Evaporation of nanoparticle droplets on smooth hydrophobic surfaces: the inner coffee ring deposits

Nguyen, Tuan A. H., Hampton, Marc A. and Nguyen, Anh V. (2013) Evaporation of nanoparticle droplets on smooth hydrophobic surfaces: the inner coffee ring deposits. Journal of Physical Chemistry C, 117 9: 4707-4716. doi:10.1021/jp3126939


Author Nguyen, Tuan A. H.
Hampton, Marc A.
Nguyen, Anh V.
Title Evaporation of nanoparticle droplets on smooth hydrophobic surfaces: the inner coffee ring deposits
Journal name Journal of Physical Chemistry C   Check publisher's open access policy
ISSN 1932-7447
1932-7455
Publication date 2013-03-01
Sub-type Article (original research)
DOI 10.1021/jp3126939
Volume 117
Issue 9
Start page 4707
End page 4716
Total pages 10
Place of publication Washington, DC, United States
Publisher American Chemical Society
Collection year 2014
Language eng
Abstract The solid surfaces used in evaporation studies of nanoparticle sessile droplets usually exhibit significant surface roughness, causing significant pinning of the three-phase contact lines and producing different types of nanoparticle deposits, from single and multiple coffee rings (formed at the initial pining of triple contact lines) to central bumps. Here we used nanometer-scale smooth hydrophobic surfaces to investigate the evaporation of sessile water droplets containing silica nanoparticles and organic pigment nanoparticles. We observed a new type of coffee ring deposits which were not formed at the initial pinning but at the later pinning. We referred them to as the inner coffee ring deposits (ICRDs). The radius of ICRDs was smaller than the radius of the initially pinned contact area and increased with increasing concentration of added salts and nanoparticles and with increasing contact angle hysteresis of hydrophobic surfaces. We also observed different dendrite deposit patterns inside ICRDs. We argue that all the deposit patterns are due to the second pinning of the three-phase contact lines, which occur when the forces on particles are balanced. The hypothesis is further supported by the transient changes of the dynamic contact angles and contact base area radius. The contact angle hysteresis, the particle concentration, and the colloidal interaction forces such as the electrical double-layer forces play a vital role in determining the size and patterns of ICRDs and the evaporation kinetics of nanoparticle sessile droplets.
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Chemical Engineering Publications
Official 2014 Collection
 
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