Permeation Barrier Properties Research Articles

Three-Dimensional Oral Mucosal Equivalents as Models for Transmucosal Drug Permeation Studies.

Oral transmucosal administration, where drugs are absorbed directly through the non-keratinized, lining mucosa of the mouth, represents a solution to drug delivery with several advantages. Oral mucosal equivalents (OME) developed as 3D in vitro models are of great interest since they express the correct cell differentiation and tissue architecture, simulating the in vivo conditions better than monolayer cultures or animal tissues. The aim of this work was to develop OME to be used as a membrane for drug permeation studies. We developed both full-thickness (i.e., connective plus epithelial tissue) and split-thickness (i.e., only epithelial tissue) OME using non-tumor-derived human keratinocytes OKF6 TERT-2 obtained from the floor of the mouth. All the OME developed here presented similar transepithelial electrical resistance (TEER) values, comparable to the commercial EpiOral™. Using eletriptan hydrobromide as a model drug, we found that the full-thickness OME had similar drug flux to EpiOral™ (28.8 vs. 29.6 µg/cm2/h), suggesting that the model had the same permeation barrier properties. Furthermore, full-thickness OME showed an increase in ceramide content together with a decrease in phospholipids in comparison to the monolayer culture, indicating that lipid differentiation occurred due to the tissue-engineering protocols. The split-thickness mucosal model resulted in 4-5 cell layers with basal cells still undergoing mitosis. The optimum period at the air-liquid interface for this model was twenty-one days; after longer times, signs of apoptosis appeared. Following the 3R principles, we found that the addition of Ca2+, retinoic acid, linoleic acid, epidermal growth factor and bovine pituitary extract was important but not sufficient to fully replace the fetal bovine serum. Finally, the OME models presented here offer a longer shelf-life than the pre-existing models, which paves the way for the further investigation of broader pharmaceutical applications (i.e., long-term drug exposure, effect on the keratinocytes' differentiation and inflammatory conditions, etc.).

Influence of peroxide cross-linking temperature and time on mechanical, physical and thermal properties of polyethylene

Abstract Polyethylene is a very common liner material for type IV pressure vessels due to its good toughness and easy processing. The property profile of the polymer can be improved by cross-linking thereby changing the nature of the polymer from thermoplastic toward more elastomeric. For this purpose, polyethylene is modified either chemically, using peroxide or silane, or physically by radiation. In the present work, a cross-linkable polyethylene grade that can be processed by rotational molding was peroxide cross-linked under variation of temperature and time. Subsequently, the material was characterized by differential scanning calorimetry, tensile tests, notched bar impact tests and permeation measurements. Two of the altogether six parameter combinations investigated did not lead to successful cross-linking resulting in very poor toughness. Stiffness, strength and permeation barrier properties, however, were much better than those of the other series due to higher crystallinity. Mechanical, physical and chemical properties changed significantly by successful cross-linking. The impact strength could be improved by a factor of more than 10. At the same time, significant losses in stiffness, strength and permeation barrier properties had to be accepted. Peroxide induced randomly distributed formation of cross-links above the melting point interfered with formation of crystalline regions upon cooling.

Comparative study of thermoplastic liner materials with regard to mechanical and permeation barrier properties before and after cyclic thermal aging

Abstract Lightweight pressure vessels of type IV for hydrogen storage consist of a thermoplastic inner liner, commonly from polyethylene or polyamide. The liner is the permeation barrier against the compressed gas and must prevent the formation of cracks, also after temperature changes, for example after refueling processes. In the present work high-density polyethylene, cross-linked polyethylene, polyamide 6 and polyamide 12 were characterized by tensile tests, single notch impact tests and permeations measurements before and after a cyclic thermal aging process. The aging only lead to slight changes of mechanical properties due to post-crystallization, but to a significant decrease of permeation properties. This decrease was contributed to weakened, amorphous regions where chain splitting occurred. Considerable differences in properties resulted from different peroxide cross-linking times of polyethylene at the same temperature. A longer holding time at 200 °C led to an improvement in impact strength by a factor of more than three. However, the permeation properties decreased by about 50 %, indicating that peroxide cross-linking in the melt inhibited the formation of crystalline regions.

