Polymer Surface Layer Research Articles

Interpretation of dielectric spectroscopy measurements of ferroelectric nematic liquid crystals

The magnitude of the relative permittivity of the ferroelectric nematic phase (NF) has been the subject of lively scientific discussion since the phase was recently discovered. Dielectric spectroscopy measurements (DSMs) give a huge value of relative permittivity, which depends on the cell thickness, but this is argued to result from a misinterpretation of the DSM results. We have conducted DSM using a set of cells differing in thickness of the NF layer, type of electrodes, and presence/absence of nanoscale-thick surface polymer layers. To model the DSM results, cells are presented by an equivalent electric circuit that includes a capacitor due to the NF layer with frequency dependent complex relative permittivity, capacitors due to surface layers, and a resistor describing the limited conductivity of electrodes. DSM results for different cells with the same liquid crystal in the NF phase are semiquantitatively reproduced by the same set of physical parameters if a huge relative permittivity of the NF, which is even orders of magnitude larger than the measured apparent values, is assumed. We show that the capacitance of surface layers should also be considered in cells with no polymer alignment layer on the electrodes. Published by the American Physical Society 2024

Study on the nanofiltration membrane fouling control and cleaning efficiency of micro- and nanobubbles

To effectively prevent membrane fouling caused by inorganic scales, which block membrane pores during the nanofiltration process for direct drinking water treatment, the effects of micro/nanobubble introduction on membrane fouling control and membrane cleaning were studied during nanofiltration. The results showed that membrane flux increased 6.3% after micro- and nanobubbles were continuous introduced during the nanofiltration process. Micro- and nanobubbles effectively controlled membrane fouling and had less of an influence on the surface functional groups and polymer layers than did scale inhibitors. The membrane flux of the nanofiltration membrane after cleaning with micro- and nanobubbles decreased gradually with increasing cleaning time, and the membrane flux of the nanofiltration membrane after four rounds of cleaning decreased by 33%. Moreover, micro/nanobubble cleaning did not change the physical or chemical properties of the nanofiltration membrane and delayed the ageing rate of the nanofiltration membrane.

Intertwined synergistic abiotic and biotic degradation of polypropylene pellets in marine mesocosms

The accumulation of plastic waste in the oceans has caused growing concern for its effects on marine life. The interactions of plastics with environmental factors have been linked to fragmentation to micro- and nanoparticles with different properties and consequences, but the mechanism of fragmentation has not been fully understood yet. In this work, we investigate the combined effect of marine communities and ultraviolet (UV) radiation towards the degradation of virgin and artificially weathered polypropylene (PP) pellets after a long-term incubation period in marine mesocosms. The surface chemical alterations and deterioration of the polymer, in conjunction with the attachment and evolution of marine bacterial communities, the development of biofilm and exopolymeric substances (EPS), as well as the colloidal properties (zeta-potential and hydrodynamic diameter) of the mesocosms were studied. The surface area of both types of pellets decreased over time, despite no concrete weight change being observed. Cell growth, EPS production and colloid particle size were correlated to the loss of area. Therefore, we propose that surface area could be effectively monitored, instead of weight loss, as an alternative indicator of polymer degradation in biodegradation experiments. Changes in the chemical structure of the polymer, in addition to the evolution of the biological factors, implied that a complex degradation process alternated between two phases: an abiotic phase, when UV irradiation contributes to the deterioration of the polymer surface layers and a biotic phase, when marine communities degrade the weathered polymer surface to reveal the underlying layer of virgin polymer. Finally, microscopic particles, produced as a result of the decrease in pellet area, promoted the aggregation of colloidal particles. The role and impacts of these colloidal particles in marine ecosystems are yet as unidentified as that of micro- and nano-sized plastic particles and call for further investigation.

