Dispersion of Pristine Carbon Nanotubes Using Conjugated Block Copolymers
Dispersion of Pristine Carbon Nanotubes Using Conjugated Block Copolymers
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DOI：
10.1002/adma.200701995
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发表时间：
2008-06
影响因子：
29.4
通讯作者：
J. Zou;Liwei Liu;Hui Chen;S. Khondaker;R. D. Mccullough;Q. Huo;L. Zhai
中科院分区：
文献类型：
--
作者：
J. Zou;Liwei Liu;Hui Chen;S. Khondaker;R. D. Mccullough;Q. Huo;L. Zhai
尽管碳纳米管（CNT）具有许多有趣的和优异的电学，机械和光学特性，[1，2]这些纳米材料的广泛应用仍然受到限制。碳纳米管研究领域的主要挑战之一是碳纳米管在不同溶剂介质和聚合物基体中的分散和稳定。由于纳米管之间的强货车范德华相互作用，所合成的CNT通常被捆绑在一起。将碳纳米管分散到溶剂和聚合物基体中有三种最广泛使用的方法：[3]物理共混，[4-6]化学官能化，[7-11]和分散剂辅助分散。[12-16]每种方法都有自己的优点和缺点。对于使用机械力如超声处理的物理共混，尽管简单且成本有效，但分散质量通常最差。当超声处理停止时，如此分散的纳米管将再次快速沉淀出来。对于化学改性和功能化，CNT用强氧化剂处理以在纳米管壁上形成官能团，例如羧酸。取决于改性程度和连接到纳米管的另外的分子部分，CNT可以被制成水或有机溶剂可溶的。尽管作为分散方法最有效，但这种处理不可避免地破坏纳米管的长程p共轭，通常导致降低的电导率、降低的机械强度和其他不期望的性质。在分散剂辅助分散中，第三组分化学品与CNT在溶液中混合。通过超声处理，碳纳米管被机械地解束，然后通过非共价相互作用被分散剂化学品稳定，因此，避免了碳纳米管的化学结构、电子和机械性能的破坏。最近，有两种类型的材料作为分散剂吸引了大量的注意力，以帮助碳纳米管分散。这些材料中的一种是共轭聚合物，例如聚（间亚苯基亚乙烯基）、[17，18]聚（3-烷基噻吩）、[19，20]和聚（亚芳基亚乙炔基）。[21这些聚合物通过与碳纳米管壁形成强的p-p堆叠相互作用来稳定碳纳米管。然而，如此形成的分散体具有有限的溶解度和稳定性，因为共轭聚合物本身由于强的链间p-p相互作用而面临溶解度和可溶解性问题。具有第三组分辅助碳纳米管分散潜力的第二类有趣材料是嵌段共聚物。[23-25]通常，嵌段共聚物以这样的方式设计，即聚合物的一个嵌段将与碳纳米管壁形成紧密的相互作用，而其他嵌段将通过在聚合物包裹的纳米管之间形成空间位阻或排斥相互作用而为剥离的纳米管提供溶解性。[26]到目前为止，广泛的带电和中性嵌段共聚物，如聚（环氧乙烷）（PEO）与聚（环氧丙烷）（PPO）（PEOPPO-PEO），[15]聚苯乙烯（PS）与聚（丙烯酸叔丁酯）（PBA）[15]或聚（乙烯基吡啶）（PVP）[23]已被报道用于碳纳米管分散体。
Despite many of the intriguing and excellent electrical, mechanical and optical properties of carbon nanotubes (CNTs),[1, 2] extensive applications of these nanomaterials are still limited. One of the main challenges in carbon nanotube research field is the dispersion and stabilization of CNTs in different solvent media and polymer matrices. The as-synthesized CNTs are often bundled together due to strong van der Waals interactions between the nanotubes. There have been three most widely used methods to disperse CNTs into solvents and polymer matrices:[3] physical blending,[4–6] chemical functionalization,[7–11] and dispersants-assisted dispersion.[12–16] Each of these methods has its own advantages and disadvantages. For physical blending using mechanical forces such as sonication, although simple and cost effective, the dispersion quality is often the poorest. The so-dispersed nanotubes will quickly precipitate out again when sonication stops. For chemical modification and functionalization, CNTs are treated with strong oxidizing reagents to form functional groups such as carboxylic acids on the nanotube walls. CNTs can be made water or organic solvent soluble, depending on the modification degree and further molecular moieties attached to the nanotubes. Although most effective as a dispersion method, such treatment inevitably disrupts the long range p conjugation of the nanotube, often leads to decreased electrical conductivity, diminished mechanical strength, and other undesired properties. In the dispersants-assisted dispersion, a third component chemical is mixed with CNTs in solutions. Through sonication, the CNTs are mechanically de-bundled and then stabilized by a dispersant chemical through noncovalent interactions, therefore, avoiding the destruction of the chemical structures, electronic and mechanical properties of the carbon nanotubes.Recently, there are two types of materials that have attracted significant amount of attention as dispersants to assist carbon nanotube dispersion. One of these materials is the conjugated polymers, such as poly (m-phenylene vinylene),[17, 18] poly (3-alkylthiophene),[19, 20] and poly (arylene ethynylene).[21, 22] These polymers stabilize carbon nanotubes by forming strong p–p stack interactions with carbon nanotube walls. However, the thus-formed dispersions have limited solubility and stability because the conjugated polymers themselves face solubility and miscibility issues due to the strong inter-chain p–p interactions. A second family of interesting materials with potential for third componentassisted carbon nanotube dispersion are block copolymers.[23–25] In general, the block copolymer is designed in such a way that one block of the polymer will form a close interaction with the carbon nanotube walls, while the other block (s) will provide the solubility to the exfoliated nanotubes by forming a steric barrier or repulsion interaction between polymer-wrapped nanotubes.[26] So far, a wide range of charged and neutral block copolymers such as poly (ethylene oxide)(PEO) with poly (propylene oxide)(PPO)(PEOPPO-PEO),[15] polystyrene (PS) with poly (t-butylacrylate)(PBA)[15] or poly (vinyl pyridine)(PVP)[23] have been reported for carbon nanotube dispersion.