Green Nanosilver as Reinforcing Eco-Friendly Additive to Epoxy Coating for Augmented Anticorrosive and Antimicrobial Behavior

Epoxy resin GY250 representing diglycidyl ethers of bisphenol-A (DGEBA) was reinforced with 1, 3 and 5wt % of surface functionalized silver nanoparticles (F-AgNPs) which were synthesized using Couroupita guianensis leaves extract with a view of augmenting the corrosion control property of the epoxy resin and also imparting antimicrobial activity to epoxy coatings on mild steel. Corrosion resistance of the coatings was evaluated by EIS, potentiodynamic polarization studies and cross scratch tests. AFM, SEM, HRTEM and EDX were utilized to investigate the surface topography, morphology and elemental composition of the coatings on MS specimens. Results showed that the corrosion resistance, hardness and T_g of the DGEBA/F-AgNPs coatings increased at 1wt % of F- AgNPs. The DGEBA/F-AgNPs coatings also offered manifold antimicrobial protection to the MS surfaces by inhibiting the growth of biofilm forming bacteria like P. aeruginosa, B. subtilis, the most common human pathogen E. coli and the most virulent human pathogenic yeast C. albicans.     

General trends in concentration and temperature behavior of equivalent conductance of <Emphasis Type="Italic">N,N</Emphasis>-diallylammonium polymers aqueous solutions: Effect of counterion nature and amine structure

The specific and equivalent conductivity of the diluted aqueous solutions of diallyammonium polyelectrolytes, initial monomers (N,N-diallylammonium trifluoroacetate, N,N-diallyl-N-methylammonium trifluoroacetate, N,N-diallyl-N,N-dimethylammonium chloride), and also potassium trifluoroacetate and trifluoroacetic acid solutions are studied. The limiting ionic mobility of diallylammonium cations and trifluoroacetate anion are found. The regularities of concentration changes in the equivalent conductance of polyelectolytes solutions are established. The degree of dissociation of diallyammonium polymers is shown to depend both on the counterion nature and on the amine structure.     

Amorphous polyamide coating resins from sugar-derived monomers

In this article, the synthesis of bio-based polyamides for powder coating applications and their evaluation in a solventborne coating system are reported. The M _n values of the resins were between 3000 and 4000 g mol^?1 and the resins displayed T _g values from 60 to 80°C. Both amine and carboxylic acid functionalities (total ~0.6 mmol g^?1) were introduced for curing purposes. The resins were cured with triglycidyl isocyanurate (TGIC) or N,N,N′,N′-tetrakis(2-hydroxyethyl)adipamide (Primid XL-552). The curing reaction was followed using rheology which indicated that TGIC achieved higher reaction rates and higher gel contents. The DSC analysis of the cured disks showed that all cured samples were amorphous as is desired for the targeted coating application. The resins required a curing temperature higher than 150°C. Aluminum panels were coated using a solventborne approach and the coatings were cured at 180°C during 1 h. Dewetting was observed on all panels. Network formation was adequate for an amine-functional resin cured with TGIC as indicated by solvent resistance testing. In conclusion, the developed bio-based polyamide resins are promising materials to be used as binder resins in powder coating applications.     

Influence of pH in the synthesis of ferric tannate pigment for application in antifouling coatings

Ferric tannate was synthesized at pH 4 and pH 7 (FT4 and FT7, respectively) as a new class of environmentally friendly antifouling pigments. The solubility of both pigments was evaluated by gravimetric tests, showing that FT4 is more soluble than FT7. A mixture of rosin/acrylic resin (9:1 w/w) was sufficient to form an antifouling coating due to improved matrix properties. Electrochemical impedance spectroscopy (EIS) measurements were used to determine the apparent water coefficient of diffusion (D) and coating behavior. The D in the coating formulated with FT4 exhibited better values than that obtained with FT7. EIS results showed that both coatings present Fickian behavior at the initial stages of immersion, while flat Nyquist plots revealed penetration of water in the films. The physicochemical characteristics of FT4 pigment were determined by thermogravimetry and Fourier transform infrared. Immersion tests in the Mediterranean Sea demonstrated the excellent efficacy of the FT4-containing coating against marine fouling after six months of immersion.     

