Morphology Dependent Microstructural Deformation and Structure-Property Relationship Studies on Styrenic Thermoplastic Elastomer Films

Thermoplastic elastomers (TPEs) containing polystyrene (PS) hold a special class of molecular chain arrangements of the hard and soft segments giving rise to many well-defined nanostructures. The orientation and ordering of these nanodomains affect the mechanical properties of TPEs to a very large extent. Accordingly in this work, we investigated this behavior and characterized the impact of different morphologies on the uniaxial tensile properties as well as the deformation of PS domains within the rubbery matrix. Various phase-separated morphologies have been obtained by solution casting bulk films of different thicknesses using four different solvents. The extent to which PS domains order and orient have been varied from 70 - 92 nm in grain sizes and parallel to vertical orientations. The domain periodicities also range from 22 nm to 26 nm. This has been correlated to the interactions of polymers and solvents and the solvent volatilities. Further, the elastic modulus decreased for laterally oriented domains compared to vertical ones and their tensile strength also reduced. Deformation resulting in anisotropic Small Angle X-ray Scattering (SAXS) has been evaluated along equatorial and meridional axes for strains until 500%. The degree of deformation (inter-domain spacing, domain distortion) swifts linearly for small strains (less than 50%) as the polystyrene domains deform in a non-affine manner throughout the extension. The study of such property dependencies play an important role in designing materials needed to withstand the requirements of specific applications.