Smart Copolymer-Functionalized Flexible Surfaces with Photoswitchable Wettability: From Superhydrophobicity with "Rose Petal" Effect to Superhydrophilicity

Photoresponsive Spiropyran and DEGMA-Based Copolymers with Photo-Switchable Glass Transition Temperatures

Herein, novel photoresponsive spiropyran (SP)-based P(DEGMA-co-SpMA) copolymers with variable percentages of SP fractions are synthesized. The SP group present in these polymers exhibited the abilities of reversible photoisomerism. Their photoresponsive, structural, and thermal properties have been investigated and compared using various characterization techniques. These light-responsive copolymers are found to exhibit photoswitchable glass transition temperature (Tg ), high thermal stability (Td > 250°C), instant photochromism as well as fluorescence upon exposure to UV light. It is demonstrated that the Tg of these synthesized polymers increased when irradiated with UV light (λ = 365 nm), as a consequence of the photoisomerization of incorporated SP groups into their merocyanine form. This increase in Tg is attributed to an increase in polarity and a decrease in the overall entropy of the polymeric system when it switches from the ring-closed SP form (less-ordered state) to the ring-opened merocyanine form (more-ordered state). Therefore, such polymers with a unique feature of phototunable glass transition temperatures provide the possibility to be integrated into functional materials for various photoresponsive applications.

Superhydrophobic Flexible Strain Sensors Constructed Using Nanomaterials: Their Fabrications and Sustainable Applications

Superhydrophobic flexible strain sensors, which combine superhydrophobic coatings with highly sensitive flexible sensors, significantly enhance sensor performance and expand applications in human motion monitoring. Superhydrophobic coatings provide water repellency, surface self-cleaning, anti-corrosion, and anti-fouling properties for the sensors. Additionally, they enhance equipment durability. At present, many studies on superhydrophobic flexible sensors are still in the early research stage; the wear resistance and stability of sensors are far from reaching the level of industrial application. This paper discusses fundamental theories such as the wetting mechanism, tunneling effect, and percolation theory of superhydrophobic flexible sensors. Additionally, it reviews commonly used construction materials and principles of these sensors. This paper discusses the common preparation methods for superhydrophobic flexible sensors and summarizes the advantages and disadvantages of each method to identify the most suitable approach. Additionally, this paper summarizes the wide-ranging applications of the superhydrophobic flexible sensor in medical health, human motion monitoring, anti-electromagnetic interference, and de-icing/anti-icing, offering insights into these fields.

Recent Developments in Two-Dimensional Materials-Based Membranes for Oil-Water Separation

The industrialization witnessed in the last century has resulted in an unprecedented increase in water pollution. In particular, the water pollution induced by oil contaminants from oil spill accidents, as well as discharges from pharmaceutical, oil/gas, and metal processing industries, have raised concerns due to their potential to pose irreversible threats to the ecosystems. Therefore, the effective treating of these large volumes of oily wastewater is an inevitable challenge to address. Separating oil-water mixtures by membranes has been an attractive technology due to the high oil removal efficiency and low energy consumption. However, conventional oil-water separation membranes may not meet the complex requirements for the sustainable treatment of wastewater due to their relatively shorter life cycle, lower chemical and thermal stability, and permeability/selectivity trade-off. Recent advancements in two-dimensional (2D) materials have provided opportunities to address these challenges. In this article, we provide a brief review of the most recent advancements in oil-water separation membranes modified with 2D materials, with a focus on MXenes, graphenes, metal-organic frameworks, and covalent organic frameworks. The review briefly covers the backgrounds, concepts, fabrication methods, and the most recent representative studies. Finally, the review concludes by describing the challenges and future research directions.