Nanoindentation as an alternative to mechanical abrasion for assessing wear of polymeric automotive coatings

Mechanical abrasion followed by transmission delta-haze measurement is a standard means to assess wear in polymeric silicone automotive hard coatings. However, the drawbacks of this abrasion–transmission (A–T) technique (drift, variability, sample size, and test time) make an alternative measurement method desirable. Literature reports have shown that the ratio of hardness to modulus can successfully predict wear performance in ceramic and metallic nanocomposite coatings. This work studied measures from both nanoindentation and nanoscratch testing to determine which could be a viable alternative to the historical A–T test for a specific polymeric coating system. Both nanoindentation measures of hardness (H) and the ratio of hardness to modulus (H/E _r) showed high repeatability compared with the other measures evaluated in this study and compared with the historical test. Of these two measures, the ratio H/E _r with an exponential fit showed the strongest correlation with A–T delta-haze measurements. Key formulation and process factors affecting abrasion resistance in automotive coatings were analyzed in a designed experiment with historical A–T delta-haze and nanoindentation H/E _r as responses. Analysis showed significant benefits to the use of the H/E _r measure of abrasion resistance in modeling coating performance.     

Facile preparation and good performance of nano-Ag/metallocene polyethylene antibacterial coatings

Metallocene polyethylene/nano-silver coatings were prepared by a facile air-spray method on polymer films. Different from the prevailing strategy to endow polyethylene with antibacterial performance, we used metallocene polyethylene sol and nano-silver as a precursor to deposit coatings on polymers at a relatively low operating temperature. Antibacterial coatings with excellent mechanical properties, water resistance, and low silver release were achieved. The composite coatings were examined in terms of surface characteristics, mechanical properties, and antibacterial activity against two representative bacterial strains including Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The composite coatings exhibited favorable microstructure, good mechanical properties, and suitable crystallinity. The antimicrobial tests indicated that the fabricated composite coatings showed promising antibacterial activity against E. coli and S. aureus. Furthermore, Ag ions released by the composite coating after 30 days were under 1.2 ppb. These results indicated a promising prospect of the composite coating for wide antibacterial applications.     

Mixed Stability and Antimicrobial Properties of Gluconamide-Type Cationic Surfactants

The stability of anionic-cationic surfactant solutions and the antimicrobial properties of novel N,N-dimethyl-N-[3-(gluconamide/lactobionamide)]propyl-N-alkylammonium bromides (CnDGPB and CnDLPB), N-methyl-N-hydroxyethyl group-N-[3-(gluconamide)-propyl]-N-alkylammonium bromide (CnMHGPB) and star-shaped gluconamide-type cationic surfactants N-dodecyl-N,N-bis[(3-d-gluconylamido)propyl]-N-alkylammonium bromide (CnDBGB) were investigated. Mixed stability in combination with sodium n-alkylbenzenesulfonate (LAS) was determined via transmittance; stability is achieved when percent transmittance was greater than 90 %. Transmittance results suggest that these cationic surfactants can form stable solutions with anionic surfactants over a broad concentration range. The inhibition activity of C _n DBGB is the best among the three kinds of glucocationic surfactants. Antimicrobial activity of C₁₂ surfactants was the best, C₁₄ was the second and C₁₀ was the worst. Moreover, antibacterial activity of glucose-based cationic surfactants was greater than lactose-based cationic surfactants.     

The effect of formulation variables on fouling-release performance of stratified siloxane–polyurethane coatings

The effects of formulation variables, such as type of polyol, solvent type and solvent content, and coating application method, on the surface properties of siloxane–polyurethane fouling-release coatings were explored. Fouling-release coatings allow the easy removal of marine organisms from a ship’s hull via the application of a shear force to the surface. Self-stratified siloxane–polyurethane coatings are a new approach to a tough fouling-release coating system. Combinatorial High Throughput Experimentation was employed to formulate and characterize 24 different siloxane–polyurethane coatings applied using drawdown and drop-casting methods. The resulting coatings were tested for surface energy using contact angle measurements. The fouling-release performance of the coatings was tested using a number of diverse marine organisms including bacteria (Halomonas pacifica and Cytophaga lytica), sporelings (young plants) of the green macroalga (Ulva linza), diatom ((microalga) Navicula incerta), and barnacle (Amphibalanus amphitrite). The performance of the majority of the coatings was found to be better than the silicone standards, Intersleek^® and Silastic^® T2. An increase in solvent content in the formulations increased the surface roughness of the coatings. Coatings made with polycaprolactone polyol appeared to be somewhat rougher compared to coatings made with the acrylic polyol. The adhesion strength of sporelings of Ulva increased with an increase in solvent content and increase in surface roughness. The adhesion strengths of Ulva sporelings, C. lytica, and N. incerta were independent of application method (cast or drawdown) in contrast to H. pacifica adhesion, which was dependent on the application method.     

