(200h) Elastic Recoil of Flexible Colloidal Chains

Elasticity describes the ability of a material to return to its original shape after being deformed by an external force. Flexible elastomers can be stretched or compressed with minimal force. Extensible elastomers can be stretched significantly before rupturing. We have developed a classic bead-spring-bead model chain to visualize elastic recoil using paramagnetic particles and DNA.  The bending rigidity of these chains can be tuned by adjusting the properties of the DNA. Semiflexible filaments, where the length, L, is comparable to the persistence length, Lp, have been designed.  The driving force for elastic recoil in a rubber-like elastomer is the increased entropy of the relaxed state relative to the stretched state.  We expect that this is the same mechanism controlling elastic recoil in DNA-linked chains.  Our semiflexible chains can be compressed with a magnetic field and the elastic recovery can be visualized.  In the absence of an external magnetic field, the chain is in its relaxed state and has higher entropy because there are many more ways of arranging  than a stretched polymer chain. The effect of an external force is to decrease the entropy, which is recovered when the magnetic field is removed and the chain recoils to its relaxed state.  Understanding how elasticity couples to the hydrodynamics of these chains, resulting in unique chain conformations will be discussed.