Controlled Folding of 2D Au–Polymer Brush Composites into 3D Microstructures

Microscale, quasi‐2D Au–polymer brush composite objects are fabricated by a versatile, controllable process based on microcontact printing followed by brush growth and etching of the substrate. These objects fold into 3D microstructures in response to a stimulus: crosslinked poly(glycidyl methacrylate) (PGMA) brushes fold on immersion in MeOH, and poly(methacryloxyethyl trimethylammonium chloride) (PMETAC) brushes fold on addition of salt. Microcages and microcontainers are fabricated. A multistep microcontact printing process is also used to create sheets of Au–PGMA bilayer lines linked by a PGMA film, which fold into cylindrical tubes. The bending of these objects can be predicted, and hence predefined during the synthesis process by controlling the parameters of the gold layer, and of the polymer brush.     

Preparation of Smart Polymer/Carbon Nanotube Conjugates via Stimuli‐Responsive Linkages

In this paper, we modified carbon nanotubes with the thiol‐reactive species, subsequently combined the thiol‐coupling reaction and reversible addition‐fragmentation chain transfer (RAFT) polymerization to prepare temperature‐responsive PNIPAAm (poly(N‐isopropylacrylamide))‐carbon nanotube conjugates. The prepared PNIPAAm‐carbon nanotube conjugates have temperature‐responsive PNIPAAm chain, and disulfide linkages between PNIPAAm and carbon nanotube which are sensitive to bio‐stimuli such as glutathione, therefore dual‐responsive polymer‐carbon nanotube conjugates have been prepared.     

Ionic Liquid–Polymer Composites: A New Platform for Multifunctional Applications

Ionic liquids (ILs) have emerged as a novel class of chemical compounds for the development of advanced (multi)functional materials with outstanding potential in applications of several areas due to their unique properties and functionalities. The combination of ILs with polymers, in a composite, allows for developing smart materials, which synergistically combine the features of specific polymers and ILs. Moreover, ILs can be extensively modified by the incorporation of functional groups with specific properties into the cation, anion, or both. Thus, it is possible to tune the IL, the polymer, or both to obtain a broad spectrum of multifunctional composites and address the specific requirements of many applications. This work focusses on advanced materials and strategies concerning ILs and polymers for the development of smart IL/polymer‐based materials for applications including responsive and sensitive sensors, actuators, environment, batteries, fuel cells, and biomedical applications.     

Stimuli‐Responsive Colloidal Systems from Mixed Brush‐Coated Nanoparticles

We report on the application of mixed polymer brushes to the reversible in situ switching colloidal systems (suspensions of responsive 200 nm in diameter particles in individual solvents and immiscible liquids). We used mixed copolymer brushes to fabricate responsive nanoparticles and employed the particles to prepare responsive colloidal systems, which demonstrated drastic transformation/switching of material properties upon external stimuli. The interaction between the particles themselves and the particles and their environment can be precisely tuned by a change of solvent and pH. We show that this behavior can be used for a reversible formation of particle aggregates, stabilization and switching between w/o and o/w emulsions, and regulation of the particle transport between immiscible liquids across the interface. We demonstrate an example of the application of the responsive colloids for the fabrication of ultrahydrophobic coatings with textured surfaces from aqueous dispersion, and no surfactant application, using the switching properties of the responsive particles.     

Positively K+‐Responsive Membranes with Functional Gates Driven by Host–Guest Molecular Recognition

A novel positively K⁺‐responsive membrane with functional gates driven by host‐guest molecular recognition is prepared by grafting poly(N‐isopropylacrylamide‐co‐acryloylamidobenzo‐15‐crown‐5) (poly(NIPAM‐co‐AAB₁₅C₅)) copolymer chains in the pores of porous nylon‐6 membranes with a two‐step method combining plasma‐induced pore‐filling grafting polymerization and chemical modification. Due to the cooperative interaction of host‐guest complexation and phase transition of the poly(NIPAM‐co‐AAB₁₅C₅), the grafted gates in the membrane pores could spontaneously switch from “closed” state to “open” state by recognizing K⁺ ions in the environment and vice versa; while other ions (e.g., Na⁺, Ca²⁺ or Mg²⁺) can not trigger such an ion‐responsive switching function. The positively K⁺‐responsive gating action of the membrane is rapid, reversible, and reproducible. The proposed K⁺‐responsive gating membrane provide a new mode of behavior for ion‐recognizable “smart” or “intelligent” membrane actuators, which is highly attractive for controlled release, chemical/biomedical separations, tissue engineering, sensors, etc.     

