Department of Applied Physics, Helsinki University of Technology, FIN-02015 TKK Espoo, Finland.
Faraday Discuss. 2009;143:95-107; discussion 169-86. doi: 10.1039/b905204f.
Self-assemblies and their hierarchies are useful to construct soft materials with structures at different length scales and to tune the materials properties for various functions. Here we address routes for solid nanofibers based on different forms of self-assemblies. On the other hand, we discuss rational "bottom-up" routes for multi-level hierarchical self-assembled constructs, with the aim of learning more about design principles for competing interactions and packing frustrations. Here we use the triblock copolypeptide poly(L-lysine)-b-poly(gamma-benzyl-L-glutamate)-b-poly(L-lysine) complexed with 2'-deoxyguanosine 5'-monophosphate. Supramolecular disks (G-quartets) stabilized by metal cations are formed and their columnar assembly leads to a packing frustration with the cylindrical packing of helical poly(gamma-benzyl-L-glutamate), which we suggest is important in controlling the lateral dimensions of the nanofibers. We foresee routes for functionalities by selecting different metal cations within the G-quartets. On the other hand, we discuss nanofibers that are cleaved from bulk self-assemblies in a "top-down" manner. After a short introduction based on cleaving nanofibers from diblock copolymeric self-assemblies, we focus on native cellulose nanofibers, as cleaved from plant cell wall fibers, which are expected to have feasible mechanical properties and to be templates for functional nanomaterials. Long nanofibers with 5-20 nm lateral dimensions can be cleaved within an aqueous medium to allow hydrogels and water can be removed to allow highly porous, lightweight, and flexible aerogels. We further describe inorganic/ organic hybrids as prepared by chemical vapour deposition and atomic layer deposition of the different nanofibers. We foresee functional materials by selecting inorganic coatings. Finally we briefly discuss how the organic template can be removed e.g., by thermal treatments to allow completely inorganic hollow nanofibrillar structures.
自组装及其层次结构可用于构建具有不同长度尺度结构的软物质，并调整材料性能以实现各种功能。在这里，我们介绍了基于不同形式自组装的固态纳米纤维的合成途径。另一方面，我们讨论了多层次自组装结构的合理“自下而上”途径，目的是更多地了解竞争相互作用和堆积受阻的设计原则。在这里，我们使用聚（L-赖氨酸）-b-聚（γ-苄基-L-谷氨酸）-b-聚（L-赖氨酸）三嵌段共聚物与 2'-脱氧鸟苷 5'-单磷酸复合。形成了由金属阳离子稳定的超分子盘（G-四联体），其柱状组装导致与螺旋聚（γ-苄基-L-谷氨酸）的圆柱状组装相竞争的堆积受阻，我们认为这对于控制纳米纤维的横向尺寸很重要。通过选择 G-四联体中的不同金属阳离子，我们可以预见其功能途径。另一方面，我们讨论了通过“自上而下”的方式从大块自组装体中切割纳米纤维的途径。在简要介绍了从两亲性嵌段共聚物自组装体中切割纳米纤维之后，我们重点介绍了从植物细胞壁纤维中切割得到的天然纤维素纳米纤维，因为它们有望具有可行的机械性能，并且可以作为功能纳米材料的模板。在水性介质中可以切割具有 5-20nm 横向尺寸的长纳米纤维，以形成水凝胶，并且可以除去水以得到高度多孔、重量轻且灵活的气凝胶。我们进一步描述了通过不同纳米纤维的化学气相沉积和原子层沉积制备的无机/有机杂化材料。通过选择无机涂层，我们可以预见功能性材料。最后，我们简要讨论了如何通过例如热处理去除有机模板，以得到完全无机的空心纳米纤维结构。
