmission rate (WVTR) of Al2O3, ZrO2 and Al2O3/ZrO2 multi-layers at 50 °C and 50% relative humidity (RH). Al2O3/ZrO2 multi-layers exhibit better barrier properties than Al2O3 and ZrO2 layers, and when more individual layers were deposited in the same total thickness, the WVTR value was reduced further, indicating a better barrier property. The WVTR of the Al2O3 and ZrO2 layers were 9.5 × 10−3 and 1.6 × 10−2 g/m2 day, respectively, but when deposited alternatively with 1 cycle of each layer, the WVTR decreased to 9.9 × 10−4 g/m2 day. X-ray diffraction results indicated that ZrO2 has a monoclinic structure but Al2O3 and Al2O3/ZrO2 multi-layers show an amorphous structure. Cross sectional Al2O3/ZrO2 multi-layer structures and the formation of a ZrAlxOy phase are observed by transmission electron microscopy (TEM). X-ray photoelectron spectrometry (XPS) results indicate that Al2O3 and ZrO2 contain 33.7% and 37.8%, respectively, Al–OH and Zr–OH bonding. However, the ZrAlxOy phase contained 30.5% Al–OH and Zr–OH bonding. The results of transmittance measurement indicate that overall, Al2O3, ZrO2 and Al2O3/ZrO2 multi-layers show high transmittance greater than 80% in the visible region.

Radio frequency plasma power dependence of the moisture permeation barrier characteristics of Al2O3 films deposited by remote plasma atomic layer deposition

In the present study, we investigated the gas and moisture permeation barrier properties of Al2O3 films deposited on polyethersulfone films (PES) by capacitively coupled plasma (CCP) type Remote Plasma Atomic Layer Deposition (RPALD) at Radio Frequency (RF) plasma powers ranging from 100 W to 400 W in 100 W increments using Trimethylaluminum [TMA, Al(CH3)3] as the Al source and O2 plasma as the reactant. To study the gas and moisture permeation barrier properties of 100-nm-thick Al2O3 at various plasma powers, the Water Vapor Transmission Rate (WVTR) was measured using an electrical Ca degradation test. WVTR decreased as plasma power increased with WVTR values for 400 W and 100 W of 2.6 × 10−4 gm−2day−1 and 1.2 × 10−3 gm−2day−1, respectively. The trends for life time, Al-O and O-H bond, density, and stoichiometry were similar to that of WVTR with improvement associated with increasing plasma power. Further, among plasma power ranging from 100 W to 400 W, the highest power of 400 W resulted in the best moisture permeation barrier properties. This result was attributed to differences in volume and amount of ion and radical fluxes, to join the ALD process, generated by O2 plasma as the plasma power changed during ALD process, which was determined using a plasma diagnosis technique called the Floating Harmonic Method (FHM). Plasma diagnosis by FHM revealed an increase in ion flux with increasing plasma power. With respect to the ALD process, our results indicated that higher plasma power generated increased ion and radical flux compared with lower plasma power. Thus, a higher plasma power provides the best gas and moisture permeation barrier properties.

Cellulose Fibers Modified with Starch-Based Microcapsules for Green Packaging

In this work, the innovative starch microcapsules enclosed with hydrophobic carnauba wax were developed, which were applied to the modification of cellulose fibers, thus increasing the water resistance of paper by reducing water vapor transmission rate (WVTR). Carnauba wax being encapsulated by crosslinking starch was confirmed by thermogravimetric analysis. The sizes of carnauba wax-starch microcapsules depended on the weight ratio (R) of starch to carnauba wax and concentration of crosslinker. The best performance on water vapor barrier of the paper was achieved by the fibers treated with the microcapsules of larger size. The lowest WVTR was given by the handsheet treated by wet-end addition with carnauba wax-starch microcapsules at Rstarch/ carnaubawax=5%, and Rcrosslinker/ carnauba wax=50%, and had a value of 348 g/m2day, a 70% drop from untreated original paper which has a WVTR value of 1176 g/m2day.

Preparation and characterization of novel antibacterial castor oil-based polyurethane membranes for wound dressing application

Preparation of novel antibacterial and cytocompatible polyurethane membranes as occlusive dressing, which can provide moist and sterile environment over mild exudative wounds is considered in this work. In this regard, an epoxy-terminated polyurethane (EPU) prepolymer based on castor oil and glycidyltriethylammonium chloride (GTEAC) as a reactive bactericidal agent were synthesized. Polyurethane membranes were prepared through cocuring of EPU and different content of GTEAC with 1,4-butane diamine. The physical and mechanical properties, as well as cytocompatibility and antibacterial performance of prepared membranes were studied. Depending on their chemical formulations, the equilibrium water absorption and water vapor transmission rate values of the membranes were in ranges of 3-85% and 53-154g m(-2) day(-1), respectively. Therefore, these transparent membranes can maintain for a long period the moist environment over the wounds with low exudates. Detailed cytotoxicity analysis of samples against mouse L929 fibroblast and MCA-3D keratinocyte cells showed good level of cytocompatibility of membranes after purification via extraction of residual unreacted GTEAC moieties. The antibacterial activity of the membranes against Escherichia coli and Staphylococcus aureus bacteria was also studied. The membrane containing 50% GTEAC exhibited an effective antibacterial activity, while showed acceptable cytocompatibility and therefore, can be applied as an antibacterial occlusive wound dressing.

