Stretching self-entangled DNA molecules in elongational fields.

Area of Science:

• Polymer Physics
• Biophysics
• Rheology

Background:

• Entanglements and knots in polymers significantly influence their mechanical properties.
• Understanding polymer stretching dynamics is crucial for various applications, from materials science to molecular biology.

Purpose of the Study:

• To experimentally investigate the stretching dynamics of self-entangled DNA molecules under planar elongational flow.
• To compare the stretching behavior of entangled DNA with unentangled DNA.
• To provide direct experimental evidence for topological friction in polymers.

Main Methods:

• Experiments involving stretching of self-entangled and unentangled DNA molecules using a planar elongational field.
• Observation and analysis of molecular configurations during stretching.
• Comparison of stretching dynamics and transient states.
• Modeling the experimental observations using a dumbbell model.

Main Results:

• Self-entangled DNA molecules exhibit a stage-wise stretching behavior with an "arrested" state.
• Stretching dynamics of entangled DNA are significantly slower (by an order of magnitude) than unentangled DNA.
• Entangled molecules show transient states with protruding ends from a knotted core, distinct from unentangled polymers.
• Experimental data is qualitatively and semi-quantitatively reproduced by a dumbbell model.

Conclusions:

• Direct experimental evidence of topological friction in polymer stretching is presented.
• Entanglements and knots dramatically alter polymer stretching dynamics, introducing significant delays.
• The study validates a dumbbell model for describing the behavior of knotted and entangled DNA molecules.