Polystyrene Phase Research Articles

Enhancing the thermal conductivity of polystyrene/polyamide 6/graphene nanoplatelets composites through elongational flow

Migration and distribution of thermal conduct fillers in polymer blend are key factors in the preparation of enhanced thermal conductivity composite. In this study, polystyrene(PS)/polyamides 6(PA6)/graphene nanoplatelets(GNPs) composites with enhanced thermal conductivity were prepared under elongational flow, and the migration and distribution of GNPs were investigated by molecular dynamics simulation and experiments. The results showed that when GNPs immigrate from PA6 phase to PS phase, the elongational flow caused the orientation of the PS phase and GNPs, reducing the migration rate of GNPs from the PA6 phase to the PS phase. At the same time, the stretching viscosity of the PS phase increases, which prevents GNPs entering the PS phase. As a result, GNPs remain within the PA6 phase near the interface of the two phases. The effective distribution density of GNPs increased, making it easier for them to interconnect and form thermal conduction paths, thereby improving the thermal conductivity of the composites. Particularly, the composite prepared under the elongational flow with the 50/50 vol ratio of PS/PA6, the in-plane thermal conductivity of PS/PA6/GNPs composites reached a maximum of 1.64 W/(m·K).

Total revalorization of high impact polystyrene (HIPS): enhancing styrene recovery and upcycling of the rubber phase

The styrene recovery from high impact polystyrene waste can be enhanced by pre-fractionation with ethyl acetate followed by pyrolysis of the isolated polystyrene phase and ethenolysis of the polybutadiene phase.

A two‐phase method of moments model for high‐impact polystyrene phase inversion conversion and molecular properties

AbstractA challenge for high‐impact polystyrene (HIPS) production and design is the more accurate and low computational cost prediction of the phase separation and phase inversion conversion, the first conversion determining the onset of the two‐phase system and the second conversion defining the pathway toward a complex, for example, salami‐like morphology. In this work, a two‐phase deterministic method of moments (MoM) model running in several minutes is therefore developed in the intermediate styrene conversion range (up to around 30%), considering for simplicity only diffusional limitations on termination on an average basis. It is showcased that the phase separation conversion can be taken as 2 m%, and the phase inversion conversion should be calculated by algebraic means. Interestingly, the latter conversion varies with the initial reaction conditions either on a time basis (e.g., variation of initial radical concentration) or both a time and conversion basis (e.g., relative contribution of rubber and St partitioning coefficient). A comparison with the commonly used pseudo‐homogeneous MoM model reveals that by accounting for mass transfer in a more representative two‐phase model, the amount of monomer consumed is slightly reduced, the grafting efficiency decreases with increasing conversion instead of increasing, and the styrene composition in the graft copolymer decreases. The current work additionally puts forward two‐phase MoM data to facilitate future benchmarking with other (stochastic) modeling approaches and enables kinetic insights into heterogeneous grafting polymerization, further promoting the production of multiphase industrial polymer products.

MEH‐PPV/SBS composite films: Localization and luminescence properties of conductive polymers with microphase separation

AbstractThis study reports the synthesis of a flexible light‐emitting polymer film by casting the solution formed by blending poly[2‐methoxy‐5‐((2‐ethylhexyl)oxy)‐1,4‐phenylenevinylene] (MEH‐PPV) with poly(styrene‐co‐butadiene‐co‐styrene) (SBS). Scanning force microscopy (SFM) and differential scanning calorimetry (DSC) confirm that MEH‐PPV molecules are selectively positioned in the polystyrene (PS) domain of the fabricated film. As MEH‐PPV molecules are dissolved in the PS phase without aggregation, the photoluminescence (PL) spectrum of the MEH‐PPV/SBS film exhibits a nanometer‐scale bicontinuous luminescent domain with low aggregation quenching. Furthermore, the MEH‐PPV/SBS film exhibits typical elastomeric characteristics (with linear elasticity, a plateau, and densification regions in its stress–strain curves), and its tensile properties are comparable to those of neat SBS films. As MEH‐PPV molecules are almost absent in the polybutadiene (PB) phase (which influences the bulk‐film elastic properties), the concentration of MEH‐PPV shows very little effect on the elastic properties of the composite film.

