The Possibility of Changing the Wettability of Material Surface by Adjusting Gravity
Apparent contact angles versus gravity. (a) AFM images of the sample solid surfaces and their section analyses. The analyses show that the surfaces are very smooth, with roughness less than 1 nm. (b) The contact angle on solid surfaces at different gravities. The contact angles show the same tendency to decrease with increasing gravity. The contact angle hysteresis was smaller than 3°, except for the cases of ethylene glycol and glycerol on PDMS9K. (c) Comparison of (the difference in contract angles at 1 G and 8 G) and (the average contact angle hysteresis). Independent -test was applied, ,,,,,, and , for water on DMDCS, water on PDMS9K, ethylene glycol on PDMS2K, glycerol on DMDCS, glycerol on PDMS2K, and glycerol on PDMS9K, respectively. Five out of the nine solid-liquid contact systems showed significant larger than , three showed comparable results. The experimental results confirmed that the decrease in the contact angle upon increasing gravity is caused by gravity, not only by the contact angle hysteresis.