INFORM March 2025

36 • inform March 2025, Vol. 36 (3)

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Surface tension of NPSC

Surface tension [mN m - 1] Surface area 80 60 40 20 0

40

Surface area [mm 2]

30

20

10

60

Surface pressure [mN m - 1] 40 20 0 0

0

1000 2000

Surfactant + Nanoparticle NanoParticle-Surfactant Complex (NPSC)

Time [s]

0.5

1

Normalized surface area

Compression

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NPSC-laden drop under large amplitude compression

Interference pattern of thin liquid film with NPSC

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Experiments Zeta potential, dynamic light scattering, high amplitude surface pressure and surface tension measurements are employed syner gistically to characterize the interfacial properties of the nanoparti cle-surfactant system. Interferometric experiments are performed to highlight the effect of surface concentration on the stability of thin liquid films. Findings The interfacial properties of surfactant/nanoparticle mixtures are primarily determined by the surfactant/nanoparticle ratio.

Below a certain ratio, free surfactant molecules are removed from the solution by the formation of surfactant-nanoparticle com plexes. Surprisingly, even though the concentration and hydro phobicity of these complexes do not seem to have a noticeable impact on the surface tension, they do significantly affect the rheological properties of the interface. Above this ratio, free surfactant monomers and nanoparticle-surfactant complexes coexist and can co-adsorb at the interface, changing both the interfacial tension and the interfacial rheology, and thus, for example, the foamability and foam stability of the system.

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