Formation Of Polymer Films Research Articles

Influence of Bronze Filler upon The Friction and Wear of Polytetrafluoroethylene and Polyoxymethylene.(Dept.M)

The present paper deals with an experimental investigation carried out to elucidate the role played by polymeric and metallic fillers upon the coefficient of friction and wear rate of Polyoxymethylene (POM) and Polytetrafluoroethylene (PTFE).Lead bronze powder and PTFE powder were added by different percentages of volume to the base material to form a Composite. The study was performed on a pin-on-disk machine under constant load of 50 N and constant sliding speed of 1.0 m/s under dry sliding conditions. The results indicate that the addition of bronze or PTFE fillers always reduces the coefficients of friction and wear rates of tested materials and that reduction increases with the increase of filler content up to about 40%. The minimum valves of friction and wear were experienced by POM containing 36% PTFE. The paper attributes the reduction in friction and wear to the formation of polymeric transfer film adhering to the steel counterface which facilitates sliding and decreases adhesion.

Structural Transitions During Formation and Rehydration of Proton Conducting Polymeric Membranes.

Knowledge of the transitions occurring during the formation of ion-conducting polymer films and membranes is crucial to optimize material performances. The use of non-destructive scattering techniques that offer high spatio-temporal resolution is essential to investigating such structural transitions, especially when combined with complementary techniques probing at different time and spatial scales. Here, a simultaneous multi-technique study is performed on the membrane formation mechanism and the subsequent hydration of two ion-conducting polymers, the well-known commercial Nafion and a synthesized sulfonated poly(phenylene sulfide sulfone) (sPSS). The X-ray data distinguish the multi-stage processes occurring during drying. A sol-gel-membrane transition sequence is observed for both polymers. However, while Nafion membrane evolves from a micellar solution through the formation of a phase-separated gel, forming an oriented supported membrane, sPSS membrane evolves from a solution of dispersed polyelectrolyte chains via formation of an inhomogeneous gel, showing assembly and ionic phase separation only at the end of the drying process. Impedance spectroscopy data confirm the occurrence of the sol-gel transitions, while gel-membrane transitions are detected by optical reflectance data. The simultaneous multi-technique approach presented here can connect the nanoscale to the macroscopic behavior, unraveling information essential to optimize membrane formation of different ion-conducting polymers.

Variety of Ordered Patterns in Donor-Acceptor Polymer Semiconductor Films Crystallized from Solution.

A huge challenge is to control the nucleation of crystallites/aggregates in the solution during polymer film formation to generate desired structures. In this work, we investigate crystallization of P(NDI2OD-T2), a donor–acceptor polymer semiconductor, with controlled solution flow along the contact line between the drying film and solution through a seesaw-like pivoting of samples during polymer drying. By controlling the pivoting frequency/amplitude, various types of line patterns can be observed: (I) an array of fishbone-like stripes oriented in the film-growth direction; (II) the pinning–depinning of contact line (PDCL)-mechanism-defined patterned wires along the contact line; and (III) periodic twined crystalline line pattern oriented in the direction of the contact line. The rich variety of pattern formation observed is attributed to the distinctiveness of the donor–acceptor conjugated polymer structure. The result measured from thin-film transistors made of the generated films/structures showed that the charge mobility of P(NDI2OD-T2) does not change much with the film morphology, which supports recent controversy over the charge-transportation mechanism of some donor–acceptor polymer semiconductors.

Thin polymer layer-covered porous alumina tubular membranes prepared via a dip-coating/phase-inversion process

Harnessing the full potential of polymers to the formation of supported thin films in other materials has been important for application in the membrane fabrication area. However, it faces the effects on the differences in properties between materials, such as chemical affinity and structure type. This paper describes a new approach for obtaining a thin polymeric film on porous supports. For this, the dip-coating/phase inversion technique was adapted. The called wet-dry process consisted of immersing a porous ceramic tube in a polymer solution (dip-coating), followed by immersion in a non-solvent bath (wet phase inversion), and finally, allowing the set to dry in a controlled atmosphere (dry phase inversion). The morphology was investigated by scanning electron microscopy to verify the efficacy of the method. The new technique proved to be effective in the formation of a thin polymer film supported on macroporous ceramic support minimizing intrusion into the support pores.

Experimental Study of High Performance Synchronous Grouting Materials Prepared with Clay.

