Polymer ejection from strong spherical confinement

TL;DR

This study investigates the dynamics of polymer ejection from a spherical capsid under strong confinement, revealing exponential growth in ejection time related to confinement free energy and finite-size effects influencing ejection behavior.

Contribution

It provides new insights into the exponential dependence of ejection time on the number of ejected monomers and links this to confinement free energy growth, using high-density molecular dynamics simulations.

Findings

Ejection time grows exponentially with the number of ejected monomers.

Confinement free energy increases exponentially with initial monomer count.

Ejection process is dominated by internal pressure and shows finite-size effects.

Abstract

We examine the ejection of an initially strongly confined flexible polymer from a spherical capsid through a nanoscale pore. We use molecular dynamics for unprecedentedly high initial monomer densities. We show that the time for an individual monomer to eject grows exponentially with the number of ejected monomers. By measurements of the force at the pore we show this dependence to be a consequence of the excess free energy of the polymer due to confinement growing exponentially with the number of monomers initially inside the capsid. This growth relates closely to the divergence of mixing energy in the Flory-Huggins theory at large concentration. We show that the pressure inside the capsid driving the ejection dominates the process that is characterized by the ejection time growing linearly with the lengths of different polymers. Waiting time profiles would indicate that the superlinear dependence obtained for polymers amenable to computer simulations results from a finite-size effect due to the final retraction of polymers' tails from capsids.