Three-dimensional relationship between the critical contact angle and the torque angle

Salt creeping is a ubiquitous phenomenon in which crystals precipitate far from an evaporating salt solution boundary, which constitutes a major problem in outdoor electronics, civil engineering, artworks, and agriculture. We report a novel experimental approach that allows to quantitatively describe the creeping mechanism and demonstrate its universality with respect to different salts. We show that there exists a critical contact angle below which salt creeping occurs, provided also the nucleation of multiple crystals is favored. The precipitation of new crystals happens ahead of the contact line by the meniscus that progressively advances over the crystals forming also nanometric precursor films. This enlarges the evaporative area, causing an exponential increase in the crystal mass in time. The self-amplifying process then results in a spectacular three-dimensional crystal network at macroscopic distances from the solution reservoir. These findings also allow us to control the creeping by using crystallization modifiers.

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Coalescence-induced jumping of immersed and suspended droplets onmicrostructured substrates

European Journal of Computational Mechanics ◽

10.13052/17797179.2017.1306830 ◽

2019 ◽

pp. 205-223

Author(s):

Samaneh Farokhirad ◽

Mahmood Mohammadi Shad ◽

Taehun Lee

Keyword(s):

Contact Angle ◽

Three Dimensional ◽

Equilibrium Contact Angle ◽

Wetting Transition ◽

Liquid Droplets ◽

Vertical Jumping ◽

Initial Placement ◽

Boltzmann Method ◽

Square Array ◽

Critical Contact

The coalescence-induced jumping of liquid droplets on superhydrophobic structured substrates is investigated numerically using a three-dimensional multiphase lattice Boltzmann method. The numerical experiments on evolution of droplets during jumping process show higher jumping velocity and height from superhydrophobic substrates structured with a periodic array of square pillars, than flat superhydrophobic substrateswith an equilibrium contact angle of 180◦. The results further reveal a strong effect of pillars on the vertical jumping velocity and the final quasiequilibrium height of the merged droplet as a function of air and liquid viscosity, as well as air inertia. As for substrate wettability, it is found that, compared to the flat superhydrophobic substrate, the critical contact angle where the merged droplet jumps away from substrate is reduced for pillared substrate and is about 120◦. It is also observed that the droplet initial placement on a substrate with a square array of pillars has an important effect on the spontaneous jumping of the coalesced droplet, and a Wenzel–Cassie wetting transition upon coalescence is observed for droplets that are initially immersed within the pillars.

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Electron Holographic Nano-Characterization of Gold Catalyst at Interface

MRS Proceedings ◽

10.1557/proc-727-r2.2 ◽

2002 ◽

Vol 727 ◽

Cited By ~ 1

Author(s):

S. Ichikawa ◽

T. Akita ◽

M. Okumura ◽

M. Haruta ◽

K. Tanaka

Keyword(s):

Contact Angle ◽

Titanium Oxide ◽

Gold Catalyst ◽

Three Dimensional ◽

High Resolution Electron Microscopy ◽

Electron Holography ◽

Gold Particles ◽

Oxide Support ◽

The Mean ◽

A Charge

AbstractThe catalytic properties of nanostructured gold catalyst are known to depend on the size of the gold particles and to be activated when the size decreases to a few nanometers. We investigated the size dependence of the three-dimensional nanostructure on the mean inner potential of gold catalysts supported on titanium oxide using electron holography and high-resolution electron microscopy (HREM). The contact angle of the gold particles on the titanium oxide tended to be over 90° for gold particles with a size of over 5 nm, and below 90° for a size of below 2 nm. This decreasing change in the contact angle (morphology) acts to increase the perimeter and hence the area of the interface between the gold and titanium oxide support, which is considered to be an active site for CO oxidation. The mean inner potential of the gold particles also changed as their size decreased. The value of the inner potential of gold, which is approximately 25 V in bulk state, rose to over 40 V when the size of the gold particles was less than 2 nm. This phenomenon indicates the existence of a charge transfer at the interface between gold and titanium oxide. The 3-D structure change and the inner potential change should be attributed to the specific electronic structure at the interface, owing to both the “nano size effect” and the “hetero-interface effect.”

