Evaporation of Nanoparticles Droplets on Nanoporous Superhydrophobic Surfaces

2009 ◽  
Author(s):  
Rajesh Leeladhar ◽  
Wei Xu ◽  
Chang-Hwan Choi
Keyword(s):  
Contact Angle ◽  
Contact Angles ◽  
Superhydrophobic Surfaces ◽  
Wetting Transition ◽  
Initial Contact ◽  
Particle Sizes ◽  
Anodized Aluminum ◽  
Sem Images ◽  
In The Beginning ◽  
Nanoparticle Sizes

In this paper, we experimentally studied the evaporative behavior of the nanofluid droplets (fluid containing metal nanoparticles) on nanoporous superhydrophobic surfaces. Uniformly dispersed in water, gold chloride (AuCl3) nanoparticles of varying sizes (10–250 nm) and concentrations (0.001–0.1% wt) were tested as nanofluids. Porous anodized aluminum oxide (AAO) with a pore size of 250 nm was tested as a nanoporous superhydrophobic surface, coated by a self assembled monolayer (SAM). During the evaporation in a room temperature and pressure, the evaporation kinetics (e.g., contact angle, contact diameter, and volume) of the nanofluid droplets was measured over time by using a goniometer. In the beginning, the initial droplet contact angles were significantly affected by the nanoparticle sizes and concentrations such that as the concentration increased, the initial contact angle decreased, which was more pronounced at larger particle sizes. During evaporation, despite the different particle sizes and concentrations, there were two distinct stages shown, especially for the change of contact angles, i.e., gradual decrease in the beginning, followed by rapid decrease in the end. No remarkable wetting transition from de-wetting (Cassie) to wetting (Wenzel) state was shown during the evaporation. Evaporation rate was influenced by nanoparticles such that it was significantly mitigated with the nanofluid droplet of the highest concentration (0.1% wt). The scanning electron microscope (SEM) images show that the ring-like dry-out pattern forms after the evaporation of nanofluids with lower concentrations (0.001%, 0.01% wt), whereas the one with higher concentrations (0.1%wt) forms a uniformly distributed pattern. These results demonstrate that nanoparticle sizes and concentrations make significant effects on interfacial phenomena in droplet evaporation on nanostructured surfaces, which will impact many engineering applications and system designs based on droplets such as microfluidics and heat transfer.

Effects of Nanofluids on Droplet Evaporation and Wetting on Nanoporous Superhydrophobic Surfaces

2009 ◽  
Author(s):  
Rajesh Leeladhar ◽  
Wei Xu ◽  
Chang-Hwan Choi
Keyword(s):  
Contact Angle ◽  
Metal Nanoparticles ◽  
Base Fluid ◽  
Superhydrophobic Surfaces ◽  
Equilibrium Contact Angle ◽  
Wetting Transition ◽  
Significant Difference ◽  
Dry Out ◽  
Nanoparticle Sizes ◽  
Contact Diameter

In this paper, nanofluid droplets (fluid containing metal nanoparticles) were subjected to evaporation on a nanoporous superhydrophobic surface to study the effects of nanoparticles on evaporation kinetics, wetting dynamics, and dry-out patterns. Metal nanoparticles (gold chloride) of three different sizes (10, 100, and 250 nm) at three different concentrations (0.001, 0.01, and 0.1% wt) were tested as nanofluids, uniformly dispersed in deionized water. Anodized alumina membranes (200 nm in pore diameter) were tested as nanoporous superhydrophobic surfaces, coated with a self assembled monolayer (SAM). During the course of evaporation in a room condition, the change of a contact angle, contact diameter, height, and volume was measured by a goniometer and compared with that of the base fluid (water) taken as a control. The initial equilibrium contact angle of the nanofluids was significantly affected by the nanoparticle sizes and concentrations. During evaporation, the evaporation behavior for the nanofluids exhibited a complete different mode from that of the base fluid. In terms of a contact angle, nanofluids showed slower decrease rate than base fluid. Nanofluid contact diameter remained almost a constant throughout evaporation with a slight change only at the very end of evaporation stage, whereas the base fluid showed a sequence of constant, increase, and mixed states of increase/decrease behavior. The nanofluids also showed a clear distinction in the evaporation rates, resulting in slower rate than base fluid. The variation of the nanoparticle sizes and concentrations did not make significant difference in the evaporation rate within the tested conditions. No abrupt change in a contact angle and diameter was observed during the evaporation, suggesting that no remarkable wetting transition from Cassie (de-wetting) to Wenzel (wetting) state occurred. The scanning electron microscope (SEM) images of the deposited nanoparticles after complete evaporation of solvent showed unique dry-out patterns depending on nanoparticle sizes and concentrations, e.g., a thick ring-like pattern with larger particle sizes while a uniformly distributed pattern with smaller particles at higher concentrations.