Droplet Impact Dynamics on Biomimetic Replica of Yellow Rose Petals: Rebound to Micropinning Transition

Rose petals exhibit a phenomenal wetting property of being sticky and superhydrophobic simultaneously. A recent study has shown that for short timescales, associated with drop impact phenomenon, lotus leaf and rose petal replicas exhibit similar wettability, thereby highlighting the difference between long and short time wettability. Also, short time wetting on rose petals of different colors remains completely unaddressed, as almost all existing study on wetting of rose petals have been performed with the classical red rose (Rosa chinensis). In this paper, we compare the drop impact studies on replicas of a yellow rose petal, with those on extensively studied red rose petal replicas and the lotus leaf over a wide range of Weber number (We), by varying the height of fall (h) from 10 to 375 mm. Our results reveal that over the replica of a yellow rose petal, the initial impact outcome varies from complete rebound to micro pinning and eventually complete pinning depending on the kinetic energy of the impacting drop, in contrast to that on red rose petal replica on which the droplet always pinned. Based on experimental finding, we present a comprehensive regime phase map of the post impact behavior of the drop on different surfaces as a function of impact height. We also present a simple scaling analysis to understand the combined effect of pattern height and periodicity on the critical h corresponding to wetting regime transition. Additionally, variation of maximum spreading diameter and spreading time with the h for the different surfaces is also discussed. The results highlight that the initial impact dynamics of a water drop over a topographically patterned substrate is a strong function of the topographical parameters and can be very different from the equilibrium wetting state.

Arylazopyrazole-Modified Thiolactone Acrylate Copolymer Brushes for Tuneable and Photoresponsive Wettability of Glass Surfaces

Photoswitches have long been employed in coatings for surfaces and substrates to harness light as a versatile stimulus to induce responsive behavior. We previously demonstrated the viability of arylazopyrazole (AAP) as a photoswitch in self-assembled monolayers (SAMs) on silicon and glass surfaces for photoresponsive wetting applications. We now aim to transfer the excellent photophysical properties of AAPs to polymer brush coatings. Compared to SAMs, polymer brushes offer enhanced stability and an increase of the thickness and density of the functional organic layer. In this work, we present thiolactone acrylate copolymer brushes which can be post-modified with AAP amines as well as hydrophobic acrylates, making use of the unique chemistry of the thiolactones. This strategy enables photoresponsive wetting with a tuneable range of contact angle change on glass substrates. We show the successful synthesis of thiolactone hydroxyethyl acrylate copolymer brushes by means of surface-initiated atom-transfer radical polymerization with the option to either prepare homogeneous brushes or to prepare micrometer-sized brush patterns by microcontact printing. The polymer brushes were analyzed by atomic force microscopy, time-of-flight secondary ion spectrometry, and X-ray photoelectron spectroscopy. Photoresponsive behavior imparted to the brushes by means of post-modification with AAP is monitored by UV/vis spectroscopy, and wetting behavior of homogeneous brushes is measured by static and dynamic contact angle measurements. The brushes show an average change in static contact angle of around 13° between E and Z isomer of the AAP photoswitch for at least five cycles, while the range of contact angle change can be fine-tuned between 53.5°/66.5° (E/Z) and 81.5°/94.8° (E/Z) by post-modification with hydrophobic acrylates.

Flexible Azo-Polyimide-Based Smart Surface with Photoregulatable Surface Micropatterns: Toward Rewritable Information Storage and Wrinkle-Free Device Fabrication

Stimulus-sensitive materials are of great fascination in surface and interface science owing to their dynamically tunable surface properties and/or morphologies. Herein, we have synthesized an azobenzene-containing polyimide (azo-PI) with enhanced chain flexibility for the fabrication of photosensitive surface patterns on a film/substrate wrinkle system or wrinkle-free devices. The phototriggered cis-trans isomerization kinetics of azobenzene groups in the novel azo-PI with various chain structures were systematically investigated. On the basis of the characteristics of stress relaxation that azobenzene reversible cis-trans isomerization induces in the wrinkled azo-PI film/substrate system, a variety of rewritable visual surface patterns with high resolution and a long legibility time (>30 days) could be easily constructed via visible-light irradiation, enabling the wrinkled azo-PI surfaces to be used as rewritable information storage media. Meanwhile, because of the visible-light irradiation strategy, these photoresponsive surfaces could find potential application in the fabrication of wrinkle-free flexible devices. This study not only sheds light on the influence of the azo-polymer chain structure on its photoresponsive behavior but also provides a versatile strategy for realizing tailor-made smart surface patterns on multilayer functional devices.

