Contact Angle Of Substrate Research Articles

Precise in-situ fabrication of perovskite single crystal arrays via cosolvent based electrohydrodynamic printing

Single crystal (SC) perovskites exhibit superior stability and optoelectronic performance compared to polycrystalline ones, offering significant potential for high-performance and low-cost photovoltaic/optoelectronic applications. However, conventional SC growth processes often require intricate cutting or transferring of SC in the manufacturing of optoelectronic devices. High-resolution, in-situ, and scalable fabrication of perovskite SC arrays remain challenging. In this work, we propose a method for in-situ deposition of cosolvent based perovskite precursor solutions using electrohydrodynamic (EHD) printing technology. The addition of a cosolvent (which exhibits good chemical compatibility with the precursor and the main solvent, accompanied by lower solubility and vapor pressure) to the mixed solution promotes early-stage supersaturation and nucleation in the solution, enabling precise control over crystal morphology, size, and positioning through in-situ EHD printing. The effect of different cosolvent ratios on SC growth and the inhibition of parasitic crystallization by altering the contact angle of substrate were investigated. Finally, the parameters for precise control of the EHD printing process were investigated, enabling the growth of SC arrays ranging from 1 to 35 μm in size. This strategy offers a direct patterning approach for SC perovskite preparation without complex temperature control or multi-step operation. The printed patterns exhibit high resolution and excellent uniformity, offering significant potential for manufacturing SC-based perovskite optoelectronic devices with precise size and positioning control.

Enhancing polytetrafluoroethylene (PTFE) coated film for food processing: Unveiling surface transformations through oxygenated plasma treatment and parameter optimization using response surface methodology.

Spray drying fruit juice powders poses challenges because sugars and organic acids with low molecular weight and a low glass transition temperature inherently cause stickiness. This study employed a hydrophobic polytetrafluoroethylene (PTFE) film to mimic the surface of the drying chamber wall. The Central Composite Design (CCD) using response surface methodology investigated the impact of power (X1, Watt) and the duration of oxygenated plasma treatment (X2, minutes) on substrate contact angle (°), reflecting surface hydrophobicity. To validate the approach, Morinda citrofolia (MC) juice, augmented with maltodextrins as drying agents, underwent spray drying on the improved PTFE-coated surface. The spray drying process for MC juice was performed at inlet air temperatures of 120, 140, and 160°C, along with Noni juice-to-maltodextrin solids ratios of 4.00, 1.00, and 0.25. The PTFE-coated borosilicate substrate, prepared at a radio frequency (RF) power of 90W for 15 minutes of treatment time, exhibited a porous and spongy microstructure, correlating with superior contact angle performance (171°) compared to untreated borosilicate glass. Optimization data indicated that the PTFE film attained an optimum contact angle of 146.0° with a specific combination of plasma RF operating power (X1 = 74 W) and treatment duration (X2 = 10.0 minutes). RAMAN spectroscopy indicated a structural analysis with an ID/IG ratio of 0.2, while Brunauer-Emmett-Teller (BET) surface area analysis suggested an average particle size of less than 100 nm for all coated films. The process significantly improved the powder's hygroscopicity, resistance to caking, and moisture content of maltodextrin-MC juice. Therefore, the discovery of this modification, which applies oxygen plasma treatment to PTFE-coated substrates, effectively enhances surface hydrophobicity, contact angle, porosity, roughness, and ultimately improves the efficacy and recovery of the spray drying process.

Evaluation and Optimization of Particle Removal with a Resist Peeling Method

The removal of particle contamination is key to maximize yield. Some common particle removal techniques are not relevant anymore when complex and fragile structures are present on the surface. This led to the development of new cleaning processes based on innovative concepts to improve particle removal efficiency without any pattern damage. Some of these processes rely on a resist film lift off. One of these particle removal processes is studied in this paper. The process consists in some resist spin-coating followed by a diluted ammonia dispense to remove this film, which results in particle removal. This specific resist film is made of two immiscible organic polymers. A study was conducted to understand how the organization of these two polymers in the film is key for the film lift-off and the cleaning efficiency. This organization was shown to depend on the substrate contact angle and the resist formulation. A surface preparation is required on hydrophobic surface to reduce their water contact angle and ensure the efficiency of the process. As a result, compared to a high velocity aerosol cleaning technique, this resist peeling process requires multiple steps and a significant process time. A Particle Removal Efficiency study was then performed on blanket wafers to determine and understand how the different process parameters impacted on the cleaning efficiency. It led to the optimization of this process efficiency on blanket wafers. A comparison between an optimized process and a high velocity aerosol cleaning technique underlined the potential of such a process. Compared to high velocity aerosol cleaning, it demonstrated higher efficiency on blanket wafers, without causing any pattern damage on patterned wafers. These results lead to promising perspectives for using this process in the cleaning of fragile structure or targeting small particles with high adhesion.

