Figure 4. Double-sided heterochromatic characteristics and light transmittance of photothermal membranes. (a) The membrane without solvent induced recrystallization (photothermal particles can only be attached to the surface). (b) The membrane with solvent induced recrystallization (photothermal particles form networks inside the membrane). (c) The pictures of double-sided heterochromatic photothermal membranes (20 µm). (d) The cross-section of double side heterochromatic photothermal membranes. (e) The gradient distribution of photothermal particles during solvent induced recrystallization. (f) Transparency of the membrane (on the fabric, the membrane covers the letter ‘A’ in ‘TSINGHUA’). (g) Cross-section of transparent membranes. (h) Amplification of (g). (i) The EDS maps of the treated membrane without CS and MWCNTs. (j) The EDS maps of the light side of photothermal membranes. (k) The EDS maps of the dark side of photothermal membranes. The red represents C, the blue represents Si, and the green represents O.