3D-Printed Parahydrophobic Functional Textile with a Hierarchical Nanomicroscale Structure

Functional textiles with superhydrophobicity and high adhesion to water, called parahydrophobic, are attracting increasing attention from industry and academia. The hierarchical (micronanoscale) surface patterns in nature provide an excellent reference for the manufacture of parahydrophobic functional textiles. However, the replication of the complex parahydrophobic micronanostructures in nature exceeds the ability of traditional manufacturing strategies, which makes it difficult to accurately manufacture controllable nanostructures on yarn and textiles. Herein, a two-photon femtosecond laser direct writing strategy with nanoscale process capability was utilized to accurately construct the functional parahydrophobic yarn with a diameter of 900 μm. Inspired by rose petals, the parahydrophobic yarn is composed of a hollow round tube, regularly arranged micropapillae (the diameter is 109 μm), and nanofolds (the distance is 800 nm) on papillae. The bionic yarn exhibited a superior parahydrophobic behavior, where the liquid droplet not only was firmly adhered to the bionic yarn at an inverted angle (180°) but also presented as spherical on the yarn (the maximum water contact angle is 159°). The fabric woven by the bionic yarn also exhibited liquid droplet-catching ability even when tilted vertically or turned upside down. Based on the excellent parahydrophobic function of bionic yarn, we demonstrated a glove that has very wide application potential in the fields of water droplet-based transportation, manipulation, microreactors, microextractors, etc.

Biology and nature: Bionic superhydrophobic surface and principle

Nature is the source of human design inspiration. In order to adapt to the environment better, creatures in nature have formed various morphological structures during billions of years of evolution, among which the superhydrophobic characteristics of some animal and plant surface structures have attracted wide attention. At present, the preparation methods of bionic superhydrophobic surface based on the microstructure of animal and plant body surface include vapor deposition, etching modification, sol-gel method, template method, electrostatic spinning method and electrostatic spraying method, etc., which have been used in medical care, military industry, shipping, textile and other fields. Based on nature, this paper expounds the development history of superhydrophobic principle, summarizes the structure and wettability of superhydrophobic surfaces in nature, and introduces the characteristics differences and applications of different superhydrophobic surfaces in detail. Finally, the challenge of bionic superhydrophobic surface is discussed, and the future development direction of this field is prospected.

Flexible Tri-switchable Wettability Surface for Versatile Droplet Manipulations

Smart surfaces with tunable wettability are promising due to their abilities to create diversified functionalities that the fixed surfaces cannot provide. However, limited by imprecise adjustment of structural geometry and almost conventional switching modes of wettability, it is still challenging to achieve the reversible switching between multiple wetting states. Herein, a novel tri-switchable wettability surface with an in situ switching ability is used for the manipulation of a given droplet, which consists of a stretchable substrate and a micron column array. The femtosecond laser direct writing technique is utilized to generate distinct wettability of the two components. Taking the advantage of good tensile properties, the surface morphology is adjusted in a rapid, reversible way to obtain diverse wetting performances from the lotus-like effect to rice-leaf-like anisotropy and then to the rose-petal-like effect. Based on the triplex wetting transition on the same surface, we further developed a multifunctional device to realize a range of in situ manipulations, including the surface self-cleaning, the directional transport of droplets, and the capture, the vertical transport, and release of droplets. This work paves the way for expanding the field of smart surfaces with tunable wettability beyond conventional dual-property wetting behavior and exhibits versatile manipulations of droplets for microfluidic applications.