Enhancement of UV-aging resistance of UV-curable polyurethane acrylate coatings via incorporation of hindered amine light stabilizers-functionalized TiO<Subscript>2</Subscript>-SiO<Subscript>2</Subscript> nanoparticles

In this study, polymeric hindered amine light stabilizers (HALS)-functionalized silica coated rutile titanium dioxide (TiO₂-SiO₂) nanoparticles were prepared by encapsulating commercially available TiO₂-SiO₂ nanoparticles with methyl methacrylate (MMA) and 1,2,2,6,6-pentamethyl-4-piperidyl methacrylate (PMPM) copolymers via miniemulsion polymerization. The obtained functional (TiO₂-SiO₂/P(MMA-co-PMPM)) fillers have been added to polyurethane acrylate (PUA) oligomers to get UV-curable nanocomposite coatings. The functionalization of the TiO₂-SiO₂ nanoparticles with polymeric HALS has been confirmed by infrared spectra (IR), thermogravimetric (TG), and X-ray photoelectron spectroscopy (XPS) analyses. The scanning electron microscope (SEM) micrographs indicated that homogeneous dispersion of TiO₂-SiO₂/P(MMA-co-PMPM) composite nanoparticles resulted in improved transparency and mechanical properties of the UV-curable PUA coatings. Rhodamine B (Rh.B) photodegradation measurement confirmed the excellent UV-shielding performance of PUA nanocomposite coatings containing TiO₂-SiO₂/P(MMA-co-PMPM). The addition of TiO₂-SiO₂/P(MMA-co-PMPM) composite nanoparticles reduced the UV-curable PUA coatings degradation rate dramatically. The UV-aging resistance of PUA coatings was improved significantly. Over all, the combination of TiO₂-SiO₂ nanoparticles and polymeric HALS offers an attractive way to fabricate the multi-functional fillers, which can be used to improve the mechanical properties and UV-aging resistance of PUA coatings simultaneously.     

Synthesis,Characterization and Surface Properties of Amidosulfobetaine Surfactants Bearing Odd-Number Hydrophobic Tail

Three amidosulfobetaine surfactants were synthesized namely: 3-(N-pentadecanamidopropyl-N,N-dimethyl ammonium) propanesulfonate (2a); 3-(N-heptadecanamidopropyl-N,N-dimethyl ammonium) propanesulfonate (2b), and 3-(N-nonadecanamidopropyl-N,N-dimethyl ammonium) propanesulfonate (2c). These surfactants were prepared by direct amidation of commercially available fatty acids with 3-(dimethylamino)-1-propylamine and subsequent reaction with 1,3-propanesultone to obtain quaternary ammonium salts. The synthesized surfactants were characterized by IR, NMR and mass spectrometry. Thermogravimetric analysis (TGA) results showed that the synthesized surfactants have excellent thermal stability with no major thermal degradation below 300 °C. The critical micelle concentration (CMC) values of the surfactants 2a and 2b were found to be 2.2 × 10^?4 and 1.04 × 10^?4 mol/L, and the corresponding surface tension (γ_CMC) values were 33.14 and 34.89 mN m^?1, respectively. The surfactants exhibit excellent surface properties, which are comparable with conventional surfactants. The intrinsic viscosity of surfactant (2b) was studied at various temperatures and concentrations of multi-component brine solution. The plot of natural logarithm of relative viscosity versus surfactant concentration obtained from Higiro et al. model best fit the surfactant behavior. Due to good salt resistance, excellent surface properties and thermal stability, the synthesized surfactant has potential to be used in various oil field applications such as enhanced oil recovery, fracturing, acid diversion, and well stimulation.     

Fabrication of thermally stable porous films from a cured epoxy resin via the <Emphasis Type="Italic">Breath Figures</Emphasis> process

In the current work, porous films based on epoxy resin have been obtained via the Breath Figures method. It was shown that the use of a low-temperature curing agent and fluoro-containing organosilicon copolymer, compatible with epoxy resin, makes it possible to obtain porous, thermostable, highly hydrophobic coatings with a pore diameter of 3–4 µm. When the epoxy resin/copolymer mixture is homogenous, the modifier prevents water droplet coalescence; otherwise, the mixture becomes heterogeneous, and the positive influence of the modifier is lost. The obtained modified porous films are highly hydrophobic and maintain their porous structure until polymer devitrification occurs. The simplicity of the Breath Figures method shows great potential for the manufacture of water-repellent paint coatings based on epoxy resin for use in a variety of applications.     

