Xuqing Liu

Polyethylene glycol functionalized dicationic ionic liquids with alkyl or polyfluoroalkyl substituents as high temperature lubricants

A series of new polyethylene glycol functionalized dicationic ionic liquids with alkyl or polyfluoroalkyl substitutents (9–17 and 19–24) has been prepared. Important physical properties of these liquids, including glass transition (Tg) and decomposition temperatures (Td), solubility in common solvents, density (d) and viscosity (η), were measured. These ionic liquids show high thermal stability and good lubricity. In general, imidazolium based dicationic liquids have higher Td (>415 °C) than their triazolium analogues. The introduction of polyfluoroalkyl groups boosts antiwear properties but also leads to a decrease in Td. These ionic liquids also exhibit excellent tribological characteristics even at 300 °C, which suggests use as high temperature lubricants.

Polyelectrolyte-bridged metal/cotton hierarchical structures for highly durable conductive yarns

A novel, facile, and versatile approach for preparing highly durable, electrically conductive cotton yarns is reported. Polyelectrolyte brushes, a polymer that covalently tethers one end on a surface, are first grown from cotton surfaces by surface-initiated atomic transfer radical polymerization. Subsequent electroless deposition of metal particles onto the brush-modified cotton yarns yields electrically conductive yarns, which have conductivity as high as approximately 1 S/cm and can be used as electrical wires in wearable, flexible electronic devices. Importantly, the formation of polymer brush-bridged metal/cotton hierarchical structures provides robust mechanical and electrical durability to the yarns under many stretching, bending, rubbing, and washing cycles. With proper selection of metal, the conductivity of the samples remains stable after they are stored in air for a few months. This chemical approach can be extended as a general method for making conductive yarns and fabrics from all kinds of natural fibers.

Matrix‐Assisted Catalytic Printing for the Fabrication of Multiscale, Flexible, Foldable, and Stretchable Metal Conductors

Matrix-assisted catalytic printing (MACP) is developed as a low-cost and versatile printing method for the fabrication of multiscale metal conductors on a wide variety of plastic, elastomeric, and textile substrates. Highly conductive Cu interconnects (2.0 × 10⁸ S/m) fabricated by MACP at room temperature display excellent flexibility, foldability, and stretchability.

Facile Synthesis of Wide‐Bandgap Fluorinated Graphene Semiconductors

The bandgap opening of graphene is extremely important for the expansion of the applications of graphene-based materials into optoelectronics and photonics. Current methods to open the bandgap of graphene have intrinsic drawbacks including small bandgap openings, the use hazardous/harsh chemical oxidations, and the requirement of expensive chemical-vapor deposition technologies. Herein, an eco-friendly, highly effective, low-cost, and highly scalable synthetic approach is reported for synthesizing wide-bandgap fluorinated graphene (F-graphene or or fluorographene) semiconductors under ambient conditions. In this synthesis, ionic liquids are used as the only chemical to exfoliate commercially available fluorinated graphite into single and few-layer F-graphene. Experimental and theoretical results show that the bandgap of F-graphene is largely dependent on the F coverage and configuration, and thereby can be tuned over a very wide range.

Programming nanostructures of polymer brushes by dip-pen nanodisplacement lithography (DNL)

We report a facile and versatile scanning probe based approach-dip-pen nanodisplacement lithography (DNL)--for manipulating nanostructures of polymer brushes. Nanostructured polymer brushes with sizes as small as 25 nm are made by DNL patterning of the initiator molecules and subsequent surface-initiated polymerization. Nanoconfinement effects including chain collapsing and spreading are observed in the nanopatterned polymer brushes. In addition to chemical structure, size, topography and shape, our approach can also readily program the grafting density, chain configuration, hierarchical structure and multiplexing of the polymer brushes, which allows for the realization of complex chemical surfaces.

3D-patterned polymer brush surfaces

Polymer brush-based three-dimensional (3D) structures are emerging as a powerful platform to engineer a surface by providing abundant spatially distributed chemical and physical properties. In this feature article, we aim to give a summary of the recent progress on the fabrication of 3D structures with polymer brushes, with a particular focus on the micro- and nanoscale. We start with a brief introduction on polymer brushes and the challenges to prepare their 3D structures. Then, we highlight the recent advances of the fabrication approaches on the basis of traditional polymerization time and grafting density strategies, and a recently developed feature density strategy. Finally, we provide some perspective outlooks on the future directions of engineering the 3D structures with polymer brushes.

Surface‐Grafted Polymer‐Assisted Electroless Deposition of Metals for Flexible and Stretchable Electronics

Surface-grafted polymers, that is, ultrathin layers of polymer coating covalently tethered to a surface, can serve as a particularly promising nanoplatform for electroless deposition (ELD) of metal thin films and patterned structures. Such polymers consist of a large number of well-defined binding sites for highly efficient and selective uptake of ELD catalysts. Moreover, the polymer chains provide flexible 3D network structures to trap the electrolessly deposited metal particles, leading to strong metal-substrate adhesion. In the past decade, surface-grafted polymers have been demonstrated as efficient nanoplatforms for fabricating durable and high-performance metal coatings by ELD on plastic substrates for applications in flexible and stretchable electronics. This focus review summarizes these recent advances, with a particular focus on applications in polymeric flexible and stretchable substrates. An outlook on the future challenges and opportunities in this field is given at the end of this paper.

High‐Resolution, Large‐Area, Serial Fabrication of 3D Polymer Brush Structures by Parallel Dip‐Pen Nanodisplacement Lithography

Parallel dip-pen nanodisplacement lithography (p-DNL) is used for high resolution, serial fabrication of 3D structures of polymer brushes over millimeter length scales. With p-DNL, 2D initiator templates consisting of arrays of nanolines and nanodots with rationally designed lateral spacings are fabricated in parallel via a locally tip-induced nanodisplacement process, from which highly defined 3D polymer structures are grown via surface-initiated atom transfer radical polymerization.

Liquid‐Mediated Three‐Dimensional Scanning Probe Nanosculpting

3D functional polymer brushes are fabricated by liquid-mediated scanning probe nanosculpting (LSPN). Surface-tethered functional polymer brushes, which are immersed in their good solvent, are mechanically cleaved away from the substrate by the AFM tip at high forces, and immediately imaged in situ with the same AFM tip at low applied forces.

Determination of flavonoids in Tibetan herbal medicine of Pyrethrum tatsienense by HPLC with photodiode array detection

A simple, precise, and rapid method was developed for the determination of four flavonoids, apigenin (AP), tricin (TR), luteolin (LU), and 4′-methoxy-tricin (MTR) in the Tibetan herbal medicine of Pyrethrum tatsienense by the high-performance liquid chromatographic technique coupled with photodiode array detection (DAD). A C18 reversed-phase column and a linear gradient elution system with acetonitrile-tetrahydrofuran-1% acetic acid as the mobile phase were employed. The method is validated in terms of the limit of detection (LOD), linearity, precision, and accuracy. The LODs were 48 ng/mL for AP, 75 ng/mL for TR, 88 ng/mL for LU, and 59 ng/mL for MTR, respectively. An excellent linear response was observed over the range specified for all analytes, as confirmed by the correlation coefficient with which from 0.9995 to 0.9999. The intraday RSDs ranged from 0.59 to 2.60%, and the interday RSDs were not higher than 0.05. The accuracy of the method was confirmed with an average recovery ranging from 95.9 to 100.0%. Since the extraction conditions can affect the extraction efficiency, nine different extracts of P. tatsienense were analyzed using different extraction solvents and extraction times. The contents of the four flavonoids in the extract of P. tatsienense were successfully determined within 18 min.