Nanofluids Evaporation Kinetics on Microstructured Superhydrophobic Surfaces

2009 ◽  
Author(s):  
Wei Xu ◽  
Chang-Hwan Choi
Keyword(s):  
Contact Angle ◽  
Evaporation Rate ◽  
Superhydrophobic Surfaces ◽  
Wetting Transition ◽  
Initial Contact ◽  
Deep Reactive Ion Etching ◽  
Surface Patterns ◽  
Teflon Coating ◽  
Kinetics Of ◽  
Evaporation Kinetics

In this paper, we experimentally studied the evaporation kinetics of sessile droplets of nanofluids with systematically varying particle sizes on superhydrophobic surfaces of well-defined micro-post structures. The superhydrophobic surface patterns were fabricated on a silicon wafer by photolithography and deep reactive ion etching (DRIE) at cryogenic temperature followed by Teflon coating. The 0.01 wt% suspensions of gold (Au) nanoparticles with varying sizes (5, 50, and 250 nm in diameter) were tested as nanofluids for the evaporation kinetics including the contact angle, base diameter, height, volume and evaporation rate by using a goniometer. The dryout patterns were investigated by using scanning electron microscopy (SEM). The results show that the surface topography and nanoparticle sizes have significant effects on the initial contact angle, profile evolution, wetting transition, evaporation rate, and dryout deposition pattern of the nanofluid droplets.

Facile Fabrication of Fluorine-Free Superhydrophobic Surfaces with SiO2 Monospheres

2021 ◽  
Vol 16 (2) ◽  
pp. 208-212
Author(s):  
Zhong-Peng Liu ◽  
Si-Nan Song ◽  
Mu Zhang
Keyword(s):  
Contact Angle ◽  
Superhydrophobic Surface ◽  
Hydrophobic Surface ◽  
Silica Particles ◽  
Superhydrophobic Surfaces ◽  
Particle Sizes ◽  
Stöber Method ◽  
Spherical Silica ◽  
Spherical Silica Particles ◽  
Facile Fabrication

Recently, superhydrophobic surface on various type of substrates have attracted much attentions in electronics field. In this work, the classic Stöber method was used to prepare spherical silica particles with different particle sizes by adding different amounts of electrolyte (potassium chloride), giving rise to size distribution ranging from 300 nm to 2.55 yitm. Herein we constructed a micro-nano lotus-like structure in a facile way, achieving a superhydrophobic surface with using any Fluorine related chemicals. In the sense, the silica particles modified with HMDS were sprayed to prepare hydrophobic surface with contact angle up to 152.96° by increasing the frequency of sprays.

