Smart Laser‐Writable Micropatterns with Multiscale Photo/Moisture Reconstructible Structure

Abstract

The design of a dynamic, versatile, convertible, and responsive micropatterned system is realized by a photo/moisture reconstructible multiscale film‐substrate bilayer structure. Specifically, a hydrophilic polyvinyl alcohol (PVA)/laponite (LP) thin film is covalently bonded to a photothermally active polydimethylsiloxane (PDMS)/carbon black (CB) soft substrate. A laser engraver can inscribe programmable aligned micro‐wrinkles by manipulating laser power and spatiotemporal control. These wrinkles can be modulated into three distinct systems 1) moisture erasable and laser re‐writable wrinkles; 2) moisture driven reversible wrinkles; 3) moisture resistant wrinkles, which are achieved by controlling a) the moisture resistance of PVA; b) the dimensional stability of PVA/LP film regulated by the LP nanostructure, which can be adjusted by the laser power and the LP ratio. This programmable system can be applied in information encryption/recording and as a moisture responsive electrical switch, offering new routes for the modulations and applications of next generation smart materials.

Dynamic multifunctional devices enabled by ultrathin metal nanocoatings with optical/photothermal and morphological versatility

“…67,000 and a degree of hydrolysis of 88%. Here, the application of PVA with a low degree of hydrolysis makes the film highly sensitive to moisture ( 17 , 24 ). Thereafter, the remaining wrinkles on the PVA film can be completely erased by moisture as the internal stress of the highly hydrophilic PVA molecular chains can be released by moisture.…”

“…Smart or stimuli-responsive materials have controllable optical, mechanical, electronic, and/or other properties that can be effectively converted by external stimuli, such as mechanical force ( 1 – 13 ), light ( 14 – 18 ), temperature ( 11 , 18 – 20 ), moisture ( 17 , 21 – 23 ), electricity ( 24 – 27 ), and so on ( 13 , 27 – 30 ). One of the major efforts in this field is to mimic the intriguing micro-/nanotopographies of numerous organisms, which serve various functions in nature.…”

“…Another vivid demonstration is the wrinkled surface, which can be created by imposing compression to a film-substrate bilayer with mismatched elastic modulus ( 31 ). These types of periodical micro-/nanotopographies possess unique light-scattering/diffraction/grating characteristics ( 16 , 17 , 21 ). Thus, wrinkle-like morphologies have been widely adopted on the petals of some flowers, such as Hibiscus trionum and Tulipa ( 32 ), to introduce vivid iridescent colors via diffraction gratings.…”

“…Analogous artificial micro-/nanotopographies, like cracks ( 3 , 9 , 11 , 18 ), wrinkles ( 17 , 21 , 31 ), creases ( 27 , 33 ), and grooves ( 34 , 35 ), have been fabricated based on bilayer structures via the coupling of a rigid thin film and a soft substrate with strong interfacial bonding. Elastomers (such as polydimethylsiloxane [PDMS]) and hydrogels are the most common candidates used as the soft substrates ( 10 , 16 , 31 ), while the rigid thin film commonly consists of a polymer ( 10 , 20 , 21 ) or its composite with inorganic fillers ( 3 , 36 ).…”

“…These disadvantages severely restrain the fabrication of thin films in submicro-/nanoscale dimensions and limit the generation of corresponding micro-/nanomorphologies, which are essential to develop new morphology-driven multifunctional devices. For instance, when a polymer-based thin film is used in a bilayer system, it is hard to decrease the average intercrack spacing to <30 μm ( 3 , 35 , 36 ) or lower the wavelength of wrinkles to <3 μm ( 17 , 21 , 24 , 37 , 38 ), which typically requires a very low film thickness (<30 nm) to achieve such a low intercrack spacing and wrinkle wavelength. Also, in a polymer-based film system, it is very challenging to precisely tailor the optical reflectance, transmittance, and photothermal effect when the thin film is <30 nm in thickness.…”