[Paper Review] Modeling of polymer phase transition from crystalline to conformationally disordered phase

V. V. Atrazhev, D. V. Dmitriev+1 more|arXiv (Cornell University)|Feb 27, 2026

Polymer crystallization and properties0 citations

TL;DR

A physics-based analytical model describes the crystalline to conformationally disordered phase transition in polymers, calibrated against molecular dynamics simulations for atmospheric pressure and validated at high pressures.

ABSTRACT

A physics-based analytical model describing the phase transition from crystalline to conformationally disordered (condis) crystalline phase is developed. In the model, the free energy is written as a function of temperature and the lattice parameter (mean distance between neighboring chains). It consists of two contributions: elastic and conformational. The elastic contribution describes the interaction between neighboring chains, while the conformational part takes into account the conformation of one chain inside the potential tube, formed by the neighboring chains. To verify this approach, polyethylene - the simplest polymer possessing the condis phase - was chosen as a modeling object. Previous experiments and molecular dynamics simulations show that the typical conformation of a polymer chain in a crystalline phase consists mainly of trans dihedrals and a small fraction of gauche dihedrals, which can be considered as defects of the crystalline lattice. These defects displace the chain inside the tube thus increasing the potential energy. The energy required to form such a defect decreases rapidly with increasing distance between neighboring chains. This leads to a first-order phase transition at a certain temperature to the condis phase, in which distance between neighboring chains is large and a fraction of gauche dihedrals is high. This physical picture of the phase transition is described by the proposed analytical model, the parameters of which were calibrated against the results of molecular dynamics simulations for atmospheric pressure. The model predictions for the pressure of 500 atm and 1000 atm are in perfect agreement with the results of molecular dynamics simulations.

Motivation & Objective

• Develop a physics-based analytical model for the crystalline to conformationally disordered phase transition in polymers.
• express free energy as a function of temperature and lattice parameter (mean interchain distance).
• capture elastic interactions between neighboring chains and conformational energy inside the potential tube formed by neighbors.

Proposed method

• Decompose free energy into elastic and conformational contributions.
• Describe interchain interactions with an elastic term.
• Model the conformational energy of a single chain within a tube defined by neighboring chains.
• Calibrate model parameters against molecular dynamics simulations at atmospheric pressure.
• Use the model to predict phase behavior and compare with MD results at 500 atm and 1000 atm.

Experimental results

Research questions

• RQ1 What is the form of the free-energy landscape governing the crystalline to condis phase transition?
• RQ2 How do elastic and conformational contributions drive the transition as temperature and interchain distance change?
• RQ3 Can the analytical model reproduce MD-observed transition pressures and conformational defect energetics?

Key findings

• The model yields a first-order phase transition to the condis phase as interchain distance increases and gauche defect fraction grows.
• Defect formation energy decreases rapidly with increasing neighboring-chain distance, promoting the phase change.
• Model parameters calibrated against MD simulations at atmospheric pressure.
• Predictions for 500 atm and 1000 atm agree with MD results.
• The condis phase is characterized by larger interchain distances and higher gauche defect fractions.