Smart shape-memory polymers can memorize and recover their permanent shape in response to an external stimulus (for example, heat). They have been extensively exploited for a wide spectrum of applications ranging from biomedical devices to aerospace morphing structures. However, most of the existing shape-memory polymers are thermoresponsive and their performance is hindered by heat-demanding programming and recovery steps. Although pressure is an easily adjustable process variable such as temperature, pressure-responsive shape-memory polymers are largely unexplored. Here we report a series of shape-memory polymers that enable unusual ‘cold' programming and instantaneous shape recovery triggered by applying a contact pressure at ambient conditions. Moreover, the interdisciplinary integration of scientific principles drawn from two disparate fields—the fast-growing photonic crystal and shape-memory polymer technologies—enables fabrication of reconfigurable photonic crystals and simultaneously provides a simple and sensitive optical technique for investigating the intriguing shape-memory effects at nanoscale.

A new type of shape-memory polymer (SMP) is developed by integrating scientific principles drawn from two disparate fields: the fast-growing photonic crystal and SMP technologies. This new SMP enables room-temperature operation for the entire shape-memory cycle and instantaneous shape recovery triggered by exposure to a variety of organic vapors.

The Taguchi method, a statistical design with an L8 orthogonal array, was adopted to optimize the synthetic conditions of mesoporous silica nanoparticles (MSNs) with respect to particle size and structural properties. The amount of the silica source (i.e., tetraethoxysilane), pH value, and reaction time were selected as significant parameters affecting the size and structural properties of the synthesized MSNs. Particle sizes ranging from 17 to 247 nm were successfully controlled by the Taguchi method, and the statistical data based on experimental results indicated that the pH value of the silica/surfactant precursor solution had a greater influence (57%) on particle size than did reaction time and the TEOS amount (29% and 13%, respectively). The effects of individual parameters on particle size and structural properties, such as surface area and structural ordering, were also investigated by changing one parameter at a time. We concluded that the pH value strongly affected mesostructural ordering and particle size. Longer reaction times in basic conditions had little effect on structural ordering but caused erosion of the MSN silica framework, resulting in smaller particle sizes. The minimum amount of TEOS for ordered MSNs was 5 mL, and more TEOS slightly increased the particle size of the synthesized MSNs. The rational design and systematic investigation of synthetic conditions for MSNs with controllable particle sizes and structural properties presented in this study show great potential for MSN-based catalytic and biomedical applications.

Here we report the synthesis of mesoporous metal oxide materials with various compositions by assembly of spherical polymeric micelles consisting of triblock copolymer poly(styrene-b-2-vinyl pyridine-b-ethylene oxide) (PS-b-PVP-b-PEO) with three chemically distinct units. The PVP block interacts strongly with the inorganic precursors for the target compositions. The hydrophobic PS block is kinetically frozen in the precursor solutions, enabling the spherical micelles to remain in a stable form. The frozen PS cores serve as templates for preparing robust mesoporous materials. The PEO corona helps the micelles to stay well dispersed in the precursor solutions, which plays a key role in the orderly arrangement of the micelles during solvent evaporation. This approach is based on assembly of the stable micelles using a simple, highly reproducible method and is widely applicable toward numerous compositions that are difficult for the formation of mesoporous structures.

Here novel chromogenic photonic crystal sensors based on smart shape memory polymers (SMPs) comprising polyester/polyether-based urethane acrylates blended with tripropylene glycol diacrylate are reported, which exhibit nontraditional all-room-temperature shape memory (SM) effects. Stepwise recovery of the collapsed macropores with 350 nm diameter created by a "cold" programming process leads to easily perceived color changes that can be correlated with the concentrations of swelling analytes in complex, multicomponent nonswelling mixtures. High sensitivity (as low as 10 ppm) and unprecedented measurement range (from 10 ppm to 30 vol%) for analyzing ethanol in octane and gasoline have been demonstrated by leveraging colorimetric sensing in both liquid and gas phases. Proof-of-concept tests for specifically detecting ethanol in consumer medical and healthcare products have also been demonstrated. These sensors are inexpensive, reusable, durable, and readily deployable with mobile platforms for quantitative analysis. Additionally, theoretical modeling of solvent diffusion in macroporous SMPs provides fundamental insights into the mechanisms of nanoscopic SM recovery, which is a topic that has received little examination. These novel sensors are of great technological importance in a wide spectrum of applications ranging from environmental monitoring and workplace hazard identification to threat detection and process/product control in chemical, petroleum, and pharmaceutical industries.

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.

Traditional shape memory polymers (SMPs) are mostly thermoresponsive, and their applications in nano-optics are hindered by heat-demanding programming and recovery processes. By integrating a polyurethane-based shape memory copolymer with templating nanofabrication, reconfigurable/rewritable macroporous photonic crystals have been demonstrated. This SMP coupled with the unique macroporous structure enables unusual all-room-temperature shape memory cycles. "Cold" programming involving microscopic order-disorder transitions of the templated macropores is achieved by mechanically deforming the macroporous SMP membranes. The rapid recovery of the permanent, highly ordered photonic crystal structure from the temporary, disordered configuration can be triggered by multiple stimuli including a large variety of vapors and solvents, heat, and microwave radiation. Importantly, the striking chromogenic effects associated with these athermal and thermal processes render a sensitive and noninvasive optical methodology for quantitatively characterizing the intriguing nanoscopic shape memory effects. Some critical parameters/mechanisms that could significantly affect the final performance of SMP-based reconfigurable photonic crystals including strain recovery ratio, dynamics and reversibility of shape recovery, as well as capillary condensation of vapors in macropores, which play a crucial role in vapor-triggered recovery, can be evaluated using this new optical technology.

Macroporous photonic crystals with optically bistable states have been fabricated by using thermoresponsive shape memory polymers. The reversible transition between an ordered permanent state and a disordered temporary state results in tremendous changes in the appearance and the optical properties of the membranes.