Light-responsive Pickering emulsions based on azobenzene-modified particles

Light-responsive particle-stabilised (Pickering) emulsions can in principle be selectively emulsified/demulsified on-demand through the remote application of light. However, despite their wide-ranging potential in applications such as drug delivery and biphasic catalysis, their rational design is extremely challenging and there are very few examples to date. Herein, we investigate a model system based on silica particles functionalised with azobenzene photoswitches to understand the key factors that determine the characteristics of light-responsive Pickering emulsions. The particle hydrophobicity is tuned through judicious variation of the spacer length used to graft the chromophores to the surface, the grafting density, and irradiation to induce trans-cis photoisomerisation. For select emulsions, and for the first time, a reversible transition between emulsified water-in-oil droplets and demulsified water and oil phases is observed with the application of either UV or blue light, which can be repeatedly cycled. A combination of surface energy analysis and optical microscopy is shown to be useful in predicting the stability, and expected light-response, of a given emulsion. Using the observed trends, a set of design rules are presented which will help facilitate the rational design, and therefore, more widespread application of light-responsive Pickering emulsions.

Multiple strategies to control the hydrophilic-hydrophobic balance of P(DMA-co-DMAEMA-co-QDMAEMA) coatings

The regulation of the hydrophilic-hydrophobic balance of polymers has an important influence not only on their aggregation behavior in aqueous solution, but also on their adhesion properties on the surface of substrates and the applications of the modified surfaces. Based on this, a random copolymer poly(dopamine methacrylamide-co-2-(dimethylamino)ethyl methacrylate) (P(DMA-co-DMAEMA)) was synthesized as a starting polymer to generate P(DMA-co-DMAEMA-co-QDMAEMA) (PDDQ) derivatives by a programmable quaternization of the DMAEMA precursor. By adjusting the pH or temperature, both the aggregation behavior in aqueous solutions and the surface adhesive behavior on the substrate surfaces of PDDQ copolymers were regulated due to the hydrophilic-hydrophobic balance. Specifically, the surface adsorption of PDDQ copolymers on surfaces was enhanced by the increased hydrophobicity of PDDQ. Stainless steel meshes (SSM) modified with the PDDQ0 copolymer without quaternization showed a superoleophobicity in acidic aqueous media, which endowed it with improved oil-water separation performance. In addition, the hydrophilic-hydrophobic balance of PDDQs and their coatings could also be tuned by changing the ratio of DMAEMA to QDMAEMA in the copolymer. From PDDQ0 to PDDQ100, by increasing the hydrophilic QDMAEMA component of PDDQ copolymers, anti-protein properties and oil/water separation efficiency of the modified surfaces were also enhanced gradually. The results provided a reference for designing P(DMA-co-DMAEMA-co-QDMAEMA) coatings in different application environments.

Role of chemistry in bio-inspired liquid wettability

Chemistry and topography are the two distinct available tools for customizing different bio-inspired liquid wettability including superhydrophobicity, superamphiphobicity, underwater superoleophobicity, underwater superoleophilicity, and liquid infused slippery property. In nature, various living species possessing super and special liquid wettability inherently comprises of distinctly patterned surface topography decorated with low/high surface energy. Inspired from the topographically diverse natural species, the variation in surface topography has been the dominant approach for constructing bio-inspired antiwetting interfaces. However, recently, the modulation of chemistry has emerged as a facile route for the controlled tailoring of a wide range of bio-inspired liquid wettability. This review article aims to summarize the various reports published over the years that has elaborated the distinctive importance of both chemistry and topography in imparting and modulating various bio-inspired wettability. Moreover, this article outlines some obvious advantages of chemical modulation approach over topographical variation. For example, the strategic use of the chemical approach has allowed the facile, simultaneous, and independent tailoring of both liquid wettability and other relevant physical properties. We have also discussed the design of different antiwetting patterned and stimuli-responsive interfaces following the strategic and precise alteration of chemistry for various prospective applications.

