Dual-layer Thin Film Research Articles

Interlayered Interface of a Thin Film Composite Janus Membrane for Sieving Volatile Substances in Membrane Distillation

Hypersaline wastewater treatment using membrane distillation (MD) has gained significant attention due to its ability to completely reject nonvolatile substances. However, a critical limitation of current MD membranes is their inability to intercept volatile substances owing to their large membrane pores. Additionally, the strong interaction between volatile substances and MD membranes underwater tends to cause membrane wetting. To overcome these challenges, we developed a dual-layer thin film composite (TFC) Janus membrane through electrospinning and sequential interfacial polymerization of a polyamide (PA) layer and cross-linking a polyvinyl alcohol/polyacrylic acid (PP) layer. The resulting Janus membrane exhibited high flux (>27 L m-2 h-1), salt rejection of ∼100%, phenol rejection of ∼90%, and excellent resistance to wetting and fouling. The interlayered interface between the PA and PP layer allowed the sieve of volatile substances by limiting their dissolution-diffusion, with the increasing hydrogen bond network formation preventing their transport. In contrast, small water molecules with powerful dynamics were permeable through the TFC membrane. Both experimental and molecular dynamics simulation results elucidated the sieving mechanism. Our findings demonstrate that this type of TFC Janus membrane can serve as a novel strategy to design next-generation MD membranes against volatile and non-volatile contaminants, which can have significant implications in the treatment of complex hypersaline wastewater.

Investigation Into the Performance of a Dual-Layer Thin-Film Organic Coating During Accelerated Low-Temperature Offshore Testing

The application of thin-film coatings is a method to protect armatures, accessories, and control elements on offshore facilities against corrosion and mechanical damages. The performance of a dual-layer thin-film (30 μm) coating system under simulated Arctic offshore exposure was investigated. The coating system consisted of polyamide-based primer and molybdenum-disulfide (MoS2)/polytetrafluoroethylene (PTFE)—modified topcoat. The investigations involved the following tests: accelerated corrosion protection/aging tests, coating adhesion tests, scanning electron microscopy (SEM)/energy-dispersive X-ray (EDX) inspections, static contact angle measurements, specific surface energy measurements, hoarfrost accretion, and abrasion resistance tests. The test conditions were adapted to Arctic offshore conditions. Effects of accelerated offshore aging on surface morphology, surface chemistry, and hoarfrost accretion were also investigated.

H2 response characteristics for sol–gel-derived WO3-SnO2 dual-layer thin films

This paper describes the deposition of SnO2 and WO3 thin films and WO3-SnO2 dual-layer thin films using the sol-gel process. The microstructure and morphology of these three thin films were analyzed with FE-SEM and X-ray diffraction. The H2 response characteristics, including response magnitude, time and transients of the three samples, were investigated at different operation temperatures and H2 gas concentrations. Although the maximum response magnitude of 29.31 towards 1000ppmH2 gas appeared at 225°C，the WO3-SnO2 dual-layer films still had a response magnitude of 24.23 at 175°C, which is much higher than those of the SnO2 (4.19) and WO3 (6.73) thin films. The linear response magnitude profile of the WO3-SnO2 dual-layer thin films toward H2 gas concentration was obtained. The mechanism of the enhanced gas response characteristics was explained by the band bending theory.

Nanotextured Polymer Substrate for Flexible and Mechanically Robust Metal Electrodes by Nanoimprint Lithography.

Metal thin film electrodes on flexible polymer substrates are inherently unstable against humidity and mechanical stresses because of their poor adhesion properties. We introduce a novel approach for improving the adhesion characteristics of metal-polymer interface based on the nanostructuring of the polymer substrate by using nanoimprint lithography. The adhesion characteristics of metal-polymer interface were measured by accelerated test, cyclic bending test and double cantilever beam (DCB) test. The interface of Au/Ti dual layer thin film and nanoimprinted PMMA substrate shows over 2.03 and 1.95 times higher adhesion energy (G(c)) than that of Au/Ti dual layer thin film and plane PMMA substrate in air and wet environments, respectively. The adhesion energy between metal thin film and polymer substrate was dramatically improved by the increased surface roughness and mechanical interlocking effect of numerous nanoscale anchors at the edges of nanoimprinted surface, which was verified by both experiment and numerical analysis.

Dual-layer ultrathin film optics: I. Theory and analysis

This paper revisits dual-layer ultrathin film optics, which can be used for functional graded refractive index thin film stack. We present the detailed derivation including s-polarized and p-polarized light under arbitrary incidence angle showing the equivalence between the dual-layer ultrathin films and a negative birefringent thin film and also the approximations made during the derivation. Analysis of the approximations shows the influence of thickness of dual-layer thin films, the incidence angle and desired refractive index of the birefringent film. Numerical comparison between the titanium dioxide/aluminum oxide based dual-layer ultrathin film stack and the equivalent birefringent film verifies the theoretical analysis. The detailed theoretical study and numerical comparison provide a physical insight and design guidelines for dual-layer ultrathin film based optical devices.

Influence of Annealing Temperatures on the Properties of Dual-Layer W-TiO<sub>2</sub> Thin Films

W-TiO2 (W, tungsten) dual-layer thin films are deposited by RF magnetron sputtering onto glass substrates and annealed at 150oC~400oC for 4hrs. The crystal structure, morphology, and trans- mittance of annealed W-TiO2 dual-layer thin films are investigated by X-ray diffraction, FESEM, and UV-Vis spectrometer, respectively. The annealing temperatures have large effect on the properties of W-TiO2 dual-layer thin films. The band gap energy values of W-TiO2 dual-layer thin films are evaluated from (h)1/2 versus energy plots. The energy gap for un-annealed W-TiO2 dual-layer thin film is 3.16 eV. As the annealing temperature increases from 150oC to 400oC, the energy gap decreases from 3.16 eV to 3.10 eV.

Dual-Layer Light Emitting Devices Based on Polythiophene Derivative

Electroluminescence (EL) and photoluminescence (PL) from dual-layer thin films made of poly(3-(2-benzotriazolo) ethylthiophene) (PBET) and Poly (2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV) have been investigated. In these devices, MEH-PPV was selected as a hole-transporting material based on the consideration of its electronic structures. The energy level of the highest occupied molecular orbital (HOMO) of MEH-PPV (-5.0 eV) lies between that of ITO (-4.8 eV) and that of PBET (-5.5 eV). We have found that the EL signal was almost exclusively generated within the emitting layer. The efficiency and the turn-on voltage measured from dual-layer device were improved 1.2 × 10−3 and 2.4 V, respectively.