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Growth constitutes a powerful method to post-modulate materials’ structures and functions without compromising their mechanical performance for sustainable use, but the process is irreversible. To address this issue, we here report a growing-degrowing strategy that enables thermosetting materials to either absorb or release components for continuously changing their sizes, shapes, compositions, and a set of properties simultaneously. The strategy is based on the monomer-polymer equilibrium of networks in which supplying or removing small polymerizable components would drive the networks toward expansion or contraction. Using acid-catalyzed equilibration of siloxane as an example, we demonstrate that the size and mechanical properties of the resulting silicone materials can be significantly or finely tuned in both directions of growth and decomposition. The equilibration can be turned off to yield stable products or reactivated again. During the degrowing-growing circle, material structures are selectively varied either uniformly or heterogeneously, by the availability of fillers. Our strategy endows the materials with many appealing capabilities including environment adaptivity, self-healing, and switchability of surface morphologies, shapes, and optical properties. Since monomer-polymer equilibration exists in many polymers, we envision the expansion of the presented strategy to various systems for many applications.
Abstract What happens when the extremely adhesive and versatile chemistry of polydopamine (PDA) is in contact with the extremely slippery surfaces known as slippery liquid-infused porous substrates (SLIPS)? Inspired by the pitcher plant, SLIPS possess excellent repellence against a variety of complex liquids and have been proposed as promising antifouling surfaces because of their successful performance even in marine environments. In the counterpart, inspired by the adhesive proteins enabling the strong adhesion of mussels to multiple substrates, PDA has been extensively studied for its ability to adhere on nearly every type of substrate. The interaction between various SLIPS systems and the highly fouling medium from the oxidative polymerization of dopamine is explored here. A PDA coating is observed on all the SLIPS evaluated, modifying their hydrophobicity in most cases. In-depth study of silicone-based SLIPS shows that hydrophobicity of PDA coated SLIPS partially recovers with time due to percolation of the lubricant through the coating. “Strongly” bound PDA species are attributed to the formation of dopamine-polydimethylsiloxane species on the crosslinked matrix, rendering a coating that withstands repeated washing steps in various solvents including water, hexane, and toluene. The results not only satisfy scientific curiosity but also imply a strategy to modify/bond SLIPS.
When the majority of efforts to control adhesion from surfaces currently focus on a direct modification of the surface, either chemically or physically, perhaps a non-superficial approach where the action occurs underneath the surface can provide a competitive alternative. In this comment we highlight a methodology used to control adhesion from flexible surfaces. This is based on 'semi-closed' flexible microfluidics systems. Three basic functionalities are derived from this methodology. In one case the system is used to improve adhesion; in an extreme opposite case to prevent adhesion and in a somehow intermediate functionality it provides a switchable system in which the surface can be reversibly changed from adhesive to non-adhesive.
Abstract It is challenging to post-tune the sensitivity of a tactile force sensor. Herein, a facile method is reported to tailor the sensing properties of conductive polymer composites by utilizing the liquid-like property of dynamic polymer matrix at low strain rates. The idea is demonstrated using dynamic polymer composites (CB/dPDMS) made via evaporation-induced gelation of the suspending toluene solution of carbon black (CB) and acid-catalyzed dynamic polydimethylsiloxane (dPDMS). The dPDMS matrices allow CB to redistribute to change the sensitivity of materials at the liquid-like state, but exhibit typical solid-like behavior and thus can be used as strain sensors at normal strain rates. It is shown that the gauge factor of the polymer composites can be easily post-tuned from 1.4 to 51.5. In addition, the dynamic polymer matrices also endow the composites with interesting self-healing ability and recyclability. Therefore, it is envisioned that this method can be useful in the design of various novel tactile sensing materials for many applications.
Selective crystallization represents one of the most economical and convenient methods to provide large-scale optically pure chiral compounds. Although significant development has been achieved since Pasteur’s separation of sodium ammonium tartrate in 1848, this method is still fundamentally low efficient (low transformation ratio or high labor). Herein, we describe an enantiomer-selective-magnetization strategy for quantitatively separating the crystals of conglomerates by using a kind of magnetic nano-splitters. These nano-splitters would be selectively wrapped into the S-crystals, leading to the formation of the crystals with different physical properties from that of R-crystals. As a result of efficient separation under magnetic field, high purity chiral compounds (99.2 ee% for R-crystals, 95.0 ee% for S-crystals) can be obtained in a simple one-step crystallization process with a high separation yield (95.1%). Moreover, the nano-splitters show expandability and excellent recyclability. We foresee their great potential in developing chiral separation methods used on different scales.
