Double-Walled Carbon Nanotube Separation by Buoyant Density
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Solution Overview
Problem
Current methods for synthesizing double-walled carbon nanotubes (DWCNTs) produce significant quantities of unwanted single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs), and existing separation techniques are ineffective in achieving highly enriched DWCNT populations with uniform electrical and optical properties, particularly due to similar thermal stabilities and overlapping diameter ranges.
Innovation Solution
The method involves using density gradient ultracentrifugation (DGU) with surface active components to separate DWCNTs from mixed populations based on wall number, diameter, chirality, and electronic type, allowing for the enrichment of DWCNTs while recovering other nanotube types without degrading their properties, using a solvent with a density gradient medium like iodixanol and selecting surface active components that confer different buoyant densities to nanotubes of varying wall numbers and electronic types.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If high temperature oxidation is used to remove SWCNT impurities, then the proportion of DWCNTs increases, but the electrical and optical properties of DWCNTs are degraded
Solution Approach 1:
The patent uses surface active components as intermediaries that selectively interact with nanotubes of different wall numbers. These components form complexes with nanotubes, enabling separation by buoyant density without requiring harsh oxidation conditions that would degrade the electrical and optical properties of DWCNTs.
Solution Approach 2:
The patent replaces thermal oxidation methods with a mechanical separation approach using density gradient ultracentrifugation. This substitution allows separation of nanotubes by wall number based on buoyant density differences, avoiding the thermal damage caused by high temperature oxidation while achieving high DWCNT enrichment.
2Quantity of substance
If density gradient ultracentrifugation is used to separate nanotubes by wall number, then DWCNT enrichment is achieved, but the method complexity increases
Solution Approach 1:
The patent utilizes changes in buoyant density as a separating parameter. By using surface active components that confer different buoyant densities to nanotubes of different wall numbers, the method achieves effective separation through density gradient ultracentrifugation, transforming a complex physical separation problem into a manageable density-based process.
3Quantity of substance
If oxidative treatment is used to increase DWCNT proportion, then SWCNT impurities are removed, but MWCNTs remain because DWCNTs and MWCNTs have similar thermal stabilities
Solution Approach 1:
Surface active components serve as intermediaries that differentially interact with nanotubes based on their wall number. The components form complexes with SWCNTs and MWCNTs that have different buoyant densities compared to DWCNTs, enabling selective separation without relying on thermal stability differences.
Solution Approach 2:
The patent replaces thermal oxidation with density-based mechanical separation. This substitution allows differentiation between DWCNTs and MWCNTs based on their different buoyant densities in the presence of surface active components, achieving complete separation without the limitations of thermal stability-based methods.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach achieves high-purity DWCNT populations with enhanced properties, suitable for applications in devices such as light emitting diodes, photovoltaics, and field-effect transistors, by increasing the DWCNT percentage from 50% to 80% or more in a single separation cycle, and can further refine the separation to achieve DWCNTs with specific electronic types and chirality.
Implementation Method 1
The carbon nanotube dispersion is subjected to density gradient ultracentrifugation (DGU) by introducing the dispersion into a fluid medium including a density gradient
Implementation Method 2
the one or more surface active components can be selected for their ability to associate differentially with carbon nanotubes of different wall numbers such that individual carbon nanotubes of different wall numbers, upon association with the surface active components, can exhibit different buoyant densities in the solvent
Implementation Method 3
the fluid medium can be agitated, for example, by ultracentrifugation, to allow separation of the carbon nanotubes by wall number along the density gradient
Data Source
AI summary
A method of separating carbon nanotubes by electronic type includes centrifuging a carbon nanotube composition in contact with a first fluid medium comprising a first density gradient; and separating the carbon nanotube composition into two or more separation fractions. The carbon nanotube composition comprises two or more non-ionic amphiphilic surface active components and a carbon nanotube population comprising double-walled carbon nanotubes having a semiconducting outer wall (s-DWCNTs), and double-walled carbon nanotubes having a metallic outer wall (m-DWCNTs). The two or more separation fractions comprise a first separation fraction comprising a carbon nanotube subpopulation comprising a higher percentage of s-DWCNTs than the carbon nanotube population, and a second separation fraction comprising a carbon nanotube subpopulation comprising a higher percentage of m-DWCNTs than the carbon nanotube population.