Reversible thermal gelation in star polymers: An alternative route to jamming of soft matter

Crowded solutions of densely branched polymers with starlike architecture u ndergo a reversible gelation upon heating. This phenomenon is characterized by slow kinetics and is attributed to the formation of clusters causing a partial dynamic arrest of the swollen interpenetrating spheres at high temp eratures. A kinetic pseudo-phase diagram of gelation temperature against th e effective volume fraction is constructed. Stars with different functional ities exhibit a different sol-gel boundary; small differences in the intern al structure of the stars (regular with spherical dense core vs irregular w ith nonspherical core but spherical overall shape) are presumably responsib le for these differences. Thermal gelation is proposed as an alternative ro ute to jamming of soft materials.