The structure of chain end-grafted nanoparticle/homopolymer nanocomposites
The structure of chain end-grafted nanoparticle/homopolymer nanocomposites
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DOI：
10.1039/c1sm05076a
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发表时间：
2011-01-01
期刊：
影响因子：
3.4
通讯作者：
Green, Peter F.
中科院分区：
文献类型：
--
作者：
Green, Peter F.
本文描述了聚合物链端接枝的均聚物与无机纳米颗粒混合物的形态结构。总体而言，在非常低的接枝密度Sigma下，这些聚合物纳米复合材料（pnc）的形态在很大程度上取决于纳米颗粒核之间的吸引焓相互作用，由接枝聚合物链的熵相互作用介导。这些相互竞争的相互作用已被证明是纳米颗粒在聚合物宿主内各向异性组织的原因。然而，在高接枝密度下，即使宿主链和接枝链具有相同的化学结构，熵刷层/自由宿主链的相互作用也占主导地位，导致混溶（纳米颗粒在聚合物宿主体内的各向同性分散）或微观和宏观相分离。在非常小的纳米颗粒的极限，半径R接近1 nm，电刷/熔体相互作用并不重要，但纳米颗粒在均聚物中表现出高度的混相倾向。本文首先讨论了纳米颗粒的体积形态，以便为随后描述薄膜刷涂纳米颗粒-均聚物混合物的形态结构提供背景。这些块状pnc和薄膜pnc之间的一个根本区别是，接枝纳米颗粒对界面的优先吸引力使得薄膜pnc在热力学上比它们的块状类似物更不稳定。形态相图描述了pnc可混溶、不相容或部分混溶的状态，其参数化包括纳米颗粒曲率、链接枝密度、接枝链聚合度N、自由宿主链聚合度P和宿主链与接枝链之间的热力学（Flory-Huggins）相互作用参数chi。
The morphological structure of mixtures of homopolymers with inorganic nanoparticles, onto which polymer chain ends are grafted, is described herein. In the bulk, at very low grafting densities, Sigma, the morphology of these polymer nanocomposites (PNCs) is largely determined by the attractive enthalpic interactions between the nanoparticle cores, mediated by entropic interactions with the grafted polymer chains. These competing interactions have been shown to be responsible for the anisotropic organization of the nanoparticles within polymer hosts. At high grafting densities, however, even in cases where the host chains and the grafted chains are of identical chemical structure, the entropic brush layer/free host chain interactions are dominant, leading to miscibility (isotropic dispersion of the nanoparticles within the polymer host) or to microscopic and macroscopic phase separation. In the limit of very small nanoparticles, radii R approximate to 1 nm, the brush/melt interactions are not important yet the nanoparticles exhibit a high tendency toward miscibility within homopolymer hosts. This paper begins with a discussion of the bulk morphology of PNCs in order to provide a context for the subsequent description of the morphological structure of thin film brush coated nanoparticle-homopolymer mixtures. A fundamental difference between these bulk and thin film PNCs is that a preferential attraction of grafted nanoparticles to interfaces renders thin film PNCs thermodynamically less stable than their bulk analogs. Morphological phase diagrams, which delineate regimes where the PNCs are miscible, incompatible or partially miscible, are parameterized in terms of the nanoparticle curvature, the chain grafting density, the grafting chain degree of polymerization, N, that of the free host chains, P, and the thermodynamic (Flory-Huggins) interaction parameter, chi, between the host and grafted chains.