Das LRC verfolgt das Ziel, zellfreie Biotechnologie für die Synthese multifunktionaler Mikro-Produktionseinheiten zu entwickeln. Mit der Entwicklung von Reaktionsplattformen für die Manipulation der mehrstufigen Biosynthese auf einer Mikroebene trägt JRG4 am INM zum Gesamtprojekt bei. Die Reaktionsplattformen müssen vier spezifischen Randbedingungen genügen: 1) kompatibel mit den für die Biosynthese angewandten Enzymkatalysatoren und inert gegenüber Reaktanten sein; 2) geschlossene Kompartimente bieten, die festgelegte Reaktionsbedingungen gewährleisten können (pH, Konzentration); 3) einen stimuli-responsiven Mechanismus zur Steuerung des Reaktionswegs enthalten, um komplexe Reaktionsketten zu vereinfachen (Produkte aus den Anfangsstufen gemischt mit Produkten aus späteren Stufen); 4) ständigen Zugriff auf Zwischenprodukte im Reaktionsprozess zur Kontrolle und Analyse gestatten. Dazu wurden drei verschiedene Plattformen entworfen und entwickelt: strukturelle Oberflächen auf Basis von Hohlsäulen, flüssigkeitsvermittelte mobile Oberflächen und thermo-magnetisch responsive Träger. Die strukturellen Oberflächen bestehen aus geometrisch angeordneten Hohlsäulen aus responsiven Materialien, die zur Einleitung und Entnahme von Reaktionslösungen dienen. In Ergänzung zu dieser Grundidee, gemäß der die Mikro-Reaktionsflüssigkeiten der Luft ausgesetzt werden, sollen die flüssigkeitsvermittelten mobilen Oberflächen die als Mikrotropfen vorliegenden Reaktionsflüssigkeiten im umhüllten Zustand manipulieren. Die mobilen Oberflächen weisen eine Struktur von porösem Substrat mit semi-infundiertem perfluoriertem Ferrofluid auf, das mithilfe magnetischer Anregung bewegt werden kann, sodass die Tropfen transportiert, gemischt und separiert werden können. Die thermo-magnetisch responsiven Träger dienen der weiteren Miniaturisierung der Reaktionsplattform. Dieses System setzt sich aus einem MNP-Kern (magnetische Nanopartikel), einer stimuli-responsiven Polymerschale und funktionalen Endgruppen zur Immobilisierung der Enzymkatalysatoren zusammen. Der MNP-Kern dient der Bewegung des Bioreaktors und dem Recycling der Reaktionslösungen, während die stimuli-responsive Polymerschale dem Anhalten bzw. erneuten Anstoßen der Bioreaktionen sowie dazu dient, die Löslichkeit der Biorektoren für das Recycling variieren zu können.[...]
Natural organic structures form via a growth mode in which nutrients are absorbed, transported, and integrated. In contrast, synthetic architectures are constructed through fundamentally different methods, such as assembling, molding, cutting, and printing. Here, we report a photoinduced strategy for regulating the localized growth of microstructures from the surface of a swollen dynamic substrate, by coupling photolysis, photopolymerization, and transesterification together. Photolysis is used to generate dissociable ionic groups to enhance the swelling ability that drives nutrient solutions containing polymerizable components into the irradiated region, photopolymerization converts polymerizable components into polymers, and transesterification incorporates newly formed polymers into the original network structure. Such light-regulated growth is spatially controllable and dose-dependent and allows fine modulation of the size, composition, and mechanical properties of the grown structures. We also demonstrate the application of this process in the preparation of microstructures on a surface and the restoration of large-scale surface damage.
The handling of droplets in a controlled manner is essential to numerous technological and scientific applications. In this work, we present a new open-surface platform for droplet manipulation based on an array of bendable nozzles that are dynamically controlled by a magnetic field. The actuation of these nozzles is possible thanks to the magnetically responsive elastomeric composite which forms the tips of the nozzles; this is fabricated with Fe3O4 microparticles embedded in a polydimethylsiloxane matrix. The transport, mixing, and splitting of droplets can be controlled by bringing together and separating the tips of these nozzles under the action of a magnet. Additionally, the characteristic configuration for droplet mixing in this platform harnesses the kinetic energy from the feeding streams; this provided a remarkable reduction of 80% in the mixing time between drops of liquids about eight times more viscous than water, i.e., 6.5 mPa/s, when compared against the mixing between sessile drops of the same fluids
Abstract Developing a novel strategy to synthesize photoresponsive polymers is of significance owing to their potential applications. We report a photoinduced strain-assisted synthesis of main-chain stiff-stilbene polymers by using ring-opening metathesis polymerization (ROMP), activating a macrocyclic π-bond connected to a stiff-stilbene photoswitch through a linker. Since the linker acts as an external constraint, the photoisomerization to the E-form leads to the stiff-stilbene being strained and thus reactive to ROMP. The photoisomerization of Z-form to E-form was investigated using time-dependent NMR studies and UV/Vis spectroscopy. The DFT calculation showed that the E-form was less stable due to a lack of planarity. By the internal strain developed due to the linker constraint through photoisomerization, the E-form underwent ROMP by a second generation Grubbs catalyst. In contrast, Z-form did not undergo polymerization under similar conditions. The MALDI-TOF spectrum of E-form after polymerization showed the presence of oligomers of >5.2 kDa.
Abstract Space cooling and heating currently result in huge amounts of energy consumption and various environmental problems. Herein, a switching strategy is described for efficient energy-saving cooling and heating based on the dynamic cavitation of silicone coatings that can be reversibly and continuously tuned from a highly porous state to a transparent solid. In the porous state, the coatings can achieve efficient solar reflection (93%) and long-wave infrared emission (94%) to induce a subambient temperature drop of about 5 °C in hot weather (≈35 °C). In the transparent solid state, the coatings allow active sunlight permeation (95%) to induce solar heating to raise the ambient temperature from 10 to 28 °C in cold weather. The coatings are made from commercially available, cheap materials via a facile, environmentally friendly method, and are durable, reversible, and patternable. They can be applied immediately to various existed objects including rigid substrates.
