Solid Substrate Materials Research Articles

Experimental Investigation on the Wind-driven Runback Motion of Water Droplets over Solid Surfaces with Different Wettabilities

Aircraft icing is widely recognized as one of the most serious weather hazards to flight safety. Specially designed hydro-/ice-phobic coatings are currently undergoing development for aircraft icing mitigation. It was found that hydro-/icephobic coatings would delay the ice accretion iover airframe surfaces so that the impacted supercooled water droplets could be blown away by the airflow from the airframe surface before being frozen into ice. It is of fundamental importance to understand the wind-driven runback behavior of water droplets over surfaces treated with different coatings, since the corresponding knowledge would be very helpful and essential to develop more efficient anti-/de-icing systems for aircraft icing protection. With the rapid development of surface engineering, a series of specially designed surface coatings succeed in icing mitigation using airflow to remove the remained water. While various hydro-/ice-phobic coatings/surfaces have been developed in recent years, the “state-of-the-art” icephobic coatings/surfaces can be generally divided into three categories, i.e., 1). Lotus-leaf-inspired superhydrophobic surfaces (SHS) with micro-/nano-scale surface textures to achieve very high contact angles (typically > 150°); 2). Pitcherplant-inspired slippery liquid infused porous surfaces (SLIPS) with a layer of liquid lubricant (which is immiscible with water) being sandwiched between ice and solid substrate materials; and 3). Icephobic elastic materials/surfaces with deformable structures/surfaces. SHS has a water droplet contact angle (CA) larger than 150° and a sliding angle (SA) less than 10° . SHS always has a hierarchical structure which is similar to the lotus leaf, and water droplets on SHS appear as water beads which can easily roll off the surface by wind or gravity before frozen. Another strategy to reduce ice adhesion strength to a solid surface is to use a layer of liquid lubricant, which is immiscible with water, between ice and the solid surface. The use of such lubricated surfaces was investigated as early as 1960s, and has gained increasing attentions again recently with the introduction of a concept called Slippery Liquid-Infused Porous Surfaces (SLIPS). SLIPS concept is inspired by the Nepenthes pitcher plants, which have evolved highly slippery, liquidinfused micro-textured rim to capture insects. SLIPS surfaces were not only found to be able to suppress ice/frost accretion by effectively removing condensed moisture even in high humidity conditions, but also exhibit at least an order of magnitude lower ice adhesion than most SHS coatings. More recently, elastic materials/surfaces, such as Polydimethylsiloxane or PDMS in short, which would be structurally deformed/altered dynamically upon applying extra mechanical stress, have also been suggested for icing mitigation. Elastic materials display ultra-low adhesion to ice due to their low work of adhesion and liquidlike deformability, while maintaining good mechanical durability due to their solid-like rigidity. It is found that water droplets would not only be more readily rebounding away from the surface after impingement, but also be able to roll away before frozen due to the hydrophobicity of PDMS. Considering the differences in wettabilities and mechanisms of water repellency, it is necessary to have a systematic understanding of how efficient the surfaces are when the aerodynamic force is applied to remove the adhered water droplets. In the present study, a comprehensive experimental campaign was conducted to characterize the transient runback behaviors of wind-driven water droplets over the surfaces of test plates coated with different hydro-/icephobic coatings (i.e., SHS, SLIPS and PDMS). A high-resolution Particle Image Velocimetry (PIV) system was used to achieve quantitative measurements of the velocity field of the airflow around the wind-driven water droplets on the test surfaces with different wettabilities. With the detailed PIV measurements of the airflow field around the runback water droplets and the droplet profiles, the aerodynamic forces and the adhesion forces acting on the water droplets were estimated. While Fig. 1 shows the experimental setup used in the present study, Fig. 2 to Fig. 3 given some of the typical measurement results. More measurement results and comprehensive analysis and discussions will be provided in the full version of this research paper.

Substrate Materials for Biomolecular Immobilization within Electrochemical Biosensors.

