Nanoparticle in a Nanofluid Film Spreading on a Surface

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Original entry by Hyerim Hwang, AP 226, Spring 2012. not finished

Reference

Alex Nikolov, Kirti Kondiparty, and Darsh Wasan, "Nanoparticle Self-Structuring in a Nanofluid Film Spreading on a Solid Surface", Langmuir 2010 26(11), 7665-7670

Keywords

Thin film stability, Nanofluids, Disjoining pressure

Introduction

Figure 1.Photomicrograph depicting nanofluid film formation.
This paper investigates the complex mechanism involved in the solid-nanofluid-oil interactions by directly observing the phenomenon of nanoparticle self-layering due to confinement of nanoparticles in a thin film. This research also shows that the effect of film size on stability of nanolfluid films on a solid substrate.
Figure 2. (a) Film with dimple in the shape of a horseshoe and (b) filme with four particle layers. (c) With time, a film with three layers of particles.

Results

Figure 3. Photomicrograph depicting particle layering of silica suspension on a solid surface.
Figure 4. (A) Photomicrograph depicting the nanofluid film and the adjoining meniscus. (B) Differential interferometry in reflected light. (C) Film-meniscus profile.
Figure 5. Profile of the nanofluid film-meniscus region as probed by differential interferometric method.
Figure 6. Film-meniscus microscopic contact angle versus film thickness and corresponding number of particle layers in a stratifying nanofluid film on a surface.

This research shows the solid-oil interactions in the presence of a silica nanoparticle aqueous suspension, using a combined differential and common reflected light interferometry by observing the three-phase contact region as presented in Figure 1. Figure 2 shows a sequence of photomicrographs depicting the development of the particle layering phenomenon during the film thinning process. It is shown that a photomicrograph depicting four different particle structural transitions inside the nanofluid film in Figure 3. Here, the experiments revealed that the nanofluid film thickness stability on a solid substrate depends on the film size. Figure 4 presents an example of a small oil drop, that shows that the nanofluid film formed between oil drop and the glass surface surrounded by the meniscus, indicated by the consecutive dark and bright Newton interference rings around the perophery of the film. The interferogram depicting the film-meniscus profile is shown in Figure 4C. Figure 5 shows the film-meniscus region profile corresponding to the maxima and minima in the interferogram.

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The film-meniscus microscopic contact angle is related to the disjoining pressure, given by the equation above which is Frunkim-Derjaguin equation. The second term on the right side of the equation is the interaction energy between the film surfaces. Thus, the film energy can be calculated from the measured values of the contact angle versus film thickness using the equation. Figure 6 is what this research got as experimental results.

Discussion

In this paper, the experimental results of the nanoparticle self-ordering and stepwise thinning of the nanofluid film fromed between an oil drop and a solid surface are reported. This also presents the measured contact angle of film-meniscus and thickness corresponding to the number of particle layers on a solid surface. These were used for getting the film energy due to the nanoparticle layering within the nanofluid film.