Superhydrophobic Surfaces Properties for Anti-Icing

2011 ◽  
Author(s):  
Mohammad Amin Sarshar ◽  
Christopher Swarctz ◽  
Scott Hunter ◽  
John Simpson ◽  
Chang-Hwan Choi
Keyword(s):  
Contact Angle ◽  
Wind Tunnel ◽  
Contact Angle Hysteresis ◽  
Contact Angles ◽  
Superhydrophobic Surfaces ◽  
Ice Formation ◽  
Flow Conditions ◽  
Water Droplets ◽  
Dynamic Flow ◽  
Static Contact

In this paper, the iceophobic properties of superhydrophobic surfaces are compared to those of uncoated aluminum and steel plate surfaces as investigated under dynamic flow conditions by using a closed loop low-temperature wind tunnel. Superhydrophobic surfaces were prepared at the Oak Ridge National Laboratory by coating aluminum and steel plates with nano-structured hydrophobic particles. The contact angle and contact angle hysteresis measured for these surfaces ranged from 165–170° and 1–8°, respectively. The superhydrophobic plates along with uncoated control ones were exposed to an air flow of 12 m/s and 20°F with micron-sized water droplets in the icing wind tunnel and the ice formation and accretion were probed by using high speed cameras for 90 seconds. Results show that the developed superhydrophobic coatings significantly delay the ice formation and accretion even with the impingement of accelerated super-cooled water droplets, but there is a time scale for this phenomenon which has a clear relation with contact angle hysteresis of the samples. Among the different superhydrophobic coating samples, the plate having the lowest contact angle hysteresis showed the most pronounced iceophobic effects, while the correlation between static contact angles and the iceophobic effects was not evident. The results suggest that the key parameter for designing iceophobic surfaces is to retain a low contact angle hysteresis, rather than to have only a low contact angle, which can result in more efficient anti-icing properties in dynamic flow conditions.

Investigation of Pre-Tungsten Silicide Deposition Wet Chemical Processing

1995 ◽  
Vol 386 ◽  
Author(s):  
A. Philipossian ◽  
M. Moinpour ◽  
R. Wilkinson ◽  
V. H. C. Watt
Keyword(s):  
Contact Angle ◽  
Polycrystalline Silicon ◽  
Silicon Surface ◽  
Morphological Characteristics ◽  
Ambient Air ◽  
Contact Angles ◽  
Silicon Surfaces ◽  
Native Oxide ◽  
Initial Contact ◽  
Air Exposure

ABSTRACTRemoving the native oxide from the poly-Si surface prior to WSix deposition is essential for achieving high quality silicides as well as sufficient film adhesion, particularly after high temperature anneal or oxidation. Contact angle studies have been used to determine initial and time-dependent surface characteristics of several types of silicon surfaces following immersions in HF-based etchants for varying amounts of time. The morphological characteristics of the surfaces before and after exposure to etchants, as well as the relative etch rates and wetting capabilities of the etchants have been used to explain the following results: With respect to initial contact angle studies, the implanted & annealed polycrystalline silicon surface has the lowest contact angle followed by polycrystalline and monocrystalline surfaces. Longer immersion times yield lower initial contact angles. The 0.1% lightly-buffered HF solution results in the highest contact angle followed by the 1% buffered HF solution with surfactant, and the 1% HF solution. With respect to contact angle changes during ambient air exposure time, the asdeposited polycrystalline silicon surface is most stable followed by monocrystalline, and implanted & annealed polycrystalline silicon surfaces. Longer immersion times improve surface stability while the 0.1% lightly-buffered HF solution results in the most stable surface followed by the 1% buffered HF solution with surfactant, and the 1% HF solution.

scholarly journals Elektro Çekim Yöntemi ile Haloysit Katkılı Biyo-Bazlı Termoplastik Poliüretan Nanolif Üretimi ve Karakterizasyonu

2020 ◽  
Vol 27 (120) ◽  
pp. 218-229
Author(s):  
Ecem AKIN ◽  
Sibel DEMIROGLU ◽  
Elif ALYAMAÇ ◽  
Özgür SEYDİBEYOĞLU
Keyword(s):  
Contact Angle ◽  
Loss Modulus ◽  
Thermoplastic Polyurethane ◽  
Contact Angles ◽  
Solution Viscosity ◽  
Fiber Axis ◽  
Ftir Analysis ◽  
Fiber Morphology ◽  
Sem Images ◽  
Electrospinning Technique

