Novel polymer-free iridescent lamellar hydrogel for two-dimensional confined growth of ultrathin gold membranes

Abstract

Hydrogels are generally thought to be formed by nano-to micrometre-scale fibres or polymer chains, either physically branched or entangled with each other to trap water. Although there are also anisotropic hydrogels with apparently ordered structures, they are essentially polymer fibre/discrete polymer chains-based network without exception. Here we present a type of polymer-free anisotropic lamellar hydrogels composed of 100-nm-thick water layers sandwiched by two bilayer membranes of a self-assembled nonionic surfactant, hexadecylglyceryl maleate. The hydrogels appear iridescent as a result of Bragg's reflection of visible light from the periodic lamellar plane. The particular lamellar hydrogel with extremely wide water spacing was used as a soft two-dimensional template to synthesize singlecrystalline nanosheets in the confined two-dimensional space. As a consequence, flexible, ultrathin and large area single-crystalline gold membranes with atomically flat surface were produced in the hydrogel. The optical and electrical properties were detected on a single gold membrane.

Organized Molecular Interface-Induced Noncrystallizable Polymer Ultrathin Nanosheets with Ordered Chain Alignment

“…35,36 The ordered structure gives the solution an iridescent color due to its Bragg reflectance of visible light. The synthesis of ultrathin polyacrylamide nanosheets was accomplished in a supramolecular system with an HGM concentration of 2 wt % in this study.…”

Thin metal nanostructures: synthesis, properties and applications

“…In the presence of 2D templates, such as lamellar hydrogels, 33,41 graphene oxide, 28 graphite 55,95–97 and lyotropic liquid crystals, 98,99 metal nanocrystals can be directed or confined to grow into nanoplates and nanosheets under appropriate conditions. For example, an iridescent hexadecylglyceryl maleate (HGM) hydrogel has been used to synthesize single-crystalline ultrathin Au nanosheets with large areas over 100 μm 2 .…”

“…For example, an iridescent hexadecylglyceryl maleate (HGM) hydrogel has been used to synthesize single-crystalline ultrathin Au nanosheets with large areas over 100 μm 2 . 41 It was found that the HGM hydrogel consisted of a periodically regular sandwich structure of lamellar bilayer membranes and 100 nm-thick water layers, which could function as a 2D template to guide the growth of ultrathin Au nanosheets from HAuCl 4 . Note that the surface of these large Au nanosheets is atomically smooth.…”

“…6C). 41 The Au membrane demonstrated conventional ohmic behavior with an extremely low electrical resistivity, 4.0 × 10 –8 Ω m, under ambient conditions. Importantly, the electrical resistivity of the Au membrane is very close to that of bulk Au (2.2 × 10 –8 Ω m) and 1–2 orders of magnitude lower than that of the thermally evaporated Au film, which might be attributed to the single-crystalline nature of the Au membrane.…”

Freestanding Ultrathin Metallic Nanosheets: Materials, Synthesis, and Applications

“…Theoretically, FUMNSs with atomic thickness possess great advantages over their bulk counterparts, since they expose surface atoms to the largest extent, so as to exhibit unique physical and chemical properties. Hence, FUMNSs have attracted considerable devotion, which has brought some exciting breakthroughs recently . For instance, Zheng and co‐workers reported the synthesis of ultrathin hexagonal palladium (Pd) NSs with a uniform thickness of 1.8 nm ( Figure a), which show promising applications in photothermal therapy.…”