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Kinetics of volume changes of responsive microgels
This project is concerned with microgels that reveal cononsolvency; i.e. a mixture of two good solvents becomes a poor solvent for the microgel. In the first funding period we focused mainly on the phase behavior and equilibrium properties and especially investigated the H-bonding pattern of the microgels. Various microgels based on N-isopropylacrylamide (NIPAM), N-n-propylacrylamide (NNPAM), N,N-diethylacrylamide (DEAAM) and N-vinylcaprolactam (VCL)) we prepared. The phase behavior of these microgels in water–methanol mixtures was studied by DLS, DSC, SANS, SAXS, NMR, FTIR, as well as by theoretical models. Our equilibrium model is able to reproduce qualitatively correct phase behavior in water/methanol for all 4 polymer systems using COSMO-RS with only one parameter, namely the solvent oxygen - solvent oxygen van-der-Waals parameter, adjusted and used for all systems. For obtaining a cononsolvency effect for NIPAM and NNPAM oligomers, it was not necessary to introduce cooperativity, which is another prominent explanation found in the literature. We assign the differences of the phase behavior of NIPAM and NNPAM oligomers on the one hand and DEAAM and VCL oligomers on the other hand to the amide proton, which is present in NIPAM and NNPAM, but not in the other two systems.
Principle Investigators:
Richtering, Walter, Prof. Dr.
Institute of Physical Chemistry
RWTH Aachen University
Bardow, André, Prof. Dr.-Ing.
Institute of Technical Thermodynamics
RWTH Aachen University