Methods for controlling density, porosity, and/or gap size within nanotube fabric layers and films
A method for controlling density, porosity and/or gap size within a nanotube fabric layer is disclosed. In one aspect, this can be accomplished by controlling the degree of rafting in a nanotube fabric. In one aspect, the method includes adjusting the concentration of individual nanotube elements dispersed in a nanotube application solution. A high concentration of individual nanotube elements will tend to promote rafting in a nanotube fabric layer formed using such a nanotube application solution, whereas a lower concentration will tend to discourage rafting. In another aspect, the method includes adjusting the concentration of ionic particles dispersed in a nanotube application solution. A low concentration of ionic particles will tend to promote rafting in a nanotube fabric layer formed using such a nanotube application solution, whereas a higher concentration will tend to discourage rafting. In other aspects, both concentration parameters are adjusted.
1. A method of preparing a nanotube application solution, comprising:
forming a nanotube application solution, said nanotube application solution comprising a first plurality of nanotube elements at a first concentration level and a second plurality of ionic particles at a second concentration level dispersed in a liquid medium; and
reducing said second concentration level of said second plurality of ionic particles such as to promote rafting within a nanotube fabric layer formed using said nanotube application solution;
wherein said second plurality of ionic particles is selected from the group consisting of ammonium salts, nitrate salts, and ammonium nitrate salts or mixtures thereof.
2. The method of claim 1 wherein said first plurality of nanotube elements are carbon nanotubes.
3. The method of claim 2 wherein said carbon nanotubes are single walled carbon nanotubes.
4. The method of claim 2 wherein said carbon nanotubes are multi walled carbon nanotubes.
5. The method of claim 1 wherein said liquid medium is an aqueous solution.
6. The method of claim 1 wherein said first concentration level of said first plurality of nanotube elements is increased.
7. The method of claim 6 wherein said first concentration level of said first plurality of nanotube elements is increased by introducing an additional volume of said liquid medium into said nanotube application solution.
8. The method of claim 1 wherein said second concentration level of said second plurality of ionic particles is decreased through a filtration process.
9. The method of claim 8 wherein said filtration process is one of a cross flow filtration process, a sonication filtration process, and a centrifugation filtration process.
10. The method of claim 1 wherein reducing said second concentration level of said second plurality of ionic particles promotes rafting by promoting at least one of van der Waals interactions and π-π interactions between nanotube elements.
11. The method of claim 1 wherein said second concentration level is reduced below 10 ppm.
12. The method of claim 1 wherein said nanotube elements are functionalized nanotubes.
13. The method of claim 1 wherein said liquid medium has a pH between 4 and 10.