Polymer dynamics

How does stress relax in a melt of unlinked ring polymers?

Unlinked rings in a melt interpenetrate, but do not reptate as linear chains do; how do they evolve from one "lattice animal" conformation to another, thus relaxing an imposed strain?


An unentangled ring polymer in a network of fixed obstacles (a proxy for the entanglement constraints of other rings in the melt) adopts a doubled-back configuration (green loop), the "backbone" of which (red segments) is called a "lattice animal". The ring moves by withdrawing protruding loops and extending the extra length nearby.

How can we simulate the dynamics of entangled
polymers most efficiently?

How can we increase the efficiency and effectiveness of slipink simulations, widely used to simulate the flow behavior of entangled linear and branched polymers?


A sequence of frames of a single polymer chain in a shear flow (velocity along x, gradient along y). The beads are colored red at one end of the chain, crossing over to blue at the other. Note how the chain stretches, retracts, and "tumbles" end over end.

How do spreading or sintering polymer droplets flow?

The early stages of two viscous droplets "sintering" or flowing together, resembles the spreading of a droplet on a wettable surface. How does the contact area grow with time?


Top: schematic of a spreading viscous polymer drop on a wettable surface. Bottom: micrographs of polystyrene spheres that have been heated to just molten, and allowed to spread on a substrate for a while, then cooled again.

How does the chiral structure of DNA affect its mechanical properties?

How does the "handedness" of DNA molecules reveal itself in terms of the elastic behavior of the molecule as it bends and fluctuates in shape?


DNA strand of three helical repeats, not quite straight, as a result of "restraint" forces that "encourage" the strand to bend. Bending and torsional angles defined in terms of the tangent vectors n1, n2, n3.

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