Modeling of thermocapillary flow to purify single-walled carbon nanotubes

Jizhou Song; Chaofeng Lu; Chenxi Zhang; Sung Hun Jin; Yuhang Li; Simon N. Dunham; Xu Xie; Frank Du; Yonggang Huang; John A. Rogers

doi:10.1039/C4RA08895F

Modeling of thermocapillary flow to purify single-walled carbon nanotubes

Jizhou Song,†*^a Chaofeng Lu,†^b Chenxi Zhang,^c Sung Hun Jin,^d Yuhang Li,^e Simon N. Dunham,^f Xu Xie,^f Frank Du,^f Yonggang Huang*^g and John A. Rogers^f

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* Corresponding authors

^a Department of Engineering Mechanics and Soft Matter Research Center, Zhejiang University, Hangzhou 310027, China
E-mail: jzsong@zju.edu.cn

^b Department of Civil Engineering and Soft Matter Research Center, Zhejiang University, Hangzhou 310058, China

^c Department of Mechanical and Aerospace Engineering, University of Miami, Coral Gables, Florida 33146, USA

^d Department of Electronics Engineering, Incheon National University, Incheon, Republic of Korea

^e The Solid Mechanics Research Center, Beihang University (BUAA), Beijing 100191, China

^f Department of Materials Science and Engineering, Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA

^g Department of Civil and Environmental Engineering, Department of Mechanical Engineering, Center for Engineering and Health and Skin Desease Research Center, Northwestern University, Evanston, Illinois, 60208, USA
E-mail: y-huang@northwestern.edu

Abstract

Single walled carbon nanotubes (SWNTs) are of significant interest in the electronic materials research community due to their excellent electrical properties. The mixture of synthesized SWNTs, however, significantly hampers device performance, particularly for potential applications in digital electronics. Recent purification techniques involve successful and complete removal of metallic SWNTs from horizontal arrays by using thermocapillary flows in thin film resists initiated by selective Joule heating. In this paper, an analytical model, as well as a fully coupled thermo-mechanical-fluid finite element model, is developed to study the physics of thermocapillary flow in this context. A simple scaling law for the film thickness profile is established in terms of the geometry (e.g., film thickness), material (e.g., thermal conductivity and viscosity) and loading parameters (e.g., power density). The results show that the normalized thickness profile only depends on three non-dimensional parameters in addition to the normalized position and normalized time. In particular, for the experimentally investigated system, the thickness profile only depends on a single non-dimensional parameter. These findings may serve as useful design guidelines for process optimization.

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Modeling of thermocapillary flow to purify single-walled carbon nanotubes

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