Highly Efficient Hyperbranched CNT Surfactants: Influence of Molar Mass and Functionalization

TL;DR

This study develops hyperbranched CNT surfactants with optimized molar mass and functionalization, achieving high dispersion efficiency and stability for carbon nanotubes in water, with insights into molecular interactions affecting performance.

Contribution

It introduces a new class of hyperbranched CNT surfactants with tunable functionalization and molar mass, demonstrating enhanced dispersion efficiency and stability.

Findings

Optimal surfactant: 5000 g/mol PG with 5.6% functionalization

Dispersed 2.85 mg CNT in 20 mL water with 1 mg surfactant

Dispersions remained stable for at least 2 months

Abstract

End-group-functionalized hyperbranched polymers were synthesized to act as a carbon nanotube (CNT) surfactant in aqueous solutions. Variation of the percentage of triphenylmethyl (trityl) functionalization and of the molar mass of the hyperbranched polyglycerol (PG) core resulted in the highest measured surfactant efficiency for a 5000 g/mol PG with 5.6% of the available hydroxyl end-groups replaced by trityl functions, as shown by UV-vis measurements. Semiempirical model calculations suggest an even higher efficiency for PG5000 with 2.5% functionalization and maximal molecule specific efficiency in general at low degrees of functionalization. Addition of trityl groups increases the surfactant-nanotube interactions in comparison to unfunctionalized PG because of pi-pi stacking interactions. However, at higher functionalization degrees mutual interactions between trityl groups come into play, decreasing the surfactant efficiency, while lack of water solubility becomes an issue at very high functionalization degrees. Low molar mass surfactants are less efficient compared to higher molar mass species most likely because the higher bulkiness of the latter allows for a better CNT separation and stabilization. The most efficient surfactant studied allowed dispersing 2.85 mg of CNT in 20 mL with as little as 1 mg of surfactant. These dispersions, remaining stable for at least 2 months, were mainly composed of individual CNTs as revealed by electron microscopy.