Fig. 4: Hierarchical supramolecular assembly of SA in aqueous media.

a Schematic illustration of the photoisomerization of SA. Light bulb designed by Dr. Roza R. Weber. b UV-Vis and c fluorescence spectral changes of SA sodium salt solutions (70 μm, above CAC value) with in situ 365 nm light irradiation for 1 h and subsequent aging process at room temperature. d Cryo-TEM images of an SA sodium salt solution (5.5 mm) before and after exposure to 365 nm light for 1 h. Micelles are indicated by white arrows. Not all micelles were indicated. Scale bar set for 100 nm. Light bulb designed by Dr. Roza R. Weber. e Schematic illustration of the hierarchical supramolecular assembly of SA across nano- to micro- and macroscopic length scales. f–i POM images (top) and 1D profiles along with the zoomed 2D SAXS patterns (bottom) of SA artificial muscles prepared from a solution of SA sodium salt (60 mm) in the presence of aqueous f MgCl2, g CaCl2, h SrCl2, and i BaCl2 solutions (150 mm).