Dr. Hiroshi Shiigi, Tomohiro Tomiyama, Maki Saito and other members of their research group in Department of Applied Chemistry, Osaka Prefecture University focused on the spontaneous hydrogen bonds between gold nanoparticles (AuNPs *1) and cellulose fibers (CNFs *2) and created a new material that is conductive and even five times stronger than the commercially available bulk gold. This material only requires 13vol. % of gold and a few steps -mixing AuNPs and CNFs, stirring, filtering and drying- to fabricate gold leaves. The spontaneous hydrogen bonds enable two pieces of wet films binding and self-healed. Their new material could be recommended for all kinds of next generation devices, such as flexible wires, electrodes, sensors and batteries as well as e-paper, e-skin and smart textiles.

The main point of research

1. 

   Figure: Gold leaf created by cellulose nanofibers and AuNP

   Mix gold nanoparticles and cellulose nanofibers in liquid solution, stir, filter, then dry-easy steps to produce a gold leaf that is flexible, conductive and resistant to tearing.By using spontaneous hydrogen bonds between AuNPs and CNFs, a gold film fabrication requires no further chemical reactions.
2. Reduce up to 85% of the gold content in gold leaves.
3. Lightweight and malleable yet five times tensile strength of bulk gold.
4. The gold leaves can be fabricated and repaired by pasting two pieces of wet thin films together.
5. The gold leaves can be made for micro substrates with various sizes and shapes.

Overview of research

Gold is one of the most beneficial metals. Its stability and conductivity are much appreciated in the process of plating, films, high-density packaging, while it has been long used as currency, accessories and traditional crafts. Thanks to its malleability and ductility, just 1 gram of gold can turn into more than 1 square meter gold leaf as thin as 100 nanometers. This gold leaf technique is quite reasonable from the perspective of gold as limited resource. However, how do we secure the quality of the malleable gold leaves without compensating mechanical strength? Failing to separate gold from silver and copper could cause liquation i.e. deterioration of mechanical strength and chemical instability. The research group created gold leaves with CNFs and AuNPs. CNF, being lightweight yet strong, is the popular material for vehicle parts, cosmetics, paintings and food products. On the other hand, AuNP owns electrical and chemical properties that are different from the bulk metals. The research group found that a gold leaf containing only 13 vol. % of gold expressed electrical conductivity as well as bulk gold. The hydrogen bonds between AuNPs and CNFs allowed to fabricate malleable and lightweight gold leaf with five times tensile strength of bulk gold.

These research results were published in online journal of ChemNanoMat.

Title: “Smart Golden Leaves Fabricated by Integrating Au Nanoparticles and Cellulose Nanofibers”.

The paper has been highlited as Magazine Articles, titled “Smart Gold Leaf Based on Nanomaterials” in ChemViews Magazine, ChemistryViews.org.

• ChemNanoMat（WILEY ONLINE LIBRARY Website）
• Full text of press release (Japanese language)（458KB）

Glossaries

*1 Gold nanoparticles（AuNP）

It is also called gold colloid. Since it exhibits red color in the dispersed state, it has been utilized by many craftsmen for stained-glass arts in Medieval Europe. In recent years, it is also used as a label in test strip for influenza and pregnancy.

*2 Cellulose nanofibers（CNF）

CNF is a Nano-structured cellulose fiber sizing from several to 100 nanometers. The material is prepared from plants or microorganisms, and is lightweight, flexible, strong and minimal thermal deformation.

Research Grant

This work was financially supported by Japan Society for the Promotion of Science (JSPS) KAKENHI (Grant Number 25288039, 26620072, 16H04137).