A Robust Smart Window: Reversibly Switching from High Transparency to Angle‐Independent Structural Color Display

Abstract

A smart window is fabricated from a composite consisting of elastomeric poly(dimethylsiloxane) embedded with a thin layer of quasi-amorphous silica nanoparticles. The smart window can be switched from the initial highly transparent state to opaqueness and displays angle-independent structural color via mechanical stretching. The switchable optical property can be fully recovered after 1000 stretching/releasing cycles.

Programmable Kiri‐Kirigami Metamaterials

“…Figure 1c-e shows that the deformed configurations of the kirigami structure ( Figure 1a) are highly dependent on the stretching method. [4][5][6] However, solutions often require a rather large strain in a switchable optical material to achieve a dramatic transparency change. When both ends are stretched simultaneously, the PDMS sheet exhibits a dual tilting orientation with the left half rotating counterclockwise while the right half rotating clockwise, leaving a domain wall in the middle (Figure 1e and Video S1, Supporting Information).…”

“…When one end of the cut sheet is uniaxially stretched with the other end fixed, all the cut units undergo either a clockwise (represented by "+" in Figure 1c) or counterclockwise rotation (represented by "−" in Figure 1d) depending on which side is fixed (Video S1, Supporting Information). [5,6] Reconfigurable metamaterials, [7][8][9][10][11][12][13] with properties arising from dynamically tunable geometrical structures rather than composition, offer a new material platform to achieve dramatic change of mechanical and optical properties via a relatively modest mechanical stress, [7,14] that lead to unique mechanical behaviors, including buckling induced programmable highly nonlinear mechanical responses, [15] origami-based reprogrammable mechanical metamaterials through lattice defects, [16] and origami-inspired designs of flexibility in deployment and controllable stiffness in transformation. Random tilting orientations, if not controlled, could largely degrade the energy saving performance of kirigami-based building envelopes due to uncontrollable light or solar heat reflection or transmission.…”

“…To differentiate it from the kirigami structure, we call it a kiri-kirigami structure due to the introduced shallow cuts as demonstrated in Figure 1b. [29] Compared to simple stretching of a flat structured sheet to change transmittance as a responsive building skin, [5,6] kirigami structures can be buckled out of plane with a small strain to reflect or transmit light [28] or heat in response to local changes of solar (2 of 9) 1604262 (Figure 1f-h and Video S2, Supporting Information). [4][5][6] However, solutions often require a rather large strain in a switchable optical material to achieve a dramatic transparency change.…”

Block copolymer structural color strain sensor

“…This property gives rise to a useful method for the low-power reflective mode visualization of strain (Table S1, Supporting information) [24][25][26][27][28][29][30][31][32][33][34][35] . In particular, SCs based on self-assembled block copolymers (BCPs) are more suitable, as their periodicities and dielectric constants are readily changed by mechanical forces such as shear, tensile, and compressive forces 24,25,29 .…”

Soft Color Composites with Tunable Optical Transmittance

“…Recent efforts have turned to devices based on optically clear elastomers, particularly polydimethylsiloxane (PDMS). These studies include surface-texturing with nanopillars, [ 18,19 ] mechanically controlled voids, [ 20 ] magnetically controlled inclusions, [ 21,22 ] nucleation of voids around silica nanoparticles, [ 23 ] and paraffi n-PDMS composites. [ 24 ] Despite the advantages in the handling and manufacturing of a PDMS-based device, fabrication techniques based on a controlled architecture of the microstructure are still cumbersome and challenging to implement.…”