Shear-Aligned Block Copolymer Monolayers as Seeds To Control the Orientational Order in Cylinder-Forming Block Copolymer Thin Films

Abstract

We study the dynamics of coarsening of a cylinderforming block copolymer thin film deposited on a prepatterned substrate made of a well-ordered block copolymer monolayer. During thermal annealing the shear-aligned bottom layer drives extinction of the disclinations and promotes a strong orientational correlation, disturbed only by dislocations and undulations along the cylinders of the minority phase. The thin film bilayer system remains stable during annealing, in agreement with self-consistent field theory results that indicate that although the thickness of a stack of two monolayers is not at the optimum thickness condition, it is very close to equilibrium. Phase field simulations indicate that the bottom layer remains undisturbed during annealing and acts as a periodic external field that stabilizes the orientation of those domains that share its orientation. Misoriented cylinders are rapidly reorganized through an instability mechanism that drives the fragmentation of the cylinders. As annealing proceeds, the fragmented cylinders are reconstructed along the direction imposed by the ordered bottom layer. This mechanism removes the disclinations completely while leaving dislocations that can be slowly annihilated during annealing. These results indicate that with appropriate control over a single self-assembling polymeric layer, it should be possible to propagate order in thick block copolymer films and to obtain structures with controlled orientational order.

Defects and defect engineering in Soft Matter

“…471 5.3.1 Defect engineering in block-copolymer self-assembly. A common approach to controlling defects in block copolymer self-assembly is to direct it by external fields such as electric fields, shear flow, and chemical guiding patterns on a supporting substrate of a thin film (like guiding lines that attract one component of the block copolymer) or geometric substrate features (like grooves) [472][473][474][475][476][477] Often, the target of such a directed self-assembly is actually to minimize the defect density, and even the fabrication of defect-free structure. Another target of this approach is the formation of device-oriented, irregular or periodic structures.…”

Non‐Native Block Copolymer Thin Film Nanostructures Derived from Iterative Self‐Assembly Processes

“…This method allows the sequential printing of BCP layers on patterned substrates while selecting the crossing angle through the transfer process of the second layer (Figure c,d). Another demonstration of film transfer process was proposed by Abate et al who deposited a free‐standing cylinder‐forming BCP monolayer on top of a shear‐aligned one . The underlying cylinder layer acts then as a seed site to control the ordering of the final assembly during a subsequent thermal annealing step, highlighting the strong orientation coupling induced by the bottom layer.…”

Variational control forces for enhanced sampling of nonequilibrium molecular dynamics simulations

“…[1][2][3] Advances in the theory and modeling of nonequilibrium steady-states [4][5][6] have resulted in an increased interest in trying to understand the behavior in systems out of equilibrium and leverage their versatility to design new functional materials. [7][8][9][10][11][12][13] However, quantifying emergent nonequilibrium behavior with computer simulations is currently hampered by the lack of robust tools to sample the rare fluctuations required to estimate response functions, overcome kinetic bottlenecks, and reach the timescales of experimental relevance. For a generic class of stochastic systems that violate detailed balance, we have developed an algorithm to compute control forces that can be used to enhance the sampling of nonequilibrium steady-states.…”