Highly ordered, near-single-crystal lamellar films of a triblock copolymer (polystyrene−polybutadiene−polystyrene, PS/PB/PS) were used to study the deformation mechanism of a structure of alternating glassy−rubbery layers, at different orientations of the deformation axis relative to the layer normal. Synchrotron radiation was used for simultaneous in-situ deformation and small-angle X-ray scattering measurements. These were augmented with direct imaging of the structure by transmission electron microscopy. The deformation mechanism depends on the orientation of the force with respect to the structure. Loading parallel to the lamellae results in yielding by propagation of a stable macroscopic neck. The glassy PS layers break up at the neck front, releasing the rubbery layers to achieve high strain. The morphology that develops by deformation of the structure in other directions is an ensemble of new tilt boundaries oriented along the deformation axis. The lamellar normals tilt away from the deformation axis with increasing strain, keeping the lamellar spacing essentially constant. The effect of force applied perpendicular to the lamellae is to fold the layers into a “chevron” morphology, similar to other layered systems such as smectic liquid crystals. At high strain, plastic deformation and fracture of the glassy PS hinges of the “chevron” structure leads to symmetric kink boundaries parallel to the force axis. In addition, nucleation of kink bands around defects and propagation of the kink boundaries into adjacent regions can lead to a similar morphology. The lamellar spacing remains constant during perpendicular stretching, and the tilt angle of the lamellar normal follows the macroscopic deformation in an affine manner. Stretching at 45° forms asymmetric kink boundaries parallel to the force axis. The major limbs of the kink band tilt with increasing strain so that the angle between the lamellar normal and the force axis increases from its initial value of 45°, while the lamellar period remains constant. The minor limbs tilt in the opposite direction and exhibit dilation of the lamellar spacing. Eventually the layers rupture, forming voids at the kink-boundary interfaces. The tilt angle of the major-limb lamellae, as a function of strain, is less than predicted by the affine model. This study suggests a general deformation mechanism for a lamellar structure of alternating glassy and rubbery layers. The layered structure responds to deformation, in any direction other then parallel to the layers, by creating new internal tilt-grain boundaries parallel to the deformation axis. At higher strain the layers yield and subsequently fracture at the kink-boundary interfaces. With increasing strain the lamellar stacks between the kink boundaries tilt toward the deformation axis until they are nearly parallel to it. Since the main features of this mechanism are independent of the initial orientation angle of the layers relative to the deformation axis, it is relevant also to polygranular, globally unoriented lamellar st...

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Films of polystyrene–polybutadiene–polystyrene (PS/PB/PS) triblock copolymer and polystyrene‐poly(ethylene/propylene) (PS/PEP) diblock copolymer were cast from toluene solutions subjected to hydrodynamic flow at room temperature using a device based on a novel casting method we term ‘roll‐casting.’ Polymer solutions were rolled between two corotating eccentric cylinders while at the same time the solvent was removed at a controlled rate. As the solvent evaporated, the block copolymers microphase separated into globally oriented structures. A discussion of the flow field that develops during roll‐casting is presented and specific attention is given to the importance of the shear and elongation rates present. For the triblock and diblock, respectively, the processed structures consisted of polystyrene cylinders assembled on a hexagonal lattice in a polybutadiene matrix, and unidirectional lamellae of alternating polystyrene and polyethylene/propylene. Small‐angle x‐ray scattering (SAXS) and transmission electron microscopy (TEM) indicated the near single‐crystal structure both types of films. SAXS also showed the styrene cylinders and the alternating lamellae to be packed closer together in roll‐cast films than in simple quiescently cast films. A molecular orientation mechanism is proposed to describe both these results as well as the changes in packing and in macroscopic sample dimensions measured after complete solvent evaporation and after sample annealing. © 1993 John Wiley & Sons, Inc.

A poly(styrene-block-isoprene-block-styrene) (SIS) triblock copolymer with a polystyrene (PS) cylinder morphology was processed via roll-casting to produce a near single-crystal texture. Deformation experiments normal to the cylinder axis were carried out using synchrotron small-angle X-ray scattering (SAXS) with the beam both parallel and perpendicular to the cylinder axis. In situ measurement of load and displacement enabled morphological information to be mapped to the stressstrain curve. Results indicate that the deformation proceeds in two stages. Deformation to strains of approximately 100-130% is nearly affine. The rubber matrix extends along the stretching direction (SD) while contraction occurs almost exclusively along the neutral direction due to the constraint imposed by the aligned PS cylinders. A measured Poisson's ratio of 0.9 compares favorably with a value of 1 expected for a perfect composite. At deformations beyond 130% an X-pattern is observed at perpendicular incidence. The angle between the arms of the X increases asymptotically, while the intercylinder spacing remains fairly constant. The initial hexagonal pattern undergoes a continuous distortion and provides further evidence for the deformation discontinuity in the rate of lateral contraction. The morphological observations in reciprocal space are interpreted in terms of a kinking instability in which the plane strain state imposed by the oriented cylinders is relieved by their kinking into a chevron pattern. The kinking transition strain is expected to be dependent on the degree of cylinder misorientation, the shear resistance of the rubber matrix, and the bending resistance of the PS cylinders.

SYNOPSISAn improved technique for casting highly oriented films of block copolymers from solutions subjected to flow is presented. Polymer solutions were rolled between two counter-rotating adjacent c9linders while at the same time the solvent was allowed to evaporate. As the solvent evaporated, the block copolymers microphase separated into globally oriented structures. Using this method known as 'rdl-casting' we present in this paper a study of the morphology of polystyrene-polybutadiene-polystyrene ( P S / PB / PS ) triblock copolymer cast with and without additional high molecular weight homopolymers. The pure copolymer films consisted of polystyrene cylinders assembled on a hexagonal lattice in a polybutadiene matrix in a near single-crystal structure. Blends of copolymer with high molecular weight polystyrene and/ or polybutadiene, phase separated into ellipsoidal regions of homopolymer embedded in an oriented block copolymer matrix. Annealing the films resulted in conversion of the homopolymer regions to spheres accompanied by some misalignment of the copolymer microdomains. The morphology of these films as revealed by TEM is discussed. A brief discussion of the flow field that develops in the experimental system is also presented and its similarity to the flow field of our previous work is shown.

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