Shield construction discharges a large amount of soil and muck. The utilization of discharged soil of shield always has high energy consumption and a low utilization rate. Meanwhile, synchronous grouting is a key process for shield tunneling. The current studies show that the synchronous grouting materials applied now generally have the problem of mismatching among filling property, fluidity, and consolidation strength. In order to study the feasibility of using the excavated soil produced by shield construction in clay stratum as synchronous grouting material, high performance synchronous grouting material was studied by taking red clay as an example, modified by epoxy resin. The fluidity, stability, and strength were measured to evaluate performance of the grout. Material test results show that the addition of waterborne epoxy resin decreases density, improves the stability, the rate of stone, and the toughness of the grouting concretion. Finally, X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) were measured to analyze the cementitious mechanism of the grout, test results demonstrated that cement hydration and curing reaction of epoxy resin happened in the grout, the formed polymer film filled the voids in the mixture and effectively bound cement hydration gel and clay particles together.

Synchronous Monitoring of Cement Hydration and Polymer Film Formation Using 1H-Time-Domain-NMR with T 2 Time-Weighted T 1 Time Evaluation: A Nondestructive Practicable Benchtop Method.

The interactions between latex and cement are still not completely understood. In this work, we would like to address the temporal changes in cement hardening and latex film formation. For this reason, the hydration process and the film formation were simultaneously monitored. This scientific issue is even more challenging as a nondestructive quantitative analysis of the film formation process is not available yet. Here, we report on simultaneous monitoring of the latex film formation and the phase development in cementitious systems via 1H-time-domain-NMR for the first time. The obtained results were validated using classical analytical methods, such as in situ X-ray diffraction, X-ray fluorescence (Rietveld analysis), and confocal laser scanning microscopy.

Lithium‐Ion Batteries: Operando Magnetometry Probing the Charge Storage Mechanism of CoO Lithium‐Ion Batteries (Adv. Mater. 12/2021)

In article number 2006629, Hongsen Li, Yunze Long, Qiang Li, and co-workers use an advanced operando magnetometry technique to probe the charge-storage mechanism of CoO lithium-ion batteries, showing that the anomalous discharge capacity in this particular system is associated with both the reversible formation of a spin capacitor and the growth of a polymeric film at low voltages. The key catalytic role of metallic Co in assisting the polymeric film formation is demonstrated, which is helpful for the design of new types of energy-storage devices and improving the energy density for future battery designs.

Corrosion integrity of oil cement modified by environment responsive microspheres for CO2 geologic sequestration wells

In order to ensure the safe and effectiveness of CO2 geological storage, an environmental responsive polymer microspheres (ERPM) was prepared to improve the corrosion resistance of cement stone. The structure and environmental response characteristics of ERPM were characterized, and then the anti-corrosion performance and anti-corrosion mechanism for ERPM were discussed. The results shown that ERPM had good environmental response characteristics and temperature resistance. ERPM could effectively suppressed the corrosion rate and the damage degree of mechanical properties of cement stone. The corrosion integrity of cement stone was improved due to the acidic response characteristic and form polymer films of ERPM, which effectively shield the direct contact between corrosion medium and hydration products.

Formation of Various Polymeric Films via Surface‐Initiated ARGET ATRP on Silicon Substrates

The growth of various polymeric films such as neutral, zwitterionic, and anionic ones was investigated over time from the initiator‐immobilized silicon substrates. The polymerization reactions were carried out under ambient conditions via activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) without any predeoxygenating process. Each of the examined polymeric films showed linear/exponential growth over reaction times according to the measurement of ellipsometric film thickness. The successful formation of various polymeric films was further proved by X‐ray photoelectron spectroscopy, contact angle goniometry, and measurement of surface free energies. We think that this study can provide a basis for other researches that require to graft polymers with the adjustable film thickness for modulating chemical/physical properties at interfaces.

Operando Magnetometry Probing the Charge Storage Mechanism of CoO Lithium-Ion Batteries.

Cobalt oxide (CoO) is a promising electrode for high-energy-density Li-ion batteries (LIBs), where the charge storage is believed to take place solely during the electrochemical oxidation/reduction processes. However, this simple picture has been increasingly challenged by reported anomalously large storage capacities, indicating the existence of undiscovered extra charge reservoirs inside the system. Here, an advanced operando magnetometry technology is employed to monitor the magnetization variation of the CoO LIBs in real time and, in this particular system, it is clearly demonstrated that the anomalous capacity is associated with both the reversible formation of a spin capacitor and the growth of a polymeric film at low voltages. Furthermore, operando magnetometry provides direct evidence of the catalytic role of metallic Co in assisting the polymeric film formation. These critical findings help pave the way for better understanding of the charge storage mechanisms of transition-metal oxides and further utilizing them to design novel electrode materials.

