Collapse transition in polymer models with multiple monomers per site and multiple bonds per edge

Area of Science:

• Statistical Mechanics
• Polymer Physics
• Computational Modeling

Background:

• Investigating polymer behavior in solution is crucial for understanding complex systems.
• Previous studies on multiple monomer per site (MMS) models suggested discontinuous phase transitions.

Purpose of the Study:

• To explore the thermodynamic behavior of MMS polymer models using Monte Carlo simulations.
• To clarify the nature of phase transitions (continuous vs. discontinuous) in these models.
• To compare models with allowed (RA) and forbidden (RF) walk reversals.

Main Methods:

• Extensive Monte Carlo simulations on square and cubic lattices.
• Analysis of polymer models with varying numbers of monomers per site (K=2, 3).
• Calculation of thermodynamic properties, including critical exponents (νt, ϕt, γt) and second virial coefficient.

Main Results:

• Both RA and RF versions of MMS models show identical thermodynamic behavior.
• In 3D, coil and globule phases are separated by a continuous line of Θ points, confirmed by exponents and second virial coefficient.
• No discontinuous collapse transition was observed, contrary to prior claims.

Conclusions:

• MMS polymer models exhibit continuous coil-globule transitions.
• The nature of the transition is independent of walk reversal rules.
• Previous observations of bimodality were likely artifacts near the Θ line.