Lamellar diblock copolymer grain boundary morphology. 1. Twist boundary characterization

Abstract

Grain boundary morphologies in poly(styrene-6-butadiene) lamellar diblock copolymers were characterized using transmission electron microscopy (TEM). Two types of twist grain boundaries were observed in which microphase separation of the two blocks was maintained in the grain boundary region by intermaterial dividing surfaces that approximate classically known minimal surfaces. The geometry of these interfaces was demonstrated by comparing experimental TEM images with ray tracing computer simulations of the model surfaces as the projection direction was systematically varied in both the experimental and simulated images. The two morphologies observed were found to have intermaterial dividing surfaces that approximate either Scherk's first (doubly periodic) surface or a section of the right helicoid. The helicoid section boundary was observed at low twist angles, less than or equal to about 15°. The Scherk surface family of boundary morphologies, which consists of a doubly periodic array of saddle surfaces, was found over the entire twist range from 0 to 90°. As the twist angle approaches 0°the Scherk surface grain boundary morphology is transformed into a single screw dislocation that has an intermaterial dividing surface with the geometry of a single helicoid. Direct TEM imaging of the detailed core structure of this screw dislocation is presented. These images demonstrate that in the lamellar diblock copolymer the screw dislocation core is nonsingular. This nonsingular core structure represents a radical classical studies of dislocations in atomic crystals.

High strain rate deformation of layered nanocomposites

“…In all impacts, kink bands are found at the sides of the penetration path. The lateral forces on the thin lamellar layers lead to the common kink-type shear band formation events seen in previous studies of slowly deformed (strain rateso1 s À 1 ) single crystal bulk block-copolymers studied using in situ small-angle X-ray scattering 22,28,29 and/or postmortem transmission electron microscopy 30 . The slowest (0.5 km s À 1 ) impact, shows kink bands near the surface created by an initial penetration of the mprojectile (Fig.…”

Twist grain boundaries in three-dimensional lamellar Turing structures

“…2) in the region where lam patterns are found: when starting from random initial conditions we often obtain structures exhibiting various perfect lamellar regions oriented orthogonally to one another and linked by boundaries whose thickness is of the order of the wavelength of the lam. This is reminiscent of the kind of TGB found in block copolymers (34) and amphiphilic systems or smectic liquid crystals (35).…”

Measuring Relative Grain-Boundary Energies in Block-Copolymer Microstructures

“…The occurrence of GB defects is inherent in quiescent organized blockcopolymer (BCP) microstructures and can be related to the nucleation and growth of ordered grains during the structure evolution process, the interaction of disclinations, or mechanically induced kinking because of inhomogeneous solvent evaporation during the late stages of film formation. The basic phenomenology of GB structures in BCP materials was first discussed by Gido and Thomas who classified and evaluated the various GB types associated with tilt and twist deformations of lamellar BCPs [6][7][8][9]. Subsequent experimental studies revealed the relevance of process parameters (such as the application of shear fields), molecular architecture, and composition on GB formation as well as the implications of GB defects on, for example, the permeability of BCP materials [10][11][12][13][14][15][16][17].…”