Smart Surfaces Research Articles

Rewritable Surface‐Grafted Polymer Brushes with Dynamic Covalent Linkages

AbstractSurface grafting of polymer brushes drastically modifies surface properties, including wettability, compatibility, responsiveness, etc. A broad variety of functionalities can be introduced to the surface via different types of polymers. Bringing together properties of two or more types of polymer brushes to one surface opens up even more possibilities in brush‐modified materials. However, while it is generally feasible to introduce several chemical compositions along the brushes via copolymerization, it is challenging to vary the types of polymer brushes along a surface. Although previous studies have demonstrated binary brushes via orthogonal polymerization techniques or partial deactivation/regrafting, they commonly limit the number of polymer types to two. Here, we propose a strategy to introduce dynamic covalent diketoenamine linkages at the root of polymer brushes. The grafting density could be precisely tuned during surface functionalization. The surface‐anchored polymer brushes were cleaved by the addition of small molecule amines. New polymer brushes can be regrafted from the surface following refunctionalization of exposed sites. The maneuverability allows tuning of the types and densities of the polymer brushes, pointing the way to the preparation of a new generation of well‐defined brush‐modified materials with mixed grafts, with potential applications in the design of smart materials and surfaces.

A novel underactuated smart surface for parts feeding and sorting

In material handling, numerous solutions have been proposed to enhance the flexibility and adaptability of transport systems. Among these solutions, smart surfaces stand out as one of the most interesting responses, utilizing an array of actuators for common feeding tasks. The current paper focuses on a novel system within this category, notable for its distinguishing factor of being underactuated. With this characteristic, the concept leads to a simplified cost-effective design and a not actively driven functioning, leveraging gravity or object own velocity to manipulate the material flow maintaining top class performances, as the sorting rate reaches 4000 pcs/h. Specifically, the article begins with an introduction of the concept design and its digital model, followed by a description of the experimental setup built to test the surface’s functionality and evaluate the predictions of the virtual counterpart. On top of that, a method to determine the essential parameters for the surface simulation is proposed and applied. As a result, the prototype successfully completed the three main intralogistic tasks experimented, i.e., sorting, slowing, and stopping of packages. Lastly, the digital model outcomes of the same operations were computed and compared with the measured results, demonstrating an accuracy of prediction with displacements and time errors below 7%.

Flexible SERS chips for rapid on-site detection of tricyclazole pesticide in agricultural products.

A flexible, ultrasensitive, and practical SERS chip is presented based on a paper/f-TiO2/Ag structure. The chip enhances the self-assembly of Ag nanoparticles on a cellulose fiber matrix, facilitated by smart functionalized TiO2 nanomaterials (f-TiO2). This design enables superior detection of the hazardous pesticide tricyclazole (TCZ) on crops using an advanced, simple, and efficient analytical method.Despite its straightforward fabrication process via a solvent immersion method, the intrinsic smart surface properties of the TiO2 bridging material -both hydrophilic and hydrophobic-enable the uniform and dense self-assembly of hydrophilic Ag nanoparticles (NPs) on the cellulose fiber paper substrate. This innovative design provides superior sensing efficiency for TCZ molecules with a detection limit reaching 2.1 × 10-9M, a remarkable improvement compared to Paper/Ag substrates lacking f-TiO2 nanomaterials, which register at 10-5M. This flexible SERS substrate also exhibits very high reliability as indicated by its excellent reproducibility and repeatability with relative standard deviations (RSD) of only 5.93% and 4.73%, respectively. Characterized by flexibility and a water-attractive yet non-soluble surface, the flexible Paper/f-TiO2/Ag chips offer the convenience of direct immersion into the analytical sample, facilitating seamless target molecule collection while circumventing interference signals. Termed the "dip and dry" technique, its advantages in field analysis are indisputable, boasting in situ deployment, simplicity, and high efficiency, while minimizing interference signals to negligible levels. Through the application of this advanced technique, we have successfully detected TCZ in two high-value crops, ST25 rice and dragon fruit, achieving excellent recovery values ranging from 90 to 128%. This underscores its immense potential in ensuring food quality and safety. As a proof of concept, flexible Paper/f-TiO2/Ag SERS chips, with a simple fabrication process, advanced analytical technique, and superior sensing efficiency, bring SERS one step closer to field applications beyond the laboratory.

