Physical Chemistry of Complex Fluids: Polymers and Colloids
Research in soft matter science focuses more than ever on mastering increasingly complex molecular structures and supramolecular assemblies. Aims are active functionalities, comprising, but also leading beyond, the so-called responsive materials. The response dynamics of such materials is strongly correlated with their characteristic length scales. In the right combination, a smartness enabling interactivity is envisioned that is characteristic of living systems but not yet achievable by synthetic means.
Crucial attributes of the stunning functionality of living systems are their differentiated structural organization over many length scales and self-assembly in an aqueous environment. The molecular structure has functionality on the nanometer scale, which translates into larger more complex entities via self-organization. Hierarchical arrangement of molecular entities into complex superstructures and their functional compartmentalization is required to enable selective and directed transport as well as controlled energy transformation. We investigate various systems including, e.g., microgels, nanoparticles, bio-colloids, hydrogels, polyelectrolytes, vesicles and emulsions.
We especially focus on micro- and nanogels. Microgels are unique colloidal systems that are distinctly different from common colloids. The microgel’s architecture is determined by its chemical connectivity within the finite-size network. Microgels are soft objects and are deformable, while still retaining its structural integrity. They have an open structure enabling exchange of solvent and solutes between microgel and environment can alter size and shape of the microgel itself.
In other words, microgels are sensitive to their environment; they interact with it through adaptation of their properties. The combination of being soft and porous while still having a stable structure through the cross-linked network allows for the possibility to introduce chemical functionality at different positions. Compartmentalization of reactive groups enables thus short-range coexistence of otherwise instable combinations of chemical reactivity. These unique conceptual combinations of structure with chemical and physical properties are illustrated in this figure.
We use various experimental techniques:
- Light scattering: static, dynamic and 3D-cross-correlation
- Small angle X-ray & neutron scattering, SAXS, SANS
- Particle sizing: Flow Particle Image Analyzer, Zeta-sizer, NanoSight
- 2-focus Fluorescence Correlation Spectroscopy
- Rheology, Rheo-optics
- Surface tension, interfacial rheology
- Compression isotherms, Langmuir trough
We also investigate the unique behaviors of microgels at interfaces. Soft microgels adsorb to oil-water interfaces and reveal properties that are distinctly different from both colloidal particles and macromolecules. We recently observed that microgels can be compressed more easily, when they are charged as compared to the uncharged state.
By employing stimuli sensitive microgels we prepare emulsions, which can be broken on demand. Such emulsions are, for example, for applications in bio-catalysis.IPC RWTH Aachen
Furthermore we study the synthesis of microgels and ineneted the non-stirred precipitation polymerization.