Stable superhydrophobic coatings Using PVDF/MWCNT nanocomposite

Thermally stable superhydrophobic coatings have been prepared using Polyvinylidene fluoride (PVDF)Multiwalled carbon nanotubes (MWCNTs) by spray coating method. The effects of MWCNT (0 – 66 wt%) and temperature (300 to 623 K) on wettability have been studied. A transformation from hydrophobic to superhydrophoic state was achieved with increase of CNT content. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) studies reveal that with increase in CNT content, -phase of PVDF decreases suggesting that MWCNT has strong effect on the phase separation of PVDF. Field emission scanning electron microscopy (FESEM) studies show that the coatings have rough surface with porous structure. With increase in CNT content the protrusion like structures decreased reaching micro/nano scales. The coatings were thermally stable upto 573 K exhibiting superhydrophobicity and thereafter transformed to superhydrophilic state at 623 K. Energy dispersive X-ray spectroscopy (EDXS) analysis show the absence of fluorine after annealing at 623 K suggesting decomposition of PVDF. X-ray photoelectron spectroscopy (XPS) of C1s and F1s core levels in as-deposited PVDFMWCNT coating show the presence of CF2 related species. Concentration of fluorine drastically decreases after heat treatment of the coating at 350 C. The main advantage of the present method is feasibility for application over large area and the coatings are stable upto 573 K

Influence of Al2O3 addition on the wear and corrosion behaviour of HVOF sprayed WC-12Co coatings

WC-12Co and 30wt.% of Al2O3 powder mixture was sprayed on EN-24 steel using high velocity oxy fuel (HVOF) method. The chemical, mechanical and tribological performances of WC-12Co and WC-12Co-Al2O3 coatings have been evaluated. XRD analysis clearly showed the presence of WC, Co and Al2O3 peaks in WC-12Co-Al2O3 coating. The FESEM studies showed a homogeneous microstructure with low amount of porosity in WC-12Co-Al2O3 samples as compared to WC-12Co coatings. )A, Rp=406 ) as compared to WC-12Co (Icorr=0.9A, Rp= 2010An improved hardness of 1100 Hv was observed with the addition of Al2O3 content compared to 950 Hv (WC-12 Co). The 3D roughness profiles show a higher roughness of Ra ~ 7.6µm for Al2O3 incorporated coatings when compared to WC-12Co coating (Ra ~ 6.5µm). Dry sliding wear results of WC-12Co-Al2O3 coating exhibited higher wear resistance as compared to WC-12Co coating. This is probably due to low porosity levels and good metallurgical bonding between the EN24 substrate and the coating. Electrochemical impedance spectroscopy (EIS) studies showed better corrosion resistance for WC-12Co-Al2O3 coatings (Icorr=0.1 coating. It is concluded that WC-12Co-Al2O3 coating exhibited better chemical, mechanical and tribological properties compared to WC-12Co coating under identical HVOF coating conditions

Water-repellent coatings prepared by modification of ZnO nanoparticles

Superhydrophobic coatings with a static water contact angle (WCA) > 150° were prepared by modifying ZnO nanoparticles with stearic acid (ZnO@SA). ZnO nanoparticles of size ∼14 nm were prepared by solution combustion method. X-ray diffraction (XRD) studies reveal that as prepared ZnO has hexagonal wurtzite structure whereas the modified coatings convert to zinc stearate. Field emission scanning electron micrographs (FE-SEM) show the dual morphology of the coatings exhibiting both particles and flakes. The flakes are highly fluffy in nature with voids and nanopores. Fourier transformed infrared (FTIR) spectrum shows the stearate ion co-ordinates with Zn2+ in the bidentate form. The surface properties such as surface free energy (γp) and work of adhesion (W) of the unmodified and modified ZnO coatings have been evaluated. The electron paramagnetic resonance (EPR) spectroscopy reveals that surface defects play a major role in the wetting behavior

Enhanced microwave absorption properties of PMMA modified MnFe2O4-polyaniline nanocomposites

