Correlation between Molecular Architecture, Morphology, and Deformation Behaviour of Styrene/Butadiene Block Copolymers

Abstract

The correlation between the molecular architecture, morphology, and micromechanical deformation behaviour of styrene/butadiene (SB) block copolymers with different architectures (linear and star block copolymers, total styrene content, ΦST = 0.74) was studied using dynamic mechanical analysis (DMA), uniaxial tensile testing, scanning force microscopy (SFM), and high voltage electron microscopy (HVEM). Deformation of the individual phases under uniaxial strain at the molecular level was monitored by Fourier transform infrared (FT‐IR) spectroscopy. It was demonstrated that the morphology and deformation behaviour of these block copolymers are strongly influenced by their molecular topology, block symmetry, and the nature of the interface between the component blocks. While the cylindrical morphology (hexagonal polybutadiene (PB) cylinders in polystyrene (PS) matrix) was observed in a symmetric SBS triblock copolymer with ΦST = 0.74, a “two‐component three‐phase” morphology was found in an asymmetric star block copolymer having an equivalent chemical composition and an SBS arm structure. Likewise, an SBS triblock copolymer with a composition identical to the former ones but with highly asymmetric PS end blocks revealed a lamellar morphology. While no locally confined deformation zones were observed in the lamellar block copolymers, the cylindrical block copolymer was found to deform through the formation of highly localised craze‐like deformation zones.

Intrinsic extracellular matrix properties regulate stem cell differentiation

“…1A), the presence of matrix itself seems to be supportive of the moderate differentiation observed. However just as on planar substrates, terminal differentiation and a better mechanistic understanding of matrix-directed lineage specification is likely to require the improved mimicry of appropriately spaced adhesion sites (Adhikari et al, 2003;Maniadis et al, 2008) to produce optimal force production. Once attached in/on a matrix, the cell begins to pull and probe its environment, and thus extensive differences in the mechanical behavior of cells are likely to exist between planar and 3D materials.…”

Fracture Behaviour of Styrene/Butadiene Block Copolymers having Different Molecular Architecture

“…The latter is strongly affected by the molecular architecture. [14] Though small, a clear indication of higher crack toughness of lamellar block copolymers than that of a cylindrical one having PS matrix was observed. However, both lamellar and cylindrical (with PS matrix) block copolymers exhibited qualitatively similar linear-elastic behaviour and an unstable crack growth mechanism.…”

“…The details of the morphology of the block copolymers used may be found in ref. [10,11,14] Electron Microscopy…”

“…On the other hand, the sample LN1-S74 possessing PB cylinders in PS matrix, whose composition is equivalent to that of lamellar star block copolymer ST2-S74, exhibited highly localised craze-like deformation zones. [14] The strain localisation in the form of craze-like deformation zones resulted in decreased tensile toughness of cylindrical block copolymer. The high value of ductility observed in sample LN4-S65 cannot be assigned to the energy absorbed during plastic deformation because most of the energy is only temporarily accumulated due to non-linear elastic behaviour of this block copolymer.…”

The properties, morphology and structure of BPDA/ PPD/ BOA polyimide fibers

“…Moreover, there are two T g s and only one for as-imidized and heat-drawn fiber at high temperature region, respectively. The phenomenon indicated that microphase separation existed in as-imidized fiber, which also appeared in many block copolymer systems [20,21] and was basically eliminated by heat-drawn process. The tanδ represents the energy consumption of the segmental movement, which is related to the structural homogeneity of the polymer.…”