Project description-1102

Project description-1102 - Self-assembly of Diblock...

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Self-assembly of Diblock Copolymer-Based Supramolecule Thin Films on Two Length Scales 1. Introduction: Functional thin films with hierarchical assembly down to molecular level are desirable to build more complex scaffolds or nanodevices. Block copolymers (BCP) are composed of covalently end-linked homopolymers, microphase separate into arrays of domains, tens of nanometer in size. 1, 2 In thin films, microdomain can be macroscopically oriented by applying external fields. 3-14 However, most studies on BCPs have focused on 2-D planar structures. Microdomains, only a few nanometers in size, are rare. Also, the built-in functionality is limited and requires post-functionalization. Small molecules, which are monodispersed, on the other hand, have rich chemical functionalities and can assemble into well-defined supramolecular structures at the molecular level. However, it is non-trivial to manipulate their assembly macroscopically and the processing conditions to fabricate functional devices using small molecule alone are demanding. Synergistic assemblies of block copolymers and small molecules combine the processibility and self-assembly of block copolymer with the rich chemical functionality and molecular assembly of small molecule. This combination can lead to hierarchical functional materials. Various block copolymer-based supramolecules have been synthesized and characterized. 15-17 In particular, Ikkala and ten Brinke developed a versatile methodology to construct supramolecules by attaching small molecules to the polymer side chain via hydrogen bonding, electrostatic interactions or metal coordination. 18-20 The methodology is versatile and has many advantages over copolymer-based supramolecules where the small molecule is covalently linked to copolymer. To date, most studies have focused on the phase behavior of these copolymer-based supramolecules in the bulk. Reports on the assemblies of supramolecules in thin films have been empirical and have focused on optimizing experimental conditions to achieve targeted assemblies. 21, 22 2. Objectives and Significance Intellectual merit: Developing an understanding of the parameters that dictate the phase behavior of these unique and interesting supramolecules will establish a base and open new roads to technologically important, functional hierarchical materials. This requires our fundamental understanding on the thermodynamics of self-assembly processes at different length scales, the inter-play between the assemblies at different length scales and more importantly, how to achieve synergistic assembly of each building block so as to use small molecule to direct the macroscopic assembly of copolymer and to use the phase separation of block copolymer to amplify the macroscopic response originated from small molecules.
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