Mechanochromic smart membranes capable of optical modulation have great potential in smart windows, artificial skins, and camouflage. However, the realization of high-contrast optical modulation based on light scattering activated at a low strain remains challenging. Here, we present a strategy for designing mechanochromic scattering membranes by introducing a Young's modulus mismatch between the two interdigitated polydimethylsiloxane phases with weak interfaces in a periodic threedimensional (3D) structure. The refractive index-matched interfaces of the nanocomposite provide a high optical transparency of 93%. Experimental and computational studies reveal that the 3D heterogeneity facilitates the generation of numerous nanoscale debonds or "nanogaps" at the modulusmismatching interfaces, enabling incident light scattering under tension. The heterogeneous scatterer delivers both a high transmittance contrast of >50% achieved at 15% strain and a maximum contrast of 82%. When used as a smart window, the membrane demonstrates effective diffusion of transmitting sunlight, leading to moderate indoor illumination by eliminating extremely bright or dark spots. At the other extreme, such a 3D heterogeneous design with strongly bonded interfaces can enhance the coloration sensitivity of mechanophore-dyed nanocomposites. This work presents insights into the design principles of advanced mechanochromic smart membranes.
The
cost-effective direct writing of polymer nanofibers (NFs) has
garnered considerable research attention as a compelling one-pot strategy
for obtaining key building blocks of electrochemical and optical devices.
Among the promising applications, the changes in optical response
from external stimuli such as mechanical deformation and changes in
the thermal environment are of great significance for emerging applications
in smart windows, privacy protection, aesthetics, artificial skin,
and camouflage. Herein, we propose a rational design for the mass
production of customized NFs through the development of focused electric-field
polymer writing (FEPW) coupled with the roll-to-roll technique. As
a proof of key applications, we demonstrate multistimuli-responsive
(mechano- and thermochromism) membranes with an exceptional production
scale (over 300 cm2). Specifically, the membranes consist
of periodically aligned ultrathin (∼60 nm) alumina nanotubes
inserted in the elastomers. We performed a two-phase finite element
analysis of the unit cells to verify the underlying physics of light
scattering at heterogeneous interfaces of the strain-induced air gaps.
By adding thermochromic dye during the FEPW, the optical modulation
of transmittance change (∼83% to 37% at visible wavelength)
was successfully extended to high-contrast thermal-dependent coloration.
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