Role of Scaffold Architecture and Excess Surface Polymer Layers in a 3D‐Interconnected Ceramic/Polymer Composite Electrolyte (Adv. Energy Mater. 19/2023)

Ceramic Electrolytes In article number 2203663, Ritu Sahore, Xi Chelsea Chen, and co-workers investigate the role of ceramic architecture and excess surface polymer layers in a 3D interconnected ceramic/polymer composite electrolyte. The cover art highlights that despite the interconnectedness, the high impedance polymer/ceramic interface at the surface is a bottleneck.

Role of Scaffold Architecture and Excess Surface Polymer Layers in a 3D‐Interconnected Ceramic/Polymer Composite Electrolyte

Abstract3D‐interconnected ceramic/polymer composite electrolytes offer promise to combine the benefits of both ceramic and polymer electrolytes. However, an in‐depth understanding of the role of the ceramic scaffold's architecture, and the associated polymer/ceramic interfaces on the electrochemical properties of such composite electrolytes is still incomplete. Here, these factors are systematically evaluated using an interconnected composite electrolyte with a tunable and well‐defined architecture. The ionic conductivity of the ceramic scaffold is strongly dependent on its porosity and tortuosity, as demonstrated experimentally and via theoretical modeling. The connectivity of the ceramic framework avoids the high interfacial impedance at the polymer/ceramic electrolyte interface within the composite. However, this work discovers that the interfacial impedance between the bulk composite and excess surface polymer layers of the composite membrane dominates the overall impedance, resulting in a 1–2 order drop of ionic conductivity compared to the ceramic scaffold. Despite the high impedance interfaces, an improved Li+ transference number is found compared to the neat polymer (0.29 vs 0.05), attributed to the ceramic phase's contributions toward ion transport. This leads to flatter overpotentials in lithium symmetric cell cycling. These results are expected to guide future research directions toward scalable manufacturing of composite electrolytes with optimized architecture and interfaces.

Controllable construction of laser-induced colorful patterns based on thermal energy transfer between carbon nanotubes substrate and polymer interface

Laser irradiation technology has been widely used in the field of polymer material patterning. Improving the laser response of polymer is the key to realize laser patterning. The traditional doping process cannot achieve pattern colors other than black and white, and will affect the performance of polymer matrix. In this paper, the locally controllable laser-induced pattern transfer between the substrate and the polymer interface is realized by preparing a carbon nanotubes (CNTs) substrate with high photothermal conversion effect. The laser beam was irradiated on the interface between the CNTs substrate and the transparent polyvinyl alcohol (PVA) film. The CNTs substrate absorbed laser energy and transferred to PVA film to produce a carbonized pattern in situ. Further, colorful inorganic pigments can be transferred from the substrate to the polymer surface layer based on this interfacial transfer technique, which makes a breakthrough to realize the colorful laser-induced pattern of polymers. Moreover, the repeatability test further proves the reliability and recycling performance of the CNTs substrate. This study provides a positive approach for the industrialization of laser-induced colorful patterns on polymers.

A new thermographic method for determining the thickness of the polymer surface layer in sound-absorbing fibrous composite materials

Sound absorption efficiency of the fibrous composite material could be increased by an additional polymer thin layer deposited on the substrate. In order to control the thickness of the polymer surface layer, a new method based on thermographic measurement is presented. The proposed method is much easier to use and does not need any expensive tools in contrast to the Optical Coherence Tomography (OCT) image analysis. The research results show the prospects of this method in the development of sound-absorbing composites. The acoustic measurements confirmed that in the case of fibrous composite materials of viscose fibres/polylactide with an additional polylactide surface layer, the nature of low frequency sound absorption depends on the thickness of this layer.

Strain-Based Chemiresistive Polymer-Coated Graphene Vapor Sensors.

