Computersimulationsuntersuchungen zur Struktur geladener Makromoleküle
Computersimulationsuntersuchungen zur Struktur geladener Makromoleküle
The understanding of the behaviour of charged marcromolecules, or polyelectrolytes, is still very poor. Nevertheless, polyelectrolytes are of great technical and scientific interest; e.g. almost all biopolymers (DNA etc.) are polyelectrolytes. The aim of the present thesis is the description of poly...
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Personal Name(s): | Micka, U. (Corresponding author) |
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Contributing Institute: |
Publikationen vor 2000; PRE-2000; Retrocat |
Imprint: |
Jülich
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
1998
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Physical Description: |
X, 188 p. |
Document Type: |
Report Book |
Research Program: |
ohne Topic |
Series Title: |
Berichte des Forschungszentrums Jülich
3451 |
Link: |
OpenAccess OpenAccess |
Publikationsportal JuSER |
The understanding of the behaviour of charged marcromolecules, or polyelectrolytes, is still very poor. Nevertheless, polyelectrolytes are of great technical and scientific interest; e.g. almost all biopolymers (DNA etc.) are polyelectrolytes. The aim of the present thesis is the description of polyelectrolytes by simplified models within the framework of statistical physics. These models are mainly analyzed by computer simulation whereby one can base on the sucessful methods for simulation of neutralpolymers. The theoretical understanding of neutral polymers is well developped. Nevertheless, the theoretical description of polyelectrolytes is extremely complicated due to additional degrees of freedom and length scales coming from the electrostatic interaction. Especially the large number of degrees of freedom of the counterions and their fluctuations cause severe problems for the analytical description. For these reasons, analytic theory mainly concentrates on single chains and uses mean-field approaches which are known not to be an appropriate description. Experiments are, in particular in the analytically accessible regime (e.g. extreme dilution), extremely difficult and sometimes impossible. Computer simulation allows to bridge the gap between theoretical approaches and experimental results and to extend them, as the whole parameter space is accessible. Based on this background, the present thesis studies the basic analytical models as well as experimentally relevant systems. The first part is concerned with the analysis of a single chain treated within the framework of the Debye-Hueckel approximation. The simulations clearly demonstrate that none of the known analytic approaches is able to describe the polyelectrolyte conformation correctly. In the general case of electrostatic and intrinsic stiffness, a length scale dependent description is indispensable. Comparison with a first set of neutron scattering data of adequate quality shows reasonable agreement. The main point of effort of the second part is the simulation of polyelectrolyte solutions using the bare Coulomb potential and explicit counter- and salt ions. First of all, a typicalexample is simulated to prove the experimental relevance ofthe Debye-Hueckel single chain results. The comparison with an earlier work of Stevens and Kremer allows conclusions on the range of validity of the Debye-Hueckel approximation. Systems of 200 hydrophilie chains (12800 charges) give interesting insight in the large scale structure of polyelectrolyte solutions. Finally, the analysis of polyelectrolytes under bad solvent conditions shows completely new types of conformations with multiple interesting properties (e.g. extreme collapse, necklace chains). By implementing a new (1993) algorithm and optimizing it for polyelectrolyte problems, the present thesis forms a basis for further studies of polyelectrolytes with explicit counterand salt ions (Fuoss law, slow mode(?), multivalent ions, polyelectrolyte gels, ... ). specially the analysis of hydrophobie moleeules is a first important step towards quantitative modelling of polyelectrolytes. |