Numerous assays were developed to measure the antioxidant activity, but each has limitations and the results obtained by different methods are not always comparable. Popular examples are the DPPH and ...ABTS assay. Our aim was to study similarities and differences of these two assay regarding the measured antioxidant potentials of 24 phenolic compounds using the same measurement and evaluation methods. This should allow conclusions to be drawn as to whether one of the assays is more suitable for measuring specific subgroups like phenolic acids, flavonols, flavanones, dihydrochalcones or flavanols. The assays showed common trends for the mean values of most of the subgroups. Some dihydrochalcones and flavanones did not react with the DPPH radical in contrast to the ABTS radical, leading to significant differences. Therefore, to determine the antioxidant potential of dihydrochalcone or flavanone-rich extracts, the ABTS assay should be preferred. We found that the results of the flavonoids in the DPPH assay were dependent on the Bors criteria, whereas the structure-activity relationship in the ABTS assay was not clear. For the phenolic acids, the results in the ABTS assay were only high for pyrogallol structures, while the DPPH assay was mainly determined by the number of OH groups.
For the last decades, nanocomposites materials have been widely studied in the scientific literature as they provide substantial properties enhancements, even at low nanoparticles content. Their ...performance depends on a number of parameters but the nanoparticles dispersion and distribution state remains the key challenge in order to obtain the full nanocomposites' potential in terms of, e.g., flame retardance, mechanical, barrier and thermal properties, etc., that would allow extending their use in the industry. While the amount of existing research and indeed review papers regarding the formulation of nanocomposites is already significant, after listing the most common applications, this review focuses more in-depth on the properties and materials of relevance in three target sectors: packaging, solar energy and automotive. In terms of advances in the processing of nanocomposites, this review discusses various enhancement technologies such as the use of ultrasounds for in-process nanoparticles dispersion. In the case of nanocoatings, it describes the different conventionally used processes as well as nanoparticles deposition by electro-hydrodynamic processing. All in all, this review gives the basics both in terms of composition and of processing aspects to reach optimal properties for using nanocomposites in the selected applications. As an outlook, up-to-date nanosafety issues are discussed.
Microplastic particles (MPs) pose a novel threat to nature. Despite being first noticed in the 1970s, research on this topic has only surged in recent years. Researchers have mainly focused on ...environmental plastic particles; however, studies with defined microplastic particles as the sample input are scarce. Furthermore, comparison of those studies indicates a discrepancy between the particles found (e.g., in the environment) and those used for further research (e.g., exposure studies). Obviously, it is important to use particles that resemble those found in the environment to conduct appropriate research. In this review, different categories of microplastic particles are addressed, before covering an overview of the most common separation and analysis methods for environmental MPs is covered. After showing that the particles found in the environment are mostly irregular and polydisperse, while those used in studies with plastic microparticles as samples are often not, different particle production techniques are investigated and suggestions for preparing realistic plastic particles are given.
Materials with high barrier properties against oxygen are required for the packaging of many sensitive foods. Since commodity polymers lack these properties, additional barrier materials are used in ...plastic-based barrier packaging. These are usually more expensive than commodity polymers and, in higher fractions, also make recycling more difficult. Current developments, therefore, aim at barrier layers that are as thin as possible but retain the barrier properties. One approach is to incorporate nanoparticles into these layers. In this study, the barrier properties of nanocomposite coatings, consisting of unmodified polyvinyl alcohol (PVA), and dispersed stick-shaped halloysite (Hal) or platelet-shaped montmorillonite (MMT) silicate nanoparticles, were investigated. The PVA was dissolved in aqueous nanoparticle dispersions, which were prepared by mechanical shearing, to produce the so-called "nanolacquer." Nanolacquers with nanoparticle concentrations of 7, 30, and 47 vol% with respect to PVA were applied in a single process step with
-bar on a polypropylene substrate film. The integration of 30 vol% platelet-shaped MMT enhances the barrier performance in comparison to pure PVA by a factor of 12 and 17 for oxygen and helium, respectively. Scanning electron microscopy (SEM) shows a homogeneous distribution and a parallel alignment of the nanoparticles within the coated layer. An increase in the crystallinity of PVA was observed due to the nanoparticle integration as demonstrated by
-ray diffraction (XRD) measurements. The investigation by Fourier transform infrared (FTIR) spectroscopy and the activation energy of the permeation coefficient indicate an interaction between the nanoparticles and the PVA. The theoretically calculated values for barrier enhancement accord well with the experimental values, which emphasizes that the gas barrier improvement for oxygen and helium is mainly dominated by the tortuous path effect.
