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Surface Properties of Beech Wood after CO2 Laser Engraving
摘要： The paper deals with the properties of a beech wood surface treated by CO2 laser engraving. The studied concerns were the discoloration, changes to morphology assessed through roughness and waviness parameters, and surface wetting with standard liquids (water and diiodomethane), with the aim of determining the wood surface free energy. The results have confirmed that the studied properties of the beech wood surface varied significantly, which were affected by the laser beam power P and raster density n. With increasing P and n, the lightness L* (expressed in CIE L*a*b* color space) decreased significantly. We also observed significant variation in the color coordinates a* and b*. At 8% laser power, the roughness and waviness parameters measured parallel as well as perpendicular to the grain increased proportionally with the increasing raster density. However, 4% laser power was not associated with distinct changes. Increasing the raster density reduced beech wood surface wetting equally with water and with diiodomethane. This was reflected in the higher contact angle values. The wood surface exhibited higher hydrophobicity at 4% laser power. At this power, the increasing raster density was reflected in the decreasing surface free energy, due to its polar component decrease. At 8% laser power, the changes in surface free energy were very minor from the practical viewpoint. The results suggest a potential good adhesion between film-forming materials and wood. However, the gluing performance may be negatively affected by the high roughness attained at 8% laser power and at higher raster densities.
关键词： color,wetting,surface properties,CO2 laser,roughness,contact angle,beech wood,surface free energy
更新于2025-09-19 17:13:59
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Triphenylamine-based hole transporting materials with thiophene-derived bridges for perovskite solar cells
摘要： A triphenylamine-based compound containing benzoyl[1,2-b:4,5-b’]dithiophene (BDT) derivative (BTPA-2) has been synthesized and employed in FA0.85MA0.15PbI3 perovskite solar cells (PSCs) as the hole transporting material (HTM). The reference BTPA-1 containing thiophene bridge was also prepared for a comparative study. Compared to the thiophene unit in BTPA-1, the hexyloxy substituted BDT unit in BTPA-2 made the HOMO energy level lower. The more conjugated system with the BDT unit can improve the conductivity and hole mobility. The BTPA-1 and BTPA-2 based FA0.85MA0.15PbI3 PSCs showed the best power conversion efficiencies (PCE) of 12.76 % and 13.97 %, respectively. Larger Voc and higher Jsc for the BTPA-2 based PSC were attributed to its reduced interfacial recombination and more conjugated system compared to the BTPA-1 based PSCs. More hydrophobic property of BTAP-2 made its PSC exhibit better environmental stability than BTPA-1.
关键词： Thiophene,Perovskite solar cells,Water contact angle,Hole transporting materials,Triphenylamine
更新于2025-09-19 17:13:59
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Caries removal with Er:YAG laser followed by dentin biomodification with carbodiimide and chitosan: Wettability and surface morphology analysis
摘要： This study aimed to investigate dentin wettability and surface morphology after selective removal of carious lesion by erbium-doped yttrium aluminum garnet (Er: YAG) laser, followed by dentin biomodification with carbodiimide (EDC) and chitosan (CHI). Seventy-eight bovine dentin specimens were submitted to caries induction. Specimens were distributed according to methods of carious removal (n = 39): bur at low-speed (40,000 rpm) or Er:YAG laser (noncontact mode, 250 mJ/pulse and 4Hz). All specimens were etched with 35% phosphoric acid, and subdivided according to dentin biomodification (n = 13): Control (no biomodification), EDC or CHI. The contact angle (n = 10) between adhesive system (3M ESPE) and dentin surface was measured by a goniometer. Eighteen specimens (n = 3) were analyzed by scanning electron microscopy. Data were analyzed by two-way ANOVA and Tukey's test (α = .05). The method used to remove carious lesion did not influence the wettability of dentinal surface (p = .748). The angles produced on the remaining dentin after biomodification were influenced (p = .007). CHI promoted higher contact angles (p = .007) and EDC did not differ from the control group (p = .586). In the bur-treated group, most tubules were open, regardless of which biomodifier was used. Laser modified the organic matrix layer. CHI promoted partially closed tubules in some areas while EDC exposed dentinal tubules. Regardless of which method was used for selective removal of carious lesion, biomodification with EDC did not affect the dentin wettability, whereas CHI changed the wettability of remaining dentin. Both biomodifiers promoted a slight change on dentin morphology.