Suspended chemiresistive graphene sensors have been fabricated using well-established nanofabrication techniques to generate sensors that are highly sensitive to pyridine and with excellent discrimination between polar and nonpolar analytes. When coated with a polymer surface layer and suspended on 3-D patterned glass electrodes, a hybrid combination of polymer and graphene yields chemiresistive vapor sensors. Expansion and contraction of the polymer layer produces strain on the suspended graphene (Gr). Hence, when organic vapors permeate into the polymer layer, the high gauge factor of the graphene induces substantial electrical resistive changes as folds and creases are induced in the graphene. The hybrid suspended polymer/Gr sensor exhibits substantial responses to polar organic vapors, especially pyridine, while also exhibiting reversibility and increased discrimination between polar and nonpolar analytes compared to previous approaches. This sensor design also allows for potential tunability in the types of polymers used for the reactive surface layer, allowing for use in a variety of potential applications.

Study of adsorption effect on orientational and relaxation properties of finite polymer chains near the solid surface

To study dynamic properties of a polymer coating, we consider a polymer chain with finite length. We take into account a chain bending rigidity and assume that the chain is located near an adsorbing flat surface of a solid. One part of the chain is fixed on the surface, and the second one remains free. It is supposed that the cause of chain stretching is the internal effective mean (molecular) field formed as a result of intermolecular interactions with free ends of other chains. Kinetic equations based on the Kubo method are obtained to calculate the relaxation time of the segments. The dependences of the long-range orientational order parameter and relaxation time on the adsorption parameter, the mean field coefficient and chain bending rigidity parameters are calculated. It is shown that a first-order phase transition occurs at the critical point, which is associated with a drastic change in the degree of the chain elongation. We discovered the “critical deceleration” effect, which consists in a sharp increase in the relaxation time near the critical point during the formation of surface polymer layers on the surface of a solid.

Study of the physicochemical properties of the biomedical composite material “Ti-Nb-Ta-Zr with a surface polymer layer”

A comprehensive study of the physicochemical properties of the created biomedical composite material “Ti-Nb-Ta-Zr with a surface polymer layer” was carried out. The polymer film does not in any way affect the radiopacity of the base material. All materials obtained are radiopaque. X-ray diffraction analysis of polyglycolide lactide (PGLA) samples with molecular weights of 45, 90, 180 kDa showed that the polymers have a completely amorphous structure. On samples with a 40-μm-thick PLA-based coating bare-metal zones are observed, which substantiate anode effects in the potential range of more than 1000 mV.

Electrophoretic mobility of a soft particle in a polymer gel medium

Approximate analytic expressions are derived for the electrophoretic mobility of a weakly charged spherical soft particle consisting of the particle core covered with a surface layer of polymers in a polymer gel medium. The particle core, the surface polymer layer, and the polymer gel medium may be charged or uncharged. The gel electrophoretic mobilities of a bare hard sphere and a spherical polyelectrolyte are covered as limiting cases. The obtained gel mobility expressions involve neither numerical integration nor exponential integrals and these approximate expressions are found to be in excellent agreement with exact numerical results. It is also found that the obtained mobility expressions reproduce all the correct limiting expressions as well as the previously derived approximate analytic expressions for the soft-particle gel electrophoretic mobility.

Approximate analytic expressions for the electrophoretic mobility of spherical soft particles.

Approximate analytic expressions are derived for the electrophoretic mobility of a weakly charged spherical soft particle consisting of the particle core covered with a surface layer of polymers in an electrolyte solution. The particle core and the surface polymer layer may be charged or uncharged. The obtained electrophoretic mobility expressions, which involve neither numerical integration nor exponential integrals, are found to be in excellent agreement with the exact numerical results. It is also found that the obtained mobility expressions reproduce all the previously derived limiting expressions and approximate analytic expressions for the electrophoretic mobility of a weakly charged spherical soft particle.

