Figure 5. Length distribution plots of laterally sliced (a) SWCNTs, (b)
double walled CNTs, and (c) MWCNTs at \(\theta\) = 45° with 7500 rpm
rotational speed at reaction times of (i) 10 mins, (ii) 30 mins, and
(iii) 60 mins, alongside their respective AFM height
images21. Coiled SWCNT toroids (d) SEM image, (e) and
(g) TEM images, (f) and (h) HRTEM for e and g, respectively, with (i) &
(j) histograms for distribution of diameter and thickness,
respectively41. (k) AFM, (l) STEM, (m) HRTEM, and (n)
TEM image of composite materials with length distribution
inset43. (o) Schematic for the processing of toroid
from SWCNTs. The diameter of the double helix is compared between
different tube types, including hemispherical and flat based tubes, and
the effect of tube diameter and increasing rotational speed on the size
of toroids and double helices. (a-c) Reproduced under the terms of the
CC BY 3.0 Unported license21. Copyright 2016, Springer
Nature. (d-j) Reprinted with permission41. Copyright
2019, American Chemical Society. (k-n) Reproduced under the terms of the
CC BY 3.0 license43. Copyright 2019, Royal Society of
Chemistry. (o) Reprint with permission42. Copyright
2022, American Chemical Society.
Luo et al. reported a tunable and effective procedure for
preparing fluorescent polyethyleneimine-based NPs with controlled
average particle sizes, as shown in Figure 6, using the VFD operating
under continuous mode26. Due to the high shear
mechanical energy alongside the elevated temperature of the air within
the VFD, chain scission and polymer degradation cause the fragmented
chains to reorganize into self-passivated NPs. Varying the flow rate of
the liquid entering the VFD allows tuning the fluorescent properties of
these NPs, all formed in the absence of any auxiliary reagents.
Enhancement of the auto-fluorescence and fluorescence intensity over an
extensive range of excitation wavelength was possible by incorporating
amide groups. Notably, cytotoxicity was significantly reduced in the
resulting NPs after processing in the VFD compared to as-received
materials, thus allowing the possibility of medical applications.