Effect of Stretching on the Structure of Cylinder- and Sphere-Forming Styrene−Isoprene−Styrene Block Copolymers

Abstract

Two styrene-isoprene-styrene block copolymers Vector 4111 and 4113, exhibiting cylindrical (18 wt % PS) and spherical (16 wt % PS) morphology, respectively, have been examined under uniaxial elongation up to 200% strain. On the basis of stress-strain data, mechanical properties are compared for isotropic and oriented polystyrene domains. The structure at various stages of deformation has been determined from SAXS patterns in three planes and two principal deformation directions with respect to orientation. Samples showed a very high degree of hexagonal packing, resulting in an X-ray pattern taken parallel to the cylinder alignment approaching single crystal ordering. Cylinders were aligned with the closest packed planes parallel to film surface. Particular attention has been paid to a lattice deformation process occurring during the first stretching and relaxation cycle. For a copolymer with oriented cylindrical morphology the deformation was affine up to 120% strain. The microdomain spacing was calculated parallel and perpendicular to the stretching direction. The cylindrical microstructure orientation, quantified by Hermans' orientation factor reduced during elongation of oriented polymer, while the elongation of isotropic sample caused an increase of orientation. Deformation of all studied morphologies was reversible.

A Computational Tool for the Microstructure Optimization of a Polymeric Heart Valve Prosthesis

“…We have already demonstrated the possibility of orienting the material microstructure in compression and injection molded flat samples [31,40]. Also, we have fabricated compression molded valves that showed acceptable hydrodynamic behavior; although, in these valves, the material microstructure was not optimized.…”

“…The mechanical behavior of block copolymers is characterized by a nonlinear stress-strain relationship which is strongly dependent on the microdomain architecture [39,40]. In fact, block copolymers with cylindrical domains can show either isotropic or anisotropic behavior, depending on the orientation of the material [40].…”

“…In fact, block copolymers with cylindrical domains can show either isotropic or anisotropic behavior, depending on the orientation of the material [40]. The mechanical behavior of block copolymers can be well described by a hyperelastic constitutive law, where the material response is determined by a strain energy function ψ.…”

Nanofluid slip flow over a stretching cylinder with Schmidt and Péclet number effects

“…1 Stasiak et al 2 have reported in detail on the influence of stretching on fluid mechanical properties of biopolymer cylinder coatings. Furthermore in Thomas and Yang 3 many applications are documented for stretching nano-bio-polymers on cylinders, sheets, wedges and other geometries to achieve modified properties.…”

A Newly Developed Tri-Leaflet Polymeric Heart Valve Prosthesis

“…2 Recently, new emerging material technologies allowed the development of novel polymeric materials with improved and tunable properties: styrenic block copolymer elastomers have a suitable morphology (i.e., stiff cylindrical micro-domains) which may mimic the function and the anisotropic structure of collagen and elastin in the native valve. [3][4][5] The aim of this work was to design, develop and test in vitro PHVs prototypes, according to the outcomes of an ad-hoc implemented finite element model which minimizes the state of stress of the PHV leaflet and optimizes the coaptation area to avoid regurgitation.…”