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.