Effect of lubricant loading in slippery liquid-infused surface for persistent anti-icing performance

Due to the vast applications in biomedical materials and aerospace industry, smart slippery liquid-infused porous surfaces (SLIPSs) have attracted remarkable attention. However, there are still challenges in the fabrication of durable SLIPS. In this work, based on linear polyurea and silicone oil, a series of durable anti-icing surface were fabricated. Based on the long-lasting secretion of lubricant, the ice adhesion strength of 60-PUa was 2.7 ± 0.5 kPa and could remain below 10 kPa even after 30 icing-deicing cycles. And the icing delay time of 60-PUa could be extended up to 870 s at a temperature of −15 °C. The introduction of large numbers of reversible hydrogen bonds in the system and silicone oil made it possible to achieve high self-healing efficiency under natural conditions. The coating system not only improved the ice removal ability, but also had excellent water-sliding properties, the droplet could slide under its own weight on 60-PUa at a tilt angle of 4.7°. This work provides an easy way to fabricate multi-functional SLIPS with durability.

Smart Wrinkled Interfaces: Patterning, Morphing, and Coding of Polymer Surfaces by Dynamic Anisotropic Wrinkling.

In contrast to traditional static surfaces, smart patterned surfaces with periodical and reversible morphologies offer limitless opportunities for encoding surface functions and properties on demand, facilitating their widespread application as functional building blocks in various devices. Advances in intelligently controlling the macroscopic properties of these smart surfaces have been accomplished through various techniques (such as three-dimensional printing, imprint lithography and femtosecond laser) and responsive materials. In contrast to the sophisticated techniques above, dynamic anisotropic wrinkling, taking advantage of dynamic programmable manipulation of surface wrinkling and its orientation, offers a powerful alternative for fabricating dynamic periodical patterns due to its spontaneous formation, versatility, convenient scale-up fabrication, and sensitivity to various stimuli. This review comprehensively summarizes recent advances in smart patterned surfaces with dynamic oriented wrinkles, covering design principles, fabrication techniques, representative types of physical and chemical stimuli, as well as fine-tuning of wrinkle dimensions and orientation. Finally, advanced applications of these smart patterned surfaces are presented, along with a discussion of current challenges and future prospects in this rapidly evolving field. This review would offer some insights and guidelines for designing and engineering novel stimuli-responsive smart wrinkled surfaces, thereby facilitating their sustainable development and progressing toward commercialization.

Active reconfigurable intelligent surface‐aided multiple‐input‐multiple‐output radar detection in the presence of clutter

AbstractReconfigurable intelligent surface (RIS) refers to a two‐dimensional smart surface consisting of massive number of reflecting elements. Both active RIS (ARIS) and passive RIS (PRIS) are promising technologies that can adapt and reconfigure the wireless environment, enhancing the reliability and capacity of wireless networks. The authors focus on enhancing the detection ability of ARIS/PRIS‐aided multiple‐input‐multiple‐output radar system in the presence of signal‐dependent clutter. Constant‐envelope constraint is imposed on the sought radar waveforms to improve the practicability of the radar system. To tackle the resultant non‐convex problem, a cyclic method based on minorisation–maximisation and alternating direction method of multipliers is derived to iteratively optimise the receive filters, the transmit waveforms, and the RIS coefficients. The major finding is that the distance between the radar and the ARIS has little to no impact on the radar signal‐to‐interference‐plus‐noise ratio (SINR). For the PRIS‐aided radar system, a simplified model can significantly improve the operational efficiency and has little impact on the radar SINR. Numerous results verify the effectiveness of the proposed algorithm.

Rewritable Surface-Grafted Polymer Brushes with Dynamic Covalent Linkages.