Electrochemical biosensors have potential applications for agriculture, food safety, environmental monitoring, sports medicine, biomedicine, and other fields. One of the primary challenges in this field is the immobilization of biomolecular probes atop a solid substrate material with adequate stability, storage lifetime, and reproducibility. This review summarizes the current state of the art for covalent bonding of biomolecules onto solid substrate materials. Early research focused on the use of Au electrodes, with immobilization of biomolecules through ω-functionalized Au-thiol self-assembled monolayers (SAMs), but stability is usually inadequate due to the weak Au–S bond strength. Other noble substrates such as C, Pt, and Si have also been studied. While their nobility has the advantage of ensuring biocompatibility, it also has the disadvantage of making them relatively unreactive towards covalent bond formation. With the exception of Sn-doped In2O3 (indium tin oxide, ITO), most metal oxides are not electrically conductive enough for use within electrochemical biosensors. Recent research has focused on transition metal dichalcogenides (TMDs) such as MoS2 and on electrically conductive polymers such as polyaniline, polypyrrole, and polythiophene. In addition, the deposition of functionalized thin films from aryldiazonium cations has attracted significant attention as a substrate-independent method for biofunctionalization.

Phase Change Characteristics of Ultra-Thin Liquid Argon Film over different Flat Substrates at High Wall Superheat for Hydrophilic/Hydrophobic Wetting Condition: A Non-Equilibrium Molecular Dynamics Study

Non-equilibrium molecular dynamics simulations have been conducted to understand the effect of solid-liquid interfacial wettability and surface material on the phase change phenomena of the thin liquid argon film placed over flat substrate at high wall superheat. The molecular system consists of a three phase simulation domain involving solid wall, liquid argon and argon vapor. After the system is thermally equilibrated at 90K and kept in equilibrium for a while, a high wall superheat (250K that is far above the critical temperature of argon) is induced at the liquid boundary so that the liquid undergoes ultrafast heating. Both hydrophilic and hydrophobic surfaces were considered in the present study in order to observe the effect of surface wettability on phase change characteristics for three different solid substrate materials namely, Platinum (Pt), Silver (Ag) and Aluminium (Al). Results obtained in the present study are discussed in terms of transient atomic distribution inside system domain, heat flux characteristics across the solid-liquid interface together with evaporative mass flux from liquid argon. Simulation results show that, depending on the surface wetting condition, the phase change process appears to be very different (explosive/ diffusive) for all three substrate materials under consideration. Among three materials considered herein, Al is found to offer the least favourable condition for phase change process while Pt and Ag show similar heat and mass transfer characteristics for both hydrophilic and hydrophobic wetting conditions. Surface wettability effect is found to be more prominent than the effect of substrate material in thin film liquid phase change phenomena.Journal of Chemical Engineering, Vol. 29, No. 1, 2017: 49-55

Nanoparticle layer deposition for highly controlled multilayer formation based on high-coverage monolayers of nanoparticles

This paper establishes a strategy for chemical deposition of functionalized nanoparticles onto solid substrates in a layer-by-layer process based on self-limiting surface chemical reactions leading to complete monolayer formation within the multilayer system without any additional intermediate layers — nanoparticle layer deposition (NPLD). This approach is fundamentally different from previously established traditional layer-by-layer deposition techniques and is conceptually more similar to well-known atomic and molecular layer deposition processes. The NPLD approach uses efficient chemical functionalization of the solid substrate material and complementary functionalization of nanoparticles to produce a nearly 100% coverage of these nanoparticles with the use of “click chemistry”. Following this initial deposition, a second complete monolayer of nanoparticles is deposited using a copper-catalyzed “click reaction” with the azide-terminated silica nanoparticles of a different size. This layer-by-layer growth is demonstrated to produce stable covalently-bound multilayers of nearly perfect structure over macroscopic solid substrates. The formation of stable covalent bonds is confirmed spectroscopically and the stability of the multilayers produced is tested by sonication in a variety of common solvents. The 1-, 2- and 3-layer structures are interrogated by electron microscopy and atomic force microscopy and the thickness of the multilayers formed is fully consistent with that expected for highly efficient monolayer formation with each cycle of growth. This approach can be extended to include a variety of materials deposited in a predesigned sequence on different substrates with a highly conformal filling.

