Aug 13, 2014
Low-cost layered polymer composites for infrared triggered actuators
The application of carbon nanotubes to polymer composites remains prohibitively expensive. This is due to the processing needed to align the nanotubes inside the composites to access their extraordinary physical properties. Now, reporting in Nanotechnology, scientists in the US and UK have been successful in making free standing self-aligned nanotube thin films in a vacuum filtration process. This enables the synthesis of low-cost layered polymer composites and infrared triggered actuators based on self-aligned nanotubes.
In the past, randomly oriented nanotube thin films known as “bucky paper” have been used for making electronic and mechanical devices. However, there remains the tricky issue of aligning the nanotubes to access their properties. The team takes advantage of the concentration gradients in a simple vacuum filtration process, which leads to the formation of nanotube liquid crystal thin films. These consist of millions of self-aligned nanotubes. Scaling up such self-aligned nanotubes may enable the low cost per unit area of nanotube thin films; not only for composites but also for electronic thin film transistor applications.
Polymer composites and remote controlled actuators
The team design a layered polymer composite consisting of top and bottom layers of poly-dimethyl siloxane (a low-cost elastomer) with the self-aligned nanotube thin film in between. Schlierien textures are noted suggesting there are highly aligned nanotube domains inside the composites. Mechanical property testing suggests around a 95% change in the elastic modulus at ~0.01 wt%. This suggests that an amount of nanotubes 100 times lower than in competing techniques is used. Near infrared light-driven actuators are also demonstrated with opto-mechanical conversion factors of ~0.5 MPaW-1. This is greater than the stress generated by human skeletal muscles.
Self-aligned nanotube/polymer composites could potentially be fabricated in strands and assembled in such a way to bio-mimic the motion of muscle fibres or create soft photo-origami structures. The team suggest that such self-aligned nanotube thin films with optimized nanotube amounts could potentially make remote controlled actuators at ~80 cents a piece.
More information can be found in the journal Nanotechnology 25 355501.
Improving graphene/polymer segregated composites for electromagnetic interference shielding (Mar 2014)
Nanotubes help turn stem cells into cartilage (Sept 2013)
Automated routine reveals dispersion and orientation of carbon nanotubes in polymer composites (Oct 2012)
About the author
The team includes Balaji Panchapakesan, head of the Small Systems Laboratory at the Worcester Polytechnic Institute (previously University of Louisville), US, his PhD student Xiaoming Fan at the University of Louisville, Robert W Cohn at the Electro-Optics Research Institute and Nanotechnology Center (ERINC) at University of Louisville and their colleagues James Loomis from MIT, Eva M Campo from Bangor University and Eugene Terentjev at the University of Cambridge, UK.