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Identifier

000286964

Title

Aλληλεπιδράσεις, δομή και ρεολογία πολυμερικών κολλοειδών και μειγμάτων

Alternative Title

Interactions, structure and rheology of ultrasoft colloidal spheres and mixtures

Author

Στειακάκης, Εμμανουήλ

Thesis advisor

Βλασσόπουλος, Δημήτρης

Abstract

The use of well defined macromolecular assemblies with tunable interactions represents the key for exploring the regime of soft-material behavior between hard spheres and polymer coils. Colloidal stars are ideal choices for such a formidable task and especially for shedding light on the formation and properties of dynamically arrested states. In this thesis, we demonstrate the rich variety of kinetic frustration phenomena that can be encountered with such ultrasoft particles. We address two specific examples in particular: the melting of star glass upon the addition of linear polymers and the reversible vitrification upon heating. In the first, star depletion appears to be the key to this effect and is related to the starlinear polymer size ratio. A detailed investigation indicates that with increasing the osmotic forces (due to the added polymer) these soft colloids first shrink and then form stable clusters. In the second, upon heating, concentrated solutions of colloidal stars in a solvent of intermediate quality (between θ and athermal) undergo a reversible glass like kinetic transition. This phenomenon can be attributed to the increase in the effective volume fraction of the stars with the temperature, which leads to the formation of clusters and causes the dynamic arrest of the solution. Due to the slow dynamics, unsteady and nonergodic behavior are typically present in this kind of transitions. To resolve these problems and obtain reliable information, we modified the classical Dynamic Light Scattering technique and developed a version of Multispeckle Autocorrelation Spectroscopy instrumentation. The application of this technique in the reversible vitrification phenomenon upon heating reveal that a logarithmic decay govern this glass-like transition.

Language

Greek

Subject

Glass transition

Jamming

Soft matter

Star polymer

Ultrasoft colloids

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