Polymer System Based on Polyethylene Glycol and TFE Telomers for Producing Films with Switchable Wettability.

Today a lot of attention is paid to the formation of thermosensitive systems for biomedical and industrial applications. The development of new methods for synthesis of such systems is a dynamically developing direction in chemistry and materials science. In this regard, this paper presents results of the studies of a new synthesized supramolecular polymer system based on polyethylene glycol and tetrafluoroethylene telomers. The films formed from the polymer substance have the property of switching wettability depending on temperature after heating activation. It has been established that the wettability changes at 60 °C. The contact angle of activated hydrophobic polymer film reaches 143°. Additionally, the system exhibits its properties regardless of the pH of the environment. Based on data obtained by the methods of infrared and x-ray photoelectron spectroscopy, differential thermal analysis and thermal analysis in conjunction with wettability and morphology, a model of the behavior of molecules in a polymer system was built that ensures switching of the hydrophilic/hydrophobic surface state. The resulting polymer system, as well as films based on it, can be used in targeted drug delivery, implantation surgery, as sensors, etc.

Composite Coatings of AMg3 Alloy Formed by a Combination of Plasma Electrolytic Oxidation and Fluoropolymer Spraying.

This paper presents the results of an investigation of the changes in the corrosion, wear resistance, and wettability of composite coatings formed on the AMg3 alloy through plasma electrolytic oxidation (PEO) and subsequent spraying with an organofluorine polymer. The evaluation of the electrochemical properties of the composite layers revealed a decrease in the corrosion current density compared with the PEO coating (from 3.8 × 10-8 to 3.1 × 10-11 A/cm2). The analysis of the wear resistance of composite coatings established that the application of this type of coating reduced the wear of the samples by two orders of magnitude when compared with the PEO layer. Using the contact-angle measurement, it was found that with an increase in the number of polymer spray applications, the wettability of coatings decreased, so the contact angle for the composite coating with triple fluoropolymer application increased by 134.3° compared to the base PEO coating.

PEO Coatings Modified with Halloysite Nanotubes: Composition, Properties, and Release Performance.

In this work, the properties of the coatings formed on the Mg-Mn-Ce alloy by plasma electrolytic oxidation (PEO) in electrolytes containing halloysite nanotubes (HNTs) were investigated. The incorporation of halloysite nanotubes into the PEO coatings improved their mechanical characteristics, increased thickness, and corrosion resistance. The studied layers reduced corrosion current density by more than two times in comparison with the base PEO layer without HNTs (from 1.1 × 10-7 A/cm2 to 4.9 × 10-8 A/cm2). The presence of halloysite nanotubes and products of their dihydroxylation that were formed under the PEO conditions had a positive impact on the microhardness of the obtained layers (this parameter increased from 4.5 ± 0.4 GPa to 7.3 ± 0.5 GPa). In comparison with the base PEO layer, coatings containing halloysite nanotubes exhibited sustained release and higher adsorption capacity regarding caffeine.

Icephobic Performance of Combined Fluorine-Containing Composite Layers on Al-Mg-Mn-Si Alloy Surface.

This paper presents the results of an evaluation of anti-icing properties of samples obtained by plasma electrolytic oxidation (PEO) with a subsequent application of superdispersed polytetrafluoroethylene (SPTFE) and polyvinylidenefluoride (PVDF). A combined treatment of the samples with SPTFE and PVDF is also presented. It is revealed that impregnation of a PEO layer with fluoropolymer materials leads to a significant increase in surface relief uniformity. Combined PVDF-SPFTE layers with a ratio of PVDF to SPTFE of 1:4 reveal the best electrochemical characteristics, hydrophobicity and icephobic properties among all of the studied samples. It is shown that the decrease in corrosion current density Ic for PVDF-SPFTE coatings is higher by more than five orders of magnitude in comparison with uncoated aluminum alloy. The contact angle for PVDF-SPFTE coatings attain 160.5°, which allows us to classify the coating as superhydrophobic with promising anti-icing performance. A treatment of a PEO layer with PVDF-SPFTE leads to a decrease in ice adhesion strength by 22.1 times compared to an untreated PEO coating.

Bioactive Coatings Formed on Titanium by Plasma Electrolytic Oxidation: Composition and Properties.