Cement mortar with enhanced flexural strength and durability-related properties using in situ polymerized interpenetration network

The low flexural strength and high brittleness of cementitious materials impair their service life in building structures. In this study, we developed a new polymer-modified mortar by in situ polymerization of acrylamide (AM) monomers during the cement setting, which enhanced the flexural and durable performances of mortars. The mechanical properties, micro-and-pore structures, hydrated products, interactions between cement hydrates and polyacrylamide (PAM), and durability-related properties of the mortars were investigated comprehensively. Mortars with 5% PAM exhibited the best performance in terms of flexural strength among all the mixtures. The mechanical strength of cement pastes modified by in situ polymerization of AM monomers was significantly superior to those modified by PAM. The chemical interactions between the polymer molecules and cement hydrates together with the formation of polymer films glued the cement hydrates and polymers and resulted in an interpenetrating network structure, which strengthened the flexural strength. Reductions in porosity and calcium hydroxide content and improvement in capillary water absorption were achieved with the addition of PAM. Finally, the chloride resistance was significantly enhanced with the incorporation of PAM.

Development of the surface plasmon resonance imaging and observation of the polymer film formation

Development of the surface plasmon resonance imaging and observation of the polymer film formation

Electrochemiluminescence Imaging of Conducting Polymer Film Structures

Conducting polymers (CPs) is a class of attractive materials that, thanks to their unique properties, structures made on-demand and new composition mixtures, finds a wide variety of applications, ranging from material science to chemistry, from energy to environmental remediation and electroanalysis. Electrochemical synthesis of CPs is usually achieved by anodic oxidation, or electropolymerization, of suitable monomer species, which generally results in the formation of polymeric films deposited onto the surface of an electrode. Nevertheless, the use of this methodology makes rather difficult, or even impossible, to tune the morphology of the final CPs materials, limiting their applicability in material science. To overcome this limitation, electrosynthesis of CPs with different geometries such as brushes, films and fiber arrays has recently been achieved exploiting the unique wireless feature of bipolar electrochemistry1. In fact, this renewed technology enables electrochemical reactions at both extremities of a wireless electrode, or bipolar electrode (BPE), through the application of an external electric field generated in a low concentration of a supporting electrolyte.In this context, alternating current (AC)-bipolar electropolymerization of 3,4-ethylenedioxythiophene (EDOT) has recently been employed for the gradual in-plane growth of the corresponding poly(3,4-ethylenedioxythiophene) (PEDOT) films at the terminal of a gold BPE laid down on a glass surface2. This notable phenomenon could paved the way for the drawing of CPs on non-conductive substrates, opening up new perspectives for their potential application for circuit patterning in organic electronic devices. The possible mechanism of films formation seems to involve the generation of PEDOT fibers that propagate in an anisotropic morphology from the terminal of the BPE, in parallel to the external electric field under electrophoretic effect, resulting in colored film depositions visible at naked eye. However, very thin layers of PEDOT films underlying the main fibers are generally transparent, making their direct visualization rather difficult.In the present contribution, we propose the use of Electrogenerated Chemiluminescence (ECL) for the morphological imaging of PEDOT films synthetized by AC-bipolar electropolymerization. ECL is the emission of light at the electrode surface following an electrochemical stimulus and, nowadays, it is widely employed as an emerging microscopy technique3. The great success of ECL imaging technology is due to the electrochemical nature of light generation that allows very low background signal and the possibility to control the ECL emission both temporally and spatially by applying a suitable potential. Our approach employs the use of the well-known luminol/hydrogen peroxide ECL system for the visualization of PEDOT films grown on non-conductive substrates used as BPEs in bipolar systems. The different potential distribution on such PEDOT systems allows ECL emission only in confined areas of PEDOT films where the potential is sufficient to trigger the ECL reaction, allowing the visualization of different structural characteristics of the polymeric films (Figure 1). This technique would represent an innovative and promising tool to accurately control the morphology of the final polymer material, opening up new perspectives in the area of electrochemical synthesis of CPs. Figure 1: Schematic illustration of the bipolar setup used for ECL imaging of PEDOT films (a). Optical image of PEDOT film synthetized by AC-bipolar electropolymerization (b). Corresponding Luminol ECL images on PEDOT film working as BPE at 25 V (c) and 70 V (d).