Enhancing compatibility and properties of polylactic acid/polystyrene (PLA/PS) bioblend for sustainable food packaging: Experimental and quantum computational insights

This study investigated the impact of incorporating maleic anhydride grafted styrene-ethylene-butylene-styrene (SEBS-g-MAH) at varying concentrations (2.5, 5.0, 7.5, and 10.0 wt%) into binary blends of polylactic acid (PLA) and polystyrene (PS) with a weight ratio of 75/25. The blends were prepared using melt mixing in an internal Brabender mixer, followed by compression molding. Various characterization techniques, including Fourier transform infrared spectroscopy (FTIR), thermogravimetric analyses (TGA), differential scanning calorimetry (DSC), tensile testing, surface hardness measurements, and scanning electron microscopy (SEM) were employed to evaluate the structural, thermo-mechanical, surface, and morphological properties of the blends. FTIR results indicated the presence of n-π interaction between PLA and PS polymers. However, the introduction of SEBS-g-MAH to the blends resulted in specific interactions. TGA investigations demonstrated that compatibilized blends exhibited more excellent stability at high temperatures than their non-compatible counterparts. The DSC data align with the mechanical tests, revealing that the addition of SEBS-g-MAH reduced the crystallinity of the blends. Tensile strength, Young's modulus, and surface hardness diminished with the addition of SEBS-g-MAH, although the elongation at break improved. SEM analysis of the PLA/PS blends illustrated that incorporating SEBS-g-MAH enhanced the PS phase's distribution throughout the PLA matrix. Furthermore, molecular dynamic simulations revealed a significant enhancement in binding interaction energies upon adding SEBS-g-MAH, increasing from 2037.972 kcal/mol to 2826.946 kcal/mol for the PLA-PS and PLA-PS (5) systems, respectively. Density of state (DOS) analysis indicated that SEBS-g-MAH played an intermediary role, promoting compatibility between PLA and PS. These findings suggest that SEBS-g-MAH can effectively be a compatibilizer for PLA-PS blends.

Quantum effects of hydrogen storage in ϵ and δ semicrystalline phases of syndiotactic polystyrene through adsorption

Syndiotactic polystyrene (sPS) is a stereoregular semicrystalline polymer which presents complex polymorphic behaviour and has been explored as an alternative for hydrogen storage using adsorption. The methodology of gas retention using a light and cheap porous material offers many advantages. To establish the adsorption capacity of a specific material, adsorption isotherms are generally measured. However, to gain a better understanding of the underlying phenomena occurring at a nanoscale level (e.g. confined interactions of in sPS) and, moreover, as a predictive tool, alternative methods such as molecular simulations are required. In this work, we present Grand Canonical Monte Carlo simulation results for hydrogen () adsorption isotherms of δ and ϵ phases of sPS. molecule was described as a 1-site model with Lennard-Jones and Exp-6 potentials, within the Wigner–Kirkwood mean-field approximation to introduce quantum corrections. Both polymer phases were modelled using an atomistic force field and the initial configurations were relaxed using molecular dynamics for temperatures , and . Adsorption isotherms for each system were obtained for both classical and semiclassical potentials. Additionally, adsorption isotherms for both phases were compared with experimental adsorption data at from previous work.

Energy-saving optimization of solar greenhouse walls in severe cold region

ABSTRACT Energy consumption of solar greenhouse depends on the thermal insulation performance and thermal storage capacity of thermal storage wall. To find the best composition scheme for heat storage wall of greenhouse in severe cold region (1A: Hailar, 1B: Anda, 1C: Shenyang), the paper uses a typical Northeast Chinese solar greenhouse as an illustration and forms 14 schemes by setting expanded polystyrene (EPS) insulation boards and phase change materials (PCMs) at different positions of the thermal storage wall, of which PCM materials have six phase change temperatures. Energy consumption, wall heat storage performance, and room temperature of these schemes are analyzed by using EnergyPlus. Energy consumption, heat storage capacity, room temperature regulation, payback period, and carbon emissions were used to compare the heat storage wall schemes. The results show that Case Ⅵ (16°C) in Hailar is the optimal scheme, its energy consumption is 46,862.886 kWh, and the added value of the payback period is 1.87 years, the second is Case a and Case e (26°C) is the worst. Case VI (16°C) in Anda is the optimal scheme, its energy consumption is 65,599.749 kWh, and the added value of the payback period is 1.59 years, the second is Case a, and Case e (26°C) is the worst. Case Ⅶ (16°C) in Shenyang is the optimal scheme, its energy consumption is 26,109780kWh, and the added value of the payback period is 1.77 years, the second is Case a, and Case f (24°C) is the worst. The reason for the difference in optimal schemes is that the outdoor temperature of Hailar and Anda is low in winter, and PCM can hardly change phase in winter, but only plays the role of heat preservation. The temperature in Shenyang is relatively high in winter, and PCM is more likely to change phase, so the closer PCM is to the room, the lower the energy consumption of the greenhouse. The research results of this paper can provide a theoretical basis for the energy-saving design of solar greenhouse.

