Solvent-mediated morphology engineering: pseudomorph of fullerene C60 microcrystals

Significance 

Crystal structure, shape, and size are some of the factors affecting the properties of fullerene crystals. To produce unique forms of fullerene crystals desirable for various applications, several growth methods have been developed. In particular, the liquid-liquid interfacial precipitation method is used in solution methods for the preparation of fullerene micro- and nanocrystals. It uses a mixture of good and poor solvents that exhibit great potential in morphology, shape and size control. The crystal precipitation is generally defined by the difference in the solubility of fullerenes for two solvents used. Thus, solvent selection is of great importance in the growth of novel micro- and nanocrystals.

In a recent paper published in the journal, Chemical Physical Letters: Saori Yamamoto, Yuto Funamori, Yuko Kaneda, Makoto Tanimura and led by Professor Masaru Tachibana from Yokohama City University developed a new method for growing C60 crystals with hexagonal shape using liquid-liquid interfacial precipitation method. Specifically, carbon tetrachloride and C60-saturated toluene solution were used as poor and good solvents respectively. Finally, the morphology transformations of the samples were investigated.

Carbon tetrachloride-solvated C60 crystals with hexagonal shapes were obtained. It was fascinating to note that the morphology of the hexagonal crystals with the growth liquid was significantly changed with drying air at 23°C. Additionally a lot of fine rod crystals appeared in the original crystal despite the hexagonal outline the original crystal being kept even after transformation. Through the transformation, the hexagonal symmetry of the original crystals was passed down to rod crystal orientation. The resulting morphology exhibited a kind of hierarchical architecture. The unique morphology was attributed to the good agreement in the periodicity for solvated crystals before and after transformation. This explained the reason for arranging the long axes of the rod crystals parallel to the edges of the original hexagonal outline.

It was necessary to prepare additional samples though solvent treatments to gain more insight into the morphological transformation. Considering that the morphology of the solvated crystals of C60 depend on the solvent, the obtained results were used to ascertain results of previous publications about the role of carbon tetrachloride and toluene in the transformation of both rod and hexagonal crystals. For instance, they expected to promote and hinder morphological transformation by introducing or removing toluene respectively.

The authors confirmed that toluene played a significant role in promoting the morphological transformation. The relationship among the three samples: as-grown crystal covered by the mother liquid, hexagonal crystal dried in the air, and rod crystal dried in the air, it was worth noting that the morphology could be related to the solvent-meditated phase transformation reported for various crystals. Furthermore, various methods such as the X-ray diffraction were used to clarify the transformation mechanism of the hexagonal and rod crystal before and after transformation.

In summary, Yokohama City University scientists reported a solvent-based phase transformation of C60 crystals with a well-defined hexagonal shape. The morphology change was attributed to the dissolution of the original crystals by toluene followed by re-precipitation of the rod crystals. Therefore, in a statement to Advances in the Engineering Professor Masaru Tachibana, the lead author mentioned their study will advance the growth of novel nano/microcrystals.

About the author

Saori Yamamoto received her B.S. in 2017 and M.S. in 2019 from Yokohama City University under Prof. M Tachibana’s supervision. She carried out this research as part of her Master’s degree work.

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About the author

Yuto Funamori received his B.S. from Yokohama City University in 2018. He is now studying on fullerene nano/microcrystals as a Master student under Prof. M Tachibana’s supervision.

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About the author

Masaru Tachibana received his PhD from Waseda University in 1995. Since 1991, he has joined as a faculty member in the Physics Department at Yokohama City University (YCU). He also joined as a visiting scientist in the Physics Department at University of Kentucky in 1998 and Pennsylvania State University in 1999. Since 2006, he has served as a Professor at YCU. Currently, he is the Dean of Graduate School of Nanobioscience at YCU.

His research interests involve the synthesis and novel physical properties of various molecular crystals such as organic semiconductors, nanocarbon materials and protein crystals. He has carried out pioneer researches on novel nanocarbon materials, especially “carbon nanowalls” and “fullerene nanowhiskers”. He is also promoting unique studies on physical properties in protein crystals.

Reference

Yamamoto, S., Funamori, Y., Kaneda, Y., Tanimura, M., & Tachibana, M. (2019). Solvent-mediated phase transformation of C60 crystals with well-defined hexagonal shape. Chemical Physics Letters, 730, 105-111.

Go To Chemical Physics Letters

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