Pickering emulsion approach for fabrication of waterborne cross-linkable polydimethylsiloxane coatings with high mechanical performance

HypothesisThe Pickering emulsion approach has been frequently employed to fabricate various emulsions. However, the direct formation of cross-linked polymer films from Pickering emulsions and double functions (emulsified and mechanical reinforcement) of Pickering agents have not been sufficiently reported. ExperimentsFumed silica was co-modified with vinyltrimethoxysilane (VTMS) and hexamethyl disilylamine (HMDS) and was further adopted to emulsify vinyl or hydrogen dimethicone. The as-obtained Pickering emulsions were mixed with Karstedt catalyst capsules to produce one-component waterborne cross-linkable polydimethylsiloxane (PDMS) coatings that were subsequently transformed into elastic films after drying at ambient temperature. FindingsThe co-modification of fumed silica with VTMS/HMDS is shown to balance the Pickering emulsion effect and film-forming ability of the coatings. Greater amounts of grafted VTMS/HMDS or higher modified silica dosages demonstrated better Pickering emulsion effects. Nevertheless, because Pickering agents hinder the coalescence of silicone oil droplets, the appropriate modified silica concentration is crucial for achieving the highest cross-link density and thus the highest mechanical strength. The grafted CC groups can endow the modified silica with hydrosilylation reactivity and can thus additionally contribute to the mechanical performance of PDMS film. In addition, the Pickering emulsion approach is shown to be superior to the traditional emulsion approach for acquiring waterborne coatings with high mechanical performance.

Characterization of electrode fouling during electrochemical oxidation of phenolic pollutant

Electrode fouling is a problem that commonly occurs during electro-oxidation water purification. This study focused on identifying the fouling behavior of Pt electrode associated with the formation of polymeric layer during electro-oxidation of phenol. The in situ electrochemical measurements and non-destructive observation of the electrode morphology were reported. The results demonstrated that the electrode fouling was highly dependent on thermodynamic process of electrode that was controlled by anode potential. At anode potential lower than 1.0 V vs SHE, the direct electro-oxidation caused the electrode fouling by the formation of polymeric film. The fouling layer decreased the electrochemically active surface area from 8.38 cm2 to 1.57 cm2, indicated by the formation of polymeric film with thickness of 2.3 µm, increase in mass growing at a rate of 3.26 µg/cm/min. The degree to which the anode was fouled was independent of anion in the electrolyte. In comparison, at anode potential higher than 2.7 V vs SHE, the anions (e.g., chloride) could exert a major influence to the behavior of electrode fouling. The presence of chloride was shown to mitigate the fouling of electrode significantly through preventing the formation of polymeric film by active chlorine (e.g., Cl• and Cl2) produced from anodic oxidation of chloride. Since chloride is the most abundant anionic species existing in both natural and engineered water system, this study not only offers a deep insight into the mechanism of electrode fouling, but also suggests strategies for anti-fouling in the presence of chloride in electro-oxidation process.

Высокотемпературная коррозия сталей в растворах кислот. Ч. 2. Ингибиторная защита сталей непредельными органическими соединениями. Обзор

The general regularities of the influence of temperature (t) of acid solutions on the protection effectiveness of steel in them by organic compounds have been considered. The effectiveness of organic compounds in slowing down the corrosion of steels, as a rule, either decreases with increasing t or passes through a maximum at 60 °C. It was noted that there is a group of high-temperature corrosion inhibitors, the temperature maximum of which lies above 60 °C, that allows them to be used in the protection of steels even in environments with t > 100 °C. The general approaches to the protection of steels in solutions of mineral acids under conditions of high-temperature corrosion (t > 80 °C) with unsaturated organic compounds (UC) and mixtures based on them were analyzed. The use of multicomponent compound containing UC is appropriate for the protection of steels in high-temperature solutions of acids, in some cases at t up to 250 °C. The ability to protect steels at such high t is due to the unique mechanism of the UC inhibitory action, which is the result of their ability to chemisorption on the metal surface and undergo deep chemical transformations leading to the formation of a protective polymer film. Limitations on the use of UC as corrosion inhibitors are associated with their chemical instability in volume of acid, as well as toxicity of UC itself and composite additives used with them.

