Stable intermediate phase of secondary structures for semiflexible polymers

Area of Science:

• Polymer physics
• Statistical mechanics
• Computational chemistry

Background:

• The coil-globule transition is a fundamental phenomenon in polymer science.
• Generalized-ensemble Monte Carlo simulations are powerful tools for studying complex systems.
• Conventional statistical methods may lack the sensitivity to detect subtle phase transitions.

Purpose of the Study:

• To investigate the detailed behavior of the coil-globule transition line in polymers.
• To identify distinct structural phases beyond the random-coil and globule states.
• To explore the influence of bending stiffness on polymer conformational transitions.

Main Methods:

• Systematic microcanonical inflection-point analysis applied to extensive generalized-ensemble Monte Carlo simulation data.
• Analysis of polymer structures, focusing on the transition from hairpin to loop formations.
• Comparison of results with conventional canonical statistical analysis.

Main Results:

• A bifurcation of the coil-globule transition line was discovered for polymers with bending stiffness above a critical threshold.
• A distinct intermediate phase, characterized by hairpin and loop structures, was identified between the toroidal and random-coil phases.
• Microcanonical analysis revealed higher sensitivity in detecting these separate phases compared to canonical analysis.

Conclusions:

• Polymer conformational transitions are more complex than previously understood, especially under specific stiffness conditions.
• The discovered bifurcation and intermediate phase necessitate a refined understanding of polymer phase diagrams.
• Advanced analytical techniques like microcanonical inflection-point analysis are crucial for uncovering subtle phenomena in complex systems.