Computational fluid dynamics simulations of silicon μ-structure formation during excimer laser modification of silicon-nanoparticle layers

The laser modification of silicon-nanoparticle layers with a nanosecond pulsed excimer laser leads to the self-organized formation of crystalline, μ-cone-shaped silicon structures with good electronic properties, which have allowed the demonstration of their potential for printed flexible electronics. With the current nanosecond laser process, silicon exhibits only short melting times, resulting in a method-defined substrate contact angle, instead of this parameter being defined by the substrate surface energy as expected for equilibrium conditions. This substrate material-independent non-equilibrium contact angle of the silicon melt was experimentally determined in this study to be Θ = 68 ± 10°. To gain deeper insight into the process of the sequential melting and the formation of the silicon μ-cone structures during laser modification, a two-dimensional computational fluid dynamics simulation was performed in COMSOL Multiphysics® solving the Navier–Stokes equation for incompressible fluids. The simulation uses an effective medium approach by applying the conservative level set method to describe the porous silicon-nanoparticle layer. Its sequential melting during the pulsed laser modification is modeled using a newly developed simulation methodology, which uses a time- and depth-dependent dynamic viscosity of the molten silicon. The simulation was carried out for different laser energy densities and verified using scanning electron microscopy images of corresponding laser-modified samples. The simulation results agree well with the experiment and were subsequently used to optimize the laser process.

Coalescence dynamics of droplets collision on substrates with different contact angles

Droplet collision coalescence is widely encountered in the petroleum industry, chemical industry, and agricultural applications. In this study, the dynamic behavior of the coalescence process of a free-falling droplet impacting a sessile droplet on substrates with different wettabilities is investigated via high-speed photography. The influences of the substrate contact angle (α) and the Weber number (We) of the droplet collision were analyzed. Based on the experiments, the process of droplet collision coalescence was divided into four stages: coalescence, spreading, retraction, and oscillation. The maximum spreading diameters, maximum jet heights, spreading velocities, and retraction velocities of droplets with different values of the substrate contact angle and We were obtained. The dynamic mechanism of different collision coalescence stages was revealed by the interconversion of inertial forces, surface tension, and wall adhesion forces. The relationship between the dimensionless spreading coefficient and the dimensionless time was established for different values of the collision We and contact angle α based on the experimental results. The effects of We and α on the coalescence process of the droplets were obtained by analysis of the energy conversion.

Study on Adhesion Force of Graphene under Cylinder–Plane Contact

There are many cylinder–plane contacts in microaccelerators, microgyroscopes, and RF switches. Adhesion is one of the main factors affecting the manufacture and use of these micro–nano devices, but its research is insufficient. Graphene is expected to be used in these fields due to its excellent electrical and mechanical properties. Therefore, it is significant to research the adhesion force of graphene under cylinder–plane. Firstly, the meniscus formation process was introduced using the variable-water-contact-angle method. Secondly, the adhesion force of the graphene surface was measured with a cylindrical atomic-force-microscope probe. Finally, the contact area was considered as a number of nanoscale cylinders in contact with the plane, and the adhesion force of the cylinder–plane model was obtained. The results showed that there was a maximum adhesion force at a relative humidity of 65%. The adhesion force was evidently not time-dependent when the relative humidity was below 45%, because the meniscus cannot be formed on the graphene surface at low relative humidity. While the graphene contact surface formed a meniscus for higher relative humidity, and the adhesion force-versus-time curves first increased and then decreased to stability. Moreover, the relationship between adhesion force and substrate contact angle, roughness, relative humidity, and dwell time was established, and the number of cylinders was determined. The error between the modified theoretical model and the experimental values was only 6%.