Chain Extension of Stimuli‐Responsive Polymer Brushes: A General Strategy to Overcome the Drawbacks of the “Grafting‐To” Approach

Stimuli‐responsive polymer brushes are smart materials for the design of bio‐interactive and responsive interfaces. The “grafting‐to” approach is a convenient preparation procedure that allows the modification of surfaces with preformed and most notably well‐defined functionalized macromolecules. However, the shortcoming of this approach is an intrinsic limitation of the grafting density, which in turn affects the stimuli‐responsive properties of the brush system. Here, a general strategy to overcome this limitation and to simultaneously improve the switching behavior of a temperature‐responsive poly(N‐isopropylacrylamide) (PNiPAAm) brush is reported. A technically simple processing step is used in combination with the thermal azide–alkyne cycloaddition to perform the chain extension of alkyne‐functionalized PNiPAAm brushes with azide‐functionalized PNiPAAm molecules.     

Structural Fabrication and Functional Modulation of Nanoparticle–Polymer Composites

This review article summarizes recent progress in the fabrication methodologies and functional modulations of nanoparticle (NP)–polymer composites. On the basis of the techniques of NP synthesis and surface modification, the fabrication methods of nanocomposites are highlighted; these include surface‐initiated polymerization on NPs, in situ formation of NPs in polymer media, and the incorporation through covalent linkages and supramolecular assemblies. In these examples, polymers are foremost hypothesized as inert hosts that stabilize and integrate the functionalities of NPs, thus improving the macroscopic performance of NPs. Furthermore, due to the unique physicochemical properties of polymers, polymer chains are also dynamic under heating, swelling, and stretching. This creates an opportunity for modulating NP functionalities within the preformed nanocomposites, which will undoubtedly promote the developments of optoelectronic devices, optical materials, and intelligent materials.     

Temperature‐Switchable Assembly of Supramolecular Virus–Polymer Complexes

Here a method is presented for the temperature‐switchable assembly of viral particles into large hierarchical complexes. Dual‐functional diblock copolymers consisting of poly(diethyleneglycol methyl ether methacry­late) (poly(DEGMA)) and poly((2‐dimethylamino)ethyl methacrylate) (poly(DMAEMA)) blocks self‐assemble electrostatically with cowpea chlorotic mottle virus (CCMV) particles into micrometer‐sized objects as a function of temperature. The poly(DMAEMA) block carries a positive charge, which can interact electrostatically with the negatively charged outer surface of the CCMV capsid. When the solution temperature is increased above 40 °C, to cross the cloud point temperature (T_cp) of the DEGMA block, the polymer chains collapse on the surface of the virus particle, which makes them partially hydrophobic, and consequently causes the formation of large hierarchical assemblies. Disassembly of the virus–polymer complexes can be induced by reducing the solution temperature below the T_cp, which allows the poly(DEGMA) blocks to rehydrate and free virus particles to be released. The assembly process is fully reversible and can sustain several heating–cooling cycles. Importantly, this method relies on reversible supramolecular interactions and therefore avoids the irreversible covalent modification of the particle surface. This study illustrates the potential of temperature‐responsive polymers for controlled binding and releasing of virus particles.     

From Membrane to Skin: Aqueous Permeation Control Through Light‐Responsive Amphiphilic Polymer Co‐Networks

The functionalization of amphiphilic polymer co‐networks with light‐responsive spiropyran and spirooxazine derivatives leads to a new type of light‐responsive materials. The material consisting of hydrophilic nanochannels shows desirable properties such as light‐responsive permeability changes of aqueous caffeine solutions, an exceptional repeatability of the photochromism, and tunable basic permeability rates. The versatility of the system is demonstrated by using different functionalization routes such as copolymerization of light‐responsive monomers or crosslinker as well as postmodification of the preformed amphiphilic network. Moreover, light‐responsive spirobenzopyran and novel spirooxazine derivatives are synthesized, which changes the properties of the light‐responsive membranes after inclusion into the amphiphilic co‐networks. Finally, the permeability of the delivery membrane can be tailored to match the properties of porcine skin, an in vitro model of human neonatal skin. One possible application might be the use of the light‐responsive membranes as key‐unit of a transdermal caffeine‐delivery system for preterm neonates.     

