Direct-Write Printed Slippery Surface for Assembling a High-Quality Graphene Structure and Its Application in Flexible Electric Actuators.

Graphene is a two-dimensional honeycomb-like nanomaterial generated by carbon atoms in sp2 hybridized orbitals to form a hexagonal lattice structure with excellent electrical, optical, and mechanical properties. The solution process method has been widely used to realize large-area patterned graphene structures for high-performance devices. In the method, graphene usually needs to be dispersed in solution, and the π-π bonding gravitational interactions between graphene sheets would lead to uncontrollable structures in solution and difficulty in obtaining high performance. In this work, a patterned graphene oxide (GO) structure with controllable thickness and layer spacing was realized by a direct-write printed slippery surface, which was used as a slippery limited template. After reducing GO into reduced graphene oxide (rGO), a flexible electric pattern with a conductivity of up to 6.425 × 103 S/m was realized. Furthermore, the patterned rGO structure was transferred on polydimethylsiloxane (PDMS), which could generate less than a 5% change in resistance after 10,000 consecutive bends, and an anisotropic expansion based on rGO and PDMS materials under electro-thermal coupling. The patterned rGO structures could meet the performance requirements of highly sensitive and complex deformation applications as flexible electric actuators. This study provides great research significance and application value for patterning high-quality graphene structures and realizing high-performance flexible electronic devices.

Direct writing concave structure on viscoelastic substrate for loading and releasing liquid on skin surface.

Droplet deposition on deformable matrix has a broad application prospect. Regular deposition and diffusion of droplet on the substrate is the key to prepare flexible concave structure. Direct writing technique is an advanced method for depositing ink droplet on various substrates, which could produce a variety of deposition forms. Meanwhile, direct writing technique has the characteristics of simplicity, convenience and strong controllability. In this work, patterned concave structure was fabricated with viscoelastic substrate by direct writing technology, depositing behavior of ink droplet, formation condition and shape control of concave structure were studied with viscoelastic substrate, and practical application of the patterned concave structure was explored in loading and releasing liquid on skin surface. This study provides an efficient method for the preparation and application of controllable concave surface.

Direct-Writing Flexible Metal Circuit with Polymer/Metal Precursor Ink and Interfacial Reaction.

In this study, flexible metal circuits are fabricated with polymer/metal precursor ink and an interfacial reaction by direct-writing technology. Poly(vinyl alcohol) (PVA) is selected as one component of ink, which could be a flexible composite in a metal circuit and an adhesive layer to connect the flexible metal circuit with the flexible substrate. Silver nitrate (AgNO3) is added to the ink as a source of metal. After the direct-writing structure was placed in contact with an ascorbic acid (VC) aqueous solution with an adjustable process, silver nanoparticles (AgNPs) with 100-400 nm uniform size could be generated on the direct-writing PVA skeleton. The resistivity of the composite silver layer could reach 10-6 Ω·m without any postprocessing. Meanwhile, the resistance change could keep within 20% with 180° bending after 10 000 repeat times. Patterned flexible metal circuits could be facilely fabricated by direct-writing technology, which presented excellent electrical conductivity and flexibility.