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Advances in Colloid and Interface Science 150 (2009) 106–115

Contents lists available at ScienceDirect

Advances in Colloid and Interface Science
j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / c i s

A review of factors that affect contact angle and implications for flotation practice
T.T. Chau a, W.J. Bruckard a, P.T.L. Koh a,⁎, A.V. Nguyen b,⁎
a
bCSIRO Minerals, Box 312 Clayton South, Victoria 3169, Australia
School of Chemical Engineering, The University of Queensland, Brisbane, Queensland 4072, Australia

article

info

Available online 12 July 2009
Keywords:
Contact angle
Wetting
Hydrophobicity
Froth flotation

abstract
Contact angle and the wetting behaviour of solid particles are influenced by many physical and chemicalfactors such as surface roughness and heterogeneity as well as particle shape and size. A significant amount
of effort has been invested in order to probe the correlation between these factors and surface wettability.
Some of the key investigations reported in the literature are reviewed here.
It is clear from the papers reviewed that, depending on many experimental conditions such as the size ofthe
surface heterogeneities and asperities, surface cleanliness, and the resolution of measuring equipment and
data interpretation, obtaining meaningful contact angle values is extremely difficult and such values are
reliant on careful experimental control. Surface wetting behaviour depends on not only surface texture
(roughness and particle shape), and surface chemistry (heterogeneity) but alsoon hydrodynamic conditions
in the preparation route. The inability to distinguish the effects of each factor may be due to the interplay
and/or overlap of two or more factors in each system. From this review, it was concluded that:
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Surface geometry (and surface roughness of different scales) can be used to tune the contact angle; with
increasing surface roughness the apparentcontact angle decreases for hydrophilic materials and increases for
hydrophobic materials.
For non-ideal surfaces, such as mineral surfaces in the flotation process, kinetics plays a more important
role than thermodynamics in dictating wettability.
Particle size encountered in flotation (10–200 μm) showed no significant effect on contact angle but has a
strong effect on flotation rate constant.There is a lack of a rigid quantitative correlation between factors affecting wetting, wetting behaviour and contact
angle on minerals; and hence their implication for flotation process. Specifically, universal correlation of contact
angle to flotation recovery is still difficult to predict from first principles. Other advanced techniques and measures
complementary to contact angle will be essentialto establish the link between research and practice in flotation.
© 2009 Elsevier B.V. All rights reserved.

Contents
1.
2.

3.

Introduction . . . . . . . . . . . . . . . . . . . . . . .
Background of contact angle . . . . . . . . . . . . . . .
2.1.
The Young equation . . . . . . . . . . . . . . . .
2.2.
The Wenzel equation . . . . . . . . . . . . . . .
2.3.
The Cassie equation .. . . . . . . . . . . . . . .
Factors affecting contact angle measurements . . . . . . .
3.1.
Roughness factor . . . . . . . . . . . . . . . . .
3.1.1.
Roughness characterisation . . . . . . . .
3.1.2.
The effect of dimension . . . . . . . . . .
3.1.3.
The effect of roughness variation . . . . .
3.1.4.
Assigning the “true” apparent contact angle
3.2.
Heterogeneity factor . . . . . . .. . . . . . . . .
3.3.
The effect of particle size on penetration kinetics and
3.4.
The effect of particle shape on contact angle . . . .

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contact angle
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⁎ Corresponding authors.
E-mail addresses: peter.koh@csiro.au (P.T.L. Koh), anh.nguyen@eng.uq.edu.au (A.V. Nguyen)....