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Development of microgel analysis techniques

Because of the structural complexity of the systems, the dynamic variation of the microgel structures and the fact that they consist, to a large extent, of the solvent, special and advanced characterization tech-niques are needed that provide information on the chemical composition, the dynamics on different length scales and the properties of the microgel system in the production and application process. By their mutual support, all research groups can rely on an exceptionally broad spectrum of techniques.

However, there is still a need for special techniques, which are developed in the G-projects: (i) the visualization by means of electron microscopy and (ii) the in-line monitoring of microgel production processes. The two G-projects have achieved tremendous progresses that consequently lead to many collaborative undertakings with other projects. This fruitful combination of methodology development and advancement of microgel research will be continued in the 2nd funding period.

Project G1 is concerned with electron microscopy. In the 1st phase of the project, novel methods for in situ-studies of microgels in liquid environment and cryo-TEM were accomplished and the feasibility has been demonstrated for a number of model systems. After establishing the in situ-TEM imaging technique and exploring the scope and limitations of the method (need for spatial immobilization of the observed object, improved resolution), the project will focus on the study of dynamic structural variations as these gain increasing relevance in the SFB. Complementary time-lapse cryo-TEM investigations in solution will be performed in order to obtain snapshots of the respective situation at higher resolution. By the combination of the time resolution of in situ-TEM with the more detailed structural information enabled by cryo-TEM, we expect new insights e.g. into the trajectories of the volume phase transitions as well as complex formation.

Complementing the activities in several B projects, project G2 aims at the development of new process analytical techniques to measure the particle size distribution, the total polymer content and the fluid phase composition by means of inline optical techniques combined with an advanced model-based optimization and control scheme. In the first funding period of project G2, methods for in-line determination of liquid phase concentrations and particle sizes during microgel synthesis were developed that involve Raman spectroscopy (evaluated via Indirect Hard Modeling) as well as an in-line DLS probe head that permits dynamic light scattering (DLS) measurements inside the stirred chemical reactor. In the 2nd period the project aims at the design and realization of a probe for a comprehensive in-line characterization of microgels that is fast enough to resolve the early stages of particle formation. As a novel approach, a miniaturized angular re-solved sensor for static light scattering will be developed for in-line measurements in undiluted samples through waveguide structures. Furthermore a combination of scattering and spectroscopy techniques based on sensor fusion and the integration the reactor model from project B4 is envisioned.