Nonbound dislocations in hexagonal patterns: pentagon lines in surface-tension-driven Bénard convection

Area of Science:

• Fluid dynamics
• Materials science
• Nonlinear dynamics

Background:

• Surface-tension-driven Bénard convection exhibits pattern transitions.
• Hexagonal convection cells are a common initial state.
• Defects within these patterns influence pattern evolution.

Purpose of the Study:

• To identify and characterize novel defects in hexagonal patterns.
• To elucidate the formation mechanism of these new defects.
• To understand the role of these defects in pattern transitions.

Main Methods:

• Analysis of defect structures in hexagonal patterns.
• Investigating defect transformations under varying supercriticality.
• Observing the role of dislocation glide and climb mechanisms.

Main Results:

• A novel class of defects, termed pentalines, has been identified.
• Pentalines originate from penta-hepta defects (PHD) at higher supercriticality.
• Pentalines are composed of two nonbound dislocations, parallel to the roll axis.

Conclusions:

• Pentalines are key intermediaries in the transition from hexagonal to square convection cells.
• The transformation of PHD into pentalines involves dislocation glide and climb.
• Understanding pentalines offers insights into pattern selection in Bénard convection.