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Adsorption of Single Walled Carbon Nanotubes onto Silicon Oxide Surface Gradients of 3-Aminopropyltri(ethoxysilane) Described by Polymer Adsorption Theory

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journal contribution
posted on 01.09.2009, 00:00 by Monica L. Usrey, Michael S. Strano
Integration of single-walled carbon nanotubes (SWNT) into complex sensing and electronic devices can necessitate the selective placement of individual nanotubes from solution onto custom-prepared surfaces. Existing studies indicate carbon nanotube adsorption can be controlled by creating hydrophilic and/or hydrophobic surfaces, depending on the nanotube surface chemistry and solvent. Various recipes exist for specific conditions, but no quantitative theoretical model describing experimental observations has been developed. This work examines the adsorption behavior of SWNT functionalized with aryl hydroxyl (OH-SWNT) or aryl carboxylic acid groups (COOH-SWNT) onto 3-aminopropyltri(ethoxysilane) (APTES) concentration gradients on SiO2 wafers. For the first time, self-consistent field polymer adsorption theory is utilized to quantitatively describe SWNT adsorption onto planar surfaces. Experimental results indicate SWNT adsorption strongly depends on three key factors: concentration of APTES molecules on the silicon oxide and the type and number of SWNT functional groups. In general, COOH-SWNT adsorb to the greatest extent, followed by OH-SWNT and P2-SWNT. The data show a distinct threshold phenomenon, with appreciable adsorption detected only when the APTES concentration exceeded 2.6 × 1014 molecules/cm2.