Hyung-Sik Jang

Thermally Switchable One- and Two-Dimensional Arrays of Single-Walled Carbon Nanotubes in a Polymeric System

Fabrication of highly ordered arrays of single-walled carbon nanotubes (SWNTs) has been of great interest for a wide range of potential applications. Here, we report thermally switchable one- and two-dimensional arrays of individually isolated SWNTs formed by cooperative self-assembly of functionalized SWNTs and a block copolymer/water system. Small-angle X-ray scattering measurements reveal that when the block copolymer/water system is in an isotropic phase, two-dimensional hexagonal arrays of SWNTs are formed by depletion attraction, and when the block copolymer/water system is in a lamellar phase, one-dimensional lattices of SWNTs intercalated in the polar regions of the polymeric lamellar structure are formed by entropically driven segregation and two-dimensional depletion attraction. These two SWNT arrays are thermally interchangeable, following the temperature-dependent phase behavior of the block copolymer/water system.

Single-walled carbon nanotube induced re-entrant hexagonal phases in a Pluronic block copolymer system

We report a new single-walled carbon nanotube (SWNT)-induced re-entrant lyotropic phase behavior of Pluronic F127 block copolymers in water which show two hexagonal phase regions. The small angle X-ray scattering measurements show that as the concentration is increased from 5 to 100 wt% by evaporation, the F127–SWNT/water system exhibits isotropic–hexagonal–(FCC/hex)–BCC–hexagonal–lamellar phase transitions, which is in contrast to the F127/water system showing isotropic–FCC–BCC–hexagonal-lamellar phase transitions. This clearly indicates that, in the F127–SWNT/water system, the 1sthexagonal phase is induced by the presence of long one-dimensional SWNTs and the 2ndhexagonal phase originates from the phase behavior of F127 itself. The presence of SWNTs also induced the shifts of phase transition concentrations and the change of domain sizes. The SWNTs in the hexagonal phases are located in the hydrophobic core (PPO domain) of F127 cylinders, making their orientation parallel to the [001] direction. The possible orientations of SWNTs (which maintain their individuality or very small bundle state) in the FCC and BCC phases were identified based on the epitaxial transitions between corresponding phases (hexagonal to FCC, FCC to BCC, and BCC to hexagonal): [110] in the FCC and 〈111〉 in the BCC.

Hydration forces between surfaces of surfactant coated single-walled carbon nanotubes

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. Here, we measured interaction force between SWNTs encapsulated with polymerized surfactant monolayer (p-SWNTs). The balance between the repulsion between p-SWNTs and the osmotic pressure exerted by poly(ethylene glycol) in aqueous solution results in two-dimensional hexagonal arrays of p-SWNTs with very small surface to surface distances (<1 nm). The interaction force measured by the osmotic pressure technique shows characteristic decay length of hydration force in its origin.

Highly Ordered and Highly Aligned Two‐Dimensional Binary Superlattice of a SWNT/Cylindrical‐Micellar System

We report a highly ordered intercalated hexagonal binary superlattice of hydrophilically functionalized single-walled carbon nanotubes (p-SWNTs) and surfactant (C12 E5 ) cylindrical micelles. When p-SWNTs (with a diameter slightly larger than that of the C12 E5 cylinders) were added to the hexagonally packed C12 E5 cylindrical-micellar system, p-SWNTs positioned themselves in such a way that the free-volume entropies for both p-SWNTs and C12 E5 cylinders were maximized, thus resulting in the intercalated hexagonal binary superlattice. In this binary superlattice, a hexagonal array of p-SWNTs is embedded in a honeycomb lattice of C12 E5 cylinders. The intercalated hexagonal binary superlattice can be highly aligned in one direction by an oscillatory shear field and remains aligned after the shear is removed.