Recent work by Prof. Sung-Min Choi’s group has been featured as the Cover Page of The Journal of Chemical Physics (Volume 138, Issue 11, 2013) which retains the top spot as the most highly cited journal in Atomic, Molecular & Chemical Physics. The interaction force between functionalized single-walled carbon nanotubes (SWNTs) plays an important role in the fabrication of self-assembled and highly ordered SWNT arrays for a wide range of potential applications.In this work, the hydration forces between surfaces of surfactant coated single-walled carbon nanotubes were measured, for the first time, using small angle x-ray scattering method. The new insights of interaction forces between functionalized SWNTs learned from this study provide key information for designing new advanced functional materials using SWNTs. This was performed by Changwoo Do (now at ORNL, US) and Hyung-Sik Jang (now at LG Chem) under supervision of Prof. Choi.