Exfoliating laminar material by ultrasonication in surfactant
Disclosed herein is a method for exfoliating a laminar material to form an exfoliated material, in which the laminar material is ultrasonicated in a solution of a surfactant for sufficient time to form the exfoliated material. At all times during the ultrasonication the concentration of the surfactant in the solution is maintained sufficient to form a complete monolayer on the surfaces of the laminar material and the exfoliated material in the solution, or sufficient to sterically stabilize the laminar and exfoliated materials against aggregation.
1. A method for exfoliating a laminar material to form an exfoliated material, said method comprising ultrasonicating said laminar material in a solution of a surfactant, wherein said solution of a surfactant has a concentration of the surfactant in the solution sufficient to achieve and maintain a surface tension of 35 to 45 mJ·m −2 , for sufficient time to form said exfoliated material, wherein at all times during the ultrasonication the concentration of the surfactant in the solution is maintained sufficient to maintain the surface tension of 35 to 45 mJ·m −2 in order to form a complete monolayer on the entire surface of the laminar material and the exfoliated material in the solution, said laminar material comprising particles comprising aggregated laminae and said exfoliated material comprising particles of the laminae which have been deaggregated and said method achieving a degree of exfoliation of at least 30%.
2. The method of claim 1 wherein the concentration is 0.5 to 5 mg surfactant per m 2 of exfoliated material.
3. The method of claim 1 wherein the surfactant is a polymeric surfactant.
4. The method of claim 1 wherein the surfactant is a non-ionic surfactant.
5. The method of claim 3 wherein the surfactant is a copolymer of ethylene oxide and propylene oxide.
6. The method of claim 1 wherein the surfactant has a dγ/dc value of less than 0.
7. The method of claim 1 wherein the laminar material is graphite and the exfoliated material is graphene.
8. The method of claim 1 wherein the concentration of the surfactant in the solution prior to the ultrasonicating is sufficient to form a complete monolayer on the surface of the exfoliated material which is formed from the laminar material in the solution.
9. The method of claim 1 wherein the concentration of the surfactant in the solution prior to the ultrasonicating is sufficient to sterically stabilise the laminar and exfoliated materials against aggregation.
10. The method of claim 1 wherein the surfactant is added to the solution during the ultrasonicating at a rate sufficient that at all times during the ultrasonication the concentration of surfactant in the solution is sufficient to form a complete monolayer on the surface of the laminar material and the exfoliated material in the solution.
11. The method of claim 1 wherein at all times during the ultrasonication the concentration and nature of the surfactant are such that the surface tension of the solution is approximately the same as the interfacial tension of the solution and the exfoliated material.
12. The method of claim 1 wherein the solution is an aqueous solution.
13. The method of claim 1 additionally comprising drying the solution having the exfoliated material therein.
14. The method of claim 13 comprising resuspending the exfoliated material in a solvent.