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Effects of bracket design on critical contact angle

The Angle Orthodontist ◽

10.2319/080112-621.1 ◽

2013 ◽

Vol 83 (5) ◽

pp. 877-884 ◽

Cited By ~ 4

Author(s):

Xiaomo Liu ◽

Peng Ding ◽

Jiuxiang Lin

Keyword(s):

Contact Angle ◽

Stainless Steel ◽

Linear Regression ◽

Resistance To Sliding ◽

The Relationship ◽

State Resistance ◽

Critical Contact ◽

Bracket Design

ABSTRACT Objective: To explore how the position of the bracket slots relative to the archwire influences the friction between them, and how bracket design affects the critical contact angle (θc). Materials and Methods: Two kinds of stainless steel archwires (0.016 and 0.019 × 0.025-inch) were tested against four kinds of brackets (Transmission Straight Archwire bracket, Domestic MBT bracket, Tip-Edge Plus bracket, and BioQuick self-ligation bracket) in the dry state. Resistance to sliding (RS) was measured as an increase in contact angle (θ). The value of θc was calculated by two linear regression lines. Results: Friction remained stable when θ < θc, then increased linearly when θ > θc. The θc values of the Tip-Edge Plus bracket and Transmission Straight Archwire bracket were significantly larger than those for the Domestic MBT bracket and BioQuick self-ligation bracket. Conclusions: The relationship between the archwire and bracket slot significantly affects the resistance to sliding. The “edge-off” structure of the Tip-Edge Plus bracket and Transmission Straight Archwire bracket could help to increase the θc value, and to expand the passive configuration range.

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Finite Element Analysis of Stress Singularities in Attached Flip Chip Packages

Journal of Electronic Packaging ◽

10.1115/1.1289768 ◽

2000 ◽

Vol 122 (4) ◽

pp. 301-305 ◽

Cited By ~ 19

Author(s):

A. Q. Xu ◽

H. F. Nied

Keyword(s):

Contact Angle ◽

Finite Element ◽

Glass Fiber ◽

Flip Chip ◽

Three Dimensional ◽

Stress Singularity ◽

Local Stress ◽

Stress Singularities ◽

Element Analysis ◽

Three Dimensional Finite Element

Cracking and delamination at the interfaces of different materials in plastic IC packages is a well-known failure mechanism. The investigation of local stress behavior, including characterization of stress singularities, is an important problem in predicting and preventing crack initiation and propagation. In this study, a three-dimensional finite element procedure is used to compute the strength of stress singularities at various three-dimensional corners in a typical Flip-Chip assembled Chip-on-Board (FCOB) package. It is found that the stress singularities at the three-dimensional corners are always more severe than those at the corresponding two-dimensional edges, which suggests that they are more likely to be the potential delamination sites. Furthermore, it is demonstrated that the stress singularity at the upper silicon die/epoxy fillet edge can be completely eliminated by an appropriate choice in geometry. A weak stress singularity at the FR4 board/epoxy edge is shown to exist, with a stronger singularity located at the internal die/epoxy corner. The influence of the epoxy contact angle and the FR4 glass fiber orientation on stress state is also investigated. A general result is that the strength of the stress singularity increases with increased epoxy contact angle. In addition, it is shown that the stress singularity effect can be minimized by choosing an appropriate orientation between the glass fiber in the FR4 board and the silicon die. Based on these results, several guidelines for minimizing edge stresses in IC packages are presented. [S1043-7398(00)00904-X]

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One-Step Acidic Hydrothermal Preparation of Dendritic Rutile TiO2 Nanorods for Photocatalytic Performance

Nanomaterials ◽

10.3390/nano8090683 ◽

2018 ◽

Vol 8 (9) ◽

pp. 683 ◽

Cited By ~ 11

Author(s):

Cheng Gong ◽

Jun Du ◽

Xiuyun Li ◽

Zhenjie Yu ◽

Jiansong Ma ◽

...

