Friday, 8 April 2016

Conductive Plastic with Carbon Nanotube-Polyurethane Colloidal Gel

In this demonstration I am going to show how I have created a conductive carbon nanotube polymer film using a gel made by mixing multi-walled carbon nanotubes with a water-based polyurethane gloss.

The nanotubes used are Multiwalled Carbon Nanotubes (CNTs)  Produced by Chemical
Vapor Deposition (CVD). Each CNT is typically 10-30nm in diameter, 5-20 microns in length. 

First it is key to do this in a well-ventilated area while wearing a gas mask and protective gloves. I have found Military-Grade Face and Hand Protection is Optimal. Free carbon nanotubes can be dangerous and potentially carcinogenic if inhaled. This is one of the reasons why we want to trap the carbon nanotubes into a polymer gel structure before applying them. Nevertheless, even when bonded to a material it is important to be responsible and to treat carbon nanotubes as you would any nanofibrous material such as asbestos.

We are using a water-based polurethane gel and since CNTs do not dissolve in water we have an effective colloidal gel. 
The gel is made by using a small volume of polyurethane, poured into a glass mixing bar.
The carbon-nanotubes are then poured into the mixing jar.
This is then mixed until we get a relatively even CNT colloidal gel.

We can then paint the gel on a suitable substrate, either plastic or paper. The substrate should be fibrous in order to properly bind the CNT+Polyurethane gel complex into the material.

Cellulose Acetate, used in laser printers and overhead projector transparencies, is an ideal fibrous material to apply the CNT colloidal gel to. Cellulose Acetate fibers themselves are noted for their absorption, particularly of water-based solvents, their effect of not shrinking easily under absorption (unlike cellulose paper) and also dyes easily, i.e. absorbing colorant particles, which is one of the reasons it is used in laser printing in the first place.

The gel is then allowed to anneal on the substrate at a low temperature, in this case in the heat of the sun.

When the conductive layer is dry we can then test the conductivity using a coin cell battery and a volt-meter.

As seen in the video, there is some loss across the conductive gel layer but this does not effect the function of an LED that uses the material to complete a circuit.

More importantly we have trapped the CNTs in a polymer gel and bonded that gel onto a fibrous polymer surface, namely the cellulose acetate substrate.

In short we have a flexible, durable and safe conductive material.

We can expand this idea further to create conductive CNT polymer frames for use in UAVs and other aerospace applications.

These frames are strong, resistant to electrical discharge, are highly conductive and absorb heat from the sun easily (important for maintaining a stable temperature in cold, perhaps icy, flying conditions).

More interesting still is the concept that it may be possible to design the frame so that the power source for the UAV being contained in the frame itself by means of using the conductive polymer frame as an electrode in a battery or supercapacitor.

Due to the potential danger of CNTs, non-experimental CNT frames for aerospace applications would most likely be further coated with a lacquer polymer to prevent any splintering of CNTs away from the frame under wear and tear. 

Another idea to take in mind is the fact that in a water-CNT colloidal solution, we can use a magnet to orient the carbon nanotubes.

Hence in a water-based polyurethane colloidal solution of CNTs, we can in principle orient the annealing position of the nanotubes by placing the substrate over an array of strong permanent magnets. This would also trap the nanotubes further into the structure and mitigate their ability to escape. 

This may also be used as a method to develop high density arrays of oriented carbon nanotube polymer films for use in energy storage technology.

Like always, every we have done is an experiment and requires much more development to see the different outcomes of this technology. 

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