The ionic–covalent hybrid cross-linked tough hydrogels have been widely applied in various fields for their superior mechanical properties, but it is challenging to fabricate the hybrid gels with a controlled ionic cross-linking distribution. Here we report a robust, one-step fabrication method for alginate/polyacrylamide hydrogels with high stretchability, toughness, and self-recovery by the glucono-delta-lactone-triggered in situ release of metal ions from premixed insoluble metal salts or alkalis. The versatility of this method is demonstrated by employing several insoluble metal salts or alkalis, including CaCO3, BaCO3, Co(OH)2, Cu(OH)2, and La2(CO3)3·xH2O. This strategy provides an alternative method to synthesize homogeneous ionic–covalent hybrid cross-linked hydrogels.

On-demand stiffening is ubiquitous in nature but not in artificial materials. Herein, we describe a self-stiffening approach that features fast stiffening rate, huge stiffening range, and excellent spatial control. The strategy is based on the continuous removal of the small transesterification products to drive the equilibrium toward the esterification state. The initial elastomers can evolve from a rubber to a plastic with a change of three orders of magnitude in modulus. Moreover, the process is also spatially controllable. These appealing features allow programming of mechanical heterogeneities and gradients as well as the shape of materials via site-specifically seeding the transesterification catalyst.

Carbon dioxide (CO2) capture from fossil-fuel-based power plants requires scalable membranes with high CO2 permeability and reasonable CO2/N2 selectivity. Conventional membranes based on polyaniline (PANi) feature a CO2 permeability of 1 Barrer or less, which is unviable for industrial applications such as separating the massive scale of CO2 emissions produced by power plants. Here, we report nanocomposites comprised of the conjugated polymer polyaniline with graphene oxide at different oxidation levels that are blended and drop-cast to form freestanding membranes for gas separations. The added graphene oxide is shown to effectively enhance the gas permeability. These hybrid membranes are characterized by Fourier-transform infrared spectroscopy to indicate clearly the presence of well-dispersed GO in the polyaniline matrix; vertical scanning interferometry and field emission scanning electron microscopy to illustrate the film homogeneity, morphology, and thickness; and thermogravimetric analysis to assess thermal stability. The outcomes highlight composited membranes that are readily scalable, tolerant to slightly elevated temperatures (up to 170 °C), and that feature CO2 permeabilities >700 Barrers and reasonable CO2/N2 selectivities. By applying a doping/dedoping/redoping process using hydrochloric acid (HCl) and ammonium hydroxide (NH4OH), the membrane selectivities can be considerably enhanced. This work thus reports the first synthesis of PANi-based nanocomposite membranes whose permeability begins to approach the upper bound indicated on a Robeson plot.

We find that changing the chemistry of the inorganic core of polymer-grafted nanoparticles (PGNPs) from Au to TiO2 in a polymer matrix having the same chemistry leads to a qualitative change in the propensity of the PGNPs to self-assemble in the polymer matrix, pointing to the significance of enthalpic interactions between the NP cores and the polymer matrix. Specifically, PGNPs having polystyrene (PS) chains grafted to a Au nanoparticle core disperse well in a PS matrix, while PGNPs under similar thermodynamic conditions having instead a TiO2 core of about the same PS grafted chains and polymer matrix, exhibit large scale self-assembly into noncompact “clusters of PGNPs” (PGNPCs) (Nat. Mater.2009, 8 (4), 354–359). We then investigated whether we could still use the method of nanopatterning established in our previous study of nonassociating PGNPs, for also directing the self-assembly of PGNPCs. We find nanoimprinting the associating PS-TiO2 particles still allows us to localize the PGNPCs to patterns through the entropic localization effect that we investigated in previous work, but the nanoimprinting process also allows us to direct the PGNPC self-assembly process, resulting in significant property changes in PGNPC nanocomposite films in comparison to films containing nonassociating PGNPs. For example, the associating PGNPC films become significantly stabilized against dewetting in comparison to the nonassociating PGNPs. We quantify the partitioning of the PGNPCs to the patterned regions by estimating the cluster partition coefficient Kc of the PGNPCs to the thicker film regions, demonstrating that selective segregation of PGNPCs to the imprinted patterns still arises from an entropic segregation of the PGNPCs associated with the alteration of the conformation fluctuations of the grafted polymers under confinement induced by the imprinting process. This form of pattern-directed self-assembly of PGNPCs can be expected to be useful for “writing” large scale patterns in thin polymer films having designed optical, electronic, mechanical, frictional properties, while at the same time enhancing the stability of the polymer film.

Highly flexible atomic-oxygen (AO)-resistant coatings emerge as essential protective materials for low earth orbit (LEO) spacecraft. However, achieving synergistic characteristics of ultraefficient AO resistance, self-healing ability, and excellent stabilities remains a critical challenge. In this work, a flexible polysiloxane coating coupled with a highly homogeneous composition is a well-organized form used as the raw material of hexamethyldisiloxane (HMDSO). This siloxane coating displays excellent flexibility and interfacial strength verified by bending and thermal cycling experiments. After an AO irradiation experiment with the accumulated flux of 2.5 × 1022 atoms/cm2 (the equivalent of 5 years), the mass loss rate of the polysiloxane-coated Kapton film is less than 0.284 ± 0.044 mg/cm2, demonstrating long-life and high-reliability characteristics. In addition, this flexible coating displayed self-healing behavior due to the formation of SiO2-durable layers during the AO irradiation, which endows the polysiloxane coating with “stiff exterior, flexible interior” characteristics based on the high flexibility. Our work shows the actual application and great potential of flexible self-healing AO protective coatings in spacecraft and provides a useful strategy to design multifunctional barrier materials.

Traditional thermosetting polyureas (TPUs) with eminently comprehensive performance have been used in a variety of industrial applications. However, they suffer from a certain intractable difficulty in achieving multiple functions such as reprocessability, shape reconfiguration, or self-healing performance due to the extremely stable covalent cross-linking. Herein, we employ hindered urea bonds (HUBs) as a reversible dynamic covalent cross-linkage to design catalyst-free hindered thermosetting polyureas (HTPUs). By incorporating HUBs into TPUs, the synthesized HTPUs can be reprocessed by using hot press or microinjection technique without any catalyst. In addition, those obtained materials have achieved great abilities of permanent shape reconfiguration and self-healing. Especially, the combination of the conventional elastic shape memory with the solid-state plastic shape reconfiguration in these HTPUs will broaden the geometrically complex shapes for shape memory polymer. Importantly, introducing longer and more bulky substituents into HTPUs can simultaneously endow the materials with excellent mechanical properties and the aforementioned multiple functions. Despite what is mentioned in this article, more potential HTPUs with excellent mechanical properties and multiple functions could be further designed by introducing longer and more bulky substituents into the formal polymers.

The high sensitivity of carbon nanotube devices as gas sensors is generally attributed to the large surface area of the material, whereas selectivity is often imparted by the “lock-and-key” mechanism. In contrast with this picture, where little function is conferred to the underlying substrate, we demonstrate that bottom gate carbon nanotube network field-effect transistors (CNN-FETs) fabricated on a variety of polymer dielectrics, but with the same pristine carbon nanotubes, show differentiated responses to analytes. Interaction with the environment thus occurs not only directly with carbon nanotubes but is often mediated by the substrate. In a broad survey of polymers, we identify several materials suitable as the gate dielectric of printed devices and that yield a vanishing gate hysteresis in ambient air. The other two classes of polymers that induce a lagging or advancing hysteresis in CNN-FETs are found desirable for gas sensing applications. Moreover, we have tested CNN-FETs with different polymer gate dielectrics against a series of analytes ranging from common alcohols to organic solvents and amines, among others. A rich set of distinct and complementary analyte signatures could be observed, identifying the polymer gate dielectric as a differentiator for chemical discrimination in a future printed cross-reactive sensor array, that is, an electronic nose.

The capabilities of additive manufacturing for fabrication of complex and thin-walled ceramic-based objects are restricted by the availability of ceramics inks. Formulations of current ink systems strictly depend on using a high content of organic additives (5–30 wt %). The high amounts of additives affect uniformity and dimensional accuracy of the final object. Here, we designed a single additive that enables printing of high aspect ratio and thin-walled structures (height/width = 58) from an ink of alumina nanoparticles that comprises very low organic content (i.e., 1.25 wt % of nanoparticles mass). In addition to the generally exploited electrostatic effect, this additive has purpose-driven tailoring to harness steric hindrance to control the viscoelastic response of ceramic suspensions and realize an optimum ink for extrusion-based 3D printing. We pursued a stepwise approach in developing such an additive through synthesis of series of copolymers with backbone monomers of 2-acrylamido-2-methylpropanesulfonic acid and acrylic acid and side chains of poly(ethylene glycol). When the optimized additive is used, the suspension attains ∼80 wt % solid loading—99% of the theoretical limit calculated by the Krieger–Dougherty equation. The shrinkage and deflection of the printed patterns as well as compactness and sinter-ability of dried structures are monitored. The printed structures did not experience any deformation or deflection during printing and reached 68% of theoretical density (TD: 3.98 g/cm3) after drying. This compactness allowed sintering at lower temperatures and improved dimensional control of the final product. Our approach to formulate ceramic inks enables the embodiment of fully aqueous systems with the utmost material content and has the potential to expand the limited portfolio of ceramic inks.

Solid-state topochemical polymerization (SSTP) requires well-defined geometries and space symmetries between the starting monomers and resulting polymer, and diacetylenes are excellent precursors, reacting through a 1,4-addition mechanism. The hydrocarbon molecule 1,4-diphenyl-1,3-butadiyne (DPB) has a four-carbon chain with alternating triple/single bonds, capped on each end with a phenyl group, i.e. centrosymmetric with unsaturated π-bonding characteristics. To fully realize its potential for photocatalytic applications, improved control over the assembly process is desirable to form well-ordered poly(diphenylbutadiyne) (PDPB). Here, it is shown that with increasing pressure, DPB undergoes a series of solid-state chemical reactions while maintaining crystalline order related to the starting monomeric structure. Quenchable PDPB compounds begin forming at ca. 5 GPa, which exhibit optically-tunable absorbance and photoluminescence that is controllable through the extent of compression. Above ca. 15 GPa, the system transforms into a nonhexagonally-packed crystalline array with mixed sp2/sp3 character. These stepwise changes with compression are irreversible in nature, as observed by in situ diffraction and spectroscopic methods. For the first time, the simple SSTP synthesis route allows well-aligned DPB molecules to directly transform into a PDPB material via self-assembly solely through pressure generation within a diamond anvil cell without the traditional use of catalysts, temperature, radiation, templates, or solvents.

Screening platforms have become a valuable tool for exploring large libraries of surface chemistries helping the discovery of new materials for especially biological applications. Methods applied in these platforms, however, are mainly based on inert bulk synthesis at picoliter scale, resulting in noncovalently attached molecules on stiff glass substrates. This is a poor representation of a potential final product from an industrial perspective. To overcome this, we have developed a screening platform capable of conducting UV-initiated free radical polymerization (FRP) directly onto a flexible polyurethane under ambient conditions. The platform allows for the study of solvent and monomer effects under industrially relevant conditions and was used to graft a series of homo- and copolymer systems (2,2,2-trifluoroethyl methacrylate (TrFEMA), N-isopropylacrylamide (NIPAAm), diethylene glycol methyl ether methacrylate-co-poly(ethylene glycol) methyl ether methacrylate, (MDEGMA-co-MPEGMA), and acrylic acid (AA)), which was confirmed by both water contact angle (WCA) and X-ray photoelectron spectroscopy (XPS) analysis. The versatility of the system was further demonstrated through investigation of terpolymer systems and direct evaluation of their antifouling properties using a fluorescein-labeled bovine serum albumin (BSA).