关键词： contact angle,biomaterials,SEM,caries-affected dentin,EDC
更新于2025-09-12 10:27:22
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Wettability analysis of water on metal/semiconductor phases selectively structured with femtosecond laser-induced periodic surface structures
摘要： Femtosecond (fs) laser-induced periodic surface structures (LIPSS) were selectively generated on the surface of an Ag-Si alloy consisting of a metallic and a semiconducting phase. For this purpose, the alloy was irradiated with linearly polarized fs-laser pulses (τ = 300 fs, λ = 1025 nm, frep = 100 kHz) using a laser peak fluence F = 0.30 J/cm2. Due to the different light absorption behavior of the semiconductor (Si) and the metal (Ag) phase that results in different ablation thresholds of the respective phase, pronounced LIPSS with a period of Λ ≈ 950 nm and a modulation depth of h ≈ 220 nm were generated solely on the Si phase. The alloy surface was characterized by scanning electron microscopy, optical microscopy, white light interference microscopy and atomic force microscopy before and after laser irradiation. Chemical analysis was carried out by energy dispersive X-ray spectroscopy, revealing surface oxidation of the Si phase and no laser-induced chemical modification of the Ag phase. The surface wettability of the alloy was evaluated with distilled water and compared to the single constituents of the composites. After fs-laser irradiation, the surface is characterized by a reduced hydrophilic water contact angle. Furthermore, the alloy selectively structured with LIPSS revealed a droplet shape change due to the distinctly different contact angles on the Si (θ = 5°) and the Ag (θ = 74°) phase. This phenomenon was evaluated and discussed by local contact angle analyses using a confocal laser scanning microscope and a Rhodamine B dye. In addition, it was shown that the shape change due to different contact angles of the components allowed a targeted droplet movement on a macroscopic material boundary (Ag/Si) of the alloy. Selectively structured metal/semiconductor surfaces might be of particular interest for microfluidic devices with a directional droplet movement and for fundamental research of wettability.
关键词： Contact angle,Wettability,Microfluidic devices,LIPSS,Ag-Si alloy,Femtosecond laser
更新于2025-09-12 10:27:22
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Wetting translucency of graphene on plasmonic nanohole arrays
摘要： Graphene- a carbon allotrope with atoms arranged in monolayer two-dimensional hexagonal lattice- exhibits wide range of applications in batteries, supercapacitors, solar cells, biosensing, light-emitting diodes, semi-conductors, materials composites, and coatings to name a few. Significant progress has been made to understand the electronic, mechanical, and optical characteristics of graphene. However, the wettability of graphene, which is important for surface modification and thermal/fluidic properties, is still not well understood. The level of transparency to van der Waals forces, chemical bonds, and electrostatic interactions between atoms and molecules on two sides of graphene single layer is partially known. Static contact angle between the edge of sessile drop and functionalized surface provides surface tension value based on Owens-Wendt model and is important for wettability studies. In this work, we investigate the surface energy of glass, silicon wafer, and plasmonic nano-hole arrays (Silver, Polymer and Gold) suspended with CVD grown and transferred single layer of graphene. Our results showed that the underlying substrate does affect the wettability of graphene monolayer due to van der Waal hydrocarbon, metal-carbide, and silica-carbon bonding which tends to provide deeper understanding of the wetting dynamics. This study elucidates the mechanism of wetting translucency of graphene on plasmonic nanohole arrays.
关键词： Plasmonic nanohole array,contact angle,graphene,surface energy
更新于2025-09-12 10:27:22
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Modification of ABS wetting properties by ultrashort and short pulse lasers
摘要： Wetting is an important property of solid surfaces, where the surface roughness has a meaningful influence on it. This study focuses on the wetting behavior of micro-textures fabricated on acrylonitrile butadiene styrene (ABS) thermoplastic polymer to provide it anti-fingerprint properties. The structuring process was performed by ultrashort (picosecond) and short (nanosecond) pulses based on square pillars. Wetting behavior was assessed by water and oleic acid static and dynamic (hysteresis) contact angles. Both sort of micro-textures displayed a water contact angle tailored from 90. Apparent color changes induced by laser were assessed to get information about the aesthetical appearance.
关键词： ultrashort pulses,polymers,wettability,short pulses.,laser radiation,contact angle
更新于2025-09-12 10:27:22
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Fiber laser induced self-organizing structures of 316L stainless steel surface
摘要： When the micro-nano groove structure is processed on the surface of 316L stainless steel by a fiber laser, a self-organizing structure with regular distribution appears. After optimizing the processing parameters, the self-organizing structure with excellent quality can be formed in the groove. In order to further research the properties of the self-organizing structure, the large-area self-organizing structures with different spacings are processed. It is found by the characterization that when the spacing is 50 um, the contact angle of the large-area self-organizing structure is increased by 43.1% with respect to the smooth surface, and its wetting property changes from hydrophilicity to hydrophobicity. The component and the phase composition of the self-organizing structure were found to be consistent with the composition of the original material, and it is preliminarily concluded that the self-organizing structure is formed by the splashing flow of molten liquid in the oxidizing molten pool.