Surface grafting of polymer brushes drastically modifies surface properties, including wettability, compatibility, responsiveness, etc. A broad variety of functionalities can be introduced to the surface via different types of polymers. Bringing together properties of two or more types of polymer brushes to one surface opens up even more possibilities in brush-modified materials. However, while it is generally feasible to introduce several chemical compositions along the brushes via copolymerization, it is challenging to vary the types of polymer brushes along a surface. Although previous studies have demonstrated binary brushes via orthogonal polymerization techniques or partial deactivation/regrafting, they commonly limit the number of polymer types to two. Here, we propose a strategy to introduce dynamic covalent diketoenamine linkages at the root of polymer brushes. The grafting density could be precisely tuned during surface functionalization. The surface-anchored polymer brushes were cleaved by the addition of small molecule amines. New polymer brushes can be regrafted from the surface following refunctionalization of exposed sites. The maneuverability allows tuning of the types and densities of the polymer brushes, pointing the way to the preparation of a new generation of well-defined brush-modified materials with mixed grafts, with potential applications in the design of smart materials and surfaces.

Inverted optical functionality of phase change material surfaces through Mie resonances of VO2@Si core–shell structures

Vanadium dioxide (VO2) has attracted extensive attention due to its reversible transition from the insulator to metal phase at a critical temperature of 68°C. Below the critical temperature VO2 transmits the infrared radiation in the insulator phase, whereas above the critical temperature VO2 reflects the infrared portion of the incident radiation. However, smart surface interfaces for high-temperature emitter surfaces require the opposite functionality within the 1–3 µm spectral range. Here, we demonstrate that a core–shell structure, composed of VO2@Si, which is deposited on a thin layer of Ag, achieves the inverted optical functionality within the 1–3 µm spectral range, making it ideal as smart interfaces for radiative heat applications as high-temperature emitters. The proposed material architecture also increases the thermal stability of VO2 in addition to enhancing its optical properties in near-infrared region. The results were obtained using numerical simulations. Our results indicate that in its metallic state, the core–shell structure with metallic underlayer promotes efficient absorption in the near-infrared spectrum. On the other hand, in its insulating state dielectric resonances within the core–shell structure along with the metallic underlayer, resulting in increased reflection, offer inverse optical functionalities. Our findings present a significant step toward designing dynamic filters that can efficiently capture and respond to changing conditions in the near-infrared spectrum.

Smart Lanceolate Surface with Fast Fog-Digesting Performance for Triboelectric Energy Harvesting.

Utilizing the ubiquitous fog in nature to create decentralized energy-harvesting devices, free from geographical and hydrological constraints, presents an opportunity to foster sustainable power generation. Extracting electrical energy from fog relies heavily on fog-digesting performance. Improving the efficiency of fogwater utilization remains a formidable challenge for existing fogwater energy-harvesting technologies. Inspired by the water-harvesting behavior of Tillandsia leaves, a smart lanceolate surface is developed to harvest triboelectric energy by rapidly digesting fog. Such a surface exhibits capabilities in fog management, encompassing precise fog capture, transportation, and critical droplet separation. Specifically, fog droplets condense at hydrophilic sites of acylated cellulose ester, subsequently migrating toward the rear under Laplace pressure, thereby producing energy as they traverse through the tail end. Such architecture yields a brief voltage restoration period (with an average of 9.36 s), can rush the capacitor to 11.59 V within 20 s, and achieves a water-digestion rate of up to 71.05 kg/m2 h. This biomimetic approach enhances the water-digestion efficacy of the atmospheric water energy apparatus and offers perspectives on mitigating deficiencies in power resources.

Flexible, transparent, and durable slippery liquid‐infused porous surface achieved by void‐centered PVDF‐co‐HFP membrane for self‐cleaning antifog coating

