Project

How strong is a polyelectrolyte complex?

If you mix a solution of positively charged polymers with negatively charged polymers, a polyelectrolyte complex is formed under the right conditions

This electrostatic complexation is encountered in nature, in for example DNA-histone complexes and the bacterial nucleoid. Nature’s approaches have been mimicked to create designed colloidal structures and materials, such as micelles, capsules, self-healing gels and photonic materials (see Fig. 1). The stability of all these materials depends mainly on the salt concentration and polymer length.

Figure 1: a) associative phase separation in mixture of oppositely charged polyelectrolytes, b) DNA-condensation by positively charged histon proteins, c) bacterial nucleoid, d) complex coacervate core micelle (C3M), e) crystals of oppositely charged colloids, f) designing raspberry colloidal assemblies.
Figure 1: a) associative phase separation in mixture of oppositely charged polyelectrolytes, b) DNA-condensation by positively charged histon proteins, c) bacterial nucleoid, d) complex coacervate core micelle (C3M), e) crystals of oppositely charged colloids, f) designing raspberry colloidal assemblies.

This project aims at a fundamental understanding of the interaction forces between oppositely charged polyelectrolytes, and the microscopic structure and dynamics of the complexes they form. The answers to questions like “how strong is a polyelectrolyte complex?” will enable us to predict and optimize the properties of polyelectrolyte complex microstructures and to design new colloidal structures and materials.

A variety of experimental techniques is used in this study. Phase diagrams describing the effects of salt concentration, polymer chain length and charge ratio are constructed using labeled polyelectrolytes. Direct measurements of interaction forces are available through atomic force microscopy (both on a collective level from colloidal probe AFM and on single molecule level) and rheology. Structural information is obtained from scattering experiments (light, x-rays, neutrons).

Complementary to experiments, theoretical modeling (self-consistent field calculations) is used to further investigate the structure of and interactions in polyelectrolyte complexes. The calculations deal with explicit charges in concentrated polymer solutions. Typically, large samples need to be taken into account to explore the experimentally observed structures.