Solventless methods of coating a carbon nanotube network and carbon nanotube networks coated with a polymer
A method of coating a carbon nanotube material with a solventless coating composition is described. The resulting coating has been shown to preserve the conductivity of the conductive layer and protect the conductive layer from the effects of subsequent coating compositions. Examples are shown in which the coating formulation comprises a polyol and an isocyanate. A layer material comprising a polyurethane coating on a carbon nanotube network layer is also described.
1. A method of making a layered carbon nanotube (CNT) composite, comprising:
providing a CNT layer that is disposed on a substrate, and
applying a solventless polymer precursor directly onto the CNT layer to form a coating over the CNT layer having a thickness of at least 0.250 μm;
wherein the solventless polymer precursor consists essentially of polyols and isocyanates and comprising a step of curing to form a polyurethane polymer;
and wherein the step of applying results in a CNT layer that comprises 50 mass % or less of the polymer in the CNT layer;
wherein the underlying CNT layer has a sheet resistance of 120 Ω/square or less.
2. The method of claim 1 wherein the resistivity of CNT layer increases by 81% or less after applying and curing the coating.
3. The method of claim 1 wherein the resistivity of CNT layer increases by 10% or less after applying and curing the coating.
4. The method of claim 1 wherein the solventless polymer precursor comprises a diisocyanate and a diol.
5. The method of claim 4 wherein the solventless polymer precursor is applied to the CNT layer by bar coating or spraying.
6. The method of claim 5 wherein the step of applying results in a CNT layer that comprises 10 mass % or less of a coating polymer within the CNT layer.
7. The method of claim 4 wherein the step of applying results in a CNT layer that comprises 10 mass % or less of a coating polymer within the CNT layer.
8. The method of claim 1 wherein the solventless polymer precursor consists essentially of a polyurethane precursor so that at least 99 mass % of the formulated coating composition remains in the dried film after cure has taken place.
9. The method of claim 1 wherein the step of applying results in the CNT layer comprising at least 50 mass % CNTs.
10. The method of claim 9 wherein the CNT layer comprises a dopant selected from the group consisting of: perfluorosulfonic acids, thionyl chloride, organic pi-acids, nitrobenzene, organometallic Lewis acids, organic Lewis acids, Bronsted acids, Nafion, hyaluronic acid, and combinations thereof.
11. The method of claim 1 wherein the solventless polymer precursor contacts the surface of the CNT network but does not fill spaces within the layer.
12. The method of claim 1 wherein the solventless polymer precursor comprises a polyisocyanate crosslinking agent.
13. The method of claim 12 wherein the polyisocyanate crosslinking agent comprises aliphatically, cycloaliphatically, araliphatically and/or aromatically bound isocyanate groups.
14. The method of claim 12 wherein the polyisocyanate crosslinking agent comprises at least one of: hexamethylene trimethylhexamethylene diisocycante, meta-α,α,α′,α′-tetramethylxylylenediisocyanate, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl cyclohexane (isophoronoe diisocyanate or “IPDI”), bis(4-isocyanatocyclohexyl)methane (hydrogenate MDI), toluene diisocyanate (“TDI”), hexamethylene diisocyanate (“HDI”) or biuret derivatives of various diisocyanates.
15. The method of claim 1 wherein the solventless polymer precursor is a liquid.
16. A method of making a layered carbon nanotube (CNT) composite:
providing a CNT layer having a thickness of at least 0.250 μm that is disposed on a substrate; and
applying a solventless polymer precursor directly onto the CNT layer to form a coating over the CNT layer having a thickness of at least 0.250 μm;
wherein the step of applying results in a CNT layer that comprises 50 mass % or less of a coating polymer in the CNT layer after the CNT layer has been coated; and
wherein the underlying CNT layer has a sheet resistance of 120 Ω/square or less.
17. The method of claim 16 wherein the step of applying results in a CNT layer that comprises 10 mass % or less of a coating polymer within the CNT layer.
18. The method of claim 16 wherein the step of applying results in the CNT layer comprising 30 to 100 mass % CNTs within the CNT layer.
19. A method of making a layered carbon nanotube (CNT) composite, comprising:
providing a CNT layer that is disposed on a substrate, and
applying a solventless polymer precursor directly onto the CNT layer to form a coating over the CNT layer having a thickness of at least 0.250 μm;
wherein the solventless polymer precursor consists essentially of polyols and isocyanates and comprising a step of curing to form a polyurethane polymer;
wherein the polyols comprise a polyester polyol and the isocyanates comprise hexamethylene diisocyanate;
wherein the step of applying results in a CNT layer that comprises 50 mass % or less of the polymer within the CNT layer; and
wherein the underlying CNT layer has a sheet resistance of 120 Ω/square or less.