| Polymer crystallization within nano-confined environments has received substantial attention over the past decade. It is well known that diblock copolymers can form various ordered morphologies on the length scale of a few nanometers, such as lamellae, double gyroid, hexagonal perforated layer (HPL), cylinder and sphere. Therefore, crystalline-amorphous diblock copolymers are usually selected as templates to develop well-defined and uniform nano-environments. Generally, crystallization of the crystallizable blocks can be efficiently confined within nano-environments when the amorphous blocks vitrify prior to the crystallization. Various crystal orientations have been reported for different samples in the flat one-dimensionally (1D) confining lamellae and the curved two-dimensionally (2D) confining cylinders. Recently our group has reported crystallization temperature (Tc)-dependent crystal orientations in 1D confining lamellae for a poly(ethylene oxide)- b-polystyrene (PEO-b-PS) diblock copolymer. With increasing Tc the crystal c-axis orientation changed from random, to parallel, to inclined, and finally to perpendicular with respect to the lamellae surface.; In this research, the PEO-b-PS diblock copolymers with different molecular weights and different compositions and their blends were used. For each sample, the order-disorder transition temperature ( TODT) was above the glass transition temperature ( Tg) of PS block, which is greater than the T c of the PEO block, so the crystallization of PEO would take place under the nano-confinement of the glassy PS phase. Using 2D simultaneous small angle and wide angle X-ray scattering (2D SAXS and WAXS), the Tc-dependence of the PEO chain orientation in the crystals has been found within lamellar, cylindrical, and hexagonal perforated layers nano-confined morphologies. The chain