Relationship of Extensional Viscosity and Liquid Crystalline Transition to Length Distribution in Carbon Nanotube Solutions
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- 作者：Dmitri E. Tsentalovich ; Anson W. K. Ma ; J. Alex Lee ; Natnael Behabtu ; E. Amram Bengio ; April Choi ; Junli Hao ; Yimin Luo ; Robert J. Headrick ; Micah J. Green ; Yeshayahu Talmon ; Matteo Pasquali
- 刊名：Macromolecules
- 出版年：2016
- 出版时间：January 26, 2016
- 年：2016
- 卷：49
- 期：2
- 页码：681-689
- 全文大小：491K
- ISSN：1520-5835
文摘
We demonstrate that the length of carbon nanotubes (CNTs) can be determined simply and accurately from extensional viscosity measurements of semidilute CNT solutions. The method is based on measuring the extensional viscosity of CNT solutions in chlorosulfonic acid with a customized capillary thinning rheometer and determining CNT aspect ratio from the theoretical relation between extensional viscosity and aspect ratio in semidilute solutions of rigid rods. We measure CNT diameter d by transmission electron microscopy (TEM) and arrive at CNT length L. By studying samples grown by different methods, we show that the method works well for CNT lengths ranging from 0.4 to at least 20 μm, a wider range than for previous techniques. Moreover, we measure the isotropic-to-nematic transition concentration (i.e., isotropic cloud point) φiso of CNT solutions and show that this transition follows Onsager-like scaling φiso ～ d/L. We characterize the length distributions of CNT samples by combining the measurements of extensional viscosity and transition concentration and show that the resulting length distributions closely match distributions obtained by cryo-TEM measurements. Interestingly, CNTs appear to have relatively low polydispersity compared to polymers and high polydispersity compared to colloidal particles.