Stretching self-interacting, partially directed, flexible and semi-flexible polymers by an external force

TL;DR

This paper models partially directed, self-interacting polymers under external force, revealing phase transitions between compact and coil states with different order depending on flexibility.

Contribution

It provides an exact solution for the force-temperature phase diagram of directed polymers, including flexible and semi-flexible cases, with new insights into transition orders.

Findings

Flexible polymers exhibit a second-order transition.

Semi-flexible polymers exhibit a first-order transition.

The phase diagrams agree with previous studies for flexible polymers.

Abstract

We study the model of a partially directed flexible or semi-flexible homopolymer on a square lattice, subject to an externally applied force, in a direction either parallel to, or perpendicular to the preferred direction. The polymer is self-interacting and can therefore undergo a collapse transition. We show that this model can be solved and we obtain the force-temperature phase diagrams which, for the case of flexible polymers, agree with that of Brak et al obtained using a different method. At sufficiently low temperatures, the polymer conformation changes from compact to coil state as the force is increased beyond a critical value. This transition is second or first order for the completely flexible or semi-flexible polymer, respectively.