Highly-impermeable Al2O3/HfO2 moisture barrier films grown by low-temperature plasma-enhanced atomic layer deposition

Polymer substrates are essential components of flexible electronic applications such as OTFTs, OPVs, and OLEDs. However, high water vapor permeability of polymer films can significantly reduce the lifetime of flexible electronic devices. In this study, we examined the water vapor permeation barrier properties of Al2O3/HfO2 mixed oxide films on polymer substrates. Al2O3/HfO2 films deposited by plasma-enhanced atomic layer deposition were transparent, chemically stable in water and densely amorphous. At 60 °C and 90% relative humidity (RH) accelerated condition, 50-nm-thick Al2O3/HfO2 had water vapor transmission rate (WVTR) = 1.44 × 10−4 g m−2 d−1, whereas single layers of Al2O3 had WVTR = 3.26 × 10−4 g m−2 d−1 and of HfO2 had WVTR = 6.75 × 10−2 g m−2 d−1. At 25 °C and 40% RH, 50-nm-thick Al2O3/HfO2 film had WVTR = 2.63 × 10−6 g m−2 d−1, which is comparable to WVTR of conventional glass encapsulation.

Indium-Free Perovskite Solar Cells Enabled by Impermeable Tin-Oxide Electron Extraction Layers.

Corrosive precursors used for the preparation of organic-inorganic hybrid perovskite photoactive layers prevent the application of ultrathin metal layers as semitransparent bottom electrodes in perovskite solar cells (PVSCs). This study introduces tin-oxide (SnOx ) grown by atomic layer deposition (ALD), whose outstanding permeation barrier properties enable the design of an indium-tin-oxide (ITO)-free semitransparent bottom electrode (SnOx /Ag or Cu/SnOx ), in which the metal is efficiently protected against corrosion. Simultaneously, SnOx functions as an electron extraction layer. We unravel the spontaneous formation of a PbI2 interfacial layer between SnOx and the CH3 NH3 PbI3 perovskite. An interface dipole between SnOx and this PbI2 layer is found, which depends on the oxidant (water, ozone, or oxygen plasma) used for the ALD growth of SnOx . An electron extraction barrier between perovskite and PbI2 is identified, which is the lowest in devices based on SnOx grown with ozone. The resulting PVSCs are hysteresis-free with a stable power conversion efficiency (PCE) of 15.3% and a remarkably high open circuit voltage of 1.17 V. The ITO-free analogues still achieve a high PCE of 11%.

Effects of formation and penetration properties of biodegradable montmorillonite/chitosan nanocomposite film on the barrier of package paper

The conventional package paper was coated with biodegradable montmorillonite/chitosan nanocomposite, in order to extend the application scope of paper. The effect of coating weight, montmorillonite dispersion rate, montmorillonite and dispersant content on the surface and penetration properties of montmorillonite/chitosan nanocomposite coated paper were being investigated. The surface properties of the coated paper were observed by using scanning electron microscope (SEM) and atomic force microscope (AFM). The water permeation and water vapor barrier properties were confirmed through penetration dynamics analyzer (PDA) and water vapor permeability tester (WVP), respectively. The results indicated that montmorillonite/chitosan nanocomposite had a poorer formation than pure chitosan, but it had better water vapor barrier properties. The paper coated with lower content of montmorillonite, or with higher dispersion speed and dispersant content, had better smoothness and elongation. Additionally, the coated paper had excellent barrier properties under the conditions of high montmorillonite and dispersant content, dispersion rate and coating weight.

Optimization of Al2O3/TiO2 nanolaminate thin films prepared with different oxide ratios, for use in organic light-emitting diode encapsulation, via plasma-enhanced atomic layer deposition.

