Abstract
The effectiveness of carbon nanotubes (CNT) deagglomeration by rapid expansion of supercritical suspensions (RESS) in nitrogen and carbon dioxide fluids was studied in this work. Two different mechanisms of deagglomeration were proposed for these two fluids at various temperature and pressure conditions. Ultrasound attenuation spectroscopy was applied as an express method of determining median diameter and aspect ratio of CNTs. At least twofold reduction of the diameter was shown for CNT bundles processed by RESS technique. Aspect ratio of processed CNTs, calculated from acoustic attenuation spectra, increased to 340. These results were in a good agreement with atomic force microscopy data.
Highlights
Uniqueness of physical properties of carbon nanotubes (CNTs) basically define by their thermodynamics state, namely, the most CNT applications in microelectronics [1], polymer nanocomposites [2,3], displays [4], solar panels [5], membranes [6], and many others [7,8], require stable homogeneous CNT dispersions without agglomerates or bundles
We have studied the characteristics of aqueous dispersions of two CNT types: Starting CNTs and CNTs modified by the method of Rapid Expansion of Supercritical Suspensions, rapid expansion of supercritical suspensions (RESS) [19,20]
The following methods were applied for characterizing CNT dispersion samples: Transmission electron microscopy (TEM) on a JEM-2100 instrument at an accelerating voltage of 200 kV, scanning electron microscopy (SEM) on a JSM-7001F apparatus at an accelerating voltage of 30 kV, atomic force microscopy (AFM) in a semi-contact mode on an Ntegra Prima instrument, and acoustic spectroscopy (AS) on a DT-500 apparatus in the frequency range of 1–100 MHz.The samples for the microscopy studies were prepared by diluting the starting dispersions by about 1000 times and depositing them onto carbon networks for the TEM and onto atomically smooth substrates made of mono-crystal silicon steel for the SEM and AFM measurements
Summary
Uniqueness of physical properties of carbon nanotubes (CNTs) basically define by their thermodynamics state, namely, the most CNT applications in microelectronics [1], polymer nanocomposites [2,3], displays [4], solar panels [5], membranes [6], and many others [7,8], require stable homogeneous CNT dispersions without agglomerates or bundles. Despite the high effectiveness of CNT deagglomeration, this method has a significant disadvantage: Such treatment can make CNTs much shorter, which leads to undesirable changes in the properties of the final product containing CNTs [10,11,12]. Depending on the application purpose, an SCF-suspension can be sprayed into a gas to obtain a dry powder (the “dry” method) or into a solvent medium to form a CNT dispersion (the “wet” method) [18]. In the latter case, it is possible to add surfactants to the liquid medium for achieving additional stabilization of CNTs in the suspension. We have studied the characteristics of aqueous dispersions of two CNT types: Starting CNTs and CNTs modified by the method of Rapid Expansion of Supercritical Suspensions, RESS [19,20]
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