Smart surfaces with reversibly switchable wettability: Concepts, synthesis and applications

As a growing hot research topic, manufacturing smart switchable surfaces has attracted much attention in the past a few years. The state-of-the-art study on reversibly switchable wettability of smart surfaces has been presented in this systematic review. External stimuli are brought about to render the alteration in chemical conformation and surface morphology to drive the wettability switch. Here, starting from the fundamental theories related to the surfaces wetting principles, highlights on different triggers for switchable wettability, such as pH, light, ions, temperature, electric field, gas, mechanical force, and multi-stimuli are discussed. Different applications that have various wettability requirement are targeted, including oil-water separation, droplets manipulation, patterning, liquid transport, and so on. This review aims to provide a deep insight into responsive interfacial science and offer guidance for smart surface engineering. It ends with a summary of current challenges, future opportunities, and potential solutions on smart switch of wettability on superwetting surfaces.

Electrically Induced Underwater Superaerophilicity/Superaerophobicity Switching on Polypyrrole-Coated Mesh Films for Selective Bubble Permeation

Recently, materials with controllable superwettability have attracted much attention. However, almost all studies focused on controlling wetting of water and oil; research on underwater gas bubble wetting control is still rare. Herein, we report a mesh film prepared by coating polypyrrole (PPy) film on Ti mesh. Briefly, the film mesh is underwater superaerophilic when PPy is doped with perfluorooctanesulfonate ions (PFOS^- ), and becomes underwater superaerophobic as the PFOS^- are removed. The transition of the wettability can be triggered by electrical stimuli, which is attributed to the cooperative effect between the rough structure and chemical components variation. The controllable wettability allows adjustable bubble permeation. It can be envisioned that the film will provide potential applications in the future, such as underwater bubble capture/release and microfluidic devices.

Durable hydrophobic Enteromorpha design for controlling oil spills in marine environment prepared by organosilane modification for efficient oil-water separation

Hydrophobic and oleophilic materials are attractive candidates for efficient oil collection due to their excellent oil-water separation. However, the most of currently reported oil adsorption materials are limited resources or require complicated preparation steps, which causes high energy consumption and not be practical for large-scale application. Herein, we report a facile strategy to modify the wettability of Enteromorpha from hydrophilic to hydrophobic, which not only greatly reduces energy consumption but also shows the outstanding capacity for oil-water separation with the maximum adsorption capacities is 11.4 g/g and the contact angle reaches 137°. The successful modification of the Enteromorpha is achieved by grafting n-octyltriethoxysilane on the surface of the pristine Enteromorpha. The hydrophobic and superoleophilic Enteromorpha guarantee adequate voids in the fibrous bundles only for oil adsorption and the oil floating on the seawater is removed by the formation of hydrogen bonding between oil and modified Enteromorpha. By optimizing test, the optimal adsorption conditions are adsorption time of 60 min, oil-water ratio of 1:10 and pH of 7. Our reported hydrophobic organosilane modified Enteromorpha will open a new avenue to control marine oil pollution and suppress the damage of Enteromorpha to the marine ecology system.

Robust Scalable-Manufactured Smart Fabric Surfaces Based on Azobenzene-Containing Maleimide Copolymers for Rewritable Information Storage and Hydrogen Fluoride Visual Sensor

