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Defect Annihilation Pathways in Directed Assembly of Lamellar Block Copolymer Thin Films
Hur, Su-Mi,Thapar, Vikram,Ramí,rez-Herná,ndez, Abelardo,Nealey, Paul F.,de Pablo, Juan J. American Chemical Society 2018 ACS NANO Vol.12 No.10
<P>Defects in highly ordered self-assembled block copolymers represent an important roadblock toward the adoption of these materials in a wide range of applications. This work examines the pathways for annihilation of defects in symmetric diblock copolymers in the context of directed assembly using patterned substrates. Past theoretical and computational studies of such systems have predicted minimum free energy pathways that are characteristic of an activated process. However, they have been limited to adjacent dislocations with opposite Burgers vectors. By relying on a combination of advanced sampling techniques and particle-based simulations, this work considers the long-range interaction between dislocation pairs, both on homogeneous and nanopatterned substrates. As illustrated here, these interactions are central to understanding the defect structures that are most commonly found in applications and in experimental studies of directed self-assembly. More specifically, it is shown that, for dislocation dipoles separated by several lamellae, multiple consecutive free energy barriers lead to effective kinetic barriers that are an order of magnitude larger than those originally reported in the literature for tightly bound dislocation pairs. It is also shown that annihilation pathways depend strongly on both the separation between dislocations and their relative position with respect to the substrate guiding stripes used to direct the assembly.</P> [FIG OMISSION]</BR>
Son, Jeong Gon,Kang, Huiman,Kim, Ki-Yeon,Lee, Jung-Soo,Nealey, Paul F.,Char, Kookheon American Chemical Society 2012 Macromolecules Vol.45 No.1
<P>We systematically investigated the effect of surfactant addition on the orientational change in polystyrene-<I>block</I>-poly(methyl methacrylate) (PS-<I>b</I>-PMMA) block copolymer films as a function of film thickness and surfactant (oleic acids (OAs)) concentration using microscopic analysis, neutron reflectivity, and theoretical calculations. The orientation of PS-<I>b</I>-PMMA films containing OAs as surfactants was found to be determined by the competitions among the surfactant-assisted neutral field and preferential fields at both top surface and bottom interface. In the case of a BCP film containing a small amount of OAs, the integer film thickness of domain spacing <I>L</I><SUB>0</SUB> (long spacing of lamellae-forming BCP) prefers to form the perpendicular orientation of microdomains while the parallel orientation is observed when the film thickness is close to the half-integers of <I>L</I><SUB>0</SUB>. We also found that the periodic orientation of block domains gradually dies out to the perpendicular orientation as the film thickness as well as the surfactant concentration is increased. Neutron reflectivity analysis of <I>deuterated</I> polystyrene-<I>block</I>-poly(methyl methacrylate) (<I>d</I>PS-<I>b</I>-PMMA) block copolymer thin films containing OA surfactants was also performed to gain insights into the orientation of BCP films across film thickness due to the addition of OAs. With the free energy calculations on BCPs mixed with OA surfactants at different film thicknesses, the periodic orientation of block domains is qualitatively confirmed.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/mamobx/2012/mamobx.2012.45.issue-1/ma201435v/production/images/medium/ma-2011-01435v_0010.gif'></P>