Electric Field Alignment of Asymmetric Diblock Copolymer Thin Films

Abstract

The electric field alignment of cylindrical microdomains in diblock copolymer thin films was studied using small-angle neutron scattering and transmission electron microscopy. The alignment process was followed with the block copolymer films in different initial states. Starting from a poorly ordered state, the cylindrical microdomain orientation was biased by the surface field that initially drove the cylindrical microdomains to be oriented parallel to the film surface. With further annealing, the cylinders were disrupted locally and formed ellipsoid-shaped microdomains that, with time, connected into cylindrical microdomains oriented in the field direction. Starting from an ordered state with cylinders parallel to the surface, the applied electric field enhanced fluctuations at the interfaces of the microdomains. The growth of the fluctuations continued until the cylindrical microdomains broke up into spherical microdomains, similar to that seen in the thermoreversible cylinder-to-sphere order−order transition. With time, the spherical microdomains deformed into ellipsoidal domains that reconnected into cylindrical microdomains oriented at ∼45° with respect to the applied field direction. Further annealing aligned the tilted cylinders along the applied field direction. This reorientation process was much slower than from the poorly ordered state. The details of the realignment process are supported by computer simulations based on dynamic self-consistent-field theory.

Block Copolymer Nanolithography: Translation of Molecular Level Control to Nanoscale Patterns

“…For example, electric fields have been successfully used to align BCP microstructures. [26,[61][62][63][64][65][66][67][68][69] The driving force is the differences in the dielectric constants, De, between blocks, and anisotropic microdomains, like cylinders or lamellae, were aligned in the direction of applied electric fields. However, complete alignment of the microdomains is not always achieved, as the applied electric fields compete with interfacial interactions that lead to a parallel orientation adjacent to the substrate.…”

Effects of Annealing Solvents on the Morphology of Block Copolymer-Based Supramolecular Thin Films

“…3−7 To do so, the above-mentioned two interactions need be eliminated or overcome, which has been achieved by surface modifications, 3,8−15 external stimuli, 16,17 and nonequilibrium approaches. 18−21 Another strategy that has been proven to be efficient is the supramolecular assembly.…”

Electroactive Nanostructured Polymers as Tunable Actuators

“…[1,18] The VHB4910 acrylic adhesive manufactured by 3M Co. (Minneapolis, MN) exhibits the largest actuation strain in this class of materials. Independent experimental [19][20][21] and theoretical [22] studies designed to elucidate the electric-field-induced response of another class of macromolecules, microphase-separated block copolymers, have been conducted in an ongoing effort to control nanostructural orientation for various emerging nanotechnologies such as optical waveguides. [23] Linear block copolymers consist of two or more chemically different homopolymers covalently linked together to form a single macromolecule.…”

“…[24,25] Such molecular self-assembly similarly transpires in the presence of other organic species (e.g., low-molar-mass solvents or other macromolecules). [26][27][28][29] Russell and co-workers have established that, due to polarizability differences between the constituent blocks, the lamellar [19] and cylindrical [21] morphologies of poly(styrene-b-methyl methacrylate) block copolymer thin films can be (re)aligned in a DC electric field. Nanostructural alignment in a block copolymer thin film is likewise achieved by annealing the film in solvent vapor, which serves to alter viscosity, interfacial tension, and surface segregation.…”