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research-article

Effects of interface velocity, diffusion rate, and radial velocity on colloidal deposition patterns left by evaporating droplets

[+] Author and Article Information
Collin T. Burkhart

Mechanical Engineering, Rochester Institute of Technology 76 Lomb Memorial Drive, Rochester NY, 14623
ctb6973@rit.edu

Kara Maki

School of Mathematical Sciences, Rochester Institute of Technology 85 Lomb Memorial Drive, Rochester NY, 14623
kmaki@rit.edu

Michael J. Schertzer

Mechanical Engineering, Rochester Institute of Technology 76 Lomb Memorial Drive, Rochester NY, 14623
mjseme@rit.edu

1Corresponding author.

ASME doi:10.1115/1.4036681 History: Received October 08, 2016; Revised April 11, 2017

Abstract

This investigation provides experimental evidence examining the role of interface capture on the transport and deposition of colloidal material in evaporating droplets. It finds that deposition patterns cannot be characterized by the ratio of the interface velocity to the particle diffusion rate alone when the two effects are of the same order. Instead, the ratio of radial velocity to the particle diffusion rate should also be considered. Ring depositions are formed when the ratio of radial velocity to the particle diffusion rate is greater than the ratio of interface velocity to diffusion. Conversely, uniform depositions occur when the ratio of radial velocity to diffusion is smaller than the ratio of interface velocity to diffusion. Transitional depositions with a ring structure and non-uniform central deposition are observed for cases where the characteristic ratios are similar in magnitude. Since both ratios are scaled by diffusion rate, it is possible to characterize the deposition patterns observed here using a ratio of interface velocity to radial velocity. Uniform patterns form when interface velocity is greater than radial velocity and ring patterns form when radial velocity is larger. However, Marangoni effects are small and DLVO forces repel particles from the surface in these cases. Further research is required to determine if the conclusions here can be extended or modified to describe deposition patterns when particles are subjected to appreciable Marangoni recirculation and attractive DLVO forces.

Copyright (c) 2017 by ASME
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