5 research outputs found
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Universal emulsion stabilization from the arrested adsorption of rough particles at liquid-liquid interfaces
Surface heterogeneities, including roughness, significantly affect the adsorption, motion and interactions of particles at fluid interfaces. However, a systematic experimental study, linking surface roughness to particle wettability at a microscopic level, is currently missing. Here we synthesize a library of all-silica microparticles with uniform surface chemistry, but tuneable surface roughness and study their spontaneous adsorption at oil-water interfaces. We demonstrate that surface roughness strongly pins the particles' contact lines and arrests their adsorption in long-lived metastable positions, and we directly measure the roughness-induced interface deformations around isolated particles. Pinning imparts tremendous contact angle hysteresis, which can practically invert the particle wettability for sufficient roughness, irrespective of their chemical nature. As a unique consequence, the same rough particles stabilize both water-in-oil and oil-in-water emulsions depending on the phase they are initially dispersed in. These results both shed light on fundamental phenomena concerning particle adsorption at fluid interfaces and indicate future design rules for particle-based emulsifiers
Universal emulsion stabilization from the arrested adsorption of rough particles at liquid-liquid interfaces
Surface heterogeneities, including roughness, significantly affect the adsorption, motion and interactions of particles at fluid interfaces. However, a systematic experimental study, linking surface roughness to particle wettability at a microscopic level, is currently missing. Here we synthesize a library of all-silica microparticles with uniform surface chemistry, but tuneable surface roughness and study their spontaneous adsorption at oil–water interfaces. We demonstrate that surface roughness strongly pins the particles’ contact lines and arrests their adsorption in long-lived metastable positions, and we directly measure the roughnessinduced interface deformations around isolated particles. Pinning imparts tremendous contact angle hysteresis, which can practically invert the particle wettability for sufficient roughness, irrespective of their chemical nature. As a unique consequence, the same rough particles stabilize both water-in-oil and oil-in-water emulsions depending on the phase they are initially dispersed in. These results both shed light on fundamental phenomena concerning particle adsorption at fluid interfaces and indicate future design rules for particle-based emulsifiers.ISSN:2041-172
Synergistic Growth of Giant Wormlike Micelles in Ternary Mixed Surfactant Solutions: Effect of Octanoic Acid
The synergistic growth of giant wormlike
micelles in ternary mixed
solutions composed of an anionic surfactant (sodium laurylethersulfate,
SLES), a zwitterionic surfactant (cocamidopropyl betaine, CAPB), and
octanoic acid (HC8) is studied. Rheological data and their analysis
in terms of Cole–Cole plots and micellar characteristic times
are presented, and the micellar structures behind the observed rheological
behavior are revealed by cryo-TEM micrographs. The surfactant composition
is fixed near the maximal micelle size of the binary SLES + CAPB system,
whereas the concentration of HC8 is varied. At a given HC8 concentration,
the viscosity of the ternary micellar solutions exhibits a very high
and sharp peak. Polarized-light optical microscopy indicates that
all investigated solutions are isotropic rather than liquid-crystalline.
The cryo-TEM imaging shows complex phase behavior: wormlike micelles
to the left of the peak, giant entangled wormlike micelles at the
peak, and long wormlike micelles coexisting with multiconnected micellar
aggregates to the right of the peak. The formation of multiconnected
micelles leads to a drop in viscosity at the higher concentrations.
The results contribute to a better understanding of the structure–rheology
relations in micellar surfactant solutions and could be useful for
controlling the properties of formulations in personal-care and house-hold
detergency
Detachment of Rough Colloids from Liquid–Liquid Interfaces
Particle
surface roughness and chemistry play a pivotal role in
the design of new particle-based materials. Although the adsorption
of rough particles has been studied in the literature, desorption
of such particles remains poorly understood. In this work, we specifically
focus on the detachment of rough and chemically modified raspberry-like
microparticles from water/oil interfaces using colloidal-probe atomic
force microscopy. We observe different contact-line dynamics occurring
upon particle detachment (pinning vs sliding), depending on both the
particle roughness and surface modification. In general, surface roughness
leads to a reduction of the desorption force of hydrophobic particles
into the oil and provides a multitude of pinning points that can be
accessed by applying different loads. Our results hence suggest future
strategies for stabilization and destabilization of Pickering emulsions
and foams