SELECTIVE PRECIPITATION OF COLLOIDAL SWCNTS FOR REDUCING SAMPLE HETEROGENEITY
Constantine Khripin, Nicholas Arnold-Medabalimi, and Ming Zheng
Single-wall carbon nanotubes (SWCNTs) are frustratingly heterogeneous, both in terms of their length and molecular structure, or chirality. SWCNT heterogeneity has held back applications of this promising material. Although several purification methods have been developed, these are too costly and/or too sophisticated for widespread use. We have recently developed a simple, accessible method for increasing the homogeneity of SWCNT samples, “selective precipitation” of colloidal SWCNTs. Under normal circumstances, colloidal SWCNTs are highly stable. However, when an inert polymer (e.g. PEG) is added to the solution, some SWCNTs self-assemble into clusters and precipitate. If there is no enthalpic interaction between the polymer and the SWCNT (as is the case for PEG) SWCNT precipitation is length-dependent. However, some other polymers show attractive enthalpic interaction with SWCNTs, and in this case precipitation is SWCNT structure-dependent. Adjustments to the colloidal environment, such as temperature and buffer type, can be used to tune the selectivity of precipitation. By changing the polymer and fine-tuning the colloidal environment, it is possible to easily obtain large amounts of SWCNTs with low variability in both length and molecular structure.