Effects of Numerical Schemes of Contact Angle on Simulating Condensation Heat Transfer in a Subcooled Microcavity by Pseudopotential Lattice Boltzmann Model

Various numerical schemes of contact angle are widely used in pseudopotential lattice Boltzmann model to simulate substrate contact angle in condensation. In this study, effects of numerical schemes of contact angle on condensation nucleation and heat transfer simulation are clarified for the first time. The three numerical schemes are pseudopotential-based contact angle scheme, pseudopotential-based contact angle scheme with a ghost fluid layer constructed on the substrate with weighted average density of surrounding fluid nodes, and the geometric formulation scheme. It is found that the subcooling condition destabilizes algorithm of pseudopotential-based contact angle scheme. However, with a ghost fluid layer constructed on the substrate or using geometric formulation scheme, the algorithm becomes stable. The subcooling condition also decreases the simulated contact angle magnitude compared with that under an isothermal condition. The fluid density variation near a microcavity wall simulated by pseudopotential-based contact angle scheme plays the role of the condensation nucleus and triggers “condensation nucleation”. However, with a ghost fluid layer constructed on the substrate or using geometric formulation scheme, the simulated fluid density distribution near the wall is uniform so that no condensation nucleus appears in the microcavity. Thus, “condensation nucleation” cannot occur spontaneously in the microcavity unless a thin liquid film is initialized as a nucleus in the microcavity. The heat flux at the microcavity wall is unphysical during the “condensation nucleation” process, but it becomes reasonable with a liquid film formed in the microcavity. As a whole, it is recommended to use pseudopotential-based contact angle scheme with a ghost fluid layer constructed on the substrate or use the geometric formulation scheme to simulate condensation under subcooling conditions. This study provides guidelines for choosing the desirable numerical schemes of contact angle in condensation simulation by pseudopotential lattice Boltzmann model so that more efficient strategies for condensation heat transfer enhancement can be obtained from numerical simulations.

Dynamic behavior of compound droplets with millimeter-sized particles impacting substrates with different wettabilities

The dynamic behavior of compound droplets, which are made up of a millimeter-sized particle and distilled water, impacting substrates of different wettabilities is investigated via high-speed photography. The effects of the size of the particle within the compound droplet, substrate contact angle, and impact height on the deformation of the droplets and the characteristics of the impact are analyzed. It is found that the collisions of compound droplets with substrates can be classified into four categories based on the observed experimental phenomena that occur during the impact. These categories are referred to as adhesion collision, rebound collision, daughter-droplet collision (or partial rebound collision), and breakup collision. We consider both the impact of water droplets and compound droplets (with one of two different-sized particles) on substrates of different wettabilities. The effects of inertia, surface tension, and adhesion between the substrate and the liquid droplet, and adhesion between the particle and the liquid droplet are considered to explain the different collision phenomena of compound droplets and reveal the evolution mechanism of the droplet morphologies in the experiments. Furthermore, the effects of the height from which the droplet is released and the contact angle of the substrate (i.e., its wettability) on the maximum spreading diameter and maximum jet height of the droplet are presented quantitatively. The effect of the size of the particle within the compound droplet and the substrate contact angle on the dynamic behavior of the compound droplet subject to impact with the substrate is also described.

Theoretical Modelling of Droplet Extension on Hydrophobic Surfaces

In this work, droplet impact dynamics on hydrophobic surfaces under different wettability and impact conditions are examined numerically. Multi-phase finite volume simulations are carried out by employing volume-of-fluid scheme and are validated against experimental results. Numerous droplet impact experiments are performed by varying Weber number, Reynolds number and substrate contact angle. Sticking, bouncing and splitting regimes are identified. It is observed that, for the same Reynolds number, the droplet attaches, rebounds or fragments depending on the Weber number. A semi-analytical representation using a single mass-spring-dashpot model is employed for the prediction of droplet height evolution during spreading and retraction. The spring and damping coefficients required for the model are estimated from the empirical correlations for contact time and restitution coefficients obtained from the simulations. Even though the Reynolds number is found to influence the coefficient of restitution significantly, it is found to have negligible influence on contact time. The theoretical forecasting exhibited good agreement with simulated results and it gives a significant reduction in computational time compared to the conventional full-field continuum simulations.

Plasma-Sprayed Hydroxyapatite-Strontium Coating for Improved Corrosion Resistance and Surface Properties of Biodegradable AZ31 Mg Alloy for Biomedical Applications

Magnesium and its alloys have been introduced as innovative orthopedic implants due to their potential in serving lightweight, bio-active, degradable, and biocompatible properties. Mg and its alloys corrode rapidly in a biological environment and result in losing mechanical properties. However, to enhance corrosion resistance and mechanical properties, Mg alloy was plasma-sprayed with pure hydroxyapatite (HA) and HA-reinforced with strontium (Sr) powder at three levels (4, 8, and 12 wt.%). Surface parameters such as microhardness, surface roughness, and wettability were examined. The electrochemical technique was used to study the corrosion behavior in Ringer’s solution. The outcomes confirmed that with the rise in Sr content in pure HA coatings, the surface properties as well as the corrosion resistance improved significantly. The contact angle of substrates under examination exhibits hydrophilic nature. Collectively, the findings of this study signify HA/Sr reinforced coatings are a promising approach to improve surface properties and corrosion behavior of Mg alloys for future bone implant applications.