This study investigates chemical grafting with fatty acid chlorides as a method for the surface modification of hydrophilic web materials. The resulting changes in the water repellence and barrier ...properties were studied. For this purpose, different grades of polyvinyl alcohol (PVOH) were coated on regenerated cellulose films ("cellophane") and paper and then grafted with fatty acid chlorides. The PVOH grades varied in their degree of hydrolysis and average molecular weight. The surface was esterified with two fatty acid chlorides, palmitoyl (C16) and stearoyl chloride (C18), by chemical grafting. The chemical grafting resulted in water-repellent surfaces and reduced water vapor transmission rates by a factor of almost 19. The impact of the surface modification was greater for a higher degree of hydrolysis of the polyvinyl alcohol and for shorter fatty acid chains. Although the water vapor barrier for palmitoyl-grafted PVOH was higher than for stearoyl-grafted PVOH, the contact angle with water was lower. Additionally, it was shown that a higher degree of hydrolysis led to higher water vapor barrier improvement factors after grafting. Furthermore, the oxygen permeability decreased after grafting significantly, due to the fact that the grafting protects the PVOH against humidity when the humidity is applied on the grafted side. It can be concluded that the carbon chain length of the fatty acid chlorides is the limiting factor for water vapor adsorption, but the grafting density is the bottleneck for water diffusing in the polymer.
•Temperature dependent quasi-stationary approximations were derived and validated.•Theoretical approximation reveals effect of temperature and pressure on permeation.•Temperature dependency of ...steady-state permeation is determined by silicon oxide.•Silicon oxide doubles the activation energy for permeation of the substrate film.•Lag time is mainly influenced by heat of sorption of polymeric intermediate layer.
Barrier layers are often used to protect sensitive organic devices from the detrimental effects of oxygen and water vapor. We investigated the effect of temperature on the time-dependent behavior of water vapor permeation in multilayer barrier films, focusing on the water vapor solubility, diffusion and permeability coefficients of individual layers and layer sequences. Activation energy measurements helped to explain the permeation mechanisms and showed the possible interactions between water and silicon oxide (SiOx). The activation energy for permeation (EP) through a two-layer film of polyethylene terephthalate (PET) coated with SiOx was 5.7 kJmol−1, about twice the EP value of the uncoated PET substrate. An intermediate ORMOCER® layer, providing a smooth surface for a second SiOx layer in an alternating structure, had only a negligible effect on the EP. Temperature dependent quasi-stationary approximations were derived for permeation through films with at least one inorganic/polymer/inorganic triplet, and were validated according to experimentally determined values. These equations showed the temperature and pressure dependencies of steady-state permeation and lag time in multilayered structures. Accordingly, the temperature dependency of steady-state permeation is determined by the EP of SiOx, whereas the lag time was mainly influenced by the heat of sorption of the intermediate polymeric layer. Furthermore, the increase in water vapor transmission rate was dominated by the partial pressure change with increasing temperature. Using these equations and experimentally determined parameters, we can predict the influence of temperature and humidity on the barrier performance of multilayered barrier structures.
Multilayer films that comprise alternating inorganic barrier and polymer layers deposited on a flexible substrate are often used to protect organic electronic devices from degradation caused by ...oxygen and water vapor. We tested films consisting of up to 11 inorganic silicon oxide barrier and polymer layers to characterize the water vapor permeability, solubility and diffusivity of each layer based on measurements of water sorption, transient water vapor permeation and lag times. The time-dependency of transient water vapor transmission rates (WVTR) of the structures containing a barrier-polymer-barrier sequence was also estimated using a so-called quasi-steady-state (QSS) approximation. The permeability values and lag times in multilayer structures predicted by QSS approximation agreed with the values determined empirically based on time-dependent WVTR measurements. The steady-state WVTR of the multilayer barrier films was dominated by the permeability of the inorganic barrier layers, whereas the solubility coefficient and thickness of the interleaved polymer layers determined the lag times. The barrier performance and lag time of multilayer structures can be predicted using the parameters obtained from sorption measurements, thus significantly reducing the time required for experiments. The results of this study will allow us to design multilayer barrier films according to the lifetime requirements of flexible organic electronic devices.
•WVTR of silicon oxide is up to five orders of magnitude lower compared to polymers.•Longer lag times for multilayers incorporating barrier-polymer-barrier triplets•Solubility and thickness of the polymer layers in BPB structures increase the lag time.•Permeability of inorganic layer dominates steady-state WVTR.•Prediction of WVTR by QSS approximation reduces experimental timeframes.
A roll‐to‐roll manufactured ultra‐high permeation barrier film based on a multilayer stack of sputtered oxide layers and ORMOCER® interlayers is presented. The reproducible large‐area water vapor ...transmission rate is less than 8·10−5 g/(m2d) at ambient condition. The film has been evaluated as substrate for and encapsulation of flexible organic electronic devices.
The contact between two NaCl nano-crystals consisting of 6000-15,000 atoms was studied using molecular dynamics computer simulations. After placing two NaCl cuboids at varying distances, the adhesion ...forces and the resulting strains were measured. We observed jump to contact and found that there is an upper limit of distance. Similarly, NaCl hemispheres possessing radii equal to 2.13, 3.26 and 4.15 nm were placed at varying distances from a NaCl cuboid. The relations between distance and force were determined. In the case of an indentation, the relations were described by power functions and compared with the widely used Hertzian theory. We were able to show that the exponent of the power function rises with increasing radius of the hemisphere. It apparently converges to a value of 1.5, which is in agreement with the Hertzian theory. It thus seems justified to assume that the studied system can be adequately described with continuum mechanics down to sizes of 5 nm. But for smaller systems continuum mechanics appears not to be adequate.
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