Keyword(s):

Electron Microscopy ◽

Contact Angle ◽

Hydrothermal Method ◽

Photocatalytic Performance ◽

Three Dimensional ◽

Tio2 Nanorods ◽

Foil Surface ◽

Rutile Tio2 ◽

X Ray ◽

One Step

Three-dimensional and dendritic rutile TiO2 nanorods were successfully fabricated on a Ti foil surface using a one-step acidic hydrothermal method. The TiO2 nanorods were characterized using X-ray diffraction (XRD), energy dispersive X-ray spectrometry (EDX), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and optical contact angle testing. The results showed that the nanorods with diameters of 100–500 nm and lengths of 100 nm to 1 μm were obtained on the Ti foil surface. The length and density of the TiO2 nanorods were perfect at the conditions of HCl concentration 0.5 mol/L, temperature 220 °C, and reaction time 12 h. The TiO2 nanorods formed parallel to the consumption of Ti and grew along the (110) direction having a tetragonal rutile crystal. The morphology of the nanorods possessed a three-dimensional structure. The contact angle of the nanorods was only 13 ± 3.1°. Meanwhile, the photocatalytic activities of the TiO2 nanorods were carried out using ultraviolet fluorescence spectrophotometry for the methyl orange detection, and the degradation was found to be about 71.00% ± 2.43%. Thus, TiO2 nanorods can be developed by a one-step acidic hydrothermal method using Ti foil simultaneously as the substrate with a TiO2 source; the TiO2 nanorods exhibited photocatalytic performance while being environment-friendly.

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Contact Angle Profiles for Droplets on Omniphilic Surfaces in the Presence of Tangential Forces

Colloids and Interfaces ◽

10.3390/colloids3040060 ◽

2019 ◽

Vol 3 (4) ◽

pp. 60 ◽

Cited By ~ 2

Author(s):

Kostoglou ◽

Karapantsios

Keyword(s):

Contact Angle ◽

Contact Line ◽

Theoretical Perspective ◽

Three Dimensional ◽

Real Life ◽

Suggested Approach ◽

Droplet Shape ◽

Tangential Forces ◽

Contact Line Motion ◽

Static Conditions

In real life, sessile droplets usually have a three-dimensional shape, making it difficult to understand their forced wetting behavior, both from an experimental and a theoretical perspective. Even in the case of spreading under quasi-static conditions, where the droplet shape is described by the Young–Laplace equation, there is no fundamental approach to describe the contact line evolution. In the present work, a few existing approaches on this issue are analyzed and assessed. It is shown that an experimentally inspired fixed shape for the contact line of droplets that are spreading under the action of tangential forces can be considered equivalent to a theory for contact line motion. There is a lack of experimental data for contact line evolution under arbitrary scenarios of forces. Such data will be very helpful for the further development of the suggested approach to contact line motion. Of particular interest is the case of small contact angle droplets, for which a top view can clearly indicate the contact line location. On the contrary, in such droplets, the direct experimental measurement of contact angle profile is very difficult. This must be estimated theoretically; thus, a special approach has been developed here for this purpose.

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Roughness and Fiber Fraction Dominated Wetting of Electrospun Fiber-Based Porous Meshes

Polymers ◽

10.3390/polym11010034 ◽

2018 ◽

Vol 11 (1) ◽

pp. 34 ◽

Cited By ~ 38

Author(s):

Piotr Szewczyk ◽

Daniel Ura ◽

Sara Metwally ◽

Joanna Knapczyk-Korczak ◽

Marcin Gajek ◽

...

Keyword(s):

Contact Angle ◽

Electrospun Fiber ◽

Three Dimensional ◽

Contact Angles ◽

Electrospun Fibers ◽

Surface Geometry ◽

Wetting Contact Angle ◽

Fiber Fraction ◽

Significant Difference ◽

Entrapped Air

Wettability of electrospun fibers is one of the key parameters in the biomedical and filtration industry. Within this comprehensive study of contact angles on three-dimensional (3D) meshes made of electrospun fibers and films, from seven types of polymers, we clearly indicated the importance of roughness analysis. Surface chemistry was analyzed with X-ray photoelectron microscopy (XPS) and it showed no significant difference between fibers and films, confirming that the hydrophobic properties of the surfaces can be enhanced by just roughness without any chemical treatment. The surface geometry was determining factor in wetting contact angle analysis on electrospun meshes. We noted that it was very important how the geometry of electrospun surfaces was validated. The commonly used fiber diameter was not necessarily a convincing parameter unless it was correlated with the surface roughness or fraction of fibers or pores. Importantly, this study provides the guidelines to verify the surface free energy decrease with the fiber fraction for the meshes, to validate the changes in wetting contact angles. Eventually, the analysis suggested that meshes could maintain the entrapped air between fibers, decreasing surface free energies for polymers, which increased the contact angle for liquids with surface tension above the critical Wenzel level to maintain the Cassie-Baxter regime for hydrophobic surfaces.

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