Accelerated aging of WPCs Based on Polypropylene and Birch plywood Sanding Dust

Abstract A lot of researchers are closely related with natural, lignocellulose fibre containing bio-composites production and studies. Various of polymer matrices, mainly polyolefins, combinations with natural fibres as a reinforcement are used. Our studies are focused on polypropylene based bio-composites containing birch plywood production by-product sanding dust (PSD) accelerated weathering processes. The obtained results showed the following sight. After the aging the surface of all samples had faded, the changes of the gloss (decreasing) and of the whiteness degree (increasing) also had taken place, but microhardness of the surface of specimens significantly has decreased. The tensile strength and modulus of the samples after UV aging diminished about 30–35%. That indicates to the changes not only in the surface layers of polymer but also inside of the polymer structure. The FTIR measurements showed that during UV aging process occurs significant changes of chemical structure of the weathered surface of all samples. DSC measurements showed an increase of degree of crystallinity of the weathered polypropylene composites after the first heating due to the recrystallization process in the polypropylene matrix and a small decreasing after second heating. The melting temperatures of all composites after UV aging considerably diminish up to 30°C.

ИССЛЕДОВАНИЕ ТЕМПЕРАТУРЫ ПОВЕРХНОСТИ МЕТАЛЛ-МЕТАЛЛОПОЛИМЕРНОЙ ДЕТАЛИ ПРИ МЕХАНИЧЕСКОЙ ОБРАБОТКЕ ПЛОСКИМ ШЛИФОВАНИЕМ

Knowing the exact heating temperature of a combined metal-metalpolymer part when processing flat grinding helps to assign cutting modes, as well as predict the durability of the processed part. Accurate monitoring of the heating temperature of the part during flat grinding allows to understand whether the temperature degradation of the surface layers of the metal polymer occurs, which can reduce the durability of the processed part due to burns of the surface layers. At the same time, accurate determination of the temperature in the cutting zone gives an understanding of the need for the use of cooling lubricants, which can not always be used without additional research when processing metal polymers with a diene matrix. The study of the temperature in the cutting zone is necessary because of the lower degradation temperature of the metal polymer relative to the metal. This article examines the process of flat grinding of a combined metal-metal polymer part using theoretical calculations, the method of finite element analysis, and analytical evaluation of the results of the experiment. The temperature in the cutting zone is estimated for the part-forming plate of the mold, which dictated the choice of a certain range of cutting modes that allow to obtain the required roughness of the plane of closing of the forming part.

Adsorption and electrokinetic studies in kaolinite/anionic polyacrylamide/chromate ions system

The use of clay minerals as adsorbents in the removal of heavy metal ions is of great interest for many researchers. Most of the studies concern the impact of various factors, such as pH value, temperature, adsorption efficiency and surface modification of individual minerals, on the heavy metal accumulation. Various heavy metals can be captured from the solution by clay minerals or their composites. The latest one can be obtained by mineral modification by organic compounds or polyelectrolytes such as anionic polyacrylamide. The polymer presence on the solid surface may contribute to stronger accumulation of heavy metal ions and as a consequence to clear reduction of their availability for organisms. Moreover, it may stimulate the particle aggregation and increase the soil resistance for erosion significantly.For this purpose, the anionic polyacrylamide impact on the chromate ions adsorption on the kaolinite surface was studied. The effects of pH value, type of anionic polyacrylamide, heavy metal ion concentration and order of adsorbates addition to the clay mineral system were determined. Spectrophotometry, potentiometric titration and microelectrophoresis methods allowed to describe the adsorption, stability and electrokinetic properties of the examined systems. In such a way the immobilization possibilities of heavy metal ions in the polymeric surface layer were investigated.

