We have made some very, very highly thermally conducting coatings of MWCNT out of water [“Advanced nanocarbon materials facilitated by novel stimuli-responsive stabilizers;” J. Texter, D. Ager, V. Arjunan Vasantha, R. Crombez, D. England, X. Ma, R. Maniglia, and N. Tambe, Chem. Lett. 41, 1377-1379 (2012); doi:10.1246/cl.120632.], but we do not yet understand why we got such good results. We understand the MWCNT thermselves are highly thermally conducting.
John Texter, can you make your paper available here in RG? I would then try to understand what you did and maybe can help to improve your understanding.
I looked into Sergei Sergeenkov's paper and would suggest to also consider the complex dispersion / flocczulation structures I have found in conductive composites:
https://www.researchgate.net/publication/229816762_Electrical_conductivity_in_heterogeneous_polymer_systems._V_(1)_Further_experimental_evidence_for_a_phase_transition_at_the_critical_volume_concentration
Article Electrical conductivity in heterogeneous polymer systems. V ...
Bernhard, The issue of understanding that is so important in thermal conductivity, the one I referred to as phonon coupling, is how heat is transferred from MWCNT to MWCNT through the matrix. This topic is disucssed int he review Sergai shared and elsewhere. In the system exemplified in the attached Chemistry Letter, the MWCNT dispersion (4% w/w MWCNT, 1.2% nanolatex, balance water) is coated onto each of two very porous substrates, mulberry paper and fiberglass tissue. We imagine MWCNT-MWCNT contacts are through one or more intervening nanolatex particles that are not very electrically conducting but adsorb strongly to MWCNT. The article is attached, and the SI can be downloaded on this site as well. The system in our paper is "matrix starved" in that air remains a major volume fraction component in the dired composite material. Heat transfer measurements were done by xenon flash lamp irradiation through an annular aperture and temperature was monitored through a radial mask on the opposite side of the disk sample. Best wishes, John
Well, the heat and electrical conductivity of CNT are quite known. however, the orientation and the joint between the CNT aggregates is a must to reach the above mentioned quality. More precisely you have to verify if you are above the percolation threshold or below it. Below this limit, most of the mechanical properties are growing with increasing the CNT concentration, however, they reach a plateau once the CNT concentration passes the percolation limit. In the case of heat and electrical conductivity such a trend may also govern.
The behavior thermal conductivity is quite different from electrical conductivity for nanocomposites. There exists the thermal boundary resistance (TBR) between 2 CNTs incontact (Rcnt-cnt) which is even higher than that between the CNT and the matrix.
[see Heat transfer in high volume fraction CNT nanocomposites: Effects of inter-nanotube thermal resistance]
Functionalization has been found to suppress TBR and maintain good dispersion. However, it can damage the intricsic thermal conductivity of the nanoinclusions. Again, whether one can observe thermal percolation remains an open question.
[see Effects of Functionalization on Thermal Properties of Single-Wall and
Multi-Wall Carbon Nanotube-Polymer Nanocomposites]
Regrading the question of John, I believe these stabilizers may help to provide better coupling between the nanoinclusion the surounding (similar to the functionalization). Also, maintaining good dispersion is benneficial to thermal conductivity since it minimize the Rcnt-cnt.
Hope that will help.
Khoa, Do you think the coupling is related to pi-pi overlap? The imidazolium ring is reputed to be a strongly adsorbing group. Other delocalized adsorbents, like many based on pyrene, are thought to adsorb strongly [at least surfactants based on this species appear to stabilize CNTs in water very well]. Are you set up to do molecular, electronic, or thermal modeling of such adsorbtion? John
Hi John, I think it is related. Performing a set of molecular dynamics simulations to calculate the energy heat flux and the phonon spectra between the nanoinclusions and the surrounding will provide a better answer. See:
[Frequency and polarization dependence of thermal coupling between carbon nanotubes and SiO2.
Thermal Behavior of Double-Walled Carbon Nanotubes and Evidence of Thermal Rectification]
This is a very interesting topic but I am currently working on other projects in Texas A&M...
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