| 摘要 |
PROBLEM TO BE SOLVED: To maintain a surface of a member in a clean state for a long period even when an illuminance of an exciting light is low and a load of adhered dirt is large and to alleviate a load by cleaning, by forming a porous portion on the surface of the member, and reducing a radius of an opening surface of the porous portion to a smaller value than a specific value of a Kelvin formula. SOLUTION: A porous portion is formed on a surface of a member, and a radius of an opening surface of the porous portion is reduced smaller than rk of a Kelvin formula. That is, the formula is 1np/p0=-2γV0cosθ/rkRT, where (p) is a vapor pressure brought into contact with a menuscus, P0 is a saturated vapor pressure on a normally flat liquid surface,γis a surface tension of a condensate, V0 is a molecula volume of the condensate,θis a contact angle between a wall of the porous portion and the condensate, rk is a radius of the porous portion (nm), R is an equilibrium constant, and T is a temperature (K). According to this, the radius of the opening surface of the portion can be set in response to using environment (temperature, humidity or the like) of the hydrophilic composite member, and the surface of the member can be hydrophilized, and hence the member can be held clean.
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