Persistence of plastic debris and its colonization by bacterial communities after two decades on the abyssal seafloor

The fate of plastic debris entering the oceans is largely unconstrained. Currently, intensified research is devoted to the abiotic and microbial degradation of plastic floating near the ocean surface for an extended period of time. In contrast, the impacts of environmental conditions in the deep sea on polymer properties and rigidity are virtually unknown. Here, we present unique results of plastic items identified to have been introduced into deep-sea sediments at a water depth of 4150 m in the eastern equatorial Pacific Ocean more than two decades ago. The results, including optical, spectroscopic, physical and microbial analyses, clearly demonstrate that the bulk polymer materials show no apparent sign of physical or chemical degradation. Solely the polymer surface layers showed reduced hydrophobicity, presumably caused by microbial colonization. The bacterial community present on the plastic items differed significantly (p < 0.1%) from those of the adjacent natural environment by a dominant presence of groups requiring steep redox gradients (Mesorhizobium, Sulfurimonas) and a remarkable decrease in diversity. The establishment of chemical gradients across the polymer surfaces presumably caused these conditions. Our findings suggest that plastic is stable over extended times under deep-sea conditions and that prolonged deposition of polymer items at the seafloor may induce local oxygen depletion at the sediment-water interface.

Refinement of Nanoporous Copper with Poly(vinyl alcohol) During Dealloying Amorphous Mg65Cu25Y10 Precursors.

Ultrafine nanoporous copper (UNP Cu) with a characteristic pore size of about 12 nm and a ligament size of about 14 nm was fabricated from amorphous Mg65Cu25Y10 precursor alloys after dealloying in a 0.1 M H₂SO₄ solution modified by poly(vinyly alcohol) polymers with a molecular weight of 105000 g/mol (PVA-124). The suppression of the surface diffusion from PVA-124 reduced the size of the nanopores and ligaments to 20 nm when the concentration of the added PVA-124 exceeded 0.1 g L-1. When the concentration of the added PVA-124 exceeded 2 g L-1, PVA-124 triggered the polymerization process. The resultant polymer surface layer on the fcc Cu ligaments was shown to reduce the rate of selective dissolution. It was also shown that extending the immersion time resulted in a suppression of coarsening. The introduction of PVA-124 polymer into acids resulted in a higher viscosity of the dealloying solutions, particularly when the concentration of PVA-124 was higher than 1.0 g L-1. This viscosity was shown not only to reduced rate of diffusion of Cu adatoms in PVA-124 solutions, but also forced the accumulation of Cu adatoms to form small scale UNP Cu.

Magnetic Particles: Their Applications from Sample Preparations to Biosensing Platforms.

The growing interest in magnetic materials as a universal tool has been shown by an increasing number of scientific publications regarding magnetic materials and its various applications. Substantial progress has been recently made on the synthesis of magnetic iron oxide particles in terms of size, chemical composition, and surface chemistry. In addition, surface layers of polymers, silica, biomolecules, etc., on magnetic particles, can be modified to obtain affinity to target molecules. The developed magnetic iron oxide particles have been significantly utilized for diagnostic applications, such as sample preparations and biosensing platforms, leading to the selectivity and sensitivity against target molecules and the ease of use in the sensing systems. For the process of sample preparations, the magnetic particles do assist in target isolation from biological environments, having non-specific molecules and undesired molecules. Moreover, the magnetic particles can be easily applied for various methods of biosensing devices, such as optical, electrochemical, and magnetic phenomena-based methods, and also any methods combined with microfluidic systems. Here we review the utilization of magnetic materials in the isolation/preconcentration of various molecules and cells, and their use in various techniques for diagnostic biosensors that may greatly contribute to future innovation in point-of-care and high-throughput automation systems.

Comprehensive study on the effects of total monomers' content and polymerization temperature control on the formation of the polymer-layer in preparation of insulin-imprinted magnetic nanoparticles

The potential of surface-modified magnetic nanoparticles was used as the support for molecular imprinting to separate insulin. The effects of the total monomers’ content (at seven levels) and overall temperature (ambient, controlled at 23 and 28 °C) during the formation of the surface polymer layer in aqueous media were for the first time explored via general factorial experimental design. Methacrylic acid (MAA) and acrylamide (AAm) were chosen as the functional monomers, and methylenebisacrylamide (MBAAm) was applied as the cross-linker. Six responses were simultaneously optimized using the desirability function. The software results demonstrated the importance of choosing proper amounts of constituents and controlling the temperature. The optimum conditions were determined to be for the magnetic molecularly imprinted polymers synthesized at 23 °C and with the molar ratio of 1:40:200:10 for Insulin:MAA:AAm:MBAAm with an imprinting factor of 2.5. TGA and VSM analyses confirmed the thin (about 7% of total weight) and uniform core-shell structure of polymers with high saturation magnetization (20.1 emu g−1). The outcomes of adsorption kinetics and rebinding isotherm revealed that the imprinted cavities located on or close to its surface, and are practical for the separation of low and high abundance of insulin. This system could be reused for at least five times cyclically.