Mechanical, thermal, and barrier properties of nanocomposites based on poly(butylene succinate)/thermoplastic starch blends containing different types of clay

AbstractNanocomposites based on blends of poly(butylene succinate) (PBS) and thermoplastic cassava starch (TPS) were prepared using a two‐roll mill and compression molding, respectively. Two different types of clay, namely sodium montmorillonite (CloisiteNa) and the organo‐modified MMT (Cloisite30B) were used. The morphological and mechanical properties of the nanocomposite materials were determined by using XRD technique and a tensile test, respectively. Thermal properties of the composite were also examined by dynamic mechanical thermal analysis and thermal gravimetric techniques. Barrier properties of the nanocomposites were determined using oxygen transmission rate (OTR) and water vapor transmission rate (WVTR) tests. From the results, it was found that by adding 5 pph of the clay, the tensile modulus and the thermal properties of the blend containing high TPS (75 wt %) changed significantly. The effects were also dependent on the type of clay used. The use of Cloisite30B led to a nanocomposite with a higher tensile modulus value, whereas the use of CloisiteNa slightly enhanced the thermal stability of the material. OTR and WVTR values of the blend composites containing high PBS ratio (75 wt %) also decreased when compared to those of the neat PBS/TPS blend. XRD patterns of the nanocomposites suggested some intercalation and exfoliation of the clays in the polymer matrix. The above effects are discussed in the light of different interaction between clays and the polymers. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1114‐1123, 2013

Evaluating Al2O3 gas diffusion barriers grown directly on Ca films using atomic layer deposition techniques

Al2O3 gas diffusion barriers grown directly on Ca films using atomic layer deposition (ALD) techniques were evaluated using several methods based on Ca oxidation. The Al2O3 ALD films were grown on Ca films at 120 °C using trimethylaluminum and H2O as the reactants. The oxidation of the Ca films was then monitored versus time at 70 °C and ∼28% relative humidity either by measuring the electrical conductance of the Ca film or by recording the photographic image of the Ca film. In the photographic images, the Ca films revealed that the Al2O3 ALD films have a small number of pinhole defects that lead to Ca film oxidation areas that grow radially around the pinhole defect versus time. A burst of new oxidation areas also appeared suddenly at later times and grew radially versus time. This rapid “blooming” may be related to another type of defect caused by water corrosion of the Al2O3 ALD films. In the electrical conductance measurements, the conductance of the Ca film initially showed little change versus time. The conductance then dropped rapidly when the oxidation area in the photographic image was a noticeable fraction of the Ca film area. The conductance measurements yielded a water vapor transmission rate (WVTR) value of ∼2 × 10−2 g/(m2 day) prior to the rapid reduction of the conductance. The photographic images of the Ca film were also analyzed to obtain a WVTR value assuming radial oxidation of the Ca film around defects. The WVTR values obtained from the electrical conductance and the photographic images were in approximate agreement and increased versus Ca film oxidation until the rapid blooming of new circular oxidation areas. The WVTR values are larger than previous measurements and may indicate that Al2O3 ALD films grown directly on Ca are less stable and degraded by Ca film oxidation. This study reveals that a range of WVTR values can be obtained from different variations of the Ca test depending on the extent of Ca film oxidation.

Improvements in barrier properties of poly(lactic acid) films coated with chitosan or chitosan/clay nanocomposite

AbstractThe feasibility of chitosan or/and clay coatings as an alternative oxygen barrier material to poly(lactic acid) (PLA) film was investigated. The coated films were composed of natural materials based on biodegradable and biocompatible polymers, which exhibit excellent oxygen‐barrier properties compared with neat PLA films. Thus, these films can contribute toward effectively reducing environmental pollution. The chitosan/clay nanocomposite solutions were effectively dispersed through the clay using an ultrasonic bath and homogenizer. The barrier and morphology properties of the PLA films were tested by measuring selected film properties such as oxygen transmission rate (OTR), water vapor transmission rate (WVTR), field emission scanning electron microscopy, X‐ray diffraction and transmission electron microscope. OTR values measured using the chitosan and chitosan/clay nanocomposite coatings were significantly lower than those measured for neat PLA film. WVTR values measured using chitosan/clay nanocomposite coatings were also lower than those measured for neat PLA film and PLA film coated with chitosan. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Wheat Gluten-Laminated Paperboard with Improved Moisture Barrier Properties: A New Concept Using a Plasticizer (Glycerol) Containing a Hydrophobic Component (Oleic Acid)

This paper presents a novel approach to reduce the water vapor transmission rate (WVTR) and water absorbance of wheat gluten/paperboard laminates by introducing a hydrophobic component (oleic acid (OA)) into the hydrophilic plasticizer (glycerol). Whereas the paperboard showed immeasurably high WVTR, the laminate with gluten/glycerol yielded finite values. More importantly, by incorporating 75 wt.% OA into the plasticizer, the WVTR and water absorbance were reduced by, respectively, a factor of three and 1.5–2. Of particular interest was that the mechanical properties were not changing dramatically between 0 and 50 wt.% OA. The results showed clear benefits of combining a gluten film with paperboard. Whereas the paperboard provided toughness, the WG layer contributed with improved moisture barrier properties. In addition, WVTR indicated that the paperboard reduced the swelling of the outer gluten/glycerol layer in moist conditions; a free standing gluten/glycerol film would yield infinite, rather than finite, WVTR values.