The next article is “Rotational dynamics of confined C60 from near-infrared Raman studies under high pressure,” PNAS (2009), Vol. 106, pp. 22135-22138, by Yonggang Zou and colleagues. Within this article, the authors use near-infrared Raman (NIR) spectroscopy to investigate the rotational properties of C60 molecules, their interaction with single walled carbon nanotubes (SWNT), and how this interaction affects their rotation. Other studies have been done using inelastic neutron scattering (INS) and NMR spectroscopy, giving the authors data to compare their Raman results. From these previous experiments, it was found that temperature changes alter the rotational states of these molecules. Using this premise, the authors examined the rotations of C60 fullerenes by using high pressure techniques with an alteration in temperature. NIR Raman was used within this study for its capabilities of detecting intermediate frequency modes (IFM) in relation to C60 orientation and polymer bonds between molecules along with the polymeric phase interaction with SWNT.
The author’s concluded that the C60 molecules do not rotate freely within SWNT but favor a specific orientation within the tubes that offer the strongest interaction. This observation leads to another question of whether the C60 molecules orient in pentagon-to-pentagon or hexagon-to-hexagon patterns. From the splitting that occurred within the Raman, it was concluded that splitting occurred heavily in the pentagonal modes with no change in the hexagonal. It was determined from these anisotropic interactions that these fullerenes favor the hexagon-to-hexagon state because it has weaker interaction with SWNT than the pentagon orientation, allowing some form of rotation, referred to as ratcheted rotation. These findings agreed with the data from previous INS and NMR spectroscopy.
Within the Raman spectroscopy, the authors noted that temperature variance provided relatively similar spectra except for the intensity ratio between two of the modes: Hg(2) and Hg(4). These modes correspond to the pentagonal interaction which also supports the conclusion. This conclusion suggests that the Hg(2) and Hg(4) modes directly relate to the pentagonal interaction with SWNT. I would like to know the nature of these modes and how they are proposed to interact with SWNT. What makes the Hg(2) and Hg(4) nodes the ones to show a difference in intensity with varying temperature? The relative intensities are given but because the C60 fullerenes are highly symmetrical, I would expect more precise results within the intensities. Is there a reason for the few intensity data points that aren’t as close in agreement with the others based on either structure or interaction? Does this suggest that there are only two pentagonal interactions (one on each side of the molecule)?
Posted by Ashley Thomas
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I think it’s interesting that the hexagonal ratcheting is more favored than the pentagonal ratcheting in the C60 SWNT scenario. The article says that the interactions between the tube and the pentagon shape are greater than the ones between the tube and the hexagons. This means that the hexagonal orientation can rotate in the tube better than the pentagonal orientation. However, I am as equally confused as Ashley as to why the Hg2 and Hg4 modes are the ones that change dramatically. I guess I don’t understand what the Hg values represent and what the difference is between Hg1 and Hg2. Why can’t Hg1 and Hg4 have the same ratio change observed?
ReplyDeleteWhen reading this article, I was really interested in the near-infrared Raman spectroscopy because I have never heard it before. So I looked it up and it basically is used to study vibrational and rotational modes of a molecule. It uses near-infrared to either bring up or down the energies of photons which interact with the electron cloud and the bonds of the molecule. They can also use this to screen cancerous cells which I thought was really cool. Here is the citation of an article that talks about it if anyone’s interested: Mahadevan- Jansen, Anita, et. all. "Near-infrared Raman spectroscopy for in vitro detection of cervical precancers." Photochemistry and Photobiology 68.1 (2008): 123-32.
ReplyDeleteUsing this Raman spectroscopy, they found that pentagons interact much more strongly with the tube than the hexagons while the hexagons are lower in energy. So if the pentagons have more energy, wouldn’t they want to rotate more freely? I think this article says that they don’t rotate more freely which confused me a little.
Julia... still can't figure out how to set up a profile.
ReplyDeleteI found this article very confusing, not only because I'm unfamiliar with most of the methods, but also because they mixed their results with other papers' results in the results/discussion section. I don't think I've ever seen this done to such an extent before. Additionally, I felt that it wouldn't have been an over-simplification for the authors to define some of the terms that they use throughout the paper.
I was really confused about what the Hg "modes" referred to -my guess is that they are rotational states which correspond to some frequency in NIR spectroscopy. I also derived that Hg(1) and Hg(2) are related to pentagonal rotation, while Hg(3) and Hg(4) are related to hexagonal rotation. On first reading the paper, I thought that the authors just selected Hg(2) and Hg(4) as representative of the pentagonal/hexagonal rotational states, however in looking at figure 2, it appears (to my eyes) that the Hg(2) and Hg(4) peaks are the only ones that change.
I also found parts of this article confusing. I am new to near infrared Raman spectroscopy and like Julia believe a succinct explanation would benefit this paper. Again I side with Julia by saying that the combined results/discussion section seemed most unusual especially because of its intermittent incorporation of findings from other papers.
ReplyDeleteWhat interested me most within this paper was the comparison of pentagonal and hexagonal orientations. I believe in the hexagonal orientation a hexagon is perpendicular to the surface of the tube and then pentagons are facing the tube wall. I am not sure where this was explained. It is proposed from the results that the pentagon faces of the C60 molecules interact more strongly than the hexagons, and thus rotation is dampened in the hexagonal orientation. The authors call this ratcheting. What I am curious about is what exactly they mean by ratcheting. Is it simply a slowed rotation or is it actually a sporadic jerking? I am also curious as to why the pentagonal surfaces of the C60 molecules show greater interactions than the hexagonal surfaces. I do not believe this was explicated in the paper, but I might have missed it. A final point: the filling ratio is mentioned briefly on the second page and again in the methods (>80%). Where exactly does this come into play?
This article was confusing to all of us because we do not know the methodology behind NIR Raman spectroscopy. The paper clearly expects readers to be familiar with certain terms particularly the Hg values and what they correspond to. I also assumed that the Hg1 and Hg2 values corresponded to the pentagonal rotation and the Hg3 and Hg4 values correspond to hexagonal rotation.
ReplyDeleteThe pentagonal/hexagonal orientations are one of the major points of the article, yet I never felt they explained exactly how they are setting up the SWNTs in C60. I found it difficult to visualize what the peapod system is and where interactions are occurring. We are told that pentagonal rotations interact more with C60 and therefore rotate slower, but there is no in depth description of this interaction. In regards to David's ratching question, I interpreted it as being sporadic jerking as the molecule is rotating.