B-Doped Amorphous Silicon Thin Films Deposited on Flexible PET Substrate by Magnetron Sputtering

Depositing amorphous silicon doped with different elements on flexible substrates offers a large potential for the roll-to-roll processes lowering the manufacturing cost of solar cells. Unique magnetron sputtering method was adopted to deposit B-doped amorphous silicon thin film on flexible PET substrate instead of solid substrate materials like glass, metal and silicon. Effects of different substrates were investigated, as well as the processing parameters including sputtering power and working pressure. The structure and performance of the samples were characterized with SEM, XRD, surface profile meter and UV-spectrophotometer. The comparison between PET and glass shows that the alternative of PET substrate significantly improved the deposition rate. Optimal results were obtained as pressure of 0.2 Pa and RF power of 120 W, which showed the lowest transmittance as well as a minimum optical band gap, both are of great significance to photovoltaic conversion. Theoretical justification and experimental data including the feasible magnetron sputtering way, PET flexible substrate and optimized process parameters to the mass production of cheap and high performance heterojunction thin film solar cells were achieved.

Repair bond strength of dual-cured resin composite core buildup materials

The reparability of dual-cured resin composite core buildup materials using a light-cured one following one week or three months storage, prior to repair was evaluated. Two different dual-cured resin composites; Cosmecore™ DC automix and Clearfil™ DC automix core buildup materials and a light-cured nanofilled resin composite; Filtek™ Z350 XT were used. Substrate specimens were prepared (n=12/each substrate material) and stored in artificial saliva at 37°C either for one week or three months. Afterward, all specimens were ground flat, etched using Scotchbond™ phosphoric acid etchant and received Single Bond Universal adhesive system according to the manufacturers’ instructions. The light-cured nanofilled resin composite (Filtek™ Z350 XT) was used as a repair material buildup. To determine the cohesive strength of each solid substrate material, additional specimens from each core material (n=12) were prepared and stored for the same periods. Five sticks (0.8±0.01mm2) were obtained from each specimen (30 sticks/group) for microtensile bond strength (μTBS) testing. Modes of failure were also determined. Two-way ANOVA revealed a significant effect for the core materials but not for the storage periods or their interaction. After one week, dual-cured resin composite core buildup materials (Cosmecore™ DC and Clearfil™ DC) achieved significantly higher repair μTBS than the light-cured nanofilled resin composite (Filtek™ Z350 XT). However, Clearfil™ DC revealed the highest value, then Cosmecore™ DC and Filtek™ Z350 XT, following storage for 3-month. Repair strength values recovered 64–86% of the cohesive strengths of solid substrate materials. The predominant mode of failure was the mixed type. Dual-cured resin composite core buildup materials revealed acceptable repair bond strength values even after 3-month storage.

Investigating the Boiling and Transition Zones and the Rewetting Process of a Substrate Plate during Submerged Liquid Jet Cooling

A numerical model is developed to simulate the flow field, as well as the conjugate heat transfer process, during transient cooling of a flat substrate plate cooled by a single submerged impinging water jet. At wall temperatures above the liquid boiling point, the vapor formation process in different boiling regimes and the interaction of the vapor phase with the developing jet-flow field are addressed in the model. The developing submerged jet flow, the conjugate heat transfer from a flat substrate plate and the resulting temperature distribution inside the plate are simulated with respect to the transient boiling phase distribution. The influence of the liquid subcooling temperature (40 K ≤ T sub ≤ 80 K), the plate thickness (0.5 ≤ h/d ≤ 15), the conductivity of the solid substrate material (18 W/(m K) ≤ λ solid ≤ 380 W/(m K)) on the transition region positions (e.g., the Leidenfrost point), and the transition temperatures are analyzed.

Testing of Different Substrate Materials for Sulphate Reducing Reactive Barrier to Treat Acid Mine Drainage

The aim of this study was to find cheap, solid substrate material for sulphate reducing bacteria (SRB) to be used in permeable reactive barrier (PRB) and infiltration beds to treat acidic, nickel-, copper- and iron-rich mine drainage. Laboratory experiments were carried out to examine the reactivity and utilisation of different substrate materials. The materials of interest were peat, sawdust, cucumber compost and cellulose. Limestone, phosphorus and nitrogen were added to the mixture to create optimum growth conditions for SRB. Based on a batch tests, cucumber compost was chosen to be examined in larger-scale column tests. Results from the column tests were promising. Nickel (43 mg L-1), copper (24 mg L-1) and iron (95 mg L-1) were precipitated almost completely and the concentration of sulphate was decreased approximately 20 %. pH values increased from 2.7 to 8. Based on laboratory tests results it appears that cucumber compost was suitable substrate material for SRB in PRBs and infiltration beds treating AMD.

