Polymers with CNT filler have proved themselves as important candidates in the category of polymer composites due to their good physical properties. Hence can we in some way align them in an easy percolation regardless of the mechanical properties?
It seems that drawing of material through the micronozzle would be the easiest way to align any filler inside it.
Good morning. If you align the nanocomposites, you lose the percolation. The percolation means tht the CNTs form a 3 D network even at concentration lower than 5 % in some cases. If you align the CNTs, they will form a 1 D network in "wires" but not a 3 D network anymore. I think that there are 2 main ways to align the CNTs depending. WIth shear pushing a flow (there are studies in rheology that shows a decrease in shear stress versus shear rate when the CNTs align) and with Electrical fields. In fact the conductivity and the rheology are the 2 principal ways to measure the percolation concentration
Please you can read the following article by Kuriger et al "Processing and characterization of aligned vapor grown carbon fiber reinforced polypropylene", there it is explained how they can align fibers by means of a converging annular die in a twin screw extrusion process.
Forced assembly co-extrusion is an very efficient way to align nanoparticles in polymer matrix. You can see the following reference:
https://www.researchgate.net/publication/259093407_Forced_Assembly_by_Multilayer_Coextrusion_to_Create_Oriented_Graphene_Reinforced_Polymer_Nanocomposites
Article Forced Assembly by Multilayer Coextrusion to Create Oriented...
you can read the following paper
http://mechano.web.itd.umich.edu/journals/033_villoria_09_movingsubstrate.pdf
and/or
Vertically Aligned Carbon Nanotubes Grown on Graphene Paper as Electrodes in Lithium-Ion Batteries and Dye-Sensitized Solar Cells
Hello,
If you mean aligning indivedual CNT witnin a polymer matrix, I think it is not possible to fully (100%) disperse CNTs from their aggregates even with surface chemical functionalization. Thus, the best that you can have is well dispersed CNTs with the presence of tiny aggregates. This tiny aggregats will favor the formation of 3D network along with the aligned indivedual tubes in the case of perfect alignement.
Now, an effective way to align such dispersed CNTs within a polymer matrix is electrospinning. I have tested the incorporation of MWNT into PAN matrix and produced nanofibers of PAN/CNT composites by electrospinning and a volume electrical percolation at 0.5 wt% loading percent of CNT was found.
The final arrangement of CNTs within the nanofibers depends firstly on the efficiancy of CNT dispersion method.
Since electrospinning uses Coulomb repulsive forces to eject the jet that will solidify finally as nanofibers, CNTs will be aligned axially because they will follow the electric field lines. Along with the presence of tiny aggregates and byeond a critical loading percent, a percolation threshold will be created.
For more information, you may read the following paper:
Measuring of Electrical Properties of MWNT-Reinforced PAN Nanocomposites
http://www.hindawi.com/journals/jnm/2012/750698/
we usually aligned SWNT in polystyrene matrix by thermal poling , see more Adv.Funct. Mater., 2012, 22,10,2177-2186.
As was mentioned above:
with orientation you loose percolation threshold, but if you are interesting about anisotropic conductivity, it should help you.
The ways you can reach it:
1. shear forces in melt or high viscous solution
2. in electric field
3.in magenetic field
4. extension in solid state
5. by attaching self-ordered structure to CNT surface
maybe others, but now I have nothing in mind
I would globally agree with Zdenko who has well synthesized the different cases. Additionally to electrical properties, the alignment of CNT can be useful to improve thermal conductivity in one direction provided that the thickness of your samples is not too important.
I think its in this paper E.S. Choi et al., Appl. Phys. Lett. 94, 6034
(2003)
We can integrate carbon nanotubes with polymer matrix to form nanocomposite using physical adsorption and electrochemical technique. In order to adsorp CNT onto the polymer matrix, first dissolve CNT in nafion solution and then dropped over polymer matrix (dried at room temperature). Then, the allingnment of CNT over polymer matrix can be conformed by investigating the morphological changes using scanning electron microscopy. By electrochemical means, applying some voltages we can incorporate the CNT over polymer matrix.
Forget CNT if you want to have important improvements on mechanical properties in polymers, thermoplastics for instance.So far is imposible to disperse them to have this mecanical improvement, despite of that we have obtained with PC conductivities arround 1 S/cm with less that 1 % in weight.
Normally if you don't have electrical conductivity you will have the best mechanical properties, because you would have aligned in some prior direction, breaking the conductive path, if you inject a polymer filled with CNT at very high speed you will have alignement. but i insist you won't improve much that 30 % your mechanical properties in thermoplastics.
regards
- Badges
- Science topic
- Similar topics
- Social Psychology
- Attitude