Confinement of Elastomeric Block Copolymers via Forced Assembly Coextrusion

Abstract

Forced assembly processing provides a unique opportunity to examine the effects of confinement on block copolymers (BCPs) via conventional melt processing techniques. The microlayering process was utilized to produce novel materials with enhanced mechanical properties through selective manipulation of layer thickness. Multilayer films consisting of an elastomeric, symmetric block copolymer confined between rigid polystyrene (PS) layers were produced with layer thicknesses ranging from 100 to 600 nm. Deformation studies of the confined BCP showed an increase in ductility as the layer thickness decreased to 190 nm due to a shift in the mode of deformation from crazing to shear yielding. Postextrusion annealing was performed on the multilayer films to investigate the impact of a highly ordered morphology on the mechanical properties. The annealed multilayer films exhibited increased toughness with decreasing layer thickness and resulted in homogeneous deformation compared to the as-extruded films. Multilayer coextrusion proved to be an advantageous method for producing continuous films with tunable mechanical response.

From equilibrium lamellae to out-of-equilibrium cylinders in triblock copolymer nanolayers obtained via multilayer coextrusion

“…SAXS patterns of these films are also shown for same direction. the orientation factor as the layer thickness decreases has also been observed on PS/SEPS systems [42].…”

“…Then, some heterogeneity in terms of individual layer thicknesses within the sample (standard deviation from the mean in the 15e20% range except for the layers thicker than 250 nm where standard deviation is close to 30%) has been observed (see also Fig. 3) and was attributed by Korley [42] to the effects of elasticity of the BCPs extruded below T odt .…”

Toward Anisotropic Materials via Forced Assembly Coextrusion

“…The ED mechanical data was previously reported. 19 Elastic Modulus. The elastic modulus of alternating lamellar composites has been routinely characterized by the Voigt average model, which considers the modulus and volume fraction of each material component.…”

“…Multilayer films of PS and SEPS were produced via coextrusion technology described in a previous publication. 19 A 257 layer alternating system was extruded with a PS layer on both sides of the films to reduce the adhesion of the elastomer to the chill roll. The total film thickness was varied between 25 and 250 μm at a constant volume composition of 50/50, providing equal layer thicknesses of PS and SEPS.…”

“…19 A cylinder-forming, styrenic BCP was coextruded between nanolayers of polystyrene (PS) in an alternating, lamellar structure and analyzed in uniaxial tension. The films were annealed to remove residual stresses of processing, and as the layer thickness decreased, the extensibility of the system increased by a factor of 12.…”