Elastic Constants in Colloidal Crystals from Microscopic Strain Fluctuations: Experiment and Computer Simulations

Beschreibung

The goal of this project is the development and application of different tools for the determination of elastic constants in colloidal model systems based on experimental and simulation analysis and to compare the results with theoretical predictions.

The simulational approach will make use of a new coarse-graining procedure which has been successfully tested for a hard disk system. In this technique, elastic strains are calculated from the instantaneous configurations of the particles and averaged over subblocks of various linear dimensions Lb<L of a system of total linear dimension L. From these data the correlation function of strain fluctuations in the thermodynamic limit can be extraced and the elastic constants then inferred from well known fluctuation formula.

This method will be applied to models of colloidal systems both in two and three dimensions using effective interparticle potentials of the DLVO and r-n(n<3 being an integer) type. Particular emphasis will be on models describing magnetic particles in 2D whose (dipole) interactions are controlled by magnetic fields, and charged (DLVO-interacting) particles in 3D, respectively, to make possible a quantitative comparison with the experimental part of the project. Also, elastic constants in anisotropic situations - where a preferred orientation and modulation is created by an external laser field - will be treated. Finally, anisotropic situations caused by thin films of thickness D will be considered in order to understand the consequences of the interplay between surface and size effects on elastic constants.


In the experimental part, the fluctuation analysis mentioned above shall be applied to real colloidal systems in two and three dimensions. In the 2D system superparamagnetic particles are confined by gravity to an air-water interface and the strength of the interparticle magnetic dipole-dipole interaction is controlled by an external magnetic field B. Conventional video-microscopy provides time dependent particle configurations. In 3D coulombic colloidal crystals will be used and particle positions measured by confocal microscopy. As a second method (possibly also in the simulation) the use of optical tweezers to induce well defined localized strains in the 2D and 3D colloidal systems will be explored as a complementary tool to probe elastic properties on a local scale.


The goal of this project is the development and application of different tools for the determination of elastic constants in colloidal model systems based on experimental and simulation analysis and to compare the results with theoretical predictions.

The simulational approach will make use of a new coarse-graining procedure which has been successfully tested for a hard disk system. In this technique, elastic strains are calculated from the instantaneous configurations of the particles and averaged over subblocks of various linear dimensions Lb<L of a system of total linear dimension L. From these data the correlation function of strain fluctuations in the thermodynamic limit can be extraced and the elastic constants then inferred from well known fluctuation formula.

This method will be applied to models of colloidal systems both in two and three dimensions using effective interparticle potentials of the DLVO and r-n(n<3 being an integer) type. Particular emphasis will be on models describing magnetic particles in 2D whose (dipole) interactions are controlled by magnetic fields, and charged (DLVO-interacting) particles in 3D, respectively, to make possible a quantitative comparison with the experimental part of the project. Also, elastic constants in anisotropic situations - where a preferred orientation and modulation is created by an external laser field - will be treated. Finally, anisotropic situations caused by thin films of thickness D will be considered in order to understand the consequences of the interplay between surface and size effects on elastic constants.


In the experimental part, the fluctuation analysis mentioned above shall be applied to real colloidal systems in two and three dimensions. In the 2D system superparamagnetic particles are confined by gravity to an air-water interface and the strength of the interparticle magnetic dipole-dipole interaction is controlled by an external magnetic field B. Conventional video-microscopy provides time dependent particle configurations. In 3D coulombic colloidal crystals will be used and particle positions measured by confocal microscopy. As a second method (possibly also in the simulation) the use of optical tweezers to induce well defined localized strains in the 2D and 3D colloidal systems will be explored as a complementary tool to probe elastic properties on a local scale.

Institutionen
  • FB Physik
Mittelgeber
NameKennzifferBeschreibungLaufzeit
Deutsche Forschungsgemeinschaft608/02keine Angabe
Weitere Informationen
Laufzeit: 01.07.2002 – 30.06.2005