Nanoparticles deposition patterns in evaporating nanofluid droplets on smooth heated hydrophilic substrates: A 2D immersed boundary-lattice Boltzmann simulation

Nanoparticles deposition dynamics and deposition patterns in evaporating nanofluid droplets on a smooth hydrophilic heated substrate in a vapor environment (0.9Tc) under zero gravity are investigated numerically by a 2D immersed boundary-lattice Boltzmann method in combination of the non-isothermal Gong-Cheng liquid-vapor phase change model. The Marangoni flow along droplet interface is found to be the dominated transportation mechanism of nanoparticles inside an evaporating nanofluid droplet when droplet contact line is freely moving. It is demonstrated that the pinning of the triple phase contact line on the substrate having a small contact angle (θ=51°) is a required condition for a ring-like deposition pattern after a nanofluid droplet evaporation. On the other hand, on a substrate with a larger contact angle (θ=74°) where the triple contact line is not pinned, the upward Marangoni flow along droplet interface has a greater strength to resist nanoparticles moving toward the edge of the heated substrate, which result in bump-like deposition patterns after a nanofluid droplet evaporation. A regime map, showing effects of substrate contact angle and substrate temperature on nanoparticle deposition patterns after droplet evaporation, is presented. It is shown that the ring-like deposition pattern occurs when the triple line is strongly pinned (at small contact angle) and the Marangoni flow is weak (small contact angle and low substrate temperature). The bump deposition pattern occurs when the droplet contact line is not pinned (at high contact angle) and the Marangoni flow is strong (large contact angle and high temperature).

Investigation of surface properties and corrosion behavior of plasma sprayed HA/ZnO coatings prepared on AZ31 Mg alloy

Magnesium and its alloys have been introduced as innovative orthopedic implants due to their potential in serving lightweight, bio-active, degradable, and biocompatible properties. Mg and its alloys corrode rapidly in a biological environment and result in losing mechanical properties. However, to enhance corrosion resistance and mechanical properties, Mg alloy was plasma-sprayed with pure hydroxyapatite (HA) and HA reinforced Zinc Oxide (ZnO) powder at three levels (4, 8, and 12 wt%). Surface parameters such as microhardness, surface roughness, and wettability were examined. The electrochemical technique was used to study the corrosion behavior in Ringer's solution. The outcomes confirmed that with the rise in ZnO content in pure HA coatings, the surface properties as well as the corrosion resistance improved significantly. The contact angle of substrates under examination exhibits hydrophilic nature. Collectively, the findings of this study signify HA/ZnO reinforced coatings are a promising approach to improve surface properties and corrosion behavior of Mg alloys for future bone implant applications.

Electrowetting-induced droplet jumping over topographically structured surfaces

We analyze the process of electrowetting-induced jumping of droplets away from a substrate with a geometric heterogeneity in the form of a cone and compare the results with those of a flat substrate in different wettabilities and hydrophobicities. Our results reveal that the droplet dynamics can be enhanced through applying a topographic heterogeneity. However, increasing the height of the cones does not always provide a better condition for the jumping and there is an optimum value for the height of the cones. The enhancement is due to the fact that more liquid flowing affects the pressure gradient within the droplet leading to a higher jumping velocity. It is shown that for the flat surface most of the kinetic energy can be converted into the oscillations of the droplet during retraction and would not contribute to the droplet jumping. The substrate contact angle has a significant effect on the jumping height of the droplet. As the contact angle increases, the maximum value of jumping height increases. Also, for the heterogeneous substrate, the surface energy decreases faster. By drawing a diagram, we specify regions that a droplet as a function of the substrate contact angle and the height of the cone at a constant Ohnesorge number is separated from the substrate. The results indicate that by reducing Ohnesorge number, the separation of the droplet occurs at smaller equilibrium contact angles. When the height of the cones becomes larger than the optimum value, the pinning of the droplet in the cone region gradually dominate and the energy barrier for the separation increases and a more hydrophobic substrate for the separation is required. The effect of Ohnesorge number on the optimum value has been discussed.

