Controlling Single-Walled Carbon Nanotube Surface Adsorption with Covalent and Noncovalent Functionalization

摘要

Carbon nanotube applications in advanced devices often require reproducible control of the placement of individual single-walled carbon nanotubes (SWNT). Directed assembly using self-assembled monolayer (SAM) patterns provides a possible solution where hydrophilic and hydrophobic surfaces are created to attract and/ or repel SWNT. In this work, control of SWNT adsorption onto SiO2 surfaces functionalized with 3-aminopropyl tri(ethoxysilane) (APTES) gradients is demonstrated using covalent and noncovalent chemistries. Noncovalent functionalization with anionic surfactant sodium dodecyl sulfate (SDS) and covalent functionalization with preformed aryl diazonium salts (-OH, -Cl, and -NO2) are utilized. Surprisingly, very low levels of covalent reaction (1-2 groups per 100 carbons) can outweigh the more prevalent SDS coverage in determining the extent of SWNT surface adsorption onto the silicon oxide surface. For aryl chloride, adsorption is enhanced, while the opposite occurs with the aryl nitro and aryl hydroxyl groups. Self-consistent field polymer adsorption theory is applied to describe the effect of functionalization on the surface adsorption energy. The model indicates SWNT adsorption extent is primarily driven by polymer stiffness and the thermodynamic stability of the suspension. However, changing the functionalization dramatically affects adsorption by altering the enthalpic energy gain upon placement on the surface.