Cloud point temperatures (Tcp) and crystallization temperatures (T1/s) were measured at different constant shear rates for the ternary system tetrahydronaphthalene/ poly(ethylene oxide)/oligo(dimethyl siloxane-b-ethylene oxide) using a rheo-optical device and in the case of T1/s additionally a viscometer. This system enables for the first time a joint investigation of both transitions with a given mixture. Shear favors the homogeneous liquid state and the formation of crystals. Tcp (liquid/liquid demixing, UCST) shifts to lower and T1/s (liquid/solid, segregation of PEO) to higher temperatures by several degrees as the shear rate, γ̇, is increased up to 500 s-1. The normalized shift in Tcp fits well into previous results for high molecular weight blends, oligomer mixtures, polymer solutions in single solvents and low molecular weight mixtures. A phase separated near critical blend was examined 1 K below its Tcp by means of a shear cell (Linkam) in the quiescent state and under shear with respect to its morphology. Upon an increase in γ̇ one observes a transition from the co-continuous structures existing in the quiescent state via deformed and oriented particles to string like morphologies. Finally, at sufficiently high shear rates the mixture becomes homogeneous and structures can no longer be seen under the microscope. The morphologies developing after the secession of shear are pointing to pronounced influences of the flow history of the system on the final structure of two phase blends.
All Science Journal Classification (ASJC) codes
- Condensed Matter Physics
- Physical and Theoretical Chemistry
- Organic Chemistry
- Polymers and Plastics
- Materials Chemistry