Photodriven,Flexural–Torsional Oscillation of Glassy Azobenzene Liquid Crystal Polymer Networks

Cantilevers composed of glassy, photoresponsive liquid crystalline polymer networks (LCNs) are shown to oscillate at high frequency (～50 Hz) and large amplitude when exposed to light from a 442 nm coherent wave (CW) laser. Added dimensionality to previously reported in‐plane oscillations is enabled by adjusting the orientation of the nematic director to the long axis of the cantilever yielding in‐plane bending accompanied by out‐of‐plane twisting (flexural–torsional oscillation). The fundamental photoresponse of this class of glassy azobenzene liquid crystal polymer networks (azo‐LCN) is further probed by examining the influence of cantilever aspect ratio, laser intensity, and temperature. The frequency of photodirected oscillations is strongly correlated to the length of the cantilever while the amplitude and threshold laser intensity for oscillation is strongly correlated to temperature.     

Switching Light Transmittance by Responsive Organometallic Poly(ionic liquid)s: Control by Cross Talk of Thermal and Redox Stimuli

A novel organometallic poly(ionic liquid) with both redox‐ and thermoresponsive properties is synthesized from a poly(ferrocenylsilane) (PFS) via a one‐step Strecker sulfite alkylation reaction by using tetraalkylphosphonium sulfite as an effective and versatile nucleophile. This dual‐responsive polymer is composed of a PFS backbone and quaternary phosphonium sulfonate side groups and exhibits a concentration‐dependent lower critical solution temperature (LCST)‐type phase transition in aqueous solution. Furthermore, the LCST‐type phase behavior of the polymer can be switched between the “off” state and “on” state by chemical or electrochemical oxidation and reduction on the ferrocene units in the polymer main chain. As a consequence, a classical LCST‐type phase transition, as well as an “isothermal” redox‐triggered phase transition can be induced by using thermal and electrochemical triggers without changing the composition of the system. On the basis of this dual responsiveness, a “smart window” device is fabricated. The optical characteristics of this device are completely unaltered after 100 thermal and/or redox cycles.     

Vapor Sorption and Electrical Response of Au‐Nanoparticle– Dendrimer Composites

Films comprising Au nanoparticles and polyphenylene dendrimers (first and second generation) are deposited onto transducer substrates via layer‐by‐layer self‐assembly and characterized by atomic force microscopy and X‐ray photoelectron spectroscopy. Their sorption behavior is studied by measuring the uptake of solvents from the vapor phase with quartz crystal microbalances (QCMs). The resistance of the films is simultaneously monitored. Both sensor types, QCMs and chemiresistors, give qualitatively very similar response isotherms that are consistent with a combination of Henry‐ and Langmuir‐type sorption processes. The sorption‐induced increase in relative differential resistance scales linearly with the amount of analyte accumulated in the films. This result is in general agreement with an activated tunneling process for charge transport, if little swelling and only small changes in the permittivity of the film occur during analyte sorption (a first‐order approximation). The relative sensitivity of the films to different solvents decreases in the order toluene ≈ tetrachloroethylene > 1‐propanol ? water. Films containing the larger second‐generation dendrimers show higher sensitivity than films containing first‐generation dendrimers.     

Efficient Mechanoluminescent Elastomers for Dual‐Responsive Anticounterfeiting Device and Stretching/Strain Sensor with Multimode Sensibility

