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

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

Shear-stress is a very efficient and especially straight forward way to align and disentangle CNTs. Be aware that the choice of the matrix can be important. Different effects play a role for semi-crystalline matrices than they do for amorphous ones. E.g., we found specific filler/matrix interactions for some semi-crystalline polymers that help in alignment. Also keep in mind that good alignment methods not necessarily are good methods to disperse the CNTs well (if I knew more about your desired application of the alignment, I would be able to provide some recommendations on the dispersion issue as well, but there are also some exhaustive discussions on this subject here on RG: https://www.researchgate.net/post/Dispersion_of_carbon_nanotubes_in_a_polymer_solution?exp_tc=tprc) .

Nevertheless, in principle you have three possibilites for shear-stress induced alignment of CNT in a polymer composite:

Alignment in the

(1) bulk

(2) film

(3) fiber

(1) Can be achieved with a double twin screw extruder or by post-casting streching of bulk samples. Especially in the later case the degree of shear that is applicable is limited by the mechanical integrety of the sample. In general, to yield a highs shear-rate can be complicated for bulk specimens on a laboratory scale.

(2) To yield aligned CNT/polymer films is a good technique because due to the thiness of the sample high shear-rates can be applied easily. For the case of a semi-crystalline matrix, the melt-drawing process gives very good alignment degrees.

If you are interested in the mechanism of alignment by shear-stress visualized in the TEM you may have a look at this paper:

https://www.researchgate.net/publication/256677944_Alignment_of_multi-wall_carbon_nanotubes_by_disentanglement_in_ultra-thin_melt-drawn_polymer_films

(3) Fibers are very good candidates for ideal alignment because the shear-stress is usally very high. For example electrospinning works pretty well (although it cannot be considered as purely shear-stress mediated alignment). In principle this is very promising as there are techniques to literally "write" polymer fibers with electrospinning and thus a cross structure of CNTs can be obtained with some post-processing. See here for a demonstration of electrospin "writing" :

https://www.researchgate.net/publication/235799748_Electrodynamic_control_of_the_nanofiber_alignment_during_electrospinning

Article Alignment of Multi-Wall Carbon Nanotubes by Disentanglement ...

Article Electrodynamic control of the nanofiber alignment during ele...

Hello!

You already receive several answers relative to alligment of CNT in a polymer matrix. I invite you to read the follow paper relative to transfer of aligned CNTs on a conductive matrix based on CNTs:

"A free-standing aligned-carbon-nanotube/nanocomposite foil as an efficient counter electrode for dye solar cells "

...if it can help you!

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.

Dear Jean-Francois,

could you elaborate on your latter claim? Do you mean when the thickness of the overall sample is in the order of the CNT length? I haven't found literature that managed to get a percolations to conduct heat so far. So this would be very interesting for me.

I think its in this paper E.S. Choi et al., Appl. Phys. Lett. 94, 6034

(2003)

Thank you all for ur interesting answer which will help me a lot.

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