Meniscus Shape around Nanoparticles Embedded in Molecularly Thin Liquid Films

Abstract

Individual nanoparticles embedded in molecularly thin films at planar substrates and the resulting film surface distortion (meniscus) adjacent to the nanoparticles are investigated by conventional optical reflection microscopy. Even for nanoparticles much smaller than the Rayleigh diffraction limit, the meniscus creates such a pronounced optical footprint that the location of the nanoparticles can be identified. This is because the decay length (lateral extension) of the meniscus exceeds the size of the nanoparticle by orders of magnitude. Therefore, for the first time, the exact shape of the meniscus of the liquid adjacent to a nanosize object could be measured and analyzed. The meniscus has a zero curvature shape (cosine hyperbolic). The liquid in the meniscus is in pressure equilibrium with the far-field planar film. The decay length decreases with the decreasing nanoparticle size. However, it is independent of the far-field film thickness. Supposedly, the decay length is determined by van der Waals interactions although it is unknown what determines its (unexpectedly large) absolute value. The presented technical approach may be used to investigate biological systems (for instance, surface distortions in supported membranes caused by proteins or protein aggregates).

Alkanes as Intelligent Surface Thermometers: A Facile Approach to Characterize Short‐Lived Temperature Gradients on the Micrometer Scale

“…These nanometer thin structures can easily be imaged with standard optical microscopy techniques. [ 29,30 ] Alkanes are inert, non‐conductive, transparent, and well characterized. Their temperature behavior, as well as, their melting and boiling points (here, 37–522 °C) depend on their chain length.…”

“…A laser is focused onto the film from underneath (spot size d spot = 40 µm, see Figure S1, Supporting Information). Since the polyimide is coated with a (sub‐)mono or multilayer of alkanes, a simple reflective optical microscope setup [ 29 ] is used to image the thin film. We used a fast high‐resolution camera with 1000 fps, which is not required but useful for in situ imaging.…”

Controlled Deposition of Nanosize and Microsize Particles by Spin-Casting

“…Optical imaging was improved by interference enhanced reflection 28 and image processing. 29 Imaging was performed with an EoSenseCL MC1362 high-speed camera (Mikrotron GmbH) of up to 1000 fps. The film-thinning behavior was derived by interferometry from the brightness variations during film thinning.…”

“…The film-thinning behavior was derived by interferometry from the brightness variations during film thinning. 1,2,27,29,30 (See the Supporting Information for thinning curves of water and ethanol. )…”

“…The spin-coater was mounted on an X – Y table to enable variable observation spots. Optical imaging was improved by interference enhanced reflection and image processing . Imaging was performed with an EoSenseCL MC1362 high-speed camera (Mikrotron GmbH) of up to 1000 fps.…”