The plasma pretreatment influence on corrosion behavior of Ion Vapor Deposition (IVD) of aluminum coating

PurposeThe purpose of this study is to investigate the effect of plasma pretreatment on the corrosion and adhesion behavior of Al coating deposited on iron steel by ion vapor deposition (IVD).Design/methodology/approachAr plasma sputtering was carried out for 0, 5, 10 and 15 min, and then IVD Al coating was performed. Surface free energy measurements were conducted on the plasma-sputtered surfaces. Cross-sectional observations were carried out on the coating/substrate interface by using scanning electron microscopy. Corrosion resistance of the deposited films was characterized using potentiodynamic polarization curve test and electrochemical impedance spectroscopy (EIS).FindingsResults demonstrated that surface free energy values were increased by increasing the sputtering time before coating process. The corrosion current density of the IVD Al coating deposited after 15 min Ar plasma pretreatment is three orders of magnitude lower than that of steel ST37 substrate. The EIS tests confirm the excellent anticorrosive properties of the Al-coated specimens.Originality/valueWith the increase in the plasma pretreatment time, coating adhesion would ameliorate because of the presence of plasma, which makes substrates a better place for Al ions to set and prevent any gap between coatings and substrates. This fact can be attributed to an increase in the surface free energy and reduction of contact angle of substrate exposed to plasma pre-treatment.

Microstructure control of macroscopic graphene paper by electrospray deposition and its effect on thermal and electrical conductivities

Macroscopic graphene paper is fabricated by an electrospray deposition approach, and the microstructure can be controlled from highly porous to highly compact geometries by varying deposition parameters including graphene colloid concentration and deposition rate. Free-standing graphene films can be separated from substrates via a simple water exfoliation method in which the surface properties of graphene films and substrates control film exfoliation. Specifically, water exfoliation can be achieved when the contact angle of substrates is 64° or below. Thermal and electrical conductivities of the macroscopic graphene paper upon thermal annealing are measured, enabling the establishment of the process-microstructure-property correlation beneficial for further development and property manipulation of graphene-based materials.

Unravelling Electrostatic Actuation on Inclined and Humped Surfaces: Effect of Substrate Contact Angle

Application of external electric field has become a well-established technique to achieve dynamic wetting over a flat surface on which the drop is resting. However, an increase in electric field can overcome the gravitational pull and the drop can climb the substrate against contact-line friction. The present study investigates droplet up-climbing for different wettability regimes using the energy minimization method. We proposed a capacitive network around an up-climbing drop for evaluation of the resultant force on it. This method captures the influence of the orientation and geometry of the surfaces on the droplet motion. Motive forces for dynamic wetting and velocity over inclined surfaces (15–75°) are predicted. Furthermore, over a humped surface, a voltage map is obtained for steady droplet motion. Variation of the voltage map for different equilibrium contact angles of the hump is also presented. A one-dimensional momentum balance equation is used to predict the temporal location of the drop and th...

The dynamic spreading of nanofluids on solid surfaces – Role of the nanofilm structural disjoining pressure

Nanofluids comprising nanoparticle suspensions in liquids have significant industrial applications. Prior work performed in our laboratory on the spreading of an aqueous film containing nanoparticles displacing an oil droplet has clearly revealed that the structural disjoining pressure arises due to the layering of the nanoparticles normal to the confining plane of the film with the wedge profile. The pressure drives the nanofluid in the wedge film and the nanofluid spreads. We observed two distinct contact lines: the inner contact line, where the structural disjoining pressure dominates the Laplace capillary pressure, and the outer contact line, given by the Laplace equation prediction extrapolated to the solid substrate where the structural disjoining pressure contribution is negligible. We report here our results of the effects of several parameters, such as the nanoparticle concentration, liquid salinity, temperature, and the substrate contact angle, on the motion of the two contact lines and their effects on the detachment of the oil droplet. We also studied the equilibrated and non-equilibrated oil/nanofluid phases, the time of adhesion of the oil droplet on the solid substrate and the drying time of the substrate. We employed the frictional model to predict the outer contact line velocity and our previous theoretical model (based on the structural disjoining pressure) to predict the inner contact line velocity. The theoretical predictions agreed quite well with the experimentally measured values of the velocities.Our experimental results showed that the motion of the inner contact line was accelerated by the increase in the nanoparticle concentration, temperature, and hydrophilicity of the substrate for the pre-equilibrated oil/nanofluid phases, which resulted in the faster detachment of the oil droplet. The speed of the two contact lines decreased upon the increase in the drying time of the substrate and the oil adhesion time on the substrate.The present results provide new insights into the complex spreading behavior of nanofluids on solid substrates.

