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Published on: June 6, 2017
Wettability effects on interfacial rheology and stability of particle-laden oil-water interfaces
Eduarda B Oliveira1, Elton L Correia1, Sepideh Razavi1
1School of Sustainable Chemical, Biological and Materials Engineering, University of Oklahoma, 100 E. Boyd Street, Norman, OK 73019, USA.
Hypothesis:
The wettability of colloidal particles alters the balance between capillary attraction and electrostatic repulsion at the oil-water interface, leading to distinct microstructures and impacting how particle-laden interfaces respond to applied stresses.
Experiments:
Silica particles (1 μm) with two tailored wettabilities were produced by controlled silanization and characterized via contact angle and zeta potential measurements. Their interfacial assembly and collapse mechanisms at the oil-water interface were probed using a Langmuir trough coupled with an optical microscope. Interfacial shear rheology using a double wall ring geometry quantified viscoelastic behavior, including strain-dependent yielding and frequency response.
Findings:
Modeling of capillary and electrostatic interaction potentials showed that neutrally wetting particles generate markedly stronger anisotropic quadrupolar capillary attraction, whereas more hydrophobic particles experience weaker capillary fields. Experimentally, neutrally wetting particles formed cohesive, fractal-like networks that collapsed through wrinkle formation and exhibited elastic, strain-thickening, and slower relaxation dynamics. In contrast, highly hydrophobic particles assembled into compact rafts that collapsed via particle expulsion and displayed fluid-like, frequency-dependent behavior with faster relaxation. Together, the interaction modeling and measurements demonstrate that particle wettability governs the interparticle force landscape that dictates network assembly, collapse mechanisms, and the viscoelastic response of particle-laden oil-water interfaces.
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