Structural changes upon annealing in a deformed styrene-butadiene-styrene triblock copolymer as revealed by infrared dichroism

Zhao, Yue

doi:10.1021/ma00044a035

Cited by 32 publications

(29 citation statements)

References 3 publications

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“…39 The feasibility for the determination of the molecular orientation of both the PS and rubbery midblocks has been shown for unoriented samples using infrared dichroism. 40,41 Wide-angle X-ray scattering (WAXS) indicates that the rubbery . Schematic of the post-kink deformation process at perpendicular incidence.…”

Section: Discussionmentioning

confidence: 99%

Perpendicular Deformation of a Near-Single-Crystal Triblock Copolymer with a Cylindrical Morphology. 1. Synchrotron SAXS

et al. 2000

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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.

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Section: Discussionmentioning

confidence: 99%

Perpendicular Deformation of a Near-Single-Crystal Triblock Copolymer with a Cylindrical Morphology. 1. Synchrotron SAXS

et al. 2000

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“…In principle, the index modulation depth of the second grating could come from three contributions: different PB chain orientations, different arrangements of PS cylindrical microdomains, or different azobenzene conformations and alignments. It has been shown from birefringence [30] and infrared dichroism measurements [34] that residual PB chain orientation exists in relaxed SBS films. Therefore, in a relaxed AE film after writing of the second grating, different residual PB orientations and different arrangements for PS cylindrical domains may exist in the excited and non-excited areas.…”

Section: Full Papermentioning

confidence: 99%

“…This implies that different residual PB chain orientations in the excited and non-excited areas could be the primary factor for the stable grating in the relaxed film. When the film is stretched, the index modulation depth may actually increase at modest strains, since different arrangements of PS cylindrical domains (anisotropic crosslink points) may lead to different PB chain orientations, [29,30,34] while under large strains the difference in PB chain orientation would become less important, resulting in a decrease in Dn. This would explain the results in Figure 8.…”

Section: Full Papermentioning

confidence: 99%

Holographic Recording in a Photoactive Elastomer

Zhao¹,

Bai

Asatryan

et al. 2003

Adv Funct Materials

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This work explores the use of photoactive elastomers as elastic holographic materials. Holographic gratings were recorded on stretched films of an azobenzene elastomer, which is composed of a side‐chain liquid‐crystalline polymer with azobenzene mesogens, grafted to the rubbery polybutadiene block of a styrene–butadiene–styrene (SBS) triblock copolymer. The grating‐formation dynamics measurements revealed the formation of two gratings of different natures resulting from the coupled mechanical and optical effects. A first grating, formed quickly upon exposure, is due to the photoisomerization of oriented azobenzene groups. A second grating, developed at longer exposure times, may originate from changes in the anisotropic structure of the SBS matrix, which is induced by the photochemical phase transition of azobenzene mesogens. The first grating is unstable, but the second grating remains in relaxed films. Both mechanisms can be enhanced by deformation of the film.

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“…Since the orientation behavior with strain is closely related to the changes in the microdomain structures, the studies of the molecular orientation by IR can be applied for the investigation of the deformation mechanism. Zhao 18 was probably the first to discuss the molecular orientation in terms of the structural changes with strain. He studied the structural relaxation in the stretched SBS copolymers with cylindrical microdomains of PS.…”

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confidence: 99%

Morphology and Deformation Mechanisms and Tensile Properties of Tetrafunctional Multigraft Copolymers

et al. 2009

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Morphology and deformation mechanisms and tensile properties of tetrafunctional multigraft (MG) polystrene-g-polyisoprene (PS-g-PI) copolymers were investigated dependent on PS volume fraction and number of branch points. The combination of various methods such as TEM, real time synchrotron SAXS, rheo-optical FTIR, and tensile tests provides comprehensive information at different dimension levels. TEM and SAXS studies revealed that the number of branch points has no obvious influence on the microphase-separated morphology of tetrafunction MG copolymers with 16 wt % PS. But for tetrafunctional MG copolymers with 25 wt % PS, the size and integrity of PS microdomains decrease with increasing number of branch point. The deformation mechanisms of MG copolymers are highly related to the morphology. Dependent on the microphase-separated morphology and integrity of the PS phase, the straininduced orientation of the PS phase is at different size scales. Polarized FT-IR spectra analysis reveals that, for all investigated MG copolymers, the PI phase shows strain-induced orientation along SD at molecular scale. The proportion of the PI block effectively bridging PS domains controls the tensile properties of the MG copolymers at high strain, while the stress-strain behavior in the low-mediate strain region is controlled by the continuity of PS microdomains. The special molecular architecture, which leads to the higher effective functionality of PS domains and the higher possibility for an individual PI backbone being tethered with a large number of PS domains, is proposed to be the origin of the superelasticity for MG copolymers.

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Structural changes upon annealing in a deformed styrene-butadiene-styrene triblock copolymer as revealed by infrared dichroism

Cited by 32 publications

References 3 publications

Perpendicular Deformation of a Near-Single-Crystal Triblock Copolymer with a Cylindrical Morphology. 1. Synchrotron SAXS

Perpendicular Deformation of a Near-Single-Crystal Triblock Copolymer with a Cylindrical Morphology. 1. Synchrotron SAXS

Holographic Recording in a Photoactive Elastomer

Morphology and Deformation Mechanisms and Tensile Properties of Tetrafunctional Multigraft Copolymers

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