Lamellar ordering in computer-simulated block copolymer melts by a variety of thermal treatments

Summary: We describe the results of Monte Carlo simulations, based on the cooperative motion algorithm, of the lamellar structure generated at finite temperature by a symmetric diblock copolymer. The (70 × 70 × 70) simulation box in which the polymer chains were embedded for each simulation was rotated, based on the interface orientation, to bring the interfacial planes of the simulated structure into parallel. We found that the interface thickness, as defined by the distribution of the junction points, became narrower at lower temperature, and that the interface plane was characterized by a waviness with a maximum peak‐to‐valley distance of 20–30 lattice bonds. Compared with the isotropic state (T/N = ∞), chains at lower temperatures were stretched in the direction perpendicular to the interface; but only modestly compressed in the direction parallel to the interface. Individual block chains within the lamellar domains still behave like random coils. The block copolymer molecules exhibit only a modest tendency to orient themselves with their end‐to‐end vector perpendicular to the plane of the lamellar interface. Considered as an ensemble average, the results we obtained are similar to those reported from small angle neutron scattering measurements for the mean conformation of the PSd blocks of symmetrical PSd‐PVP diblock copolymers.2‐D projections onto the X‐Z plane of the end beads for the A‐ and B‐chains (gray) and the junction points J (black) at T/N = 0.2. The interface plane is oriented parallel to the Y‐Z plane by rotating the simulation box. The distribution profiles of junction points and the end beads across the system in the direction of interface normal are shown in the lower part of the figure.image2‐D projections onto the X‐Z plane of the end beads for the A‐ and B‐chains (gray) and the junction points J (black) at T/N = 0.2. The interface plane is oriented parallel to the Y‐Z plane by rotating the simulation box. The distribution profiles of junction points and the end beads across the system in the direction of interface normal are shown in the lower part of the figure.

Section: Determination Of the Orientation Of Lamellar Interfacementioning

confidence: 99%

Interface Orientation and Chain Conformation in Simulated Symmetric Diblock Copolymer Lamellar Systems

Yang

Winnik

Pakuła

2005

“…Several former simulations of block copolymer systems have identified that there are one or two peaks in each C v curve. [38,[51][52][53] In the case where only one peak is identified, the peak is usually considered as order-disorder transition (ODT) related. [38,51,53] Using a cooperative motion algorithm, Banaszak et al observed a low-temperature C v peak besides the ODT related one from quenching simulations.…”

Section: The Variation Of Morphologies and Chainmentioning

confidence: 99%

“…[38,51,53] Using a cooperative motion algorithm, Banaszak et al observed a low-temperature C v peak besides the ODT related one from quenching simulations. [52] Furthermore, we perform a detailed examination of morphologies as a function of the reduced temperature to locate the ODT. We find that each system commences an ordered morphology from the disordered state with a slight variation in T, and typical examples are shown in Figure 17.…”

Section: The Variation Of Morphologies and Chainmentioning

confidence: 99%

Simulated Annealing Study of Self‐Assembly of Symmetric ABA Triblock Copolymers Confined in Cylindrical Nanopores

Wang

Jin

et al. 2008

We report a simulated annealing study of the self‐assembly of symmetric lamella‐forming ABA triblock copolymers confined in cylindrical nanopores. We systematically examine the dependence of the self‐assembled morphologies and structural parameters on the degree of confinement and the strength of the surface preference. We find that the confined morphologies for the symmetric ABA triblocks with fA = 1/2 are similar to those for the symmetric or nearly symmetric AB diblock copolymers under the same confinement. We also find that different structural parameters can reflect different information. The predicted bridging fraction value for the bulk phase is in good agreement with previously established values, whereas the predicted values for the confined morphologies change with both the degree of confinement and the strength of the surface preference. We further explore the self‐assembling process by examining the morphology and various ensemble‐averaged thermodynamic quantities and structure parameters as a function of the reduced temperature.

“…This is because the possible arrangements of the triblock chains are different from those of the diblock chains. In particular, the triblock chains can form loop and bridge configurations, which are distinguishable in the ordered microphases 9–11. In a loop configuration both ends of the B block are located on the same interface, whereas in the bridge configuration the two ends lie on different interfaces 7…”

Section: Introductionmentioning

confidence: 99%

Self‐Assembly of Cylinder‐Forming ABA Triblock Copolymers under Cylindrical Confinement

Wang

Jin

et al. 2008

The self‐assembly of two types of linear ABA triblock copolymers confined in cylindrical nanopores is studied using simulated annealing. The effects of pore size and block copolymer chain architecture on morphology, chain conformations and bridging fraction are investigated. For the bulk cylinder‐forming copolymers, novel structures such as helices and stacked toroids form, which depend sensitively on the pore size. Several significant differences between the two types of copolymers are predicted and explained based on the differences in their chain conformations and chain architectures. A simple model is proposed to explain the mean square radius of gyration for the bridge and loop chains.magnified image