Regulation of dewetting and morphology evolution in spin-coated PS/PMMA blend films via graphene-based Janus nanosheets

Spin-coated blend films with complex phase-separated morphology find broad applications while precise tailoring of the morphology is still challenging. In this study, graphene oxide (GO)-based Janus nanosheets were synthesized by interfacial polymerization in a GO nanosheet stabilized Pickering emulsion with polystyrene (PS) and poly(hydroxyethyl methacrylate) synchronously being grafted to the GO nanosheet from the oil and water sides. The Janus nanosheets make the morphology of spin-coated PS/poly(methyl methacrylate)(PMMA) blend films tunable over the full height of the film until the substrate as their preferential assembly at the PS/PMMA interface and attachment on the glass substrate drive the top PS phase to migrate towards the substrate and the bottom PMMA phase to dewet from the substrate towards the air. By varying blend composition and Janus nanosheet loading, morphologies are readily transformed from a PS network on top of PMMA to PS droplets in the PMMA matrix and from PS encapsulated by PMMA to PMMA cavities in the PS network, etc.. This enables generating thin films with various morphologies ranging from a flat surface to cavity-network structures, droplet-matrix structures or bi-continuous structures, etc. at will. Moreover, the morphologies trapped by jammed nanosheets at the interface are super stable against further evolution upon annealing.

Theoretical and experimental investigation of selective gas permeability in polystyrene/polyolefin elastomer/nanoclay nanocomposite films

Nanoclay (NC) has gas barrier properties that, when used in food packaging, protects food against spoilage. Moreover, food packaging frequently makes use of rigid and foamed polystyrene (PS). In this work, reactive blending in a co-rotating twin-screw extruder was used to process PS, polyolefin elastomer (POE), and NC blends, leading to microphase-separated PS/POE/NC nanocomposite films. The structural and CO2 and N2 barrier properties of the resulting films were determined. The distribution of the NC platelets in the blends was theoretically predicted using the wetting coefficients. Nearly all NC platelets were found in the PS phase, in agreement with the theoretical predictions. Moreover, the NC platelets were found to be concentrated at the interfacial zones between the polymer phases when a compatibilizer was added to the blend. Scanning electron microscopy, wide-angle X-ray scattering, and transmission electron microscopy were used to examine the microstructure of the PS/POE/NC nanocomposites. Adding NCs as a gas barrier component to the PS/POE blend resulted in a decrease in CO2 and N2 permeability. For a better understanding of the gas diffusion in the pure PS and POE, as well as PS/POE blend, molecular dynamics simulations were performed to enable the calculation of gas diffusion coefficients in the different systems. The simulation results confirmed the experimental trends observed in this work.

Performance of Poly(caprolactone) (PCL) as an Impact Modifier for Polystyrene (PS): Effect of Functionalized Compatibilizers with Maleic Anhydride and Glycidyl Methacrylate

