This paper describes morphological development in solvent-cast polystyrene (PS)-polybutadiene (PB)-polystyrene (SBS) triblock copolymer thin films (30 wt % PS) as a function of solvent evaporation rate and post-evaporation annealing. Films were cast onto NaCl substrates to a thickness of order 100 nm. Plan-view and cross-sectional measurements by transmission electron microscopy show that the equilibrium morphology of in-plane cylinders is generated when films are given relatively long exposure to high solvent concentration or to elevated temperature. Alternate and metastable morphologies are generated under kinetically constrained conditions. Fast evaporation (∼200 nL/s) produces a microphase-separated microstructure with no long-range order. Intermediate evaporation (∼5 nL/s) generates hexagonally packed (vertical) PS cylinders in a PB matrix with the cylinder axis perpendicular to the film plane. Slow evaporation (∼1.5 nL/s) leads to a duplex microstructure of PS cylinders with domains of either vertical or in-plane cylinders. Post-evaporation annealing of films supported by a Cu TEM grid (18 h, 140 °C) converts the duplex morphology into one with only in-plane PS cylinders. Very slow solvent evaporation (∼0.2 nL/s) produces a fully in-plane cylinder microstructure. A distortion of the hexagonal PS array in the as-cast in-plane structure suggests that the as-cast block copolymer is affected by anisotropic deswelling during the final stages of solvent evaporation.

This paper presents the results of transmission electron microscopy (TEM) studies on the distribution of polystyrene/polyisoprene/polystyrene (SIS) triblock copolymer compatibilizer in polystyrene-polyethylene homopolymer blends. The principal independent variable studied is the major-phase rheological properties (PSmajor/PEminor and PEmajor/PSmimor blends). The polyisoprene block was preferentially stained by OSO4 and could be clearly identified in cryo-ultramicrotomed TEM sections. The microstructural data show that when the Theologically strong PS phase is the major constituent, the compatibilizer follows the classical model localizing itself at the PS/PE interface. In the PEmajor/PSminor blends, however, the SIS compatibilizer is not localized at the PE/PS interface. Instead microdispersions of PS in SIS form which in turn are dispersed in the PE matrix. While the various microstructures are affected by the mixing protocol and polymer rheology, quiescent annealing after mixing indicates that the compatibilizer distribution is in part driven by thermodynamic effects.