AbstractBioinspired smart surfaces, such as slippery liquid‐infused porous surfaces (SLIPS), have garnered significant attention due to their efficacy in self‐cleaning, antifouling, and antibacterial applications. Despite their advantages, SLIPS exhibit limitations such as compromised transparency, insufficient stability, and limited slippery performance, which have hindered their widespread practical use. To address these challenges, this article proposes a rational design utilizing a void‐centered poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF) membrane for slippery liquid‐infused porous surfaces with exceptional flexibility, transparency, durability, and superior slippery performance. These advancements promise to enhance high‐performance, self‐cleaning, and antifogging coatings. The membranes, featuring large‐area, thickness‐customizable void‐centered PVDF, are fabricated through a two‐step process involving phase separation and selective etching. The utilization of PVDF polymer, which has a refractive index similar to that of silicon‐based lubricant oil, enhances transparency, while macrovoids positioned at the membrane's center, acting as oil reservoirs, improve the stability and performance of the SLIPS surfaces. Experimental findings demonstrate remarkable transparency of up to 93% in the visible light range and a lubricant oil uptake of 2.32 at a porosity of 70%. Moreover, the developed SLIPS exhibit outstanding durability, maintaining slippery performance with sliding angles of <10° following exposure to either 400 consecutive droplets or aging for up to 40 days. This study significantly contributes to the development of future SLIPS, particularly for applications such as antifogging coatings on vehicle glass and solar panels, and self‐cleaning surfaces.

Influence of a Solid Surface on PNIPAM Microgel Films.

Stimuli-responsive microgels have attracted great interest in recent years as building blocks for fabricating smart surfaces with many technological applications. In particular, PNIPAM microgels are promising candidates for creating thermo-responsive scaffolds to control cell growth and detachment via temperature stimuli. In this framework, understanding the influence of the solid substrate is critical for tailoring microgel coatings to specific applications. The surface modification of the substrate is a winning strategy used to manage microgel-substrate interactions. To control the spreading of microgel particles on a solid surface, glass substrates are coated with a PEI or an APTES layer to improve surface hydrophobicity and add positive charges on the interface. A systematic investigation of PNIPAM microgels spin-coated through a double-step deposition protocol on pristine glass and on functionalised glasses was performed by combining wettability measurements and Atomic Force Microscopy. The greater flattening of microgel particles on less hydrophilic substrates can be explained as a consequence of the reduced shielding of the water-substrate interactions that favors electrostatic interactions between microgels and the substrate. This approach allows the yielding of effective control on microgel coatings that will help to unlock new possibilities for their application in biomedical devices, sensors, or responsive surfaces.

Developing a durable anti-frost surface: Integrating the passive anti-icing properties of salt, saline, and bulk ice for enhanced frost prevention

Icing on surfaces presents significant challenges for the aviation industry and life in cold alpine regions. Developing smart surfaces to mitigate icing effects is highly desirable. When icing cannot be completely avoided in the atmosphere, limiting it to a small area on the surface is a practical solution. We have created a hydrophilic pattern on superhydrophobic surfaces using laser fabrication, which allows saline droplets to adhere to the pattern. As these droplets dry, salt grains cover the pattern, making the surface primarily superhydrophobic. Under frost conditions, the salt grains turn into saline beads, which then freeze into ice beads. Frost forms only on the tops of these ice beads within the pattern. Due to the lower saturated vapor pressure of salt, saline, and ice compared to the supersaturated vapor pressure for condensation, there is not enough humidity around the pattern for water vapor to condense and form frost. As a result, water vapor continuously deposits inside the pattern, significantly reducing frost formation around it. This combination of salt, saline, and ice, with their lower saturation vapor pressures below zero Celsius, ensures a dry perimeter during rapid temperature drops and increased humidity. By designing the pattern size appropriately, the dry perimeters overlap, keeping the entire surface outside the pattern free of frost. This approach offers a promising solution for reducing frosting on surfaces.

Diatom Cribellum-Inspired Hierarchical Metamaterials: Unifying Perfect Absorption Toward Subwavelength Color Printing.

