Fractal structures of single-walled carbon nanotubes in biologically relevant conditions: Role of chirality vs. media conditions

Abstract

Aggregate structure of covalently functionalized chiral specific semiconducting single-walled carbon nanotubes (SWNTs) was systematically studied employing static light scattering (SLS). Fractal dimensions (Df) of two specific chirality SWNTs—SG65 and SG76 with (6, 5) and (7, 6) chiral enrichments—were measured under four biological exposure media conditions, namely: Dulbecco’s Modified Eagle Medium (DMEM), Minimum Essential Medium (MEM), Roswell Park Memorial Institute (RPMI) 1640 medium, and 0.9% saline solution. The SWNTs exhibited chiral dependence on Df with SG65 showing more fractal or loosely bound aggregate structures, i.e., lower Df values (range of 2.24 ± 0.03 to 2.64 ± 0.05), compared to the SG76 sample (range of 2.58 ± 0.13 to 2.90 ± 0.08). All the Df values reported are highly reproducible, measured from multiple SLS runs and estimated with ‘random block-effects’ statistical analysis that yielded all p values to be <0.001. The key mechanism for such difference in Df between the SWNT samples was identified as the difference in van der Waals (VDW) interaction energies of these samples, where higher VDW of SG76 resulted in tighter packing density. Effect of medium type showed lower sensitivity; however, presence of di-valent cations (Ca2+) in DMEM and MEM media resulted in relatively loose or more fractal aggregates. Moreover, presence of fetal bovine serum (FBS) and bovine serum albumin (BSA), used to mimic the in vitro cell culture condition, reduced the Df values, i.e., created more fractal structures. Steric hindrance to aggregation was identified as the key mechanism for creating the fractal structures. Also, increase in FBS concentration from 1% to 10% resulted in increasingly lower Df values.

Fate of single walled carbon nanotubes in wetland ecosystems

“…Modeling and experimental work also predict limited mobility of SWNTs in porous media due to homo-and heteroaggregation and sediments as the major long-term sink for SWNTs. [11][12][13][14][15][16] Several studies have reported little-to-no uptake of SWNTs into tissues of benthic organisms 4,8,17,18 or fish 19 exposed to SWNT amended sediments over short exposure periods up to one month, however bioaccumulation studies have not been performed under realistic, field-mimetic conditions.…”

Enhanced dispersion and electronic performance of single-walled carbon nanotube thin films without surfactant: A comprehensive study of various treatment processes

“…The nitric acid treated SWCNTs post-processed with urea resulted in aggregates that are more monodisperse and rod-like in morphology (fractal dimension closer to unity) compared with the more polydisperse plate-like aggregates of acid treated only SWCNTs (fractal dimension closer to 2). [28][29][30] This enhanced dispersion is confirmed through zeta potential measurements of the different SWCNT dispersions; the magnitude of the zeta potential of SWCNTs treated for longer times and with urea is greater, underlining increased electrostatic stability. 31 While all of the chemical treatment methods enhance the extent of SWCNT dispersion, those treatment conditions resulting in equivalent or better dispersion compared to surfactant modified SWCNTs are identified and discussed as promising alternatives to the conventional surfactant methods.…”

“…(3) 28,30,44,46 As such, D f is determined from the slope of the best fit line to the log-log plot of the scattered light intensity (I) versus the scattering angle (q), calculated from Equation 3 and shown in Figure S4a-b. 28,30,44 Several studies have used SLS to evaluate the dispersed aggregate morphology of carbon nanotubes as either sphere-(D f = 3), plate-(D f = 2), or rod-(D f = 1) like.…”

“…28,30,44 Several studies have used SLS to evaluate the dispersed aggregate morphology of carbon nanotubes as either sphere-(D f = 3), plate-(D f = 2), or rod-(D f = 1) like. 28,30,44,46 Figure 1c shows …”

Aggregation Behavior of Multiwalled Carbon Nanotube-Titanium Dioxide Nanohybrids: Probing the Part-Whole Question

“…It is to be noted that these D f values are indicative of the starting cluster sphericity and are likely to differ significantly as aggregation progressed over time and under different ionic conditions. 43 The noted asphericity of these clusters thus has also contributed to the deviation of the DLVO model—a model that is derived for sphere−sphere interaction.…”