Assessment of nanoparticle immersion depth at liquid interfaces from chemically equivalent macroscopic surfaces
Date Issued
2022-04
Abstract
Hypothesis: We test whether the wettability of nanoparticles (NPs) straddling at an air/water surface or oil/water interface can be extrapolated from sessile drop-derived macroscopic contact angles (mCAs) on planar substrates, assuming that both the nanoparticles and the macroscopic substrates are chemically equivalent and feature the same electrokinetic potential.
Experiments: Pure silica (SiO2) and amino-terminated silica (APTES-SiO2) NPs are compared to macroscopic surfaces with extremely low roughness (root mean square [RMS] roughness ≤ 2 nm) or a roughness determined by a close-packed layer of NPs (RMS roughness ∼ 35 nm). Equivalence of the surface chemistry is assessed by comparing the electrokinetic potentials of the NPs via electrophoretic light scattering and of the macroscopic substrates via streaming current analysis. The wettability of the macroscopic substrates is obtained from advancing (ACAs) and receding contact angles (RCAs) and in situ synchrotron X-ray reflectivity (XRR) provided by the NP wettability at the liquid interfaces.
Findings: Generally, the RCA on smooth surfaces provides a good estimate of NP wetting properties. However, mCAs alone cannot predict adsorption barriers that prevent NP segregation to the interface, as is the case with the pure SiO2 nanoparticles. This strategy greatly facilitates assessing the wetting properties of NPs for applications such as emulsion formulation, flotation, or water remediation.
Experiments: Pure silica (SiO2) and amino-terminated silica (APTES-SiO2) NPs are compared to macroscopic surfaces with extremely low roughness (root mean square [RMS] roughness ≤ 2 nm) or a roughness determined by a close-packed layer of NPs (RMS roughness ∼ 35 nm). Equivalence of the surface chemistry is assessed by comparing the electrokinetic potentials of the NPs via electrophoretic light scattering and of the macroscopic substrates via streaming current analysis. The wettability of the macroscopic substrates is obtained from advancing (ACAs) and receding contact angles (RCAs) and in situ synchrotron X-ray reflectivity (XRR) provided by the NP wettability at the liquid interfaces.
Findings: Generally, the RCA on smooth surfaces provides a good estimate of NP wetting properties. However, mCAs alone cannot predict adsorption barriers that prevent NP segregation to the interface, as is the case with the pure SiO2 nanoparticles. This strategy greatly facilitates assessing the wetting properties of NPs for applications such as emulsion formulation, flotation, or water remediation.
Subjects
Contact angle
;
Nanoparticles
;
Liquid surface/interface
;
Immersion depth
;
Zeta (electrokinetic) potential
;
Electrophoretic mobility
;
Sessile drop
;
Atomic Force Microscopy
;
Streaming current
;
X-ray reflectivity
Publisher
Elsevier Science
Institution
Type
journal article
Journal/Edited collection
Band
611
Start page
670
End page
683
Secondary publication
Yes
Document version
Postprint
Language
English
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