Encapsulation is essential for protecting the air-sensitive components of organic light-emitting diodes (OLEDs), such as the active layers and cathode electrodes. Thin film encapsulation approaches based on an oxide layer are suitable for flexible electronics, including OLEDs, because they provide mechanical flexibility, the layers are thin, and they are easy to prepare. This study examined the effects of the oxide ratio on the water permeation barrier properties of Al2O3/TiO2 nanolaminate films prepared by plasma-enhanced atomic layer deposition. We found that the Al2O3/TiO2 nanolaminate film exhibited optimal properties for a 1 : 1 atomic ratio of Al2O3/TiO2 with the lowest water vapor transmission rate of 9.16 × 10(-5) g m(-2) day(-1) at 60 °C and 90% RH. OLED devices that incorporated Al2O3/TiO2 nanolaminate films prepared with a 1 : 1 atomic ratio showed the longest shelf-life, in excess of 2000 hours under 60 °C and 90% RH conditions, without forming dark spots or displaying edge shrinkage.

Characteristics of Al2O3/ZrO2 laminated films deposited by ozone-based atomic layer deposition for organic device encapsulation

We investigated the characteristics of 100nm-thick Al2O3/ZrO2 laminated films grown by ozone (O3)-based atomic layer deposition (ALD) at low temperature (100°C) as thin film encapsulation (TFE). Calcium (Ca) test was performed at a relative humidity (RH) of 50% with a temperature of 50°C to derive the water vapor transmission rates (WVTRs) of aluminum oxide (Al2O3)-, zirconium oxide (ZrO2)-, and Al2O3/ZrO2-laminated films. Al2O3/ZrO2-laminated films exhibited better permeation barrier properties than Al2O3 or ZrO2 single layer films. In Al2O3/ZrO2 laminated films, permeation barrier properties improved as the number of alternating layers increased. Permeation barrier properties were closely related to the number of interfaces because of the ZrAlxOy phase that formed at the interface between the Al2O3 and ZrO2 sublayers. The ZrAlxOy phase was denser than single layers of Al2O3 and ZrO2 and had a homogeneous amorphous structure. The formation of a ZrAlxOy phase in Al2O3/ZrO2 laminated film effectively improved the permeation barrier properties of the film.

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.

Poly (3-hydroxybutyrate)/cellulose nanocrystal films for food packaging applications: Barrier and migration studies

This article reports the fabrication of poly (3-hydroxybutyrate) (PHB)/cellulose nanocrystal (CNC) based nanobiocomposite films with improved gas barrier and migration properties for food packaging applications. Acid hydrolysis of cellulose pulp from bamboo (Bambusabalcooa) yields CNCs with diameter of 15–20 nm and length of 400–600 nm. Evaluation of d-spacing using XRD indicates intercalation of PHB matrix with CNC at optimum loadings of 2 wt%. Overall migration values in presence of both polar and nonpolar food simulants are found within standard limits. After migration studies on PHB/CNC films, significant decrease in crystallization temperature (by 15°C) is observed, with subsequent presence of multiple melting peaks. The oxygen transmission rate (OTR) decreases significantly (by ∼65%), even at low CNC (∼2 wt%) loadings. Permeation activation energy (calculated from Arrhenius equation) and barrier properties, such as solubility and diffusivity, improved (decreased by ∼57 and 17%, respectively) with loading fractions (∼2 wt%) due to the hydrogen bonded interaction of PHB with CNCs as well as tortuous path provided towards oxygen permeation. POLYM. ENG. SCI., 55:2388–2395, 2015. © 2015 Society of Plastics Engineers

The impact of the nano-pore filling on the performance of organosilicon-based moisture barriers

Promising results in terms of moisture and oxygen permeation barrier properties have been reported for organic/inorganic multilayers, but the impact of the organic interlayer on the overall barrier performance is still under discussion. It is generally accepted that the organic interlayer acts as a smoothening layer, allowing for the decoupling between defects/pinholes present in the polymer substrate and the inorganic layer. It is, however, also hypothesized that the organic interlayer infiltrates into the nano-pores present in the inorganic barrier layer, therefore affecting the barrier properties at microstructural level. In the present work, the moisture permeation barrier performance of SiO2/organosilicon multilayers deposited by means of initiated- and plasma enhanced-chemical vapor deposition is investigated. Calcium test measurements were used to discriminate between the overall water permeation (effective water vapor transmission rate, WVTR) through the layer and the permeation through the matrix porosity (intrinsic WVTR). The improvement in terms of intrinsic barrier performance was found to correlate with the residual nano-porosity content, due to the filling/infiltration of the organosilicon monomer in the SiO2 nano-pores. However, such improvement upon the deposition of the organosilicon interlayer is limited to a factor four. These results, in combination with the analysis of the local defects present in the multilayer structure, lead to the conclusion that the main contribution of the organosilicon interlayer to the overall barrier performance is the decoupling of the above-mentioned local defects/pinholes.

