Rheological Control of Microemulsions via Multifunctional Thermoresponsive Polymer Surfactants

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Aim of the project is the temperature control of the rheological properties of microemulsions by the addition of novel amphiphilic thermoresponsive polymers. In order to achieve a controlled viscosity increase with increasing temperature we will design copolymers with segments, that show an LCST transition from hydrophilic to hydrophobic behaviour, which then induces a structural reorganisation on the mesoscopic level. Via a systematic variation of type, number and position of the thermoresponsive blocks we will obtain tailor-made polymer architectures in order to induce a controlled complex structural and rheological behaviour of the microemulsion/polymer hybrid systems as a function of temperature. The other main aim is to gain a thorough understanding of the mechanism of the structural interaction. The polymer surfactants will be synthesized by controlled radical polymerisation, which allows for a very variable approach to such well-defined polymer structures. These will then become incorporated into biocompatible microemulsions and the formed structures will become studied as a function of temperature comprehensively by means of static and dynamic light scattering as well as small-angle neutron scattering (SANS), where SANS will yield detailed structural information by using contrast variation. This will become importantly complemented by cryogenic-transmission electron microscopy (cryo-TEM) for a comprehensive mesoscopic structural characterisation. In addition, fluorescence measurements will yield information regarding the connectivity of the formed network. In parallel, these network systems will be investigated comprehensively by rheology over the whole relevant temperature range. Particularly interesting and challenging will be synthesis and investigation of polymers with two different LCST blocks. They shall exhibit a particularly complex aggregation behaviour (with mixed or separated hydrophobic domains as cross-linking points) with corresponding rheological properties. Our aim then is to derive for the different polymer/microemulsion hybrid systems detailed correlations between the molecular structure of the polymer surfactants, the mesoscopic structure of the switchably cross-linked aggregates, the structure and concentration of the microemulsion and the resulting macroscopic rheological properties. Such systems are not only of fundamental scientific interest but also highly interesting for applications, e g. in pharmacy or cosmetics, especially when the high solubilisation capacity of microemulsions is to be combined with high viscosity or even gel-like behaviour.