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Issue 39, 2017
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Stratification in binary colloidal polymer films: experiment and simulations

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Abstract

When films are deposited from mixtures of colloidal particles of two different sizes, a diverse range of functional structures can result. One structure of particular interest is a stratified film in which the top surface layer has a composition different than in the interior. Here, we explore the conditions under which a stratified layer of small particles develops spontaneously in a colloidal film that is cast from a binary mixture of small and large polymer particles that are suspended in water. A recent model, which considers the cross-interaction between the large and small particles (Zhou et al., Phys. Rev. Lett., 2017, 118, 108002), predicts that stratification will develop from dilute binary mixtures when the particle size ratio (α), initial volume fraction of small particles (ϕS), and Péclet number are high. In experiments and Langevin dynamics simulations, we systematically vary α and ϕS in both dilute and concentrated suspensions. We find that stratified films develop when ϕS is increased, which is in agreement with the model. In dilute suspensions, there is reasonable agreement between the experiments and the Zhou et al. model. In concentrated suspensions, stratification occurs in experiments only for the higher size ratio α = 7. Simulations using a high Péclet number, additionally find stratification with α = 2, when ϕS is high enough. Our results provide a quantitative understanding of the conditions under which stratified colloidal films assemble. Our research has relevance for the design of coatings with targeted optical and mechanical properties at their surface.

Graphical abstract: Stratification in binary colloidal polymer films: experiment and simulations

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Publication details

The article was received on 27 Jun 2017, accepted on 19 Aug 2017 and first published on 18 Sep 2017


Article type: Paper
DOI: 10.1039/C7SM01267E
Citation: Soft Matter, 2017,13, 6969-6980
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    Stratification in binary colloidal polymer films: experiment and simulations

    D. K. Makepeace, A. Fortini, A. Markov, P. Locatelli, C. Lindsay, S. Moorhouse, R. Lind, R. P. Sear and J. L. Keddie, Soft Matter, 2017, 13, 6969
    DOI: 10.1039/C7SM01267E

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