Long-term stable water vapor permeation barrier properties of SiN/SiCN/SiN nanolaminated multilayers grown by plasma-enhanced chemical vapor deposition at extremely low pressures

We investigated the water vapor permeation barrier properties of 30-nm-thick SiN/SiCN/SiN nanolaminated multilayer structures grown by plasma enhanced chemical vapor deposition at 7 mTorr. The derived water vapor transmission rate was 1.12 × 10−6 g/(m2 day) at 85 °C and 85% relative humidity, and this value was maintained up to 15 000 h of aging time. The X-ray diffraction patterns revealed that the nanolaminated film was composed of an amorphous phase. A mixed phase was observed upon performing high resolution transmission electron microscope analysis, which indicated that a thermodynamically stable structure was formed. It was revealed amorphous SiN/SiCN/SiN multilayer structures that are free from intermixed interface defects effectively block water vapor permeation into active layer.

Growth behavior and improved water–vapor-permeation-barrier properties of 10-nm-thick single Al2O3 layer grown via cyclic chemical vapor deposition on organic light-emitting diodes

We have investigated the growth behavior and water vapor permeation barrier properties of cyclic chemical vapor deposition (C-CVD)-grown 10-nm-thick single layer of Al2O3. Al2O3 layers grown by C-CVD showed a high density of 3.298g/cm3 and were amorphous without grain boundaries. A deposition rate of 0.46nm/cycle was obtained. The C-CVD system was self-limiting, as in the case of atomic layer deposition, which enables precise control of the thickness of the Al2O3 layer. A water vapor transmission rate of 1.51×10−5(g/m2)/day was obtained from a Ca degradation test performed at 85°C and 85% relative humidity. Moreover, the performance of organic light-emitting diodes, passivated by a C-CVD-grown 10-nm-thick Al2O3 single layer, was not affected after 24,000h of turn-on time; this is strong evidence that C-CVD-grown Al2O3 layers effectively prevent water vapor from diffusing into the active organic layer.

Gas Permeation, Mechanical Behavior and Cytocompatibility of Ultrathin Pure and Doped Diamond-Like Carbon and Silicon Oxide Films

Protective ultra-thin barrier films gather increasing economic interest for controlling permeation and diffusion from the biological surrounding in implanted sensor and electronic devices in future medicine. Thus, the aim of this work was a benchmarking of the mechanical oxygen permeation barrier, cytocompatibility, and microbiological properties of inorganic ~25 nm thin films, deposited by vacuum deposition techniques on 50 µm thin polyetheretherketone (PEEK) foils. Plasma-activated chemical vapor deposition (direct deposition from an ion source) was applied to deposit pure and nitrogen doped diamond-like carbon films, while physical vapor deposition (magnetron sputtering in pulsed DC mode) was used for the formation of silicon as well as titanium doped diamond-like carbon films. Silicon oxide films were deposited by radio frequency magnetron sputtering. The results indicate a strong influence of nanoporosity on the oxygen transmission rate for all coating types, while the low content of microporosity (particulates, etc.) is shown to be of lesser importance. Due to the low thickness of the foil substrates, being easily bent, the toughness as a measure of tendency to film fracture together with the elasticity index of the thin films influence the oxygen barrier. All investigated coatings are non-pyrogenic, cause no cytotoxic effects and do not influence bacterial growth.

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.

