Stabilization of carbon nanotube coatings to moisture
A method of making CNT films is described in which the film is washed with a mild acid treatment. The method generates a CNT film that is not sensitive to moisture or fluctuations in moisture. The method involves the use of anionic polysaccharides or anionic glycosaminoglycans such as hyaluronic acid, sodium salt, as aqueous dispersing agents and their modification to a hydrophobic matrix after deposition. In the course of conducting the work described here, we made the surprising discovery that washing with an aqueous acidic solution resulted in a decrease in resistance through the material. The invention also includes CNT composites made by the inventive methods and a CNT composite comprising CNTs and anionic polysaccharides or anionic glycosaminoglycans further characterized by a low cationic content and a high conductivity and/or small CNT particle size as measured by SEM.
1. A CNT composite, comprising:
a solid dispersion comprising CNTs and a glycosaminoglycan or polysaccharide;
wherein the dispersion comprises at least 20 wt % of the glycosaminoglycan or polysaccharide;
wherein the sum of Na, K, Mg, and Ca associated with the glycosaminoglycan or polysaccharide is less than 1 wt % of the dispersion; and
wherein the solid dispersion possesses one or more of:
a bulk conductivity of 500 S/cm or greater, and
a volume average size of CNT particles, as observable by SEM, of 5 μm or less, where size is the largest dimension observed in the SEM.
2. The CNT composite of claim 1 wherein the dispersion comprises CNTs and an anionic glycosaminoglycan; wherein the dispersion comprises CNTs and hyaluronic acid.
3. The CNT composite of claim 2 wherein the sum of all cations associated with the glycosaminoglycan or polysaccharide make up less than 1 wt % of the dispersion; or wherein the sum of Na, K, Mg, and Ca associated with the glycosaminoglycan or polysaccharide is 0.5 wt % or less of the dispersion.
4. The CNT composite of claim 1 wherein the CNT dispersion, without any topcoat, possesses moisture resistance such that, if a polyurethane topcoat that is about 1 mil (0.025 mm) thick is applied over the CNT dispersion and if the polyurethane coated CNT films is exposed to relative humidity of 40% at 60° C. for 60 hours, between the time of 30 to 60 hours of the exposure, the resistance of the composite increases by no more than 0.5%.
5. The CNT composite of claim 2 wherein the CNT composite comprises: a substrate, a primer layer, the CNT dispersion as a layer, and a polymeric topcoat.
6. The CNT composite of claim 1 wherein the solid dispersion has a bulk conductivity of 1000 S/cm or greater.
7. The CNT composite of any of claim 1 wherein the majority by the mass of the CNTs are single-walled CNTs.
8. The CNT composite of claim 1 wherein the dispersion comprises between 30 and 60 wt % CNTs.
9. The CNT composite of claim 1 wherein the dispersion comprises between 30 and 70 wt % glycosaminoglycan or polysaccharide.
10. The CNT composite of claim 1 further comprising a polymeric coating disposed over at least one surface of the dispersion.
11. The CNT composite of claim 1 wherein the dispersion has a resistance of 0.5 to 5 Ω/square or a conductivity of 1000 to 6000 S/cm.
12. The CNT composite of claim 2 wherein the sum of all cations associated with the glycosaminoglycan or polysaccharide make up less than 0.5 wt % of the dispersion; or wherein the sum of Na, K, Mg, and Ca associated with the glycosaminoglycan or polysaccharide is 0.2 wt % or less of the dispersion.
13. The CNT composite of claim 1 wherein the mass average molecular weight of the glycosaminoglycan or polysaccharide is in the range of 1000 to 100,000.
14. The CNT composite of claim 1 wherein the CNTs in the dispersion have a G/D of 12 to 17.
15. The CNT composite of claim 1 wherein the dispersion is a layer within a laminate.
16. The CNT composite of claim 1 having a polymeric topcoat over the CNT dispersion, the topcoat having a thickness of about 1 mil, and wherein the CNT dispersion possesses moisture resistance such that, if the CNT composite is exposed to a relative humidity of 40% at 60° C. for 60 hours and the resistance of the CNT dispersion is measured at the times of 30 to 60 hours of the exposure, the resistance of the CNT dispersion preferably increases by no more than 1% between the times of 30 to 60 hours of the exposure.
17. The CNT composite of claim 1 wherein the CNT dispersion, without any topcoat, possesses moisture resistance such that, if heated to 120° C. for 2 hours and cooled to room temperature for 10 minutes, the resistance increases by less than 100%.
18. A method of making the composite material according to claim 1 comprising:
providing a dispersion comprising CNTs and an anionic glycosaminoglycan or an anionic polysaccharide;
depositing a dispersion onto a surface to form a film;
wherein the film comprises the CNTs and the anionic glycosaminoglycan or anionic polysaccharide; and
washing the film with an aqueous acidic solution having a pH between 0 and 4.