title: Control of the orientation of symmetric poly(styrene)-block-poly(D,L-lactide) block copolymers using statistical copolymers of dissimilar composition.
abstract: The interactions of block copolymers with surfaces can be controlled by coating those surfaces with appropriate statistical copolymers. Usually, a statistical copolymer comprised of monomer units identical to those of the block copolymer is used; that is, typically a poly(styrene)-stat-poly(methyl methacrylate) (PS-stat-PMMA) is used to direct the alignment of poly(styrene)-block-poly(methyl methacrylate) (PS-block-PMMA), and poly(styrene)-stat-poly(2-vinylpyridine) (PS-stat-P2VP) has been used for poly(styrene)-block-poly(2-vinylpyridine) (PS-block-P2VP). Reports of controlling the orientation of block copolymers with statistical copolymers with a dissimilar composition are limited. Here, we demonstrate that this method can be further extended to show that PS-stat-PMMA can be used to control the wetting properties of poly(styrene)-block-poly(D,L-lactide) (PS-block-PDLA). Surfaces were modified with a series of cross-linked PS-stat-PMMA-stat-glycidyl methacrylate terpolymers, and the surface chemistries and energies were assessed using angle-dependent X-ray photoelectron spectroscopy and the two-liquid harmonic method, respectively. From these experiments, an expected neutral compositional window was identified for symmetrical PS-block-PDLA. Moreover, high-resolution SEM, AD-XPS, and grazing-incidence SAXS measurements were used to evaluate the morphology of PS-block-PDLA as a function of the surface composition of the underlying cross-linked copolymer films, and the neutral composition was found to range from 32 to 38 mol % of PS, in the bulk polymer. Ultimately, we demonstrated the determination of nonpreferential surface compositions that allow the self-assembly of lamellae with sizes in the sub-10 nm regime that are oriented perpendicular to the substrate. These findings have important implications for the use of PS-block-PDLA block copolymers in directed self-assembly, most specifically in advanced lithographic processes.
authors.affiliation: Australian Institute of Bioengineering and Nanotechnology, The University of Queensland, St. Lucia, Queensland 4072, Australia.
authors.forename: Imelda
authors.initials: I
authors.lastname: Keen
authors.forename: Anguang
authors.initials: A
authors.lastname: Yu
authors.forename: Han-Hao
authors.initials: HH
authors.lastname: Cheng
authors.forename: Kevin S
authors.initials: KS
authors.lastname: Jack
authors.forename: Timothy M
authors.initials: TM
authors.lastname: Nicholson
authors.forename: Andrew K
authors.initials: AK
authors.lastname: Whittaker
authors.forename: Idriss
authors.initials: I
authors.lastname: Blakey
mesh_terms: D015394:Molecular Structure; D011091:Polyesters / Q000737:chemistry*; D011137:Polystyrenes / Q000138:chemical synthesis / Q000737:chemistry*
chemical_list: D011091:Polyesters; D011137:Polystyrenes; C579785:poly(styrene)-block-poly(D,L-lactide); C033616:poly(lactide)