Discrete Arrays of Liquid‐Crystal‐Supported Proteolipid Monolayers as Phantom Cell Surfaces

The phospholipid bilayers of living cell membranes exist almost universally in a liquid state. This enables motion and spatial reorganization of membrane components on multiple length scales, which is an essential feature of many biological processes. There is great interest in the development of molecularly defined interfaces between synthetic materials and living cells. To this end, there is a need for solid substrate materials that can be derivatized with fluid, membrane-like interfaces. Herein, we describe array fabrication of discrete liquid-crystal areas supporting phospholipid monolayer membranes, and characterize the interactions with several different membrane surface proteins [avidin series, cholera toxin, green fluorescent protein (GFP), intercellular adhesion molecule (ICAM) and major histocompatibility complex (MHC)]. Three different linkage strategies (biotin, nickel chelating lipids complexing with histidine, and the choleratoxin binding unit (CTB) associating with G(M1) are evaluated. Additionally, experiments with live immunological T cells forming active synapses at the interface exhibit the specific nature of the surface.

Nucleation of c-BN on various substrate materials under high-pressure–high-temperature conditions

Whereas the low-pressure synthesis of diamond from the gas phase has become a well-established technology, equivalent low-pressure c-BN synthesis is not yet possible. So far, macroscopic crystalline c-BN powders can only be synthesized by high-pressure/high-temperature methods. For a successful low-pressure synthesis of c-BN, both nucleation and, subsequently, a continuous growth on appropriate solid substrate materials are required. It is shown that heteroepitaxial c-BN nucleation and growth do occur on various solid materials from Li3BN2 melts at high pressure/high temperature. Random nucleation and growth of c-BN aggregates could be observed on various substrates, such as CVD diamond and B4C (single and polycrystalline) as well as on surface-treated refractory metal substrates. On B4C and on diamond substrates, even larger individual c-BN crystals could be grown, and on some substrates, even continuous layers occurred. Due to the polycrystalline nature of the substrates, any epitaxial c-BN nucleation was difficult to prove. From the present results, we can conclude that c-BN nucleation and growth do occur on the appropriate substrate materials, such as diamond and B4C.

New designs for far-infrared beam splitters

We explore theoretically the design of multilayer beam splitters for the far-infrared that are based on coated pellicles as well as on solid substrates. The specific design criterion considered is as high a value as possible of the efficiency E = 4RT throughout the 10-140-µm spectral region. Here R and T are the reflectance and the transmittance of the beam splitter, respectively. In the numerical study the refractive indices of the substrates and coating materials varied between 1.50 and 4.00. To survey the range of designs, we make a number of simplifying assumptions, the significance of which is later investigated. Various potential manufacturing problems are considered. It is shown that the performance of the beam splitters is not sensitive to the accuracy with which the layer thicknesses can be controlled. However, it does depend strongly on the lowest available refractive index of the coating materials. The performance is particularly sensitive to the extinction coefficients of solid substrate materials. Multilayer designs presented should be useful for use in Fourier-transform spectrometers, as well as in other applications that do not require as high a spectral resolution.

Poly(vinyl alcohol) as Solid Substrate Material for Room-Temperature Phosphorimetry

A mixture of poly(vinyl alcohol) (PVA) and a small amount (5%) of cellulose (CLL) was pressed under ∼280 kg/cm 2 to form a disk of 1 mm thickness, and the prepared disk was used as a solid substrate for room-temperature phosphorescence (RTP). The addition of CLL was to reduce the fragility of the disk and enhance the permeability of sample solutions into the disk surface. The sample solution spotted PVA-CLL solid substrates were dried in a microwave oven conveniently. The efficiency of PVA-CLL solid substrates was monitored by RTP intensity of p-aminobenzoic acid (PABA) spotted on them, and the results showed that the RTP signal of PABA was largely enhanced as compared to that on the conventional paper solid substrates. Another prominent feature of the PVA-CLL solid substrate is that the RTP signal can be observed sufficiently even without a dry gas flush during the RTP measurement, while a dry gas flush is essential for the conventional substrates. A calibration curve for PABA was linear from 7.3 to 1200 pmol/spot. The results for the RTP measurements of chlorpromazine hydrochloride and tetracaine hydrochloride were also reported. The limits of detection of PABA and the other two drugs were 0.03, 0.16 and 1.26 ng, respectively.