Functionalized materials with reversible color switching are highly attractive in many application fields, especially as rewritable media for information storage. It is critical yet challenging to develop a cost-effective strategy for the fabrication of stimulus-responsive chromogenic systems. Herein, we present a versatile dip-coating approach to fabricate robust smart textile with acid/base-driven chromotropic capability. Owing to the introduction of novel maleimide-based copolymers bearing azobenzene derivative moieties, smart textiles possess rapid color switching between yellow and orange-red, which is triggered by acid-base stimulations with the resulting reversible protonation/deprotonation of maleimide moieties. As a proof of concept of the application of the smart textile for high-performance rewritable media, various rewritable elaborate patterns can be fast trifluoroacetic acid-printed/triethylamine-erased (within 20 s) with excellent cycling stability and long legible duration (>30 days). Meanwhile, the smart textile can be employed as a visual sensor for the detection of hydrogen fluoride gas leakage. It is highlighted that the as-prepared robust smart textiles with superhydrophobic surfaces have excellent antifouling properties and chemical/mechanical stabilities, which can tolerate harsh environmental conditions and repetitive mechanical deformation. The robust smart textiles with simple low-cost large-scale production may find more advanced potential applications besides information storage and sensors demonstrated.

Smart Bionic Surfaces with Switchable Wettability and Applications

In order to satisfy the needs of different applications and more complex intelligent devices, smart control of surface wettability will be necessary and desirable, which gradually become a hot spot and focus in the field of interface wetting. Herein, we review interfacial wetting states related to switchable wettability on superwettable materials, including several classical wetting models and liquid adhesive behaviors based on the surface of natural creatures with special wettability. This review mainly focuses on the recent developments of the smart surfaces with switchable wettability and the corresponding regulatory mechanisms under external stimuli, which is mainly governed by the transformation of surface chemical composition and geometrical structures. Among that, various external stimuli such as physical stimulation (temperature, light, electric, magnetic, mechanical stress), chemical stimulation (pH, ion, solvent) and dual or multi-triggered stimulation have been sought out to realize the regulation of surface wettability. Moreover, we also summarize the applications of smart surfaces in different fields, such as oil/water separation, programmable transportation, anti-biofouling, detection and delivery, smart soft robotic etc. Furthermore, current limitations and future perspective in the development of smart wetting surfaces are also given. This review aims to offer deep insights into the recent developments and responsive mechanisms in smart biomimetic surfaces with switchable wettability under external various stimuli, so as to provide a guidance for the design of smart surfaces and expand the scope of both fundamental research and practical applications.

Spontaneous Adsorption-Induced Salvinia-like Micropillars with High Adhesion

Superhydrophobic surfaces with high adhesion provide high potential for underwater applications. Inspired by Salvinia leaf, here, we have reported a simple method for fabricating adhesive Salvinia-like micropillars via photolithography and spontaneous adsorption of organic molecules from the atmosphere. With continuous hydrocarbon adsorption on sputtered cerium dioxide (CeO₂) films, the surface gradually evolved and eventually became chemically heterogeneous. Huge wetting contrast from superhydrophilic to superhydrophobic over exposure time was observed; meanwhile, the wetting mode changed from the Wenzel (W) state to Cassie-Baxter (C-B) state. As a result, hydrophobic hydrocarbons (C-C/C-H) and trapped air between adjacent pillars contributed to the high apparent contact angle (CA), while the hydrophilic domains of C-O/O═C-O and CeO₂ on the top layer made the surface highly adhesive with water droplets. In comparison with traditional fluorinated superhydrophobic surfaces, CeO₂-coated surfaces showed high adhesive force with water droplets and can be used as a "mechanical hand" for water droplet transport. The adsorption-induced Salvinia-like micropillars with high adhesion may find many other droplet-based applications in microfluidic fields.

Magnetically Responsive Superhydrophobic Surface with Switchable Adhesivity Based on Electrostatic Air Spray Deposition