Износостойкость сопряжений с зазором, восстановленных полиамидоэпоксидными пористыми покрытиями

The using of polymeric materials as coatings for the restoration of worn–out machine parts has found application in the industry of repairment. Their wider use is hampered because of poor adhesion strength, shrinkage, ageing, low wetting ability and other properties of polymeric materials. To improve the physical and mechanical properties of polyamide P12, it is advisable to add to the composition of various substances that help to reduce shrinkage, ageing, increase wear resistance. It is proposed to increase the oil absorption of the surface layers of polymer composite coatings by introducing 5...10% of sodium chloride (NaCl) into the composition. The obtained porous coatings were further subjected to wear tests under various lubrication conditions. The wear rate of the composite material under different lubrication conditions is different, so after 240 hours of testing, friction wear without lubrication was 18.8 ±2 μm, when using water – 16.8 ±2 μm, and when using LITOL 24 grease – 10±1 μm ... When using LITOL 24, a positive gradient of interfacial resistance of molecular bonds and surface layers is provided. Abrasion of the latter, as a rule, is not abrasive, but frictional and manifests itself in the separation of different, configurations of particles from the surface layer. Also, the lubricant is in the friction zone for longer because it is retained in the artificially formed pores of the surface layer of the coating. The presence of grease in the friction zone reduces the wear rate of the metal counter body. In those cases when there was no lubrication or there was water, the wear rate of the metal counter body was higher and practically had the same character. So, after 240 hours of testing, the following results were obtained: with friction and without lubrication In.l.=14 ±1 µm; friction in the presence of running water Iwater=13±1 µm; friction when using Litol 24, I=9±1 μm. Based on the results obtained, it can be stated that for a metal–porous polymer composite sliding friction pair, the types of lubricants affect the intensity of their wear. It should be noted that during the first hundred hours of testing, the evolution of the wear of the friction pair with different types of lubricant is practically the same and has a tendency to increase smoothly. This type of wear can be explained by the transfer of the composite material to the metal counter body. After removing this layer from the metal counter body, the process of its wear is different and depends on the type of lubricant. Metal counter bodies practically do not change the nature of wear when using water as a lubricant, as well as when friction without lubrication, but when using LITOL 24 lubricant, the wear rate is much less. The durability of friction pairs largely depends on the size of the gap. Thus, for the friction pairs studied with friction without lubrication, the linear intensity of the change in the gap value for 240 hours of testing will be 6.03 ∙ 10–8, for the condition of friction in running water and with Litol 24 lubricant, respectively 5.5 ∙ 10–8 and 3.6 • 10–8. In other words, we can say that in the studied area of 240 hours, the gap in friction pairs with friction without lubrication increased by 60 μm per 1 km of the distance travelled, when using water at 55 μm/km and 36 μm/km when using Litol 24 lubricant. It was found that the intensity of the increase in the gap in the friction pair when using a porous polymer coating based on a polyamide epoxy composition as a counter body in a metal–polymer friction pair, under lubrication conditions with Litol, is 1.64 times less than when using such coatings without pores. The obtained porous coatings showed higher wear resistance when using water as a lubricant (1.1 times less than that of the base one). The results obtained confirm that the creation of a porous surface layer in the coating of the polymer composition will contribute to an increase in the service life of the recovered friction pairs by replacing the usual metal–metal pair with a metal–polymer one.