Effect of nitrogen to niobium atomic ratio on superconducting transition temperature of δ-NbN<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> powders

Powders of cubic niobium nitride δ-NbN _x with a particle size of below 20 μm were prepared by reactive diffusion at T = 1455?1475°C under nitrogen pressures of P ₁(N₂) = 0.1?3 MPa and P ₂(N₂) = 25 MPa. For these powders, the values of the stoichiometric coefficient x, lattice parameter a, and the superconducting transition temperature Tc were measured and the a(x), T _c(x) and T _c(a) functions were analyzed. The T _c values were found to linearly grow with increasing a (decreasing structure imperfection). A maximum value of T _c (15.8 K) corresponded to a maximum value of a (4.3934 Å). Maximain the a(x) and T _c(x) curves were found to correspond to a slightly substoichiometric nitride with x = 0.98. Having synthesized cubic niobium nitrides with 0.892 < x < 1.062, we managed to measure the dependences of a and T _c on x all over the almost entire homogeneity range for δ-NbN _x . Our a(x) and T _c(a) functions were found to reasonably agree with those previously reported for SHS-produced δ-NbN _x powders.     

Effect of the Molecular Structure on the Adsorption Properties of Cationic Surfactants at the Air–Water Interface

The surface activity and thermodynamic properties of adsorption at the air–water interface of two series of cationic surfactants based on isourea: the O-dodecyl-N,N′-diisopropylisourea hydrochloride, hydrobromide, and hydroiodide and the O-tridecafluorooctyl-N,N′-diisopropylisourea hydrochloride and hydrobromide were studied. The effect of structural parameters as the nature of the halide counter ion and the nature of the non-polar chain on the surface activity and thermodynamic properties of adsorption were investigated. The surface parameters, the maximum surface excess concentration (Γ _max), the minimum area per molecule (A _min) at the aqueous solution-air interface, effectiveness of surface tension reduction (π_CMC), and efficiency of surface tension reduction (pC ₂₀) were estimated. The standard Gibbs free energy of adsorption, (ΔG°_ads) change has been calculated at different temperatures.     

Impedance sensor for the early failure diagnosis of organic coatings

A miniature impedance sensor used for field diagnosis of the early failure of coatings has been developed based on microelectronics and electrochemical impedance spectroscopy (EIS). The aging process of polyurethane-based coatings in salt spray test chamber was studied using the impedance sensor. Several critical indexes related to EIS such as phase angle (θ_10Hz, θ_15kHz), breakpoint frequency (f_b), specific capacitance (C_10Hz, C_15kHz), and impedance modulus (Z_0.1Hz) were proposed to evaluate the severity of coating degradation. The results indicated that the impedance sensor could accurately monitor the degradation process of coatings, and once Z_0.1Hz?<?10⁶ Ω cm², f_b?>?100 Hz, or θ_10Hz?<?20°, the coating may be regarded as completely degraded and fails to protect the metal substrate.     

β-SiAlON-TiN/TiB<Subscript>2</Subscript>-BN composites by infiltration-mediated SHS under high pressure of nitrogen gas

Infiltration-mediated SHS of β-Si_6–z Al _z O _z N_8–z –TiN/TiB₂–BN composites was explored upon variation in applied nitrogen pressure, amount of combustible and inert components in green mixture, sample size, and BN content of resultant composites. Synthesized ceramics of different density and phase composition were characterized by their strength parameters, tribological behavior, electrical resistance, and thermal shock resistance.     

A Comprehensive Study on the Synthesis and Micellization of Disymmetric Gemini Imidazolium Surfactants

Two groups of disymmetric Gemini imidazolium surfactants, [C₁₄C₄C _m im]Br₂ (m = 10, 12, 14) and [C _m C₄C _n im]Br₂ (m + n = 24, m = 12, 14, 16, 18) surfactants, were synthesized and their structures were confirmed by ¹H NMR and ESI–MS spectroscopy. Their adsorption at the air/water interface, thermodynamic parameters and aggregation behavior were explored by means of surface tension, electrical conductivity and steady-state fluorescence. A series of surface activity parameters, including cmc, γ _cmc, π _cmc, pC ₂₀, cmc/C ₂₀, Γ _max and A _min, were obtained from surface tension measurements. The results revealed that the overall hydrophobic chain length (N _c) for [C₁₄C₄C _m im]Br₂ and the disymmetry (m/n) for [C _m C₄C _n im]Br₂ had a significant effect on the surface activity. The cmc values decreased with an increase of N _c or m/n. The thermodynamic parameters of micellization (ΔG _m ^θ , ΔH _m ^θ , ΔS _m ^θ ) derived from the electrical conductivity indicated that the micellization process of [C₁₄C₄C _m im]Br₂ and [C _m C₄C _n im]Br₂ was entropy-driven at different temperatures, but the contribution of ΔH _m ^θ to ΔG _m ^θ was enhanced by increasing N _c or m/n. The micropolarity and micellar aggregation number (N _agg) were estimated by steady-state fluorescence measurements. The results showed that the surfactant with higher N _c or m/n can form larger micelles, due to a tighter micellar structure.     