A manganese based spinel ferrite, chemically modified with polymethyl methacrylate (PMMA) and polyaniline (PANI) are synthesized and their composites are used as electromagnetic interference (EMI) shielding materials. X-ray diffraction studies show that the as-prepared manganese ferrite crystallizes in a cubic spinel structure. The particles are highly agglomerated and nanocrystalline as indicated by transmission electron microscopy. Manganese exists in +2 and +4 oxidation states and Fe in +2 and +3 oxidation states. Modified manganese ferrite and polyaniline composites in different weight ratios are evaluated for their EMI shielding properties. It is observed that composites containing the PMMA modified ferrite show enhanced total shielding effectiveness (SET) compared to those containing the unmodified ferrite in the X band frequency range (8-12 GHz). The optimized ratio of the PMMA modified ferrite and PANI demonstrates SET values as high as 44 dB in the X band frequency range

Optical absorption and emission properties of Pr3+Pr^{3+} and Er3+Er^{3+} in mixed alkali borate glasses

his article presents the optical absorption and emission properties of $Pr^{3+}$ and $Er^{3+}$ in mixed alkali borate glasses of the type $68B_2O_3.xLi_2O.(32-x)Cs_2O$ (where x= 8, 12, 16, 20 and 24 ). The variation of Judd-Ofelt intensity parameters $(\Omega_{\lambda})$, the peak wavelength of the hypersensitive transitions, radiative transition probabilities $(A_{rad})$ and peak emission cross-sections $(\sigma_p)$ with x in the glass matrix has been discussed in detail. The changes in position of hypersensitive transition and intensity parameters with x are correlated to the structural changes in the host matrix. The estimated radiative lifetimes $(\tau_R)$ of certain excited states of both $Pr^{3+}$ and $Er^{3+}$ in lithium cesium mixed alkali borate glasses are reported. Branching ratios $(\beta)$ and integrated absorption cross sections $(\Sigma)$ for certain important transitions are presented. Peak stimulated emission cross-sections $(\sigma_p)$ are calculated for the observed emission peaks of $Pr^{3+}$ and $Er^{3+}$ ions in this glass matrix

Effect of wettability and surface roughness on ice-adhesion strength of hydrophilic, hydrophobic and superhydrophobic surfaces

The anti-icing properties of hydrophilic, hydrophobic and superhydrophobic surfaces/coatings were evaluated using a custom-built apparatus based on zero-degree cone test method. The ice-adhesion reduction factor (ARF) of these coatings has been evaluated using bare aluminium alloy as a reference. The wettability of the surfaces was evaluated by measuring water contact angle (WCA) and sliding angle. It was found that the ice-adhesion strength on silicone based hydrophobic surfaces was ~ 43 times lower than compared to bare polished aluminium alloy indicating excellent anti-icing property of these coatings. Superhydrophobic coatings displayed poor anti-icing property in spite of their high water repellence. Field Emission Scanning Electron Microscope reveal that Silicone based hydrophobic coatings exhibited smooth surface whereas the superhydrophobic coatings had a rough surface consisting of microscale bumps and protrusions superimposed with nanospheres. Both surface roughness and surface energy play a major role on the ice-adhesion strength of the coatings. The 3D surface roughness profiles of the coatings also indicated the same trend of roughness. An attempt is made to correlate the observed ice-adhesion strength of different surfaces with their wettability and surface roughness. It was concluded that smooth surface with low surface energy are responsible for low ice-adhesion strength

Influence of annealing temperature on Raman and photoluminescence spectra of electron beam evaporated TiO2 thin films

Titanium dioxide (TiO(2)) thin films were deposited on fused quartz substrates by electron beam evaporation method at room temperature. The films were annealed at different temperatures in ambient air. The surface morphology/roughness at different annealing temperatures were analyzed by atomic force microscopy (AFM). The crystallinity of the film has improved with the increase of annealing temperature. The effect of annealing temperature on optical, photoluminescence and Raman spectra of TiO(2) films were investigated. The refractive index of TiO(2) films were studied by envelope method and reflectance spectra and it is observed that the refractive index of the films was high. The photoluminescence intensity corresponding to green emission was enhanced with increase of annealing temperature. The peaks in Raman spectra depicts that the TiO(2) film is of anatase phase after annealing at 300°C and higher. The films show high refractive index, good optical quality and photoluminescence characteristics suggest that possible usage in opto-electronic and optical coating applications

