Theoretical Prediction of the Optical Waveguiding Properties of Self-Assembled Block Copolymer Films

Abstract

Block copolymers represent a potentially new class of materials for integrated optics. Before these materials can be used as optical waveguide materials, however, their optical waveguiding properties need to be well understood. In this paper, lamellar-forming block copolymer waveguides are treated and modeled as ideal multilayer structures in which the lamellae are oriented parallel to the substrate and superstrate interfaces. A computer program based on an N-layer waveguide formalism is used to calculate the propagation constants and plot the optical field intensity distributions of some sample diblock and triblock copolymer thin-film waveguides. In a block copolymer thin film, individual block copolymer domains can have anisotropic optical properties due to chain stretching, in the case of coil-coil block copolymers, or due to the presence of a liquid crystalline block, in the case of rod-coil block copolymers.As a result, optical anisotropy of the layers is also treated in the waveguide formalism. Theoretical waveguide calculations show that block copolymer films with a domain size smaller than about A/5 behave optically like homogeneous uniaxial films. Consequently, block copolymers represent a convenient way of making waveguides with a controlled birefringence. In contrast, block copolymer films with a domain size larger than about U3 but less than the wavelength of light are found to preferentially segregate the light into the high refractive index domains. When the low-index layer is at the air interface, only the high-order modes are supported and a greater segregation of the light can be achieved. ABC triblock copolymer films, in which the refractive index of the B and C blocks is larger than that of the A block, are found to exhibit even better confinement of the light into the high-index regions. The optical waveguiding properties predicted for large domain size block copolymers are not seen in single slab homopolymer waveguides and may have potential device applications.

Local Orientation of Polystyrene at the Interface with Poly(methyl methacrylate) in Block Copolymer

“…Polymer alloys represented by block copolymers (BCPs) and polymer blends are one of the most widely studied areas in the field of polymer science and engineering. − In particular, various studies related to the interface for a phase-separated polymer pair have been conducted from the viewpoint of the miscibility and compatibility. − This is because the interfacial structure is of pivotal importance not only for inherent academic interest but also for cutting-edge industrial applications, such as thin film devices, including next-generation lithography, − in addition to the traditional ones based on mechanical − and optical properties. − Polymer chains change the aggregation states at the interface so as to minimize the interfacial energy, which is one of the controlling factors of the interfacial thickness. Thus, it is crucial to obtain a deeper understanding of the phase-separated polymer interface at the molecular level.…”

Stability of a Block-Copolymer Lamella in a Strong Electric Field

“…Researchers are now exploiting this self-assembly to fabricate nanoscale structures [2], either directly from the block-copolymer material [3], as scaffolds for arranging other molecules or nanoparticles [4,5], or as templates for nanolithography [6]. Possible applications and devices include high-density information storage [6], waveguides [7], nanoporous membranes [3,4], and nanowires [5,8]. Although the self-assembly process is exceptionally efficient, it does not always produce the desired pattern; the common examples being that lamellar and cylindrical domains tend to orient parallel to the substrate, as opposed to perpendicular where they exhibit a more useful lateral structure.…”

Hierarchically porous polystyrene membranes fabricated via a CO2-expanded liquid selective swelling and in situ hyper-cross-linking method

“…[1][2][3][4][5] Although a mass of hierarchically porous inorganic materials have been prepared, it is still a challenge to fabricate hierarchical porous polymeric materials. [6][7][8][9][10][11] Currently, the most widely used methodology for creating porosity in polymers is based on the micro-phase separation of block copolymers (BCPs), [12][13][14][15][16][17][18] thus several techniques for preparing hierarchical porous polymeric materials have been devised. For example, Russell et al prepared hierarchically porous polymeric membranes with diblock copolymer polystyrene-b-poly(n-butyl methacrylate) (PS-b-PnBMA).…”