Fig. 1: 2D and 3D fluorescence microscopy of fluorophore-labeled polymers after complete isothermal crystallization showing internal and surface structure.

a1-a4, 2D micrographs of ∼10 µm thick film of iPP doped with 0.05 wt % Nile Red during isothermal crystallization at 125 °C: (a1, a3) cross-polarized and (a2, a4) FM; the dye is seen to be partially rejected from the growing spherulites. a5 FM of fully crystallized PLA; cavitation and Newton interference contours are seen. b Comparison of 1-photon and 2-photon confocal microscopies: (b1) z-scans across a sharp end of a glass fiber embedded in NR-doped polystyrene (PS) — blue = 1-photon, red = 2-photon; (b2) 1-photon (blue), and 2-photon (red) fluorescence intensity vs. depth in a sheet of NR-doped PS illuminated by 543 nm and 1000 nm lasers, respectively. c NR-labeled iPP crystallized at 120 °C: (c1–c9) selected z-slices as recorded by 2-photon microscopy, bottom to top, using false-color scale at the bottom right; (c10) 3D solid reconstructed therefrom (see Supplementary Video 1); (c11,c12) vertical (xz and yz) slices along dashed lines in c10. d Labeling by infiltration: neat iPP was crystallized at 130 °C and subsequently immersed in NR/p-xylene solution; (d1) “porous” 3D rendering; (d2) vertical section along the dotted line in d1. e NR-doped PLA crystallized at 120 °C showing surface cracks (cf. 2D image in a5); (e1) gray scale solid (bright = high fluorescence, black = 0); (e2) vertical slice along dashed line in (e1). Exceptionally, the crack areas (zero fluorescence) in (d2) and (e2) are shown white.