Enhanced light collection in fluorescence microscopy using self-assembled micro-reflectors.

In fluorescence microscopy, the signal-to-noise ratio (SNR) of the optical system is directly linked to the numerical aperture (NA) of the microscope objective, which creates detection challenges for low-NA, wide-field and high-throughput imaging systems. Here we demonstrate a method to increase the light collection efficiency from micron-scale fluorescent objects using self-assembled vapor-condensed polyethylene glycol droplets, which act as micro-reflectors for fluorescent light. Around each fluorescent particle, a liquid meniscus is formed that increases the excitation efficiency and redirects part of the laterally-emitted fluorescent light towards the detector due to internal reflections at the liquid-air interface of the meniscus. The three-dimensional shape of this micro-reflector can be tuned as a function of time, vapor temperature, and substrate contact angle, providing us optimized SNR performance for fluorescent detection. Based on these self-assembled micro-reflectors, we experimentally demonstrate ~2.5-3 fold enhancement of the fluorescent signal from 2-10 μm sized particles. A theoretical explanation of the formation rate and shapes of these micro-reflectors is presented, along with a ray tracing model of their optical performance. This method can be used as a sample preparation technique for consumer electronics-based microscopy and sensing tools, thus increasing the sensitivity of low-NA systems that image fluorescent micro-objects.

Influence of substrate nature and β-lactoglobulin on cleanability after soiling by suspension spraying and drying

Glass and stainless steel (StSteel, AISI304-2R), previously cleaned with ethanol (-Eth) or with ethanol and UV–Ozone treatment (-UVO), were soiled with quartz suspensions in water and in a β-lactoglobulin (β-LGB) solution, and dried. The cleanability (ease of quartz particle detachment) in water was evaluated using a radial-flow cell. The soiling suspension containing β-LGB was used as such or after heating for 4h at 75°C, which provoked coagulation of about 75% of β-LGB. The substrate–solution interfaces were characterized by X-ray photoelectron spectroscopy (XPS) analysis of conditioned substrates and by contact angle measurements. The substrate surfaces are covered by a layer of organic contaminants which are not removed by pre-cleaning or are adsorbed from the surroundings. The presence of β-LGB in the soiling suspension leads to protein adsorption, but a significant amount of contaminants remains at the surface.For three of the substrates tested (Glass-Eth, Glass-UVO, StSteel-UVO) the increase of cleanability when the soiling suspension contained β-LGB may be explained by lower capillary forces acting upon drying. Capillary forces are proportional to the liquid surface tension and depend in a less important way on substrate contact angle. However the order of cleanability observed for the substrates soiled with a suspension of quartz particles in water (Glass-Eth≅Glass-UVO<StSteel-UVO<StSteel-Eth) and the influence of β-LGB on the cleanability of StSteel-Eth may not be explained only by computed capillary forces. The contact angle may exert a direct influence on droplet spreading and particle–substrate contact. The organic contaminants present on the surfaces, which are often neglected by supposing model solid surfaces, may have a significant influence on cleanability through physico-chemical processes which remain to be appreciated.

Nanofluids alter the surface wettability of solids.

We report the results of our studies on the changes in the contact angle and interfacial tension using a nanofluid composed of silica nanoparticles dispersed in water on three different solid substrates: gold (partially hydrophobic), glass (hydrophilic), and a silicon wafer (hydrophilic). We used both the goniometric method and drop-shape analysis to make the measurements. On the basis of the results of the drop-shape analysis using the Laplace equation, we evaluated the contributions of the interfacial tension change to the equilibrium contact angle and the presence of nanoparticles near the solid substrate, thereby elucidating the change in the wettability of the solid substrate. We found that the nanoparticles decrease the contact angle of the substrate with the increase in the nanoparticle concentration. To rationalize our experimental observations on the decrease in the contact angle of the solid substrate in the presence of nanoparticles, we calculated the surface volume fraction of the nanoparticles in the layer near the solid substrate using the particle layering model (based on the nanoparticles' excluded volume effect). We found that the volume fraction of the nanoparticles in the layer close to the substrate increased with an increase in the nanoparticle volume fraction in the bulk and correlated qualitatively with the change in the substrate wettability. The extent of the wettability alteration depends on the volume fraction of the nanoparticles, their size, and the type of substrate. We found a strong correlation between the change in the substrate wettability and the nanoparticle volume fraction in the layer closer to the substrate surface.