Direct Writing of Three-Dimensional Macroporous Photonic Crystals on Pressure-Responsive Shape Memory Polymers

Abstract

Here we report a single-step direct writing technology for making three-dimensional (3D) macroporous photonic crystal patterns on a new type of pressure-responsive shape memory polymer (SMP). This approach integrates two disparate fields that do not typically intersect: the well-established templating nanofabrication and shape memory materials. Periodic arrays of polymer macropores templated from self-assembled colloidal crystals are squeezed into disordered arrays in an unusual shape memory "cold" programming process. The recovery of the original macroporous photonic crystal lattices can be triggered by direct writing at ambient conditions using both macroscopic and nanoscopic tools, like a pencil or a nanoindenter. Interestingly, this shape memory disorder-order transition is reversible and the photonic crystal patterns can be erased and regenerated hundreds of times, promising the making of reconfigurable/rewritable nanooptical devices. Quantitative insights into the shape memory recovery of collapsed macropores induced by the lateral shear stresses in direct writing are gained through fundamental investigations on important process parameters, including the tip material, the critical pressure and writing speed for triggering the recovery of the deformed macropores, and the minimal feature size that can be directly written on the SMP membranes. Besides straightforward applications in photonic crystal devices, these smart mechanochromic SMPs that are sensitive to various mechanical stresses could render important technological applications ranging from chromogenic stress and impact sensors to rewritable high-density optical data storage media.

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

“…This could significantly impede their optical applications in active devices (e.g., optical switches and displays), which typically require fast response speed. [60][61][62] Unfortunately, these hydrophilic copolymers with very low T g (≈−40 °C) and Young's modulus (E < 10 MPa) are highly brittle and susceptible to water, impeding their applicability in durable nanooptics. Room-temperature "cold" programming has been demonstrated for a variety of SMP systems, such as epoxies, polyurethanes, natural rubbers, polylactic acid-polyurethane blends, and copolymers comprising poly(ε-caprolactone) (PCL).…”

“…[34,59] We have developed a series of SMPs, which are copolymers of ethoxylated acrylates, to enable unconventional all-roomtemperature SM effects. [60][61][62] Unfortunately, these hydrophilic copolymers with very low T g (≈−40 °C) and Young's modulus (E < 10 MPa) are highly brittle and susceptible to water, impeding their applicability in durable nanooptics. Recently, a hydrophobic polyurethane-based SMP with higher T g (≈32 °C) and E (≈150 MPa for a solid membrane and ≈41.7 MPa for a macroporous film) has been demonstrated to show mechanical compression-induced "cold" programming and room-temperature SM recovery triggered by various vapors and solvents.…”

Toward Direct Laser Writing of Actively Tuneable 3D Photonic Crystals

“…However, direct write fabrication brings the flexibility to engineer arbitrary structures such as tuneable lenses, [10,11] and produce a series of 2D and 3D tuneable optical systems that are optically active over a wide wavelength range. [12][13][14][15] Currently, many routes to tuneable optical systems exploit mechanisms such as swelling of the optical material, [3,10] thermally controlled dimensional changes, [5] or interaction between solvents and optical structures. [7,10] The focus of this study is on using materials that undergo refractive index changes (and tuning), induced by a chemical reaction that transfers the materials from a dielectric to a conducting state.…”

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

“…These heat‐demanding processes can significantly complicate the design and operation of SMP‐based chemical sensors. By integrating scientific principles drawn from SMPs and photonic crystals, we have developed a series of macroporous SMP photonic crystals that enable unusual “cold” programming and instantaneous shape recovery at ambient conditions triggered by multiple stimuli, such as static pressure, vapors, heat, lateral shear stress, and various liquids (e.g., ethanol and acetone) …”

“…These heat-demanding processes can significantly complicate the design and operation of SMP-based chemical sensors. By integrating scientific principles drawn from SMPs and photonic crystals, we have developed a series of macroporous SMP photonic crystals that enable unusual "cold" programming and instantaneous shape recovery at ambient conditions triggered by multiple stimuli, such as static pressure, [50] vapors, [51] heat, [46] lateral shear stress, [52] and various liquids (e.g., ethanol and acetone). [53] Here we report a new type of SMP-based chromogenic photonic crystal sensor that enables the selective detection of many swelling analytes (e.g., ethanol, acetone, and dichloromethane) in nonswelling solvents (like gasoline and water).…”