Bio-/Environment-Friendly Cationic Gemini Surfactant as Novel Corrosion Inhibitor for Mild Steel in 1 M HCl Solution

Bio-/environment-friendly cationic gemini surfactant, ethane-1,2-diyl bis(N,N-dimethyl-N-hexadecylammoniumacetoxy)dichloride, referred to as 16-E2-16, was synthesized and characterized. Corrosion inhibition effects of 16-E2-16 on mild steel (MS) surface in 1 M HCl solution at 30, 40, 50 and 60 °C were evaluated using gravimetric analysis, potentiodynamic polarisation and electrochemical impedance spectroscopy measurements. The nature of the protective inhibitor film formed on the MS surface was analysed by SEM, EDAX and FT-IR, while TGA was used to assure the thermal behaviour and stability of the film at high temperature. The formation of [inhibitor-Fe²⁺] on the surface of MS was confirmed by UV–visible spectroscopy. The inhibition efficiency of the studied inhibitor increased with increasing concentration and solution temperature. The compound behaved as a mixed type inhibitor and acted by blocking the electrode surface by means of adsorption obeying the Langmuir adsorption isotherm. Surface active properties and corrosion inhibition effects of 16-E2-16 in the presence of inorganic (NaI) and organic (NaSal) salts were also investigated and are discussed. Density functional theory calculations have been carried out to correlate the efficiency of the compound with its intrinsic molecular parameters.     

β-SiAlON–BN composites by infiltration-mediated SHS under high pressure of nitrogen gas

Infiltration-mediated SHS of β-S_i6–z Al _z O _z N_8–z –BN composites was explored upon variation in applied nitrogen pressure, amount of combustible and low-melting components in green mixture, sample size, and BN content of resultant composites. Synthesized ceramic composites of different density and BN content were characterized by their strength parameters, tribological behavior, and thermal shock resistance.     

Electrochemical impedance study for modeling the anticorrosive performance of coatings based on accelerated tests and outdoor exposures

In this study, the atmospheric corrosive protection characteristics of four organic coatings were modeled based on the evolution of low-frequency impedance (|Z| _ω→0) over time when subjected to accelerated tests and outdoor exposures. Environmental characteristics such as the time of wetness, chloride and sulfate depositions, and ultraviolet radiation were defined as explanatory variables. The results obtained helped to establish a relationship between |Z| _ω→0, acquired from electrochemical impedance spectra, and the explanatory variables. An adjustment factor was calculated for each coating against the most aggressive natural exposure, resulting in a good prediction of |Z| _ω→0 and the performance of the coatings for other outdoor tests.     

The role of molecular structure on impact resistance and bending strength of photocured urethane-dimethacrylate polymer networks

The objective of this study was to investigate the influence of molecular structure on impact resistance (a _n) and bending strength (σ) of photocured urethane-dimethacrylate polymer networks. Urethane-dimethacrylate (UDMA) monomers were synthesized through reaction of oligoethylene glycol monomethacrylate (OEGMMA) with diisocyanate (DI). OEGMMA varied within the length of the oligooxyethylene chain, which consisted of one to four oxyethylene units. DI varied in chemical character: aliphatic, cycloaliphatic or aromatic. The molecular structure of UDMA polymers was characterized by X-ray powder diffraction, which allowed the calculation of the d-spacing (d) and dimensions of microgel agglomerates (D). The measurements of the polymerization shrinkage were used for the determination of the degree of conversion (DC), whereas the concentration of double bonds was used as a measure of the crosslink density (q). It was found that all structural parameters depend on the UDMA chemical structure. The increasing length of the oligooxyethylene chains caused the decrease in d and q, in contrast to the increase in D and DC. The DI chemical character caused the increase in the DC and q accordingly: symmetrical cycloaliphatic or aromatic < asymmetrical cycloaliphatic and aromatic < substituted aliphatic < linear aliphatic. The compact packing and high DC in polymers derived from aliphatic DIs gave rise to the decrease in d and the increase in D. The non-planar conformation of cycloaliphatic DIs emerged in high d as well as D. The planar conformation of aromatic DIs resulted in the decrease in d as well as D. The study indicated that mechanical behavior of UDMA polymer networks can be explained in terms of the structural parameters. DC and q appeared to be the main factors determining both mechanical properties of poly(UDMA)s. The a _n was also shown to be affected by d. Particularly high linear correlations were found on a semi-logarithmic scale for the DC and d with a _n. a _n increased as the DC increased, whereas d decreased.