Effect of Surfactant Structure on the Stability of Carbon Nanotubes in Aqueous Solution

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• 作者：Qi Wang ; Yuchun Han ; Yilin Wang ; Yujun Qin ; Zhi-Xin Guo
• 刊名：Journal of Physical Chemistry B
• 出版年：2008
• 出版时间：June 19, 2008
• 年：2008
• 卷：112
• 期：24
• 页码：7227 - 7233
• 全文大小：411K
• 年卷期：v.112,no.24(June 19, 2008)
• ISSN：1520-5207

文摘

The suspending behaviors of multiple-wall carbon nanotubes (MWNTs), including pristine MWNTs (p-MWNTs) and acid-mixture-treated MWNTs (MWNTCOOH), stabilized by cationic single-chain surfactant, dodecyltrimethylammonium bromide (DTAB), and cationic gemini surfactant hexyl-α,β-bis(dodecyldimethylammonium bromide) (C₁₂C₆C₁₂Br₂) were studied systematically. The surfactant structure influences the suspendability of MWNTs dramatically as well as the surfactant adsorption behavior on the nanotubes. Although both the surfactants can disperse the MWNTs effectively, they actually show different stabilizing ability. DTAB is not capable of stabilizing these two MWNTs below critical micelle concentration (CMC). However, C₁₂C₆C₁₂Br₂ can suspend both the nanotubes effectively even well below its CMC. Moreover, the adsorption of these two surfactants reaches equilibrium at twice the CMC with the original MWNT concentration of 2 mg/mL, 2 mM for C₁₂C₆C₁₂Br₂, and 30 mM for DTAB. After the adsorption equilibrium, the maximum amounts of the two suspended MWNTs in C₁₂C₆C₁₂Br₂ solution are about twice as much as those in DTAB solution. The strong hydrophobic interaction among the C₁₂C₆C₁₂Br₂ molecules and between the C₁₂C₆C₁₂Br₂ molecules and the nanotubes as well as the high charge capacity of C₁₂C₆C₁₂Br₂ lead to its much stronger adsorption ability on the MWNTs and result in its superior stabilizing ability for the MWNTs in aqueous phase. The gemini surfactant provides a possibility to effectively stabilize the MWNTs in aqueous solutions even at very low surfactant concentration well below its CMC.