A level-set method for large-scale simulations of three-dimensional flows with moving contact lines

AbstractLiquid bridges with moving contact lines are relevant in a variety of natural and industrial settings, ranging from printing processes to the feeding of birds. While it is often assumed that the liquid bridge is two-dimensional in nature, there are many applications where either the stretching motion or the presence of a feature on a bounding surface lead to three-dimensional effects. To investigate this we solve Stokes equations using the finite-element method for the stretching of a three-dimensional liquid bridge between two flat surfaces, one stationary and one moving. We first consider an initially cylindrical liquid bridge that is stretched using either a combination of extension and shear or extension and rotation, while keeping the contact lines pinned in place. We find that whereas a shearing motion does not alter the distribution of liquid between the two plates, rotation leads to an increase in the amount of liquid resting on the stationary plate as breakup is approached. This suggests that a relative rotation of one surface can be used to improve liquid transfer to the other surface. We then consider the extension of non-cylindrical bridges with moving contact lines. We find that dynamic wetting, characterized through a contact line friction parameter, plays a key role in preventing the contact line from deviating significantly from its original shape as breakup is approached. By adjusting the friction on both plates it is possible to drastically improve the amount of liquid transferred to one surface while maintaining the fidelity of the liquid pattern.

Download Full-text

Simulation of Directed Nanocrack Patterns for the Fabrication of Nanowires [PowerPoint Submission]

MRS Proceedings ◽

10.1557/proc-978-0978-gg02-05 ◽

2006 ◽

Vol 978 ◽

Author(s):

David Salac ◽

Wei Lu

Keyword(s):

Level Set Method ◽

Level Set ◽

Large Scale ◽

Scanning Tunneling ◽

Small Scale ◽

Crack Tips ◽

Multiple Materials ◽

Material Fracture ◽

Recent Experimental Work ◽

Large Scale Simulations

Abstract While material fracture is generally considered undesirable, recent experimental work has indicated that cracking can be utilized to create small scale nanowire structures with diameters of 100nm and smaller. Typical nanowire fabrication techniques include the use of a scanning tunneling microscope and electrochemical deposition. Compared to fracture fabricated nanowire structures current fabrication techniques are either extremely slow or require large amounts of post-processing. To become a viable nanowire fabrication technique the cracking of materials must be directed. We propose a computational model to predict propagation paths in large scale crack systems. We utilize the level set method to investigate the creation of nanoscale crack patterns. The level set method allows for large scale simulations of many crack tips while easily accommodating large scale deformations. Unlike traditional methods such as finite elements explicit modeling of the cracks is not needed. We show that the use of multiple materials and etched regions can effectively direct the cracking of a thin film. Using these patterns nanowire structures can be constructed which would be difficult to obtain otherwise.

Download Full-text