Effect of particle size and dopant concentration on photophysical properties of Eu3+-doped rare earth oxysulphide phosphor coatings

Europium-doped rare-earth oxysulphides (red phosphors) are often used as reference luminophore in pyrene-based pressure sensor coatings for aerodynamic applications. Different red phosphor samples were characterized for their particle size, chemical composition, photoluminescent properties and temperature sensitivity. The red phosphor samples were characterized using energy-dispersive X-ray spectroscopy (EDX) for elemental analysis and scanning electron microscopy (SEM) for morphology and particle size measurement. The particle size was in the range of 1.5–5.7�m with morphology of hexagonal or spherical shape. It was found that phosphor with higher europium content exhibited higher luminescent emission intensity. The phosphor coatings were prepared by spraying a dispersion of the material in silicone resin. Smooth coatings were obtained by using phosphor samples with smaller particle size. Upon 334nm excitation, the coatings showed characteristic luminescence 5D0→7FJ (J=0, 1, 2, 3, 4) of the Eu3+ ions. The electronic transition located at 626nm (5D0→7F2) of Eu3+ ions was stronger than the magnetic dipole transition located at 595nm (5D0→7F1). Luminescence decay curves obeyed double exponential behaviour. The phosphor samples showed temperature sensitivity of −0.012 to −0.168%/◦C in the temperature range of 25–50 ◦C

Optical absorption and emission properties of Pr3+Pr^{3+} and Er3+Er^{3+} in lithium cesium mixed alkali borate glasses

This article presents the optical absorption and emission properties of $Pr^{3+}$ and $Er^{3+}$ in mixed alkali borate glasses of the type $68B_2O_3{\cdot}xLi_2O{\cdot}(32-x)Cs_2O$ (where x=8, 12, 16, 20 and 24). The variation of Judd–Ofelt intensity parameters $(\Omega_{\lambda})$, the peak wavelength of the hypersensitive transitions, radiative transition probabilities $(A_{rad})$ and peak emission cross-sections $({\sigma}_p)$ with x in the glass matrix have been discussed in detail. The changes in position of hypersensitive transition and intensity parameters with x are correlated to the structural changes in the host matrix. The estimated radiative lifetimes $(\tau_R)$ of certain excited states of both $Pr^{3+}$ and $Er^{3+}$ in lithium cesium mixed alkali borate glasses are reported. Branching ratios $(\beta)$ and integrated absorption cross-sections $(\Sigma)$ for certain important transitions are presented. Peak stimulated emission cross-sections $(\sigma_p)$ are calculated for the observed emission peaks of $Pr^{3+}$ and $Er^{3+}$ ions in this glass matrix

Spectral studies of Sm3+Sm^{3+} and Dy3+Dy^{3+} doped lithium cesium mixed alkali borate glasses

The effect of host glass composition on the optical absorption and fluorescence spectra of $Sm^{3+}$ and $Dy^{3+}$ has been studied in mixed alkali borate glasses of the type $67B_2O_3{\cdot}xLi_2O{\cdot}(32-x)Cs_2O$ (x=8, 12, 16, 20 and 24). The Judd-Ofelt intensity parameters $(\Omega_2, \Omega_4\hspace{2mm}and\hspace{2mm}\Omega_6)$ are calculated. The radiative transition probabilities (A), radiative lifetimes $(\tau_R)$, branching ratios $(\beta)$ and integrated absorption cross sections $(\Sigma)$ are computed for certain excited states of $Sm^{3+}$ and $Dy^{3+}$ ions for different x values in the glass matrix. Stimulated emission cross sections (sp) are obtained for certain emission transitions of two ions in these mixed alkali borate glasses. These parameters are compared for different x values in the glass matrix. Variation of these parameters with x in the glass matrix has been studied