In this work, an environmentally friendly and novel oxide‐based mechanoluminescent material, Sr₃Al₂O₆: Eu³⁺, which can serve as the alternative for the widely used but environmentally hazardous transition metal–doped sulfides is reported. This oxide could exhibit highly efficient photoluminescence, but even more efficient mechanoluminescence as embedded into polydimethylsiloxane matrix under mechanical stimulation. The emitting color of the resultant Sr₃Al₂O₆: Eu³⁺/polydimethylsiloxane elastomer composites could be further manipulated by adjusting the synthesis atmosphere of the Sr₃Al₂O₆: Eu³⁺ based on its unique self‐reduction characteristic. Moreover, by combining the wavelength selectivity of photoluminescence and dynamic stress response of mechanoluminescence, Sr₃Al₂O₆: Eu³⁺ enables the design of two types of intriguing devices. They are a dual‐responsive anticounterfeiting flexible device activated by either photons or mechanics, and a comprehensive stretching/strain sensor capable of sensing both strain level and stretching states. In comparison to the conventional luminescent materials, with a rare combination of efficient photoluminescence, highly sensitive mechanoluminescence, and facile color tunability, Sr₃Al₂O₆: Eu³⁺ is much more versatile and ideal for various advanced applications.     

Reversible Water Transportation Diode: Temperature‐Adaptive Smart Janus Textile for Moisture/Thermal Management

“Air‐conditioning” textiles with thermal‐ or moisture‐managing functions are of high interest for not only improving human comfort but also reducing energy consumption. However, making the textile sensitive to the surrounding environment and exhibit adaptive thermal/moisture management still remains a great challenge. Herein, a double‐sided synergetic Janus textile is developed, featuring reversible diode‐like water transportation and adjustable thermal convection upon temperature change. The incorporated responsive polymer networks with inverse transitions on the opposite sides provide synergistic surface energy gradients and capillary gradients that generate drying and cooling effects (with 50% faster water evaporation and 1.2–2.3 °C cooler than with cotton fabric) in hot weather while offering thermal preservation (120 s longer needed to be cooled down and maximumly 3.3 °C warmer than with cotton fabric) in a cold environment. This method could provide ideas for the development of more adaptive textiles and clothing to address maximum personal comfort in demanding situations.     

One‐Pot Synthesis of Luminescent Polymer‐Nanoparticle Composites from Task‐Specific Ionic Liquids

A multifunctional polymerizable ionic liquid, diallyldimethylammonium tetrafluoroborate (DADMA BF₄), is used in a one‐pot synthesis of novel luminescent polymer‐nanoparticle composites. First, small monodisperse lanthanide fluoride nanoparticles are formed by microwave irradiation in the presence of Ln(OAc)₃·xH₂O (Ln = Gd, Eu, Tb; OAc = acetate) in the ionic liquid. The nanoparticles can be precipitated for structural characterization or kept in the solution, which yields after irradition by high intensity UV light colorless, processable polymer materials with good photophysical properties. Both green‐emitting Tb‐containing and red‐emitting Eu‐containing IL‐ polymers are described.     

Polymer Microcapsules with Carbohydrate‐Sensitive Properties

Carbohydrate‐sensitive polymer multilayers are assembled onto flat substrates and colloidal CaCO₃ particles via reversible covalent ester formation between the polysaccharide mannan and phenylboronic acid moieties grafted onto poly(acrylic acid) (PAA). The resulting multilayer films are sensitive to several carbohydrates, and show the highest sensitivity to fructose. The response to carbohydrates arises from the competitive binding of small molecular weight sugars and mannan to boronic acid groups within the films, and is observed as a rapid dissolution of the multilayers upon contact with a sugar‐containing solution above a critical concentration. In addition, carbohydrate‐sensitive multilayer capsules are prepared, and their sugar‐dependent stability is investigated by following the release of encapsulated tetramethylrhodamine isothiocyanate‐bovine serum albumin (TRITC‐BSA).     

Easily Processable and Programmable Responsive Semi‐Interpenetrating Liquid Crystalline Polymer Network Coatings with Changing Reflectivities and Surface Topographies

The fabrication of stimulus‐responsive coatings that change both reflectivity and topography is hampered by the lack of easy processable, patternable, and programmable elastomers. Here, an easily applied reflective coating based on a semi‐interpenetrating polymer network composed of a liquid crystal elastomer and a liquid crystal network (>15 wt%) is reported. The reflective wavelength of these polysiloxane elastomer photonic coatings can be readily programed by the concentration of chiral reactive mesogen dopant that forms the network. The coatings show a fast and reversible decrease in reflection band intensity with increasing temperature, which can be tuned by the polymer network density. In addition, hierarchical surface relief structures are prepared, which can be reversibly changed with temperature.