Tunable Structural Color with Gradient and Multiaxial Polydimethylsiloxane Wrinkling

Abstract

in dragonflies Rhyothemis resplendens. [20] Randomly oriented wrinkles were demonstrated to produce uniform bright structural colors with broad viewable angles, which can further be tunable using light sensitive polymers skins. [23] Mechanochromic response, that is, the change of color under stress, of wrinkled structures has been recently reported, employing various bilayer film structures. [22,24,25] The use of soft matter substrates, including elastomers, is advantageous as it readily allows optical properties to be tuned by the applied strain, by adjusting surface periodicity and amplitude, in addition to film thickness and mechanical modulus. Further, a wide range of surface patterns, including uniand multiaxial and hierarchical wrinkles, can be readily fabricated. Bilayers are generally fabricated by deposition or lamination of a thin and stiff film, typically a few 10-100 nm and GPa modulus, atop a thicker (mm) and softer (≈MPa), for instance an evaporated metal of a spun-coated glassy polymer supported by a polydimethylsiloxane (PDMS) elastomer. The mismatch in mechanical properties between films, provided that there is strong adhesion between them (to minimize delamination, crack formation, etc.), leads to surface buckling under strain. Strain can be induced thermally, by film evaporation/shrinkage, and commonly, by mechanical strain.Plasma oxidation provides a facile route to generating a thin, glass-like film onto PDMS, [26] enabling precise control of film thickness growth kinetics. [27][28][29] We have previously demonstrated the design of tunable optical gratings [30] using this method (building on the previous demonstrations with polymer bilayer laminates [31] ). The impact of the PDMS substrate thickness on the mechanochromic response of 1D plasma oxidized PDMS films has been recently reported, [32,33] and color tunability according to illumination and viewing angle examined. Recently, the incorporation of polystyrene nanoparticles and the use of wire-bar coating (yielding regular arrays) was demonstrated to produce both angle-independent and -dependent structural colors, upon plasma exposure and wrinkling. [34] In this study, we build upon the structural color and mechanochromic response exhibited by 1D plasma oxidized wrinkled PDMS topographies ranging from nano to the micronscale, and quantitatively examines the emergence of color mixing, by superposition of diffraction orders of distinct colors at similar observation angles. We then quantify the joint roles of amplitude and periodicity in color brightness, and finally consider The generation of structural color from wrinkled polydimethylsiloxane (PDMS) surfaces, fabricated by plasma exposure, subjected to uni-and multi-axial, and sequential strain fields is examined. The approach is based on the well-known, mechanically-induced, buckling instability of a supported bilayer, whereby the top glassy "skin" is formed by plasma oxidation. Surface periodicities 200 nm ≲ d ≲ 3 μm, encompassing the visible spectrum, are investigated in terms of the obs...

Mitigation of Cellular and Bacterial Adhesion on Laser Modified Poly (2-Methacryloyloxyethyl Phosphorylcholine)/Polydimethylsiloxane Surface

“…As PDMS cools, contraction occurs, inducing compressive stress, and, respectively, relieving. This final step induces a buckling, and therefore wave-like features were observed (marked by the white arrows), as reported in the literature [ 33 , 34 ].…”

Wrinkle nanostructures generate a novel form of blue structural color in great argus flight feathers

“…These shared features of surface keratin nanostructures among archosaurs ( Figure 3 ) hint at a possible homology of their underlying developmental mechanisms. While wrinkle structures are widely found in living organisms, 32 , 33 and are actively under consideration for biomimetic applications, 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 this is the first example of a biophotonic (i.e., color-producing) wrinkle nanostructure in birds.…”

Multifaceted Structurally Coloured Materials: Diffraction and Total Internal Reflection (TIR) from Nanoscale Surface Wrinkling

“…Surface topography and, specifically, undulations caused by buckling or wrinkling, are found in a range of flowers and insects [ 25 , 26 , 27 , 28 , 29 ], where these wrinkled surfaces, effectively acting as diffraction gratings, can yield brilliant structural colours which depend on pattern periodicity d and sufficiently large pattern amplitudes, and observation angle. Pattern orientation, from uni-directional to isotropic (or random), can further restrict or modulate the viewable angles of the perceived structural colour [ 30 , 31 ]. When white light impinges onto a wrinkled surface, it can diffract in transmission or reflection, or both, and propagate further.…”