In-situ assessment of the water-penetration resistance of polymer modified cement mortars by μ-XCT, SEM and EDS

Anti-water-penetration techniques are important to raise the durability of cement-based materials (CBMs). Here the water penetration resistances of cement mortars with ethylene-vinyl acetate copolymer (EVA) and styrene butadiene rubber (SBR) were in-situ and non-destructively probed by micro-focus X-ray computed tomography (μ-XCT). Caesium Chloride (CsCl) was mixed in water to enhance the contrast gradients of μ-XCT images. SEM and EDS tests were provided to assess the mortar microstructure changes induced by water penetration. Results show that the CsCl enhancement helps trace the water penetration fronts, while exerting minor influences on the water penetration kinetics. The polymers can greatly raise the resistance against the water penetration into the cement mortars. The pore blocking induced by the formation of polymer films on the surfaces of cement grains and aggregates may account for the enhanced water-penetration resistance. The findings of this work provide a new method to track the water penetration in CBMs by μ-XCT and deepen the knowledge in the anti-water mechanisms of polymer-modified cement materials.

A new polymeric thin film by using electropolymerization: thin film of poly(phenazine-salen) obtained from 2,2'-[1,2-ethanediylbis(nitrilomethylidyne)] -bis[4-amino-phenol

Abstract In the last years, the study of the formation of a polymer containing multidentate Schiff-base ligand as subunits has been performed. In general, the electropolymerization occurs through the interaction between the phenyl rings and metallic centers. However, in this paper, we proposed a new polymeric thin film formation from 2,2'-[1,2-ethanediylbis(nitrilomethylidyne)]bis[4-amino-phenol] obtained by electropolymerization. The electropolymerization mechanism for poly(phenazine-salen) formation was based on the carbon-nitrogen coupling. The effect of experimental parameters such as scan rate, applied potential range, supporting electrolyte, and solvent type on the electropolymerization process was also evaluated. The poly(phenazine-salen) film was characterized by cyclic voltammetry and electrochemical impedance spectroscopy in an inert supporting electrolyte showing a redox couple ascribed to pyrazine moieties. The Mott-Schottky plot of the electropolymerized material indicated that the polymer is an n-type semiconductor. The results indicate a polymeric formation controlled by the electropolymerization parameters and the electrochemical behavior tuned by the ions insertion/extraction from supporting electrolyte.

Influence of humidity on the mechanical properties of polymer-modified cement-based repair materials

Portland cement–aluminate cement–hemihydrate gypsum ternary binder repair mortars, as a type of road repair material, have the advantages of fast hardening and early strength, micro-expansion, stable strength, and good mechanical performance. However, problems on high brittleness, fast loss of fluidity, and poor toughness are also encountered. The effects of styrene butadiene copolymer and styrene acrylate on the construction performance of a ternary binder repair mortar composed of Portland cement, aluminate cement, and hemihydrate gypsum and the effects of different curing humidity conditions on the mechanical properties of the polymer-modified ternary repair mortar were investigated. Both polymers enhanced the fluidity and decreased the fluidity loss rate of the ternary binder cement paste and prolonged its setting time. Moreover, both polymers improved the toughness and reduced the water absorption of the ternary repair mortar in concordance with their filling effect and film-forming roles under different humidity curing conditions. Different curing humidity conditions affected the ettringite crystal morphology and polymer film formation of the polymer-modified ternary binder repair mortar. The polymer under natural curing conditions presented the best modification effect in terms of mechanical properties, and the inner structure was the densest of the repair mortar for the ternary binder. The toughness and flexural strength of the specimens were markedly improved.

CELLULOSE MATERIALS MODIFIED BY SILVER NANOPARTICLES AND THE STUDY OF THEIR ANTIBACTE-RIAL PROPERTIES

The article discusses a method for producing silver nanoparticles (NPs) in aqueous solutions by reducing sodium borohydride in the presence of polyvinyl alcohol; selected optimal conditions for the synthesis. The resulting silver NPs have a spherical shape, with a diameter of from 30 to 130 nm. NPs are stable, do not precipitate and do not change color for 3–4 weeks. Electron microscopic images confirm the formation of a thin polymer film on the surface of cellulose fiber and show a change in the morphological surface of the treated samples compared to untreated ones. The energy dispersive microanalysis data showed that the raw cotton fabric contains C – 57.02%, O – 42.98%. After processing, nanoscale particles of silver are encapsulated on the surface of the fabric – 0.18–0.28%, which are distributed rather unevenly. Modification of cellulosic textile materials of silver NPs imparts a stable antimicrobial effect , as well as improves their physico-mechanical and hygienic properties. The air permeability indicators for cotton original fabric 180 dm3/m2×sec., For the treated composition based on polyvinyl alcohol, NaBH4, and silver nitrate – 175 dm3/m2×sec. The breaking load of the fabric is: for the initial – 311 N, for treated – within 320–360 N. The indicators of air permeability and strength characteristics of cotton fabric treated with the proposed composition comply with the regulatory requirements for this group of fabrics.