In this work, the copolymers ethylene-glycidyl methacrylate (E-GMA), ethylene methyl methacrylate-glycidyl methacrylate (EMA-GMA), and styrene-(ethylene-butylene)-styrene grafted with maleic anhydride (SEBS-g-MA) were used to compatibilize polystyrene (PS)/poly(caprolactone) (PCL) blends. The blends were processed in a co-rotating twin-screw extruder and injection molded. Samples were investigated by torque rheometry, capillary rheometry, impact strength, tensile strength, heat deflection temperature (HDT), dynamic-mechanical thermal analysis (DMTA), thermogravimetry (TG), and scanning electron microscopy (SEM). Torque rheometry indicated that glycidyl methacrylate functional groups and maleic anhydride groups interact with PCL. Capillary rheometry evidenced that at shear rates lower than 10,000 s−1, the PS/PCL/SEBS-g-MA blends presented the highest apparent viscosity among the blends. Such behavior was possibly due to the good interaction between SEBS-g-MA and the PS and PCL phases. Consequently, the properties of impact strength, elongation at break, tensile strength, and elastic modulus were improved by 30%, 109%, 33.8%, and 13.7%, respectively, compared with the non-compatibilized PS/PCL system. There was a reduction in the HDT of all blends compared with neat PS, given the elastomeric characteristics of PCL and compatibilizers. The DMTA results revealed two independent peaks in the blends (one around −53 °C concerning the PCL phase and another at 107 °C related to PS), confirming their immiscibility. The PS/PCL/SEBS-g-MA blends showed higher morphological stability, confirming their good mechanical properties.

Constructing PA6/PS composite foam with porous and hybrid isolation structure to synergistically control absorption and electromagnetic interference shielding effectiveness

AbstractIsolation structure has been proven to be an effective method for constructing electromagnetic shielding composites, achieving high electrical conductivity with shallow filler content and high‐efficiency electromagnetic shielding. However, there are still many challenges in further optimizing the design and improving absorption. This article designed a hybrid isolation structure using nylon magnetic microspheres and polystyrene (PS). First, we prepared PA magnetic microspheres (Ni@PA6M) with Ni nanoparticles uniformly dispersed by the reaction induced phase separation (RIPS) method, then mixed with MWCNT and PS at high speed and formed by hot pressing. Under the optimized ratio, the hybrid structure has more interfaces and a more complete conductive network. Simultaneously, the magnetic microspheres can promote the absorption of electromagnetic waves, thereby improving the electromagnetic shielding performance of the material. When the MWCNT content is 7 wt%, Ni@PA6M:PS = 7:3, the total shielding effectiveness (EMI SET) and reflection coefficient (R) of the composite reached 28.6 dB and 0.77, respectively, while the EMI SET and R of the composite constructed with pure nylon microspheres and PS are 26.1 dB and 0.74, respectively. Further, using supercritical CO2 foaming technology to foam the PS phase in the composite to form many cells can improve the impedance matching and absorption of electromagnetic waves. The results show that introducing the cell structure reduces the reflection coefficient (R) from 0.77 to 0.69, and the EMI SET drops to a certain extent. Introducing the hybrid isolation and porous structure we designed provides a new idea for creating electromagnetic shielding materials for isolation structures.

Visualization of Macrophase Separation and Transformation in Immiscible Polymer Blends

Visualization of Macrophase Separation and Transformation in Immiscible Polymer Blends

Finely Modulated LDPE/PS Blends via Synergistic Compatibilization with SEBS-g-MAH and OMMT

Melt blending is an effective way to prepare new composite materials, but most polymers are incompatible. In order to reduce the interfacial tension and obtain fine and stable morphology with internal symmetric micro-textures, suitable compatibilizers should be added to the blend. The two immiscible polymers, low-density polyethylene (LDPE) and polystyrene (PS), were compatibilized by styrene/ethylene/butylene/styrene block copolymers grafted with maleic anhydride (SEBS-g-MAH) and organomontmorillonite (OMMT). The scanning electron microscope results indicated that the size of the PS phase decreased with increasing the content of SEBS-g-MAH. By introducing OMMT into LDPE/PS/SEBS-g-MAH composites, the compatibility of composites was further improved. The rheological analysis and Cole–Cole plot analysis indicated that the addition of SEBS-g-MAH and OMMT increased the interaction between the two phases. The tensile strength, elongation at break, and impact strength of the LDPE/PS/SEBS-g-MAH (70/30/7, wt%) composite increased by 64%, 255%, and 380%, respectively, compared with the LDPE/PS (70/30, wt%) composite. A small amount of OMMT could synergistically compatibilize the LDPE/PS composite with SEBS-g-MAH. After adding 0.3% OMMT into the LDPE/PS/SEBS-g-MAH system, the tensile strength, elongation at break, and impact strength of the composite were further increased to 18.57 MPa, 71.87%, and 33.28 kJ/m2, respectively.

