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Research Papers

Precursor Film Formation Process Ahead Macroscopic Contact Line of Spreading Droplet on Smooth Substrate

[+] Author and Article Information
Ichiro Ueno1

 Tokyo University of Science,2641 Yamazaki, Noda,Chiba 278-8510, Japan e-mail: ich@rs.tus.ac.jp Graduate School at Tokyo University of Science,2641 Yamazaki, Noda,Chiba 278-8510, Japan

Kanji Hirose, Yusuke Kizaki, Yoshiaki Kisara, Yoshizumi Fukuhara

 Tokyo University of Science,2641 Yamazaki, Noda,Chiba 278-8510, Japan e-mail: ich@rs.tus.ac.jp Graduate School at Tokyo University of Science,2641 Yamazaki, Noda,Chiba 278-8510, Japan

1

Corresponding author.

J. Heat Transfer 134(5), 051008 (Apr 13, 2012) (4 pages) doi:10.1115/1.4005638 History: Received April 14, 2010; Revised February 21, 2011; Published April 11, 2012; Online April 13, 2012

The authors pay their special attention to formation process of wafer-thin liquid film, known as “precursor film,” ahead moving macroscopic contact line of a droplet spreading on a solid substrate. The spreading droplet on the solid substrate is accompanied with the movement of a visible boundary line so-called “macroscopic contact line.” Existing studies have indicated there exits a thin liquid film known as precursor film ahead the macroscopic contact line of the droplet. The present author’s group has dedicated their special effort to detect the formation process of the precursor film by applying a convectional laser interferometry and a high-speed camera, and to evaluate the spreading rate of the precursor film. In the present study, existing length of the precursor film at a very early stage of the droplet spreading is evaluated by applying a Brewster-angle microscopy as well as the interferometer. The authors extend their attention to the advancing process of the precursor film on inclined substrate.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

Grahic Jump Location
Figure 1

Interaction between the particle on the Si substrate and the precursor film ahead the macroscopic contact line (M-CL) of 2-cSt silicone oil. Original interferograms (top) and the images obtained by subtracting the basic image in the case of without any droplets and particles (bottom) are indicated. Zoomed views in the square of the first four frames in the bottom are superimposed on the frames. Morphological changes near the particle (arrow) are clearly seen in prior to the macroscopic contact line reaches at the particle position. These changes correspond to the interaction between the particle on the substrate and the precursor film. Width of the frame corresponds to 0.1 mm.

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Figure 2

Experimental apparatus: Brewster-angle microscopy (BAM)

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Figure 3

Examples of (a) detected image with BAM, and (b) time series of a brightness of BAM image at a certain measuring point

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Figure 4

Typical example of spatiotemporal variation of the negative brightness obtained with the BAM

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Figure 5

Temporal variations of the positions of the M-CL (lines) and the edge of the spreading precursor film (marks); dashed line and circle mark represent the results with the BAM, and solid line and triangle mark with the laser interferometer and the data analysis with the wavelet transformation [9]

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Figure 6

Precursor film length ahead the front macroscopic contact line (M-CL) of a droplet spreading on horizontal or inclined substrate as a function of nondimensional number Ca. “Front” and “Rear” indicate the edges located lower and higher on the substrate, respectively. Predicted length by Hervet and de Gennes [3] for the adiabatic precursor film is drawn as the dashed line.

Grahic Jump Location
Figure 7

Temporal variations of the of precursor film length ahead M-CL of droplet on horizontal or inclined substrate. Angle indicates the attitude of the substrate. Front and rear indicate the edges located lower and higher on the substrate, respectively.

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