Bioactive coatings on VT1-0 commercially pure titanium were formed by the plasma electrolytic oxidation (PEO). A study of the morphological features of coatings was carried out using scanning electron microscopy. A composition of formed coatings was investigated using energy-dispersive spectroscopy and X-ray diffractometry analysis. It was shown that PEO-coatings have calcium phosphate in their composition, which increases the bioactivity of the surface layer. Electrochemical properties of the samples were studied by potentiondynamic polarization and electrochemical impedance spectroscopy in different physiological media: simulated body fluid and minimum essential medium. The data of electrochemical studies indicate more than 15 times decrease in the corrosion current density for the sample with coating (5.0 × 10-9 A/cm2) as compared to the bare titanium (7.7 × 10-8 A/cm2). The formed PEO-layers have elastoplastic properties close to human bone (12-30 GPa) and a lower friction coefficient in comparison with bare metal. The wettability of PEO-layers increased. The contact angle for formed coatings reduced by more than 60° in comparison with bare metal (from 73° for titanium to 8° for PEO-coating). Such an increase in surface hydrophilicity contributes to the greater biocompatibility of the formed coating in comparison with commercially pure titanium. PEO can be prospective as a method for improving titanium surface bioactivity.

Effect of Microstructure on the Corrosion Resistance of TIG Welded 1579 Alloy.

The paper studies microstructure, chemical composition and corrosion activity of the tungsten inert gas welded joint of the Al-Mg-Sc alloy. An intensive corrosion attack of the heat affected zone (HAZ) was found due to precipitation of secondary phases at recrystallized grain boundaries. The ccorrosion process initiated along the boundary of α-Al grains, where a high concentration of anodic (Mg2Si and Mg2Al3) and cathodic phases ((MnFe)Al6) was observed. Increased temperatures during welding led to coalescence of the anodic phases in HAZ. Additionally, HAZ was found to be enriched with hard intermetallic compounds (Mg2Si and (MnFe)Al6). This area had a higher microhardness (930 MPa) compared to base metal (BM, 895 MPa) and fusion zone (FZ, 810 MPa). The volume fraction of secondary phases was 26% in BM, 28% in FZ and 38% in HAZ. The average grain size increased in the following order: (9 ± 3) µm (BM) < (16 ± 3) µm (HAZ) < (21 ± 5) µm (FZ). A plasma electrolytic oxidation (PEO) coating of aluminum-based material was applied to protect the weld from oxidation. The PEO-coating provided a high corrosion protection in the aggressive Cl--containing environment.

Corrosion of the Welded Aluminium Alloy in 0.5 M NaCl Solution. Part 2: Coating Protection.

The high electrochemical activity of the aircraft 1579 aluminium alloy with a welded joint and the necessity of the coating formation to protect this material against corrosion as well as to increase the stability of the weld interface in the corrosive medium has been previously established. In this work, two suggested methods of protective coating formation based on plasma electrolytic oxidation (PEO) in tartrate-fluoride electrolyte significantly increased the protective properties of the welded joint area of the 1579 Al alloy. The electrochemical properties of the formed surface layers have been investigated using SVET (scanning vibrating electrode technique) and SIET (scanning ion-selective electrode technique), EIS (electrochemical impedance spectroscopy), OCP (open circuit potential), and PDP (potentiodynamic polarization) in 0.5 M NaCl. The less expressed character of the local electrochemical processes on the welded 1579 Al alloy with the composite coating in comparison with the base PEO-layer has been established. Polymer-containing coatings obtained using superdispersed polytetrafluoroethylene (SPTFE) treatment are characterized by the best possible protective properties and prevent the material from corrosion destruction. Single SPTFE treatment enables one to increase PEO-layer protection by 5.5 times. The results of this study indicate that SVET and SIET are promising to characterize and to compare corrosion behaviour of coated and uncoated samples with a welded joint in chloride-containing media.

Corrosion of the Welded Aluminium Alloy in 0.5 M NaCl Solution. Part 1: Specificity of Development.

This work consists of two parts. In the first part, the kinetics and mechanism of corrosion on the surface of the welded joint area of the aircraft 1579 aluminium alloy have been studied using SVET (scanning vibrating electrode technique) and SIET (scanning ion-selective electrode technique) in 0.5 M NaCl. The results have revealed the corrosion process development within the weld interface due to the presence of microdefects in the morphological structure. Features of the 1579 Al alloy corrosion have also been investigated through immersion experiments, quantitative analysis of dissolved alloying elements by means of atomic absorption spectroscopy, and corrosion products characterization using XRD (X-ray diffraction) analysis. The presence of Mg as an alloying element in the 1579 Al alloy sufficiently increases the bulk pH values as a result of the intensive dissolution of Mg. These factors accelerate the corrosion activity of the studied material in the 0.5 M NaCl solution. Corrosion evolution analysis of the 1579 Al alloy sample showed the importance of the coating formation to protect this alloy against corrosion and to increase the stability of this system in the corrosive media.