Diatom exoskeletons, known as frustules, exhibit a unique multilayer structure that has attracted considerable attention across interdisciplinary research fields as a source of biomorphic inspiration. These frustules possess a hierarchical porous structure, ranging from millimeter-scale foramen pores to nanometer-scale cribellum pores. In this study, this natural template for nanopattern design is leveraged to showcase metamaterials that integrates perfect absorption and subwavelength color printing. The cribellum-inspired hierarchical nanopatterns, organized in a hexagonal unit cell with a periodicity of 300nm, are realized through a single-step electron beam lithography process. By employing numerical models, it is uncovered that an additional induced collective dipole mode is the key mechanism responsible for achieving outstanding performance in absorption, reaching up to 99%. Analysis of the hierarchical organization reveals that variations in nanoparticle diameter and inter-unit-cell distance lead to shifts and broadening of the resonance peaks. It is also demonstrated that the hierarchical nanopatterns are capable of color reproduction with high uniformity and fidelity, serving as hexagonal pixels for high-resolution color printing. These cribellum-inspired metamaterials offer a novel approach to multifunctional metamaterial design, presenting aesthetic potential applications in the development of robotics and wearable electronic devices, such as smart skin or surface coatings integrated with energy harvesting functionalities.

Synergy of 6G technology and IoT networks for transformative applications

SummaryThe rapid growth of Wi‐Fi networking and intelligent systems, fueled by the emergence of the Internet of Things (IoT), has enabled significant transformative advancements. The imminent arrival of sixth‐generation (6G) wireless networks offers more opportunities as fifth‐generation (5G) wireless networks improve IoT connections. This study explores the potential advantages of 6G technology and IoT networks, focusing on edge intelligence, reconfigurable smart surfaces, Terahertz communications, and blockchain integration. The study examines potential implementation challenges and highlights the potential impact of 6G on IoT device usage. This research outlines potential applications of 6G in many sectors like the internet of vehicles, healthcare, autonomous driving, unmanned aerial vehicles, satellite television, and industrial IoT. This research elaborates on specific research topics related to 6G‐IoT technologies to enhance understanding and practical applicability.

A Thioether‐Bridging Surface Modification of Polymeric Microspheres Offers Nonbiological Protein A‐Mimetic Affinity for IgG

AbstractSurface modification of polymeric materials to control their interaction with proteins has been studied extensively, leading to widespread bio‐applications. However, the development of nonbiological, smart polymer surfaces, mimicking the recognition ability of biomolecules, remains a challenge. The present study presents a thioether‐bridging surface modification of polymeric microspheres as a new approach for mimicking protein A affinity for immunoglobulin G (IgG). The bridge‐modified surface is created through an epoxide linking reaction of porous polymeric microspheres with potassium thioacetate in a 2:1 molar ratio, acting as a protein A ligand, which is essential for industrial IgG purification. This surface exhibits buffer responsiveness and selective high‐affinity binding to the IgG Fc region. Remarkably, a comparison among the binding behaviors of a series of thioether‐modified microspheres indicates that bridging structures composed of β,β′‐dihydroxysulfide play a predominant role in IgG recognition. This straightforward approach can lead to the development of economical and practical nonbiological alternatives to protein A‐conjugated materials, providing solutions for various applications such as biosensors and site‐specific reagents utilizing the affinity of the IgG Fc region. The improved understanding of protein interactions at bridged/non‐bridged interfaces can be valuable in various applications such as implant materials and biomaterials.

Breaking of Lateral Symmetry in Two-Dimensional Crystallization-Driven Self-Assembly on a Surface.

Symmetry breaking is prevalent in nature and provides distinctive access to hierarchical structures for artificial materials. However, it is rarely explored in two-dimensional (2D) entities, especially for lateral asymmetry. Herein, we describe a unique symmetry breaking process in surface-initiated 2D living crystallization-driven self-assembly. The 2D epitaxial growth occurs only at one lateral side of the immobilized cylindrical micelle seeds, accessing unilateral platelets with the yield increasing with the seed length, the growth temperature, and poly(2-vinylpyridine) corona length (maximum = 92%). Generally, the tilted immobilization of seeds blocks one lateral side and triggers the lateral symmetry breaking, where the intensity and spatial arrangement of seed-surface interactions dictate the regulation. Segmented unilateral platelets with segmented corona regions are further fabricated with the addition of different blended unimers. Remarkably, discrete slope-like and dense blade-like platelet arrays grow off the surface when seeds are compactly aligned either with spherical micelles or themselves. This strategy provides nanoscale insights into the symmetry breaking in long-range self-assembly and would be promising for the design of innovative colloids and smart surfaces.

