Use of a chondroitin sulfate isomer as an effective and removable dispersant of single-walled carbon nanotubes.

Three isomers of chondroitin sulfate (CS), i.e., CS-A, CS-B, and CS-C, are investigated as nanotube dispersants and are found to have vastly different abilities to disperse single-walled carbon nanotubes (SWNTs) in water due to their different intramolecular interactions. Only CS-A and CS-C effectively disperse SWNTs into small bundles or individual tubes while CS-B disperses SWNTs poorly. Computer simulation and circular dichrosim show that neat CS-A and CS-C have weak intramolecular hydrogen bonding and extended conformations in solution resulting in energetically more favorable interactions with nanotubes. CS-B has relatively strong intramolecular Coulombic interaction and more alpha-helical secondary structure in solution resulting in energetically less favorable interaction with the nanotubes. Atomic force microscopy images show helical wrappings of CS-A and CS-C around the SWNTs. Transmission electron microscopy corroborates the helical wrapping of CS-A. Different isomeric forms of a polymer can have vastly different dispersing power because of their different intramolecular interactions and conformations. The easy removability of CS-A from nanotubes is confirmed with X-ray photoelectron spectroscopy showing almost no detectable sulphur content after washing with water and by application of washed CS-A dispersed SWNTs in field-effect transistors.

Gel electrophoresis using a selective radical for the separation of single-walled carbon nanotubes.

We have applied agarose gel electrophoresis (AGE) to single-walled carbon nanotubes (SWNTs) that have been pre-reacted with metallic-selective ionic radicals and then re-suspended with sodium cholate (SC) surfactant to obtain highly purified (up to 98%) semiconducting single-walled carbon nanotubes (s-SWNTs). The proposed combination method exploits the preferential reactivity with the metallic nanotube of the radicals generated from an azo naphthalene compound (Direct Blue 71(I)) to preferentially increase the surface charge, and therefore the electrophoretic mobilities, of the metallic nanotube population under the influence of the electric field in AGE. The excellent separation achieved was verified by UV-vis-NIR and Raman spectroscopy as well as by the performance of field effect transistors fabricated with semiconducting-enriched SWNTs. FETs fabricated with -assisted AGE-separated semiconducting nanotubes exhibited mobilities of ∼3.6 to 11.7 cm(2) V(-1) s(-1) and on/off ratios from 10(2) to 10(6).

Role of interface in dispersion and surface energetics of polymer nanocomposites containing hydrophilic POSS and layered silicates.

Three different hydrophilic nanofillers--natural and synthetic layered silicate as well as octaammonium polyhedral oligomeric silsesquioxane (POSS)--were incorporated into polyamide-6 by a solution-mixing method. The surfaces of the resulting polymer nanocomposites were characterized by X-ray diffraction, polarized optical microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and contact angle measurements. All polymer nanocomposites displayed enhancement in surface hydrophilicity as well as increase in surface free energy due to surface enrichment of the nanofillers. The degree of enhancement was found to depend on both nanofiller type and dispersion state. Interfacial interactions in the form of hydrogen bonding played an important role in affecting the dispersion state of the layered silicates. Exfoliated layered silicates caused a larger increase in hydrophilicity than aggregated layered silicate. On the other hand, aggregated POSS molecules were able to induce a large increase in hydrophilicity. Significant spreading of water was also observed on surfaces containing POSS molecules. Surface models have been proposed to explain these phenomena.

Synthesis of novel hybrid films of a layered silicate and alkylammonium cations on rough polymeric surfaces by Langmuir-Blodgett method.

Hybrid films of a layered silicate and an amphiphilic alkylammonium (hexadecyltrimethylammonium) cation have been prepared by Langmuir-Blodgett (LB) method and transferred onto a polyamide surface by dip coating. This is the first time that stable LB hybrid monolayer and multilayer films have been formed on rough polymeric surfaces. The films were characterized by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM) and water contact angle measurements. XRD and FTIR showed that the hybrid multilayer was well-organized and the thickness of one layer was calculated to be 1.6nm. Furthermore, the layered silicate was determined to be on the substrate side and the amphiphilic molecule layer was exposed to the air side. This provides a novel methodology for the surface modification of polymers.