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Low Temperature Reliability of Carbon Nanotube/Silicone Superhydrophobic Coatings
Keywords: superhydrophobic, carbon nanotube, composite materials
Carbon nanotube (CNT) based composite materials have been investigated for various applications to improve electrical and thermal performances or mechanical characteristics of conventional composite materials. Among the applications, superhydrophobic coating is also of great importance. In the present work, we studied anti-frosting effect and low temperature reliability of the composite coatings was investigated under zero degree Celsius. Composite materials of CNT/silicone was deposited by spraying them on Al and Si substrate and the CNT content in the composite coatings was varied (5~40vol.%) to investigate a correlation between the microstructures and their reliabilities. With low CNT content of 5 & 10vol.%, the CNTs were found to be embedded in silicone matrix. Little CNTs were found on the surface of the silicone matrix. As the CNT content increases, a great number of porosities were formed inside the composite. In this case, individual CNTs and CNT bundles were entangled with each other with the nano-pores inside them. Each of them was covered with thin silicone layer on its surface. For superhydrophobic characteristics, clear differences were shown for the two different microstructures. The former displayed small contact angles (<140˚) and large sliding angles (~90˚). On the contrary, the latter presented large contact angles (~150˚) and small sliding angles (<5˚). The largest contact angle (and the smallest sliding angle) was found in CNT 20vol.% composite specimen. Temperature cycling test (-30˚C ~ room temperature) was conducted to confirm the reliability of the CNT/silicone superhydrophobic coatings. The cyclic operation was conducted from -30˚C (40min) to room temperature (20min after power off) and was prolonged up to 4000 times. The composite with MWNT 20vol.% passed 4000 cycles without any serious damage of the superhydrophobic coatings. On the other hand, the composite with MWNT 10vol.% degraded only after 400 cycles. Numerous cracks were formed inside silicone matrix in these specimens. The CNTs were found to be aligned vertically to crack forming directions. Anti-frosting effect of the CNT/silicone superhydrophobic coatings was also investigated with the CNT 20vol.% specimens. Thicknesses of the frosts grown during refrigeration at -30˚C were measured and compared with those formed on bare Al substrate. The onset of frost growth was delayed for one hour and average thickness of the frosts was about half for the case of bare Al substrate.
Yoonchul Sohn, Research Staff Member
Samsung Advanced Institute of Technology, Samsung Electronics
Yongin, Gyeonggi-do 446-712,
Korea


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