Thermoresponsive Shape‐Memory Photonic Nanostructures

Abstract

516 wileyonlinelibrary.com COMMUNICATION www.MaterialsViews.com www.advopticalmat.depreparation of compression sensitive inverse opals which allow the mechanical tuning of the photonic stopgap position. [ 18 ] Elastomers have also played a fundamental role for studying color tunable photonic crystals (PCs), [ 19,20 ] whose lattice parameter might be controlled by deformation (mechanochromic effect) or elastomer swelling. [ 21 ] An equivalent approach was proposed for the development of tunable phononic crystals. [ 22 ] Another active area of research concerns fl exible systems implemented, for instance, as UV-fi lters [ 23 ] and light emitting diodes or displays. [ 24 ] The present work addresses the fabrication of periodic nanofeatures with SME by using a replica molding approach for imprinting a 2D photonic nanostructure on the surface of a shape-memory elastomer. Structural and optical characterization of the as-produced system allowed to demonstrate its shape-memory functionality for confi guring the lattice parameter or erasing the nanopattern. This property might be very attractive, for example, for the development of reusable or self-healing photonic elements with adaptive properties.Polydiolcitrates (PDCs), fi rst described by Ameer and colleagues in 2004, [ 25 ] have been recently identifi ed as thermoresponsive elastomers presenting SME. [ 26 ] However, as far as we know, their applicability in the accomplishment of photonic nanostructured systems has not been reported in the literature yet. The synthesized polyester networks were obtained upon:(1) increase of the mol ratio of hydroxyl to carboxyl groups in the reaction mixture (4:3 in hydroxyl-dominant PDCs versus 1:1 in the original ones) and (2) the use of a more hydrophobic diol (e.g., 1,12-dodecanediol, DD). These polymers include covalent netpoints responsible for the permanent shape and hydrophobic micro-domains (either pre-polymer or DD-rich domains) physically cross-linked by intermolecular hydrophobic interactions as switch structures to fi x the temporary shape. To investigate the SME of these polymers for potential photonic applications, we followed the general procedure depicted in Figure 1 . The fi rst step consisted of the synthesis of the pre-polymer solution composed of DD and citric acid. 1 H nuclear magnetic resonance ( 1 H-NMR) confi rmed the mol ratio expected for both components (1.5) and the beginning of the condensation reaction (e.g., multiplicity of peaks at 2.6-2.9 ppm) (see Supporting Information (SI), Figure S7). Nanopatterning of the elastomer surface was achieved by using an approach inspired in soft-lithography [ 27 ] and, more specifi cally, in replica molding (Figure 1 a). [ 28,29 ] Briefl y, the pre-polymer solution was spread over the template, in our case a colloidal monolayer composed of polystyrene (PS) spheres of 870 nm in diameter ( d ). After curing at 90 °C for 12 h, the resulting cross-linked poly mer (PDDC-HD) was peeled off from the monolayer. When evaluating the cross-linking degree of the so-produced elast...

Programmable Macroporous Photonic Crystals Enabled by Swelling‐Induced All‐Room‐Temperature Shape Memory Effects

“…[19] Thermoresponsive SMPs have recently been utilized in fabricating smart, programmable nanooptical components, such as diffraction gratings and optical beam-power splitters. [38][39][40][41][42][43][44] However, heatdemanding SM programming and recovery steps greatly limit the broad applications of thermoresponsive SMPs in integrated nanooptical devices, including reconfigurable photonic crystals. In addition, the response speeds (for both programming and recovery steps) of thermoresponsive SMPs are controlled by the heat transfer rate through the bulky samples, though most polymers are not good heat conductors.…”

Tuning of Structural Colors Like a Chameleon Enabled by Shape‐Memory Polymers

“…This ability arises from the special molecular structure of those polymers in combination with a specific programming cycle . Although SMPs have been introduced to the field of optics only recently, their applicability has been already proven . The SMP utilized in this study is a thermoplastic, thermally‐activated poly(ether urethane) block‐copolymer (TecoflexEG‐72D, Lubrizol, USA).…”

“…[20][21][22][23][24][25] Although SMPs have been introduced to the field of optics only recently, their applicability has been already proven. [26][27][28][29][30][31][32] The SMP utilized in this study is a thermoplastic, thermally-activated poly(ether urethane) block-copolymer (TecoflexEG-72D, Lubrizol, USA). Since it is completely amorphous it is transparent in the visible range and it is very robust and docile in terms of its shape memory features.…”

Chromogenic Photonic Crystal Sensors Enabled by Multistimuli‐Responsive Shape Memory Polymers

“…sensors. Being responsive to various external stimuli, such as heat, light, solvent, and electromagnetic fields, functional SMPs have been widely explored in biomedical devices, [39,40] reconfigurable morphing structures, [41] sensors and actuators, [42][43][44] tunable nanooptics, [45][46][47][48] and smart textiles, [49] among many others. However, traditional thermoresponsive SMPs, which are mostly studied and utilized in practical applications, require heat to trigger shape transitions during shape memory (SM) programming and recovery steps.…”