| Budget Amount *help |
¥3,700,000 (Direct Cost: ¥3,700,000)
Fiscal Year 2005: ¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 2004: ¥2,300,000 (Direct Cost: ¥2,300,000)
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| Research Abstract |
It is well known that liquid mercury hardly wets non-metallic substances such as glasses or sapphire under ambient conditions. However, mercury wets sapphire substrate under high temperature and pressure conditions near the liquid-gas critical point (1478℃、167MPa), and the thickness of the wetting film jumps discontinuously at a line on the pressure-temperature plane. This is the 1st order phase transition called the prewetting (PW) transition. In the present work, we studied the static and dynamic properties of the wetting film by using optical methods such as (1) optical reflectivity, (2) optical emissivity, (3) static light scattering and (4) dynamic light scattering, and tried to unveil the crossover between the 2-and the 3-dimensional critical phenomena.
From the static light scattering, we observed that diffuse scattering appears around the specularly reflected light spot when the wetting film is present. Interestingly, this diffuse scattering is strong along the vertical directio
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n, and weak along the horizontal direction. This result indicates that the gravity plays important role on the structure of the light scatterer in the wetting film. In the PW transition region, there exist contact lines between the thick and the thin wetting films, and the gravity makes the contact lines aligned along the horizontal direction, resulting in the strong diffuse scattering along the vertical direction. From the dynamic light scattering, we observed intermittent fluctuations in the scattering intensity, and these fluctuations are interpreted to be caused by the movement of the contact line across the laser light spot. We estimated the velocity of the contact line, and found that the contact line moves mainly along the vertical direction.
As a related study, we studied the wetting phenomena of selenium-thallium mixtures on a quartz substrate. This system transforms from semiconductor to metal with increasing thallium concentration, and has a similarity to mercury, which shows metal-nonmetal transition with decreasing density. Surprisingly, "critical point dewetting" phenomena was observed : the wetting film is not formed near the critical temperature but is formed in the lower temperature region. This is completely opposite to the Cahn's prediction of "critical point wetting" and is very interesting phenomena. Less
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