Complex, method for producing complex, dispersion liquid, method for producing dispersion liquid, and optical material

1. A complex comprising:

a flat plate-like metal fine particle formed of at least one metal or metal species; and at least one piece of finely-disintegrated cellulose combined with the flat plate-like metal fine particle,

wherein at least a part of each piece of the finely-disintegrated cellulose is incorporated into the flat plate-like metal fine particle, and a remaining part is exposed from a surface of the flat plate-like metal fine particle,

wherein a method for producing the complex of the plate-like metal fine particle and the finely-disintegrated cellulose, comprising the steps of:

preparing finely-disintegrated cellulose;

dispersing the finely-disintegrated cellulose in a solvent to obtain a finely-disintegrated cellulose dispersion liquid;

mixing the finely-disintegrated cellulose dispersion liquid with a solution containing metal ions to obtain a mixed solution;

reducing and precipitating the metal ions in the mixed solution to grow the flat plate-like metal fine particle, and combining the flat plate-like metal fine particle and the finely-disintegrated cellulose with each other;

wherein the finely-disintegrated cellulose has a content of carboxyl group between 0.1 mmol or more and 5.0 mmol or less per 1.0 g of cellulose on a crystal surface of the finely-disintegrated cellulose, and an amount of the metal ions during the reduction and precipitation step is 0.002 mmol or more and 0.1 mmol or less with respect to 1.0 g of the finely-disintegrated cellulose, and

wherein the finely-disintegrated cellulose dispersion liquid has a maximum value of absorbance with respect to a given wavelength in a range of a wavelength of 400 nm or more and 1500 nm or less.

2. The complex of claim 1 , wherein the flat plate-like metal fine particle and the finely-disintegrated cellulose are inseparable.

3. The complex of claim 1 , wherein the flat plate-like metal fine particle is silver.

4. The complex of claim 1 , wherein the flat plate-like metal fine particle has a particle diameter that is two times or more larger than a particle thickness of the flat plate-like metal fine particle.

5. The complex of claim 1 , wherein the finely-disintegrated cellulose has a crystal structure of cellulose type I.

6. The complex of claim 1 ,

wherein the finely-disintegrated cellulose has a fibrous form derived from a microfibril structure of native cellulose.

7. The complex of claim 1 ,

wherein the finely-disintegrated cellulose has a number average minor axis diameter of 1 nm or more and 100 nm or less, and a number average major axis diameter of 50 nm or more, the number average major axis diameter being 10 times or more longer than the number average minor axis diameter.

8. A dispersion liquid including the complex of claim 1 , the complex being dispersed in water or an organic solvent.

9. An optical material including the complex of claim 1 .

10. The complex of claim 1 , wherein the carboxyl group is introduced by an oxidation reaction using an N-oxyl compound.