关键词： self-organizing structure,fiber laser,contact angle,component,316L stainless steel
更新于2025-09-12 10:27:22
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[IEEE 2018 Iranian Conference on Electrical Engineering (ICEE) - Mashhad (2018.5.8-2018.5.10)] Electrical Engineering (ICEE), Iranian Conference on - Theoretical and Simulational Study of Electrowetting on Dielectric (EWOD) Effect
摘要： Electrowetting mechanism has been recently employed to enhance the manipulation process in biomedical engineering. In this research, we have described the Electrowetting on thermodynamic Dielectric phenomenon by using classical approach. The droplet motion has been numerically studied by finite element method. The electrowetting mechanism has been investigated by solving the coupled electrostatic and droplet physics. Simulation results revealed 50 V threshold voltage for the system. The droplet velocity increases linearly by increasing the applied electric field and the maximum velocity of 0.04 mm/s has been achieved for 250 V excitation voltage. Based on the results, for the above 250 V there is no velocity increases.
关键词： Digital microfluidics,Electrowetting,Contact angle,Electrowetting on dielectric (EWOD),Surface tension,hydrophobic layer
更新于2025-09-11 14:15:04
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Ultrapure Films of Polythiophene Derivatives are Born on a Substrate by Liquid Flow
摘要： Almost all ?lms of conjugated polymers are composed of mixtures of two di?erent structures called H- or J-aggregates, which are side-by-side and head-to-tail structures, respectively, between polymer chains. The mixture of H- and J-aggregates is responsible for the mixed optical and/or electrical properties of a conjugated polymer ?lm. If a highly puri?ed conjugated polymer ?lm composed of only a single species of aggregate was obtained, its properties would enable the realization of new soft electronics, such as ?exible solar cells, wearable sensors, and arti?cial skin. However, there have been no reports on a method to prepare such a highly puri?ed polymer ?lm so far. Here, we show a facile method to obtain an ultrapure 99.8% H-aggregate polymer ?lm by dropping a solution of poly(3-hexylthiophene) (P3HT) on a substrate at room temperature, inspired by the co?ee-ring e?ect.According to contact angle measurements, photoluminescence and Raman spectroscopy, and X-ray di?raction, a critical step for achieving the ultrapure H-aggregate ?lm was a two-step drying process of the polymer solution droplet on a speci?c substrate. The pinning of the droplet caused this drying process and yielded a ?ow-induced extension of the P3HT chains on the substrate, followed by the formation of ultrapure H-aggregates. We also found a 6-fold enhancement in carrier density using the ultrapure (99.8%) H-aggregate P3HT ?lm. Furthermore, ?ve conjugated polymers of polythiophene derivatives, used as state-of-the-art polymer solar cells, revealed the same trends to ultrapure H-aggregates, whose structure enhances performance of solar cell. The proposed method could provide a new approach to make solution-processable ?lms for next-generation soft and ?exible electronics.
关键词： π-conjugated polymer,contact angle,aggregate,soft electronics,co?ee ring
更新于2025-09-10 09:29:36
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Numerical investigation of electrowetting-based droplet splitting in closed digital microfluidic system: Dynamics, mode, and satellite droplet
摘要： In this paper, the splitting of microdroplet in a closed electrowetting-based digital microfluidic system has been studied via a numerical model. The governing equations for the fluid flow are solved by a finite volume formulation with a two-step projection method on a fixed computational domain. The free surface of the liquid is tracked by a coupled level-set and volume-of-fluid method, with the surface tension at the free surface computed by continuum surface force scheme. Contact angle hysteresis is implemented as an essential component of electrowetting modeling, and a simplified viscous force model is adopted to evaluate the viscous stress based on the Hele-Shaw model. Excellent agreement has been achieved between the numerical and published experimental results. A parametric study has been performed in which the effects of viscous stress, channel height, static contact angles, contact angle hysteresis, and electrode size on the splitting process have been analyzed. Three distinct splitting modes, which are “splitting with satellite droplet,” “normal splitting,” and “splitting cessation,” have been discussed. Based on the competition between the curvature in the z-direction (κz) and that on the x-y plane (κxy), the physical mechanism that separates the splitting into these three modes has been revealed. More importantly, a dimensionless parameter ?κ has been proposed, which can be used for (a) determining the splitting mode and (b) estimating satellite droplet volume for electrowetting-induced droplet splitting process.
关键词： contact angle hysteresis,digital microfluidic system,droplet splitting,electrowetting,numerical model
更新于2025-09-10 09:29:36