The effect of argon plasma treatment on the permeation barrier properties of silicon nitride layers

In this work we produce and study silicon nitride (SiNx) thin films deposited by Hot Wire Chemical Vapor Deposition (HW-CVD) to be used as encapsulation barriers for flexible organic photovoltaic cells fabricated on polyethylene terephthalate (PET) substrates in order to increase their shelf lifetime. We report on the results of SiNx double-layers and on the equivalent double-layer stack where an Ar-plasma surface treatment was performed on the first SiNx layer. The Ar-plasma treatment may under certain conditions influences the structure of the interface between the two subsequent layers and thus the barrier properties of the whole system. We focus our attention on the effect of plasma treatment time on the final barrier properties. We assess the encapsulation barrier properties of these layers, using the calcium degradation test where changes in the electrical conductance of encapsulated Ca sensors are monitored with time. The water vapor transmission rate (WVTR) is found to be ~3×10−3g/m2·day for stacked SiNx double-layer with 8min Ar plasma surface treatment.

Moisture Barrier Properties of Al2O3 Films deposited by Remote Plasma Atomic Layer Deposition at Low Temperatures

We report the effect of process temperature on moisture permeation barrier properties of Al2O3 films deposited by remote plasma atomic layer deposition (RPALD) at various low temperatures from 50 to 200 °C. XPS analysis of O 1s peak reveals that the O–H ratio decreases with process temperature from 38.1% at 50 °C to 25.8% at 200 °C. The water transmission rates using electrical Ca degradation test indicates that the 100 nm Al2O3 film enhances the moisture barrier performance from 2.0×10-2 to 5.0×10-4 g m-2 day-1 with increasing the process temperature. This result indicates that increasing the process temperature improves the moisture permeation barrier properties significantly even in RPALD process. It is attributed to the increase in the Al2O3 mass density due to the decrease of relatively O–H ratio with increase in temperature as revealed by XPS O 1s peak deconvolution and FTIR analysis in the Al2O3 films.

Effect of Substrate Surface Oxidation on Tritium Permeation Barrier Properties of MOD Er2O3 Coating

Metal organic decomposition (MOD) Er2O3 coating for tritium permeation barrier was fabricated on two ferritic steels with dip-coating method. The interfacial layers, which were formed by the oxidation of the substrates, were found under the coating with different compositions and thickness according to the elemental depth profile of XPS. Their formations depended on the substrate materials (JLF-1: Fe–9Cr–2W based reduced activation ferritic/martensitic steel; SUS430: 18Cr based commercial ferritic steel) and the baking atmosphere (air or Ar). The main reason could be selective oxidation of main elements in the substrates at high temperature with the different baking atmosphere. For the coated JLF-1 samples, the surface smoothness and the hydrogen barrier performance of Er2O3 coatings were improved significantly by changing the baking atmosphere from air to Ar. The composition change in the oxidized interfacial layer from iron oxide to chromium oxide may be the reason for the improved surface smoothness and permeation barrier performance.

Characterization of reactively sputtered permeation barrier materials on polymer substrates

Transparent permeation barrier layers are not only used for food packaging but are also needed to encapsulate flexible electronic devices. Magnetron sputtering allows the deposition of high quality oxide barrier layers with a low water vapor and oxygen permeation. This paper compares different metal oxide layers which are deposited onto a polyethylene terephthalate (PET) film using a reactive dual magnetron sputtering process. The oxides of aluminum, silicon, titanium, zinc and a zinc-tin alloy are compared regarding their permeation barrier, structural and surface properties to determine the relationship between the layer structure and the gas permeation. Thereby, scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to characterize the morphology and surface structure of the layers and X-ray diffraction analysis (XRD) was used to determine the solid state phase.Cross-section images taken with SEM show a very compact structure for both aluminum oxide and zinc-tin oxide layers. These materials also have the lowest water vapor permeation compared to all other materials. Zinc oxide and titanium oxide layers both exhibit a columnar structure. Zinc oxide is polycrystalline and has a surprising low water vapor and oxygen permeation. In contrast to that the amorphous titanium oxide layers show a high water vapor and oxygen permeation which is not decreasing with an increasing layer thickness above 40nm.