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Wettability of Complex Fluids and Surfactant Capped Nanoparticle-Induced Quasi-Universal Wetting Behavior
A. R. Harikrishnan, ,
Published in American Chemical Society
2017
PMID: 28585819
Volume: 121
   
Issue: 24
Pages: 6081 - 6095
Abstract
(Graph Presented) Even though there are quite large studies on wettability of aqueous surfactants and a few studies on effects of nanoparticles on wettability of colloids, to the best of authors' knowledge, there is no study reported on the combined effect of surfactant and nanoparticles in altering the wettability. The present study, for the first time, reports an extensive experimental and theoretical study on the combined effect of surfactants and nanoparticles on the wettability of complex fluids such as nanocolloids on different substrates, ranging from hydrophilic with a predominantly polar surface energy component (silicon wafer and glass) to near hydrophobic range with a predominantly dispersive component of surface energy (aluminum and copper substrates). Systematically planned experiments are carried out to segregate the contributing effects of surfactants, particles, and combined particle and surfactants in modulating the wettability. The mechanisms and the governing parameters behind the interactions of nanocolloids alone and of surfactant capped nanocolloids with different surfaces are found to be grossly different. The article, for the first time, also analyzes the interplay of the nature of surfaces, surfactant and particle concentrations on contact angle, and contact angle hysteresis (CAH) of particle and surfactant impregnated colloidal suspensions. In the case of nanoparticle suspensions, the contact angle is observed to decrease for the hydrophobic system and increase for the hydrophilic systems considered. On the contrary, the combined particle and surfactant colloidal system shows a quasi-unique wetting behavior of decreasing contact angle with particle concentration on all substrates. Also interestingly, the combined particle surfactant system at all particle concentrations shows a wetting angle much lower than that of the only-surfactant case at the same surfactant concentration. Such counterintuitive observations have been explained based on the near-surface interactivity of the particle, fluid, and surfactant molecules based on effective slip length considerations. The CAH analyses of colloidal suspensions at varying surfactant and particle concentrations reveal in-depth physical insight into contact line pinning, and a unique novel relationship is established between the contact angle and differential energy for distorting the instantaneous contact angle for a pinned sessile droplet. A detailed theoretical analysis of the governing parameters influencing the wettability has been presented invoking the principles of DLVO (Derjaguin-Landau-Verwey-Overbeek), surface energy and interaction parameters influencing at the molecular scale, and the theoretical framework is found to support the experimental observations. © 2017 American Chemical Society.
About the journal
JournalData powered by TypesetJournal of Physical Chemistry B
PublisherData powered by TypesetAmerican Chemical Society
ISSN15206106
Open AccessNo
Concepts (21)
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    Colloids
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    Contact angle
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    Hydrophilicity
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    Hydrophobicity
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    Interfacial energy
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    Liquids
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    Molecules
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    Nanoparticles
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    Silicon wafers
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    Substrates
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    Surface active agents
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    Suspensions (fluids)
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    Colloidal suspensions
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    CONTACT ANGLE HYSTERESIS
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    EFFECTIVE SLIP LENGTHS
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    Interaction parameters
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    Nanoparticle suspension
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    Particle concentrations
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    POLAR SURFACE ENERGY COMPONENTS
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    Surfactant concentrations
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    Wetting