A new method was reported for preparing a magnetically responsive superhydrophobic surface by electrostatic air spray deposition (EASD) and magnetic induction. The mixture was fully atomized under the combined action of the electrostatic field and the high-speed airflow field, and a dense array of micropillars was formed. The atomization mechanism of EASD was explored. The distribution and physical parameters of the micropillars were evaluated and counted. Switchable adhesion characteristics of the surface and the reversibility in 10 cycles were examined. The influences of different electrostatic voltages, component concentration, spray distance, air pressure, and magnetic field intensity on the surface morphology and hydrophobicity were analyzed. The prepared surface can be reversibly transformed between the high-adhesion state (with a contact angle of 108°) and the low-adhesion state (with a contact angle of 154°) by on/off switching of an external magnetic field. After a 2.2 kPa pressure load was applied, the surface contact angle was 144° with an applied magnetic field of 0.4 T. After heated at 90 °C for more than 90 min, the surface can almost obtain superhydrophobicity (with a contact angle of 148°) in the absence of a magnetic field. By utilizing the switchable surface adhesion characteristics, various kinds of droplet transmissions were realized. When the cured surface was spray-coated with carbon nanoparticles (CNPs), active droplet manipulation can be achieved by simply moving the magnet. The advantages of this method include a simple preparation process without chemical surface modification.

Photo-switchable smart superhydrophobic surface with controllable superwettability

An azobenzene-based smart superhydrophobic surface undergoes reversible transformations among multiple bioinspired superwetting states through photo-manipulation, demonstrating promising potential on a rewritable platform for droplet transportation.

Recent advances in light-induced cell sheet technology

Various stimuli have been applied to harvest complete cell sheets, including temperature, magnetic, pH, and electrical stimuli. Cell sheet technology is a convenient and efficient approach with beneficial effects for tissue regeneration and cell therapy. Lights of different wavelengths, such as ultraviolet (UV), visible light, and near infrared ray (NIR) light, were confirmed to aid in fabricating a cell sheet. Changes in the wettability, potential, or water content of the culturing surfaces that occur under light illumination induce conformational changes in the adhesive proteins or collagens, which then leads to cell sheet detachment. However, the current approaches face several limitations, as few standards for safe light illumination have been proposed to date, and require a careful control of the wavelength, power, and irradiation time. Future studies should aim at generating new materials for culturing and releasing cell sheets rapidly and effectively.

Biological and bioinspired materials: Structure leading to functional and mechanical performance

Nature has achieved materials with properties and mechanisms that go far beyond the current know-how of the engineering-materials industry. The remarkable efficiency of biological materials, such as their exceptional properties that rely on weak constituents, high performance per unit mass, and diverse functionalities in addition to mechanical properties, has been mostly attributed to their hierarchical structure. Key strategies for bioinspired materials include formulating the fundamental understanding of biological materials that act as inspiration, correlating this fundamental understanding to engineering needs/problems, and fabricating hierarchically structured materials with enhanced properties accordingly. The vast, existing literature on biological and bioinspired materials can be discussed in terms of functional and mechanical aspects. Through essential representative properties and materials, the development of bioinspired materials utilizes the design strategies from biological systems to innovatively augment material performance for various practical applications, such as marine, aerospace, medical, and civil engineering. Despite the current challenges, bioinspired materials have become an important part in promoting innovations and breakthroughs in the modern materials industry.

Design Principles for Aqueous Interactive Materials: Lessons from Small Molecules and Stimuli-Responsive Systems

Interactive materials are at the forefront of current materials research with few examples in the literature. Researchers are inspired by nature to develop materials that can modulate and adapt their behavior in accordance with their surroundings. Stimuli-responsive systems have been developed over the past decades which, although often described as "smart," lack the ability to act autonomously. Nevertheless, these systems attract attention on account of the resultant materials' ability to change their properties in a predicable manner. These materials find application in a plethora of areas including drug delivery, artificial muscles, etc. Stimuli-responsive materials are serving as the precursors for next-generation interactive materials. Interest in these systems has resulted in a library of well-developed chemical motifs; however, there is a fundamental gap between stimuli-responsive and interactive materials. In this perspective, current state-of-the-art stimuli-responsive materials are outlined with a specific emphasis on aqueous macroscopic interactive materials. Compartmentalization, critical for achieving interactivity, relies on hydrophobic, hydrophilic, supramolecular, and ionic interactions, which are commonly present in aqueous systems and enable complex self-assembly processes. Relevant examples of aqueous interactive materials that do exist are given, and design principles to realize the next generation of materials with embedded autonomous function are suggested.