In this study, it was aimed to produce biocomposite nanofibers by using electrospinning technique and to form biocomposite structure, bio-based thermoplastic polyurethane (BioTPU) and halloysite (HST) mineral obtained from natural sources were used. Electrospinning parameters have been optimized for the production of nanofibers with smooth morphology and the polymer solution with the most suitable parameter was determined. Different concentrations of HST filled BioTPU nanofibers were produced and the rheological behavior of the solutions was investigated with a rotational rheometer before electrospinning to observe the effects of halloysite on fiber morphology. Fourier transform infrared spectroscopy (FTIR) analysis was carried out to determine the chemical composition of acquired nanofibers, and scanning electron microscopy (SEM) was used to monitor surface morphologies. Contact angle measurements were carried out to observe the effects of halloysite on the hydrophilicity of nanofiber. According to rheology results, it has been found out that the solution viscosity, storage modulus (G') and loss modulus (G'') of halloysite increased up to a certain concentration (0.3 % HST), but later caused falls on viscosity. According to the results of FTIR analysis, there is no chemical bond between halloysite and BioTPU, but SEM images show that halloysite was added to the structure of nanofibers. It was also found that the halloysite added to the structure increased the fiber diameters and that the fiber cross-section was not uniformly distributed along the fiber axis. The results of contact angle analysis indicated that acquired nanofibers have hydrophobic surface and the added halloysite decreases contact angles of nanofibers.

Line Tension Effect on Alkane Droplets Near the Wetting Transition

1996 ◽  
Vol 464 ◽  
Author(s):  
A. D. Dussaud ◽  
M. Vignes-Adler
Keyword(s):  
Contact Angle ◽  
Droplet Size ◽  
Salt Concentration ◽  
Classical Method ◽  
Line Tension ◽  
Contact Angles ◽  
Positive Sign ◽  
Wetting Transition ◽  
Droplet Shape ◽  
Order Of Magnitude

ABSTRACTWe have investigated n-octane droplets resting on the surface of sodium chloride solutions as a function of the salt concentration in a saturated, closed cell. For high salt concentration, the system approaches a wetting transition : the contact angles are very small (∼ 1°), the macroscopic droplet is unstable, and it breaks up spontaneously into microdroplets. The stable polydisperse population of microdroplets (5 μm < r < 250 μm) allowed us to analyze the dependence of the contact angle on droplet size. Because of the low contact angle values, accurate measurement ofcontact angles was obtained by interferometry. Moreover the accuracy of the classical method was significantly improved through the systematic use of three wavelengths. The relationship between the contact angle and the size droplet size indicated a positive line tension, τ, and the order of magnitude of τ was in good agreement with the theoretical prediction, τ, varies between (8.6 ± 0.9). 10−11 N and (1 ± 0.1).10−9 N and was dependent on the salt concentration. The positive sign of τ and its significant effect on droplet shape were related to the fact that the system was approaching the wetting transition.

Investigation of Optimizing Arrangement Forms for Combined Angular Contact Ball Bearings

2017 ◽  
Author(s):  
Bin Fang ◽  
Jinhua Zhang ◽  
Jun Hong ◽  
Yongsheng Zhu ◽  
Xu Wang ◽  
...  
Keyword(s):  
Mathematical Model ◽  
Contact Angle ◽  
Load Distribution ◽  
Contact Angles ◽  
Rotating Machinery ◽  
Initial Contact ◽  
Ball Bearings ◽  
Heavy Load ◽  
Initial Contact Angle ◽  
Machinery System

