| Böker, A.: Control of Block Copolymer Microdomain Orientation from Solution using Electric Fields - Governing Parameters and Mechanisms in A. V. Zvelindovsky: Nanostructured Soft Matter: Experiment, Theory, Simulation and Perspectives, Springer, 199-230 (2007) | |
| Abstract: As nanotechnology increasingly gains importance in daily life, the need for novel small scale structures also rises exponentially. For example, to keep up with Moore's law, the packing density of integrated circuits has to increase on an almost daily basis. Considering the growing number of electronically stored data, it is also clear that novel data storage techniques have to be devised aiming to increase the information density on a hard disk. For such applications, the microstructures formed by block copolymers via their microphase separation present an ideal template for the fabrication of nanoscale patterns ranging from 10 - 100nm. In order to profit from the self-assembly of block copolymers into various microstructures, one has to be able to control the parameters that govern this unique self-ordering process. In addition, it would be desirable to guide self-assembly via external fields to form macroscopically oriented, highly ordered structures. Block copolymer microphase separation has been studied extensively over the past two decades both experimentally and theoretically. In the phase separated state, these materials exhibit highly regular mesoscopic microdomain structures with characteristic length scales of the order of several tens of nanometers. Similar to polycrystalline materials, typically small grains of microdomains are formed, the size of which may be of the order of microns. As a consequence, although a single grain may have a highly anisotropic structure (e.g. in the case of cylindrical or lamellar structures), a bulk sample of a block copolymer typically exhibits isotropic materials properties. Control of the orientation of a block copolymer microstructure allows the development of polymeric materials with novel and interesting properties. Anisotropic mechanical, optical, electrical or mass transport properties can be tailored by proper orientation of the block copolymer microstructure. For example, alignment of glassy microphase-separated cylinders in a rubbery matrix gives a material with a glassy modulus along the cylindrical axis and a rubbery modulus along the transverse directions. If the cylinders are made conductive, the material becomes a directional conductor. Quantum dots or wires could be made from block copolymers with a spherical or cylindrical microstructure. The birefringence inherent in lamellar or cylindrical block copolymers could be useful for optical applications. To create macroscopically anisotropic materials, various techniques aiming towards macroscopic microdomain alignment have been devised. Most prominently, shear fields, temperature gradients and electrical fields have been successfully applied to orient block copolymer microdomains from melt and solution. Springer Series: NanoScience and Technology: A. V. Zvelindovsky (ed.): Nanostructured Soft Matter: Experiment, Theory, Simulation and Perspectives  |
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