3.4. Double-sided heterochromatic characteristics and light
transmittance of photothermal membranes
Membranes of different thicknesses will achieve two-sided
heterochromatic features and translucency through solvent-induced
recrystallization. The loose and porous structure of the electrospun
membrane provides a deep penetration network for the photothermal
particles, creating a microscopic 3D photothermal absorption space (Fig.
4a and b). The gradient photothermal network creates a two-sided
heterochromatic appearance (Fig. 4c, thick membranes
(~20 µm, Fig. 4d and Fig. S9)) and allows for excellent
photothermal performance on the light side, which greatly improves the
fashionability of photothermal materials [25]. Then, with the rapid
evaporation of the solvent and the action of PDMS, the fiber film
rapidly densifies and tightly crosslinks, binding the photothermal
particles inside the membrane, which greatly enhances the internal
photothermal factor embedding and the integrated photothermal
performance. Also, it creates a gradient distribution between dark and
light faces (Fig. 4e).
When the fiber membrane is very thin, the photothermal particles can
easily pass through the membrane, so the two-sided heterochromatic
feature disappears and is replaced by transparency (Fig. 4f and Fig.
S10, thin thickness (~6.5 µm, Fig. 4g, h and Fig. S11
and S12)). The EDS distribution of the transparent cross section is
shown in Fig. S13 and S14. The main substance compositions of the
photothermal particles CS and MWCNTs are shown in Fig. S15 and S16. Both
the double-sided heterochromatic feature and the transparency can
improve the shortcoming of the conventional photothermal membrane, which
can only be dark in color, and enhance the fashionability of wearable
textiles. For the SEM images of APLLA and photothermal membranes (Fig.
S17), the EDS distribution (Fig. 4i-k and Fig. S18) show that the
adhesive PDMS is uniformly distributed throughout the membrane,
providing sufficient adhesive sites. The CS/MWCNTs/APLLA light and dark
surfaces show the obvious existence of elemental C, indicating the large
distribution of CS particles and MWCNTs particles. Obviously,
agglomerated C is also observed in its holes, suggesting that the
photothermal particles can penetrate into the interior of the film. The
elemental spectrum of the light-colored photothermal film surface is
shown in Fig. S19. C and O are the main components, and Si also has big
components, displaying the arrangement of the adhesive and the
photothermal components.