posted on 2017-02-02, 16:25authored byIgnacio Martin-Fabiani, Andrea Fortini, Jennifer Lesage de la Haye, Ming L. Koh, Spencer E. Taylor, Elodie Bourgeat-Lami, Muriel Lansalot, Franck D'Agosto, Richard P. Sear, Joseph L. Keddie
Stratified coatings are used to provide properties at a surface, such as hardness or refractive index, which are different from underlying layers. Although time-savings are offered by self-assembly approaches, there have been no methods yet reported to offer stratification on demand. Here, we demonstrate a strategy to create self-assembled stratified coatings, which can be switched to homogeneous structures when required. We use blends of large and small colloidal polymer particle dispersions in water that self-assemble during drying because of an osmotic pressure gradient that leads to a downward velocity of larger particles. Our confocal fluorescent microscopy images reveal a distinct surface layer created by the small particles. When the pH of the initial dispersion is raised, the hydrophilic shells of the small particles swell substantially, and the stratification is switched off. Brownian dynamics simulations explain the suppression of stratification when the small particles are swollen as a result of reduced particle mobility, a drop in the pressure gradient, and less time available before particle jamming. Our strategy paves the way for applications in antireflection films and protective coatings in which the required surface composition can be achieved on demand, simply by adjusting the pH prior to deposition.
Funding
European Union Seventh Framework Programme BARRIER-PLUS project (FP7-SME-2012-2, No. 304758).
History
School
Aeronautical, Automotive, Chemical and Materials Engineering
Department
Materials
Published in
ACS Applied Materials and Interfaces
Volume
8
Issue
50
Pages
34755 - 34761
Citation
MARTIN-FABIANI, I. ... et al, 2016. PH-switchable stratification of colloidal coatings: surfaces "on demand". ACS Applied Materials and Interfaces, 8 (50), pp. 34755-34761.
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