Researchers at Polytechnique Montréal have devised a conductive, 3D-printable composite which can be used to detect and characterise liquids in real time.
It seems that there have been few scientific advances proposed of late for which the solution has not been “carbon nanotubes.” As with wonder-material graphene, the ubiquitous allotrope of carbon has a near-endless list of applications, in particular in reinforcing the strength of new and existing materials, or endowing them with additional properties.
It is reassuring, then, that a new paper from a team at Polytechnique Montréal has broken new ground with just such a process. More topical still, the researchers can enhance the advantages of nanotubes using another revolutionary technique – 3D printing – to devise a polymer composite with enough electrical conductivity to enable its use in real-time sensing and liquids detection.
The outcome of the group’s most recent paper is essentially a porous cloth made of 3D-printed, nanotube-enhanced filament. When exposed to a liquid, this material will swell, altering its conductivity. The extent of alteration can then be used to determine both the presence and type of liquid in contact with the material. The team hopes that the innovation could find significant applications in the aerospace, hydrocarbons and manufacturing industries. The paper – “3D Printing of Highly Conductive Nanocomposites for the Functional Optimization of Liquid Sensors” – was published in the journal SMALL in September 2016, and backed by the Research Centre for High-Performance Polymer and Composite Systems (CREPEC), the Canada Research Chairs, the Natural Sciences and Engineering Research Council of Canada (NSERC), Mitacs and the Canada Foundation for Innovation (CFI). InnovOil spoke with lead author Professor Daniel Therriault about his involvement in the project, and where future refinements of the technique could lead.
Fully comp The benefits of composite materials have been extolled for years, and although the oil industry has been comparatively slow in its uptake, they are beginning to gain traction.
Professor Therriault has been in the composite field for years, working mostly in the developing applications for the aerospace industry – where lightweight, strong and durable materials are of particular importance and interest. “In investigating those composites, I looked at their properties like thermal conductivity, and then I looked at electrical conductivity,” he explained, from his office in Montreal. “We discovered that there was a very big gain in electrical conductivity by adding those fillers in the plastics. We tried to push the boundaries and make them as conductive as possible so we developed a lot of expertise on how to mix those particles in the plastic.”
With a sound understanding of nanotube dispersal, and the extent to which properties could be conferred to the polymers, Therriault and the group set about devising a method for constructing them into something useful. The process begins a thermoplastic, which remains solid at room temperature. This is dissolved in a solvent, and placed in a container with solid particles – in this case carbon nanotubes – supplied as a fine black powder. These are mixed together in the lab by machine in accordance with a specific “recipe” the team has developed – and patented – which ensures the nanotubes are optimally dispersed for the application.
By adjusting the viscosity of the liquid, this process can produce a 3D-printable ink which can be loaded into the print head of a 3D printer. “The special thing here is that our ink solidifies very rapidly,” Therriault added. “When pushed through the high-precision nozzle, the solvent evaporates very rapidly and the ink becomes solid in a matter of seconds. It comes out as a wire or a filament and solidifies, and can be glued to a surface or onto other filaments, allowing them to achieve 3D geometries.”
By stacking up these layers, the system can be used to design 3D architectures which are optimised for sensing liquids. By connecting the material to an electrical connection and equipment for measuring resistance, liquid can be detected and characterised by immersion or simply by contact.
The material’s conductivity is approaching that of some metals, Therriault said. The paper describes the system achieving 2,000-3,000 siemens per metre, “highly conductive for a polymer, but still several orders of magnitude away from the most conductive metal,” he explained. Nevertheless, it is still enough to characterise a number of liquids, and conductivity has reportedly been improved since the original publication.
Fluid model With the concept proven, more work has to be done on liquid characterisation. So far, the sensors have been used to identify liquids ready to hand in a laboratory – acetone, isopropanol and a few more – which have produced clear, but by no means extensive results. “Right now we’re focusing on just a few kinds of liquids, but we’ve seen that depending on the liquid, the response changes. We believe that with the right material and the appropriate calibration we could tailor the sensors to detect specific liquids. We think it’s possible and it’s something we’d like to investigate further.”
However, the sensitivity reported in the initial results points to its suitability in applications where any ingress of liquid would be detrimental. Sensors could be calibrated to pick up minute amounts of fluid, sounding alarms before any damage is done to infrastructure or equipment.
The team envisions a few different commercial scenarios for the technology. Therriault is already exploring the possibility of supplying the polymer itself as a conductive paste for microelectronics and other industries. Beyond that, the team has proposed a portable 3D printer concept, which could be used on live worksites and would allow users to 3D print the material directly where it is required. Monitoring points could then be custom-made to fit desired dimensions and locations.
Another scenario would be to integrate the sensor in a factory assembly. Customers could specify the size and shape of the sensor depending on the liquid in question, and the equipment could then be shipped, allowing customers to install as required.
In particular, both would be of use to the pipeline industry. “For the oil industry, detecting leakage is a big topic,” Therriault noted. A composite – calibrated according to the liquid being transported – could be laid down at the flanged connection points in pipelines. In the event of a leak, and liquid touching the sensors, operators could be given very precise, instant information on its location.
For now, the group is looking to improve the detecting properties of the ink. For that, Therriault said, industry input will be crucial in guiding how they develop new applications: “We’re interested in discussing with partners to understand the needs of industry and adapt what we’ve done. If we know the needs of partners they can guide the effort: for example, do we need to be more sensitive, do we need larger sensors, what porosity is required for that application? That would guide research in the future.”
With major US and Canadian projects such as Keystone XL now back on the political table, such sensor technology may be put to good use sooner rather than later.
Contact: Professor Daniel Therriault Tel: +1-514-340-4711 ext. 4419 Email: email@example.com Web: www.polymtl.ca/lm2