Magnetic field alignment of block copolymers and polymer nanocomposites: Scalable microstructure control in functional soft materials

Abstract

Block copolymers (BCPs) offer an exciting range of structures and functions that are of potential utility in existing as well as emerging technologies. Although this is generally acknowledged, with few exceptions, viable strategies for establishing scalable and robust control of BCP microstructure are underdeveloped. Magnetic field alignment offers great potential in this regard. The physics bears much in common with electric field alignment, but the absence of dielectric breakdown concerns and the more flexible, space pervasive nature of magnetic fields make it possible to design processes for high-throughput fabrication of well-ordered films with appro-priate materials. In this perspective, we highlight the use of magnetic fields for control of microstructure in BCPs as well as polymer nanocomposites involving anisotropic nanomaterials. A brief review of efforts to date is given. Open questions related to field-polymer interactions and future directions for magnetic alignment of these systems are discussed. V C 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 50: 2-8, 2012

Order-Disorder Transition and Alignment Dynamics of a Block Copolymer Under High Magnetic Fields byIn SituX-Ray Scattering

“…Thus, we expect as shown in Eq. (2) and that the orientational order parameter which captures the degree of alignment evolves exponentially according to this time scale as hP 2 i $ 1 À exp ðÀt=Þ [30,33]. Any contributions from the influence of the field on the order parameter Á are small as discussed above and can be reasonably neglected.…”

“…Because of the absence of dielectric breakdown concerns and their space pervasive nature, magnetic fields are particularly well suited for this purpose. They couple to the magnetic susceptibility anisotropy, Á, and effectively permit arbitrary control of texture in appropriately field-responsive materials, even in complex geometries [2]. Typical block copolymers (BCPs) such as poly(styrene-b-methyl methacrylate) exhibit vanishingly small anisotropies with Á Oð10 À9 Þ (SI units).…”

Block copolymer–nanoparticle composites: Structure, functional properties, and processing

“…The difference in magnetic susceptibility between two adjacent polymeric domains in BCPs is typically small [330], therefore improving the alignment of ordered BCPs by applying magnetic field is difficult. However, incorporation of magnetic NPs can enhance the magnetic susceptibility contrast between two adjacent polymeric domains [331] and thus, can facilitate the alignment of BCP-NP composites upon the application of a magnetic field [332][333][334].…”

Magnetic Alignment of Block Copolymer Microdomains by Intrinsic Chain Anisotropy

“…Under appropriate circumstances, magnetic fields can also dictate the alignment of BCP mesophases in a highly efficacious manner [6]. Orientational order develops due to anisotropic field interactions that are sufficiently large to overcome thermal forces.…”