Design and development of a not actively driven modular device for parts feeding and sorting

The current paper focuses on developing and designing a not actively driven module for material handling operations in the field of intra-logistic. This device, belonging to the class of systems known as smart surfaces, is planned to be assembled with others to create manipulative arrays. As a novel feature, the reported concept aims to generate the frictional forces required for surface operation avoiding motors and with a simplified design. The article not only presents the design of the concept, but also the analytic models used to describe its operation and handling forces. In addition, a characterization of the fundamental parameters and the validation of the mentioned analytic descriptions together with the functioning itself are reported. As result, the analysis and the measurements presented show a real solution for a not actively driven concept, along with a methodology to characterize it and predict its handling capabilities. Specifically, the validation test proved that the model is able to represent the behavior of the friction forces with relative errors mainly in the range of 10% or lower.

Responsive self-assembly of nanomaterials: Mechanisms, applications, and future perspectives

In the development of nanotechnology, responsive self-assembly has been an important research theme. Responsive self-assembly is a technique where nanoparticles form structures in response to external stimuli like temperature and light. Thermo-responsive and photo-controlled self-assembly processes are outstanding compared with traditional methods, and theyve been applied in drug delivery and smart surfaces. Yet, the two processes still have their own challenges in practical applications. This review explores both techniques for explaining how these external stimuli work and the role of nanomaterial properties in the processes. Then it dives deep into their applications, specifically focusing on their strengths and challenges. Thermo-responsive and photo-controlled self-assembly are eco-friendly and reversible, ensuring their wide applications in various conditions. However, thermo-responsive materials, notably UCST-based polymers, are limited in scope, sensitive to the environment, and extremely expensive, while the effectiveness of the photo-controlled assembly process is limited by certain light conditions. Future research should focus on exploring their potential and overcoming the challenges.

Reliability Analysis and Optimization of a Reconfigurable Matching Network for Communication and Sensing Antennas in Dynamic Environments through Gaussian Process Regression.

During the implementation of the Internet of Things (IoT), the performance of communication and sensing antennas that are embedded in smart surfaces or smart devices can be affected by objects in their reactive near field due to detuning and antenna mismatch. Matching networks have been proposed to re-establish impedance matching when antennas become detuned due to environmental factors. In this work, the change in the reflection coefficient at the antenna, due to the presence of objects, is first characterized as a function of the frequency and object distance by applying Gaussian process regression on experimental data. Based on this characterization, for random object positions, it is shown through simulation that a dynamic environment can lower the reliability of a matching network by up to 90%, depending on the type of object, the probability distribution of the object distance, and the required bandwidth. As an alternative to complex and power-consuming real-time adaptive matching, a new, resilient network tuning strategy is proposed that takes into account these random variations. This new approach increases the reliability of the system by 10% to 40% in these dynamic environment scenarios.

Closed-Loop Optical Tracking of a Micro-Conveyor over a Smart Surface

In this work, a closed loop control system is developed to optically localize and track micro-robots with high precision. These micro-robots (i.e., micro-conveyors) are in motion simultaneously across a smart surface.The developed method’s primary objectives are to optimize their trajectories, avoid collisions between them, and control their position with micrometric resolution. This article presents and characterizes the tracking of a single micro-conveyor, and the method works similarly when multiple micro-robots move over the surface. Our tracking method starts with a scanning phase, where a 2D steering mirror, placed above the smart surface, reflects a laser beam toward the conveying surface seeking for the target. Localization occurs when this light beam reaches the micro-conveyor. By adding a retro-reflective element, that reflects the light in the same direction of the the incident light, onto the surface of the micro-conveyor, the light will be reflected towards a photodetector. Depending on the feedback from the photodetector, the steering mirror rotates to track the trajectory of the micro-conveyor. The tip-tilt angular values of the steering mirror allows the micro-conveyor position to be obtained via calibrated localization system. The aim of this work is to regulate the micro-conveyor, within a closed-loop control system, to reduce the positional error between the actual and desired position. The actual position value is measured in real-time application using our developed optical sensor. Results for tracking in the x-and y-axis have validated the proposed method, with an average tracking error less than 30 µm within a range 150 mm × 150 mm.