The combined angular contact bearings are widely used in numerous rotating machinery system, but few research works on the combined angular contact ball bearings have been reported. To solve the problem about inconsistency fatigue life of the bearings in the combined bearings with asymmetric arrangement, this paper proposed a special combined bearings arrangement form in which the bearings with different contact angles are used simultaneously for the bearing combination. In order to validate the effectiveness of the proposed method, a mathematical model is proposed to analyze the load distribution, life and stiffness of the combined bearings, and the combined bearings with three different arrangements are comparatively calculated and analyzed. The results show that the whole life of combined bearings is mainly depend on the life of the bearing under heavy load, and the new arrangement form in which the initial contact angle of the bearing under heavy load is increased that can improve the whole life of combined bearings.

Time-Related Contact Angle Measurements with Human Plasma on Biomaterial Surfaces

1998 ◽  
Vol 21 (1) ◽  
pp. 35-39
Author(s):  
G. Rakhorst ◽  
H.C. Van Der Mei ◽  
W. Van Oeveren ◽  
H.T. Spijker ◽  
H.J. Busscher
Keyword(s):  
Contact Angle ◽  
Protein Adsorption ◽  
Human Plasma ◽  
Platelet Adhesion ◽  
Contact Angles ◽  
Initial Contact ◽  
Angle Measurements ◽  
Contact Angle Measurements ◽  
Albumin Adsorption ◽  
Fibrinogen Adsorption

Axisymmetric drop shape analysis by profile (ADSA-P) was used to assess in time contact angle changes of human plasma drops placed on four different biomaterials. Results were related with conventional blood compatibility measurements: albumin adsorption, fibrinogen adsorption and platelet adhesion. While contact angle measurements with water are material-related but constant in time, contact angle measurements with plasma changed over time owing to protein adsorption on the solid-liquid interface. The contact medium plasma did not influence the initial contact angle. Contact angles on PDMS decreased most in time (41 degrees) and demonstrated highest levels of conventionally measured albumin and fibrinogen adsorption and platelet adhesion. PTFE, with the lowest contact angle decrease over a 500 minutes period (19 degrees), showed low fibrinogen and albumin adsorption as well as low platelet adhesion. PU and HDPE demonstrated almost similar initial contact angles with plasma and contact angle decreases (26 and 27 degrees), intermediate protein adsorption, and platelet adhesion. We conclude that biocompatibility properties of the tested materials may be more related to the behaviour of their contact angles in time, than to the initial hydrophobic or hydrophilic state.

Superhydrophobic surfaces by dynamic nanomasking and deep reactive ion etching

2007 ◽  
Vol 221 (2) ◽  
pp. 41-48 ◽  
Author(s):  
Ying Song ◽  
Min Zou
Keyword(s):  
Contact Angle ◽  
Au Nanoparticles ◽  
Reactive Ion Etching ◽  
Thin Layers ◽  
Superhydrophobic Surfaces ◽  
Sem Images ◽  
Water Contact ◽  
Ion Etching ◽  
Deep Reactive Ion Etching ◽  
Wetting Properties

This paper reports a study on fabricating superhydrophobic surfaces with micro- and nanohierarchical topography by dynamic nanomasking (DNM) and deep reactive ion etching (DRIE). In this study, thin layers of gold (Au) were sputtered on silicon (Si) wafers followed by annealing the samples in a conventional furnace to break the thin films into Au nanoparticles attached to the Si surfaces. These randomly distributed nanoparticles served as dynamic nanomasks during DRIE processes, in which sulphur hexafluoride (SF6) and octofluorocyclobutane (C4F8) were used as etching and polymerization gases, respectively. Surface topography and wetting properties of the samples were characterized by scanning electron microscopy (SEM) and a video-based optical contact angle meter (VOCAM). SEM images show that this technique created micro-sized craters with Au nanoparticles residing on the ridges of the microstructures. The largest water contact angle (WCA) obtained by this method is about 163°. The surface superhydrophobicity is attributed to the combination of micro- and nano-hierarchical topography and surface polymerization.

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