Selective Plasticization of Poly (ethylene oxide) (PEO) Block in Nanostructured Polystyrene− PEO− Polystyrene Triblock Copolymer Electrolytes

The plasticization of a polymer electrolyte usually promotes its ionic conductivity but decreases its storage modulus due to the increased polymer chain flexibility. Herein, we show that such a tradeoff between the ionic conductivity and the mechanical robustness of the polymer electrolyte can be alleviated by selective plasticization of the ion-conductive block, such as poly(ethylene oxide) (PEO) in a polystyrene (PS)− PEO−PS block copolymer (SEO) electrolyte using an ether type plasticizer, tetraethylene glycol dimethyl ether (TEGDME). At maximum plasticizer loading, the room temperature ionic conductivity increases by up to 3 orders, whereas the storage modulus, G′ reduces to half, is still on the order of 102 MPa. At above the melting temperature of the PEO block, the dynamic storage modulus, G′ of the plasticized membrane surpasses its dry PS-PEO-PS counterpart. Such a phenomenon results from that, a) TEGDME co-crystallizes with PEO to promote its crystallinity and hence the storage modulus, b) TEGDME swells the amorphous PEO phase to enhance the polymer chain segmental mobility and hence ionic conductivity, and c) the PS phase remains intact from TEGDME to keep the SEO elastic.

Janus micro‐thread to micro‐nanodroplets using dynamic contact line lithography

AbstractDynamic contact line lithography (DCLL) is generally used for the template‐less but well‐ordered deposition of polymer micro/nanostructures from the solution of homopolymer. DCLL from the blend of several polymers in a common suitable solvent can generate rich morphologies including nanostructured Janus micro threads on a surface which might be challenging to fabricate using any other method. A blend of polystyrene (PS) and poly(methyl methacrylate) (PMMA) in toluene with different compositions and concentrations are used for DCLL at a constant contact line speed of 10 μm/s. Variations of compositions and the overall concentration of polymer, engender Janus micro threads to undulated threads and multi‐layered micro/nanodroplets of PS/PMMA. Interestingly, the more soluble PS phase separates first compared to less soluble PMMA near the contact line due to the enhanced local concentration of PS during the convective flow of the solvent toward the contact line. This is also verified by DCLL using PS/PMMA blend in ethyl acetate as well. In that case, more soluble PMMA deposits first near the contact line compared to marginally less soluble PS in the solvent.

The synthesis of functional Janus nanosheets as compatibilizers for the immiscible polyamide 6 /polystyrene (PA6/PS): Formation of the nanosilica monolayer at the interface

The non-spherical Janus nanosheets (JNSs) have been large-scale synthesized by grafting polystyrene (PS) chains and epoxy group on the opposite sides of JNS, denoted as epoxy-silica-PS JNS. The functional JNSs are employed as compatibilizer in the immiscible polyamide 6 (PA6)/polystyrene (PS) blend. In the melt-blending process, the JNS with epoxy group can react with carboxyl (amino)-capped PA6 and in-situ form the PA6-silica-PS JNS. Owing to the amphiphilicity and Pickering effect, the JNSs can be exclusively located at the polymeric interface and assemble into the nanosilica monolayer at 0.5 wt% loading. With increasing the JNSs loading, the size of dispersed PS phase is decreased gradually and the JNSs still maintain the single layer structure at the interface. The dynamic moduli of the blends have been effectively improved for the JNSs at the interface. This report provides an extended application of Janus nanosheets to stabilize and functionalize the polymeric interface.

Mechanism of Post-Radiation-Chemical Graft Polymerization of Styrene in Polyethylene.

Structural and morphological features of graft polystyrene (PS) and polyethylene (PE) copolymers produced by post-radiation chemical polymerization have been investigated by methods of X-ray microanalysis, electron microscopy, DSC and wetting angles measurement. The studied samples differed in the degree of graft, iron(II) sulphate content, sizes of PE films and distribution of graft polymer over the polyolefin cross section. It is shown that in all cases sample surfaces are enriched with PS. As the content of graft PS increases, its concentration increases both in the volume and on the surface of the samples. The distinctive feature of the post-radiation graft polymerization is the stepped curves of graft polymer distribution along the matrix cross section. A probable reason for such evolution of the distribution profiles is related to both the distribution of peroxide groups throughout the sample thickness and to the change in the monomer and iron(II) salt diffusion coefficients in the graft polyolefin layer. According to the results of electron microscope investigations and copolymer wettability during graft polymerization, a heterogeneous system is formed both in the sample volume and in the surface layer. It is shown that the melting point, glass transition temperature and degree of crystallinity of the copolymer decreases with the increasing proportion of graft PS. It is suggested that during graft polymerization a process of PE crystallite decomposition (melting) and enrichment of the amorphous phase of graft polymer by fragments of PE macromolecules occurs spontaneously. The driving force of this process is the osmotic pressure exerted by the phase network of crystallites on the growing phase of the graft PS.

Waste to Value-Added Product: Developing Electrically Conductive Nanocomposites Using a Non-Recyclable Plastic Waste Containing Vulcanized Rubber.

This study intends to show the potential application of a non-recyclable plastic waste towards the development of electrically conductive nanocomposites. Herein, the conductive nanofiller and binding matrix are carbon nanotubes (CNT) and polystyrene (PS), respectively, and the waste material is a plastic foam consisting of mainly vulcanized nitrile butadiene rubber and polyvinyl chloride (PVC). Two nanocomposite systems, i.e., PS/Waste/CNT and PS/CNT, with different compositions were melt-blended in a mixer and characterized for electrical properties. Higher electrical conduction and improved electromagnetic interference shielding performance in PS/Waste/CNT system indicated better conductive network of CNTs. For instance, at 1.0 wt.% CNT loading, the PS/Waste/CNT nanocomposites with the plastic waste content of 30 and 50 wt.% conducted electricity 3 and 4 orders of magnitude higher than the PS/CNT nanocomposite, respectively. More importantly, incorporation of the plastic waste (50 wt.%) reduced the electrical percolation threshold by 30% in comparison with the PS/CNT nanocomposite. The enhanced network of CNTs in PS/Waste/CNT samples was attributed to double percolation morphology, evidenced by optical images and rheological tests, caused by the excluded volume effect of the plastic waste. Indeed, due to its high content of vulcanized rubber, the plastic waste did not melt during the blending process. As a result, CNTs concentrated in the PS phase, forming a denser interconnected network in PS/Waste/CNT samples.

Stress-Strain and Stress-Relaxation Behaviors of Solution-Coated Layers Composed of Block Copolymers Mixed with Tackifiers.

The relationship between the mechanical properties and the structure of block copolymers mixed with tackifiers whose relative solubility to the respective components of block copolymers differs was examined. Coated layers were prepared by solution coating using a block copolymer composed of polystyrene (PS) and polyisoprene (PI), which forms spherical microdomains of PS in the PI matrix, mixed with three types of tackifiers: aliphatic (C5) resin, aliphatic–aromatic (C5–C9) resin, and rosin ester (RE) resin. Furthermore, the correlation between the changes in the nanostructure and mechanical properties including the stress-relaxation behaviors was clarified by two-dimensional small-angle X-ray scattering measurement. The amount of the PI-bridge conformation in the case of C5 resin is the lowest, resulting in the lowest stress. On the contrary, the largest amount of RE resin was solubilized in the PS phase so that it can be considered that pulling out of the PS chains took place easily. We were able to explain the stress-relaxation behavior by fitting with the three-component exponent functions. The triple exponential decay functions indicate the hierarchy of the structures that are the origins of the ″fast mode″ relating to the local relaxation due to the rotation of the repeating unit of polymer chains; the ″intermediate mode″ of the disentanglement of the mid-PI chains; and the ″slow mode″ relating to, in this particular case, pulling out of the PS chains from the PS sphere.

Water\ufeff vapor induced self-assembly of islands/honeycomb structure by secondary phase separation in polystyrene solution with bimodal molecular weight distribution

The formation of complex structures in thin films is of interest in many fields. Segregation of polymer chains of different molecular weights is a well-known process. However, here, polystyrene with bimodal molecular weight distribution, but no additional chemical modification was used. It was proven that at certain conditions, the phase separation occurred between two fractions of bimodal polystyrene/methyl ethyl ketone solution. The films were prepared by spin-coating, and the segregation between polystyrene phases was investigated by force spectroscopy. Next, water vapour induced secondary phase separation was investigated. The introduction of moist airflow induced the self-assembly of the lower molecular weight into islands and the heavier fraction into a honeycomb. As a result, an easy, fast, and effective method of obtaining island/honeycomb morphologies was demonstrated. The possible mechanisms of the formation of such structures were discussed.