Conformational Transitions in Polymer Brushes
A polymer brush is formed by densely grafting the chain ends of polymers onto a surface. This tethering of the long macromolecules has considerable influence on the surface properties, which can be additionally modified by changing the environmental conditions. In this context it is of special inter...
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| Format: | Doctoral Thesis |
| Language: | English |
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Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden
2014
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| Online Access: | http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-139354 http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-139354 http://www.qucosa.de/fileadmin/data/qucosa/documents/13935/Dissertation_Romeis_TUDresden.pdf |
| Summary: | A polymer brush is formed by densely grafting the chain ends of polymers onto a surface. This tethering of the long macromolecules has considerable influence on the surface properties, which can be additionally modified by changing the environmental conditions. In this context it is of special interest to understand and control the behavior of the grafted layer and to create surfaces that display a desired response to external stimulation.
The present work studies densely grafted polymer brushes and the effects that such an environment imposes on an individual chain molecule in the grafted layer. For this purpose we developed a new self-consistent field approach to describe mixtures of heterogeneous chains comprised of differently sized hard spheres. Applying this method to the case of polymer brushes we consider a fraction of grafted molecules to be different from the majority brush chains. The modification of these chains includes a variation in the degree of polymerization, a different solvent selectivity behavior and a variable size of the free end-monomer. Due to the computational efficiency of the present approach, as compared for example to direct simulation methods, we can study the conformations of the modified 'guest' chains systematically in dependence of the relevant parameters. With respect to brush profile and the distribution of the free chain ends the new method shows very good quantitative agreement with corresponding simulation results. We also confirm the observation that these 'guest' chains can undergo a conformational transition depending on the type of modification and the solvent quality.
For the cases studied in the present work we analyze the conditions to achieve a most sensitive behavior of this conformational switching. In addition, an analytical model is proposed to describe this effect. We compare its predictions to the numerical results and find good agreement. |
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