Elucidation of viscoelastic phase separation in polymer systems
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Abstract :
To further understand phase separation as a fundamental phenomenon in the development and control of spatially heterogeneous patterns in polymer systems, it was argued that phase separation in these systems is generally belongs to “viscoelastic phase separation”, in which the morphology of the system is influenced not only by the mechanical equilibrium of thermodynamic force, but also by viscoelastic force. The origin of the viscoelastic force is the dynamic asymmetry between the components of the polymeric mixture, which can be caused by size differences or differences in glass transition temperatures between the components. Such dynamic asymmetry usually occurred in polymer solutions and polymer blends, which universally lead to a new kinetic path, called a transient gel state, upon their phase separation. A transient gel is a state in which the characteristic deformation rate produced by phase separation is faster than the characteristic rheological relaxation rate. The basic features of viscoelastic phase separation, which originates from transient gel formation, were predicted to be common to any “dynamically asymmetric” fluids with large size differences between the constituent components, such as polymer solutions. Furthermore, the evolution of the structural pattern in polymer solutions and polymer blends is essentially similar and there is no qualitative difference between the two cases, suggesting a universal nature of viscoelastic phase separation in dynamically asymmetric mixtures regardless of the origin of the asymmetry
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