Coarse-grained molecular dynamics modeling of the kinetics of lamellar block copolymer defect annealing

Protracted Colored Noise Dynamics Applied to Linear Polymer Systems

“…To determine the kinetic rate of defect annihilation in BCP simulations, defects were intentionally built into initial simulations and then allowed to heal, as done in previous simulations . Simulation volumes were five times the natural lamellar repeat distance of the BCP in the x dimension, three times the natural repeat distance of the BCP in the y dimension, and equal to the natural repeat distance of the BCP in the z dimension.…”

“…They were initialized with chains randomly placed in the simulation volume as described in Section . After initial minimization, an external potential was applied to produce a defect (see Peters et al for details of external potential). Once the defect formed, the external potential was turned off and the simulation continued, allowing defect annihilation.…”

“…[6,[33][34][35][36] The data for the defect annihilation rate for a BCP of length N = 64 at various χN values without PCND (using the simulations from Peters et al [6] ) is shown by the black data points in Figure 7A. While the rate of defect annihilation remains relatively constant at low χN, suggesting a barrier free transition at low χN, [6,33] the rate drastically drops after a χN of ∼30. If the rates are extrapolated to χN = 55, a simulation would need to run for approximately a year on the hardware used here to observe defect annihilation.…”

“…Annealing of defects in such morphologies is challenging because of the energetic incompatibility of the two blocks, indicated by a relatively high Flory–Huggins enthalpy of mixing parameter (χ) of the two differing blocks in the polymer. The product of this parameter and the number of monomeric units in the blocks ( χN ) must be sufficiently high to result in phase separation, but this increases the transition energy of the defect annealing because the blocks must diffuse through domains of each other . Coarse‐grained simulations of defects using relatively short BCPs at realistic χN values would require simulations on the timescale of months or years to anneal a single defect.…”

“…The product of this parameter and the number of monomeric units in the blocks (χN) must be sufficiently high to result in phase separation, but this increases the transition energy of the defect annealing because the blocks must diffuse through domains of each other. [6] Coarse-grained simulations of defects using relatively short BCPs at realistic χN values would require simulations on the timescale of months or years to anneal a single defect. Field models, such as Self-Consistent Field Theory, [5] do not always accurately model certain phenomena such as fluctuations, [7] or nonpolymeric objects, [8,9] and often have difficulty addressing dynamics or nonequilibrium states and properties.…”