Design of Active Interfaces Using Responsive Molecular Components

Responsive interfaces are interfaces that show a defined and reversible change in physical properties in response to external stimuli. Typically, responsive interfaces result from the immobilization of responsive molecular components at the interface that translate a nanoscale signal into a macroscopic effect. Responsive interfaces can also be obtained if the topology of the interface can be reversibly changed using an external stimulus. As the surface of any material is its connection to the environment, responsive interfaces provide opportunities for interactive materials which are not only able to change properties upon demand, but also sense their environment and act autonomously. The application of responsive molecular components at interfaces, however, requires chemical and physical compatibility with the material surface of interest, posing a challenge not least in the retention of the responsive functionality. The state of the art in "active" interfaces which display responsive wettability, permeability, or adhesion is discussed, with a particular emphasis on microscale and nanoscale patterning since patterned interfaces can give rise to unique material properties. Finally, perspectives in the development of responsive interfaces, as well as promising approaches for bypassing the most prominent challenges are discussed.

Path-Guided Hierarchical Surface Relief Gratings on Azo-Films Induced by Polarized Light Illumination through Surface-Wrinkling Phase Mask

Surface relief gratings (SRGs) with hierarchical microstructures are highly needed owing to their diverse applications in various fields. Here, we introduce surface-wrinkling templates as novel nonlithographic phase masks to direct the generation of hierarchical well-prescribed SRGs on nonconformally contacted azo-films by a simple single-beam illumination. The light-induced SRGs have controlled microstructures including single/double/triple wavelengths and single/double orientations as well as their organizations. These microstructures can be well tailored by the wavelength of the surface-wrinkling phase masks and the polarization direction of incident light relative to the wrinkling patterns in the phase masks. Interestingly, we find that the larger wavelength is induced prior to the smaller ones, offering another new strategy to tailor the microstructures of SRGs through simple manipulation of the illumination duration. In particular, path-guided SRGs with unprecedented well-organized hierarchical microstructures have been available in the case of controlled moving of the light illumination through the surface-wrinkling phase mask. As demonstrated, the obtained hierarchical SRGs with the capability of multiple optical inscription/erasure have great application potentials in fields such as confidential information (or pattern) records and encryption/decryption.

Light-printable epoxy oligomer wrinkle-forming surface for rewritable information storage

Smart surfaces with controlled topography show broad and fantastic applications in optics, biology and information science. Herein, we report a simple visible-light-illumination approach to fabricate a smart wrinkle-forming surface with photo-controllable hierarchical surface patterns as well as rewritable high-resolution patterns of information by using an azobenzene-containing epoxy-based oligomer. The epoxy oligomer was synthesized via the ring-opening polymerization of bisphenol AF diglycidyl ether (BADFGE) with p-aminoazobenzene (AAB) and characterized using FTIR, ¹H NMR and ¹⁹F NMR spectroscopies. When the epoxy oligomer film was deposited on an elastic substrate, the formation of surface wrinkles was triggered via a circulation of heating/cooling and photo-tailored due to photo-softening together with the release of stress induced by cycles of photoisomerization of azobenzene in the oligomer. The wrinkles in selectively light-exposed regions could be photo-erased within tens of seconds, yielding a different pattern of information. The high-resolution photo-printed images were shown to be rewritable for multiple cycles and legible for over 3 months in dark ambient conditions. The as-formed epoxy oligomer wrinkle-forming surface was found to be inexpensive and its fabrication was easily amenable to scale up, indicating its great potential as ink-free light printable media for rewritable information storage.

A novel rapidly responsive media for rewritable information storage comprised of an azobenzene-containing epoxy-based oligomer displaying surface wrinkling was developed.