275385 Morphological Characterization of Self-Assembled ABC Triblock Terpolymer Thin Films
Self assembly provides the ability to create well-controlled nanostructures with electronic or chemical functionality that are central to many areas of technological interest including nanolithography, membranes, photonics and OPVs (organic photovoltaic). The utility of diblock copolymers for creation of a wide range of self-assembled nanoscale morphologies with feature size of 10-50 nm is well established. Triblock terpolymers have the potential of creating self-assembled morphologies that are not attainable with diblock copolymers, examples include the CSH (core-shell hexagonal phase), the LAM+BD (lamellar phase with beads inside or at the interface), the HEX+BD (hexagonal phase with beads at the interface), and theTET2 (tetragonal cylinders).
In this study, we have performed three dimensional Self-Consistent Field Theory (SCFT) based simulations to elucidate how interaction parameters and confinement can be used to realize the aforementioned self-assembled morphologies in symmetric linear Triblock terpolymer melts. Specifically, bulk simulations have been performed to ascertain the relationship between the volume fraction of the middle block (B) and formation of lamellae, tetragonal cylinders, spheres and network morphologies. In turn, the effect of confinement on self-assembled structures has been studied. To this end, the influence of neutral parallel walls on self-assembly of the ABC triblock terpolymers at various film thicknesses ranging from d= 0.5-2 L0, where L0 is the bulk domain spacing of the system has been studied. Our result show distinct orientation of different morphologies with respect to the walls for a wide range of film thickness; for instance, lamellae are in perpendicular layers with respect to the neutral confining walls while cylinder layers are formed parallel to them. Finally, we demonstrate how substrate chemistry can be utilized (selective affinity to the middle block) to create a highly desirable morphology for device fabrications, namely, cylindrical domains with square-array symmetry that are formed perpendicular to the substrate. Overall, our simulations demonstrate how surface chemistry and confinement can be used to create a host of novel and technologically relevant morphologies in ABC triblock terpolymers.
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