In insulating polymers with low or high degree of crystallinity, if a conductive nanoparticle is added,will the electrical conductivity of the composite depend on the degree of crystallinity of the polymer?
Will a high degree of crytallinity lead to a high electrical conductivity?and how?
In most cases the (ionic) conductivity of the amorphous phase is higher than that of the crystalline phase. Therefore more crystalline polymers exhibit usually lower conductivity. The addition of conductive nanoparticles (e.g carbon nanotubes) increases the conductivity but only above the percolation threshold where the nanoparticles contact each other and form a conducting network. The nanoparticles tend to concentrate in the amorphous (inter.crystalline) phase, so it may happen that the percolation occurs at lower concentration if the matrix polymer exhibits higher crystallinity.
Thank you very much. I have some more questions
1) Why is the conductivity of the amorphous phase higher than that of the crystalline phase?
2)In semicrystalline polymer composites having conductive nano particles,above the percolation threshold,if the degree of crystallinity could be controlled in a way(by the cooling or rates or other methods..),would higher or lower degree of crystallinity result in higher electrical conductivity?
3)how does the electron transfer between the amorphous and crystalline phases effect conductivity?
I appreciate your help
Crystalline polymers often have sharp grain boundaries within the material that block conductivity so amorphous materials usually have higher conductivity.
Dear Dr Fallahi - the explanation may be different for various classes of polymers. In most insulating polymers (such as polyolefins, polyesters, polyamides) the conductivity is mainly determined by residual ions (impurities) - the electronic conductivity becomes important at high fields only. In this case the ionic conductivity is determined by the ion concentration and mobility. In the amorphous phase the free volume is higher, therefore (assuming homogeneous ion concentration) the mobility (thus the conductivity) is higher in the amorphous phase. If you use conductive nanoparticles the conductivity will be determined ONLY by the filler network, which is usually electron conductive. There the conductivity is determined by the number of contacts and by the contact resistance between the particles.
Dear Prof Banhegyi -Thank you very much for your time.I read some articles about the composites of polymers and conductive nanoparticles. They have stated that there are relationships between the degree of crystallinity or the size of the crystals of the polymer (matrix)and the electrical conductivity of the composites.You have mentioned that conductivity is determined only by the filler network(in case of using conductive fillers).Does it mean that it is only the percentage of the conductive nanoparticle which affects the electrical conductivity of the nanocomposite?
The relationship they are referring to is what determines how the nanoparticles assemble in the polymer. If the polymer is amorphous (no crystals) it's easy for the particles to form connected structures in the polymer at some minimum volume fraction (called percolation) and thus produce a conductive composite material. These structures act like wires to conduct electrons through the insulating polymer which is why the composite becomes conductive but the polymer itself is still an insulator.
If the polymer can crystallize, then the crystals can block the conductive channels that the nanoparticles want to form, preventing percolation which results in a poorly (or not at all) conducting composite.
In some cases, crystallization can actually help form the conductive nanoparticle structures by pushing around and squeezing the nanoparticles together as the polymer crystallizes. This might cause percolation to occur at lower volume fractions than typical.
Good Luck.
Dr Remy already gave the answer. The filler is the decisive factor if the filler is conductive. If the nanoparticles are also insulating (e.g. ceramics) the situation is more complicated. This latter topic is "nano-dielectrics" which is amply documented also here on RG.
Thank you Shahryar. Actually the article you have attached is one of the articles I've already read and made me ask the question cause in this article higher crystallinity led to higher conductivity!
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