No abstract

Stretchable, wearable and highly sensitive strain sensors are vital to the development of health monitoring systems, smart robots and human machine interfaces. The recent sensor fabrication progress is respectable, but it is limited by complexity, low sensitivity and short service life. Herein we present a facile, cost-effective and scalable method for the development of high-performance composite strain sensors and stretchable conductors based on a composite film consisting of graphene platelets (GnPs) and silicon rubber. Through calculation by the tunnelling theory using experimental data, the composite film has demonstrated ideal linear and reproducible sensitivity to tensile strains, which was contributed by the superior piezoresistivity of GnPs having tunable gauge factors 27.7 -164.5. The composite sensors fabricated in different days demonstrated pretty similar performance, enabling the application as a health-monitoring device to detect various human motions from finger bending to pulse. They can be used as an electronic skin, a vibration sensor, and a human-machine interface controller. Stretchable conductors were made by coating and encapsulating GnPs with polydimethyl siloxane to create a composite; this structure allows the conductor to be readily bent and stretched with sufficient mechanical robustness and cyclability.

A scalable approach for the mass production of chemically modified graphene has yet to be developed, which holds the key to the large‐scale production of stable graphene colloids for optical electronics, energy conversion, and storage materials, catalysis, sensors, composites, etc. Here, a facile approach to fabricating covalently modified graphene and its polymer nanocomposites is presented. The method involves: i) employing a common furnace, rather than a furnace installed with a quartz tube and operated in inert gas as required in previous studies, to treat a commercial graphite intercalation compound with thermal shocking and ultrasonication and fabricate graphene platelets (GnPs) with a thickness of 2.51 ± 0.39 nm that contain only 7 at% oxygen; ii) grafting these GnPs with a commercial, long‐chain surfactant, which is able to create molecular entanglement with polymer matrixes by taking advantage of the reactions between the epoxide groups of the platelets and the end amine groups of the surfactant, to produce chemically modified graphene platelets (m‐ GnPs); and iii) solution‐mixing m‐GnPs with a commonly used polymer to fabricate nanocomposites. These m‐GnPs are well dispersed in a polymer with highly improved mechanical properties and a low percolation threshold of electrical conductivity at 0.25 vol%. This novel approach could lead to the future scalable production of graphene and its nanocomposites.

No abstract

We have developed a hierarchical process that combines linear triblock copolymers into concentric globular sub-units through strong chemical bonds and is followed by their supramolecular assembly via weak non-covalent interactions to afford one-dimensionally-assembled, dynamic cylindrical nanostructures. The molecular brush architecture forces triblock copolymers to adopt some intramolecular interactions within confined frameworks and then drives their intermolecular interactions in the mixtures of organic solvent and water. In contrast, the triblock copolymers, when not pre-connected into the molecular brush architectures, organize only into globular assemblies.

No abstract

The orthogonality of RAFT and ROMP chemistries are exploited for a highly efficient “grafting through” strategy to afford cylindrical molecular brushes. The ROMP of α‐norbornenyl‐functionalized poly(t‐butyl acrylate) macroRAFT chain transfer agents, catalyzed by a modified 2nd generation Grubbs' catalyst, achieved completion in minutes under air. Following hydrolysis, functionalizable water‐soluble poly(acrylic acid) molecular brushes were afforded. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.]

Self-assembly of synthetic macromolecules, inspired by the organization of biomolecules in nature, is a powerful approach for fabricating novel nanostructures, whose potential applications in nanomedicine are of significant interest. 1,2 Using amphiphilic linear copolymers as building blocks, various supramolecular architectures have been constructed, whose compositions, sizes, and morphologies are all tunable. [3][4][5] In spite of that, those nanostructures, made from synthetic macromolecules, are still primitive compared with those from biomolecules, which exhibit high complexity developed by evolution for millions of years. Our interest to attain nanostructures with higher complexities, approaching those of biological systems, drives our design of more types and sizes of macromolecular and nanoscopic building blocks, extending beyond simple linear block copolymers.Our initial targets are hetero-grafted diblock molecular brushes, 6,7 in which two different types of polymeric side chains are grafted sequentially along a backbone. These structures are designed as nanoscopic molecular frameworks having defined three-dimensional shape and control over the entire compositional profile, to mimic some features of the globular shape and compositional heterogeneities of protein building blocks. Three strategies are often used to synthesize molecular brushes: "grafting from", 8-11 "grafting onto", 12,13 and "grafting through". 14-18 The first two strategies can afford molecular brushes with relatively long and well-defined backbones. In the synthesis of hetero-grafted diblock molecular brushes, [19][20][21][22] for which the block segments of differing compositions are distributed along the primary molecular brush backbone, the "grafting through" strategy has several conveniences and advantages in avoiding many side reactions and providing significant structural control 6 due to the use of presynthesized polymers that are then polymerized to afford the final brush structure. To polymerize the highly diluted chain end groups of the polymers that ultimately become the grafted side chains, ring-opening metathesis polymerization (ROMP) is often applied. 14,15 Herein, by exploiting the orthogonality and livingness of reversible addition-fragmentation chain transfer (RAFT) polymerization 23 and ROMP, 24-26 we have developed a facile and efficient "grafting through" strategy to synthesize hetero-grafted diblock molecular brushes with precisely controlled architecture. These structures were transformed into amphiphilic diblock molecular brushes, which were then investigated as nanoscopic building blocks for the assembly of supramolecular nanostructures in aqueous medium.The amphiphilic hetero-grafted diblock molecular brush was produced by a highly efficient, one-pot "grafting-through" process, involving the sequential ROMP of norbornenylterminated macromonomers, followed by a deprotection reaction (Scheme 1). R-Norbornenyl poly(tert-butyl acrylate) (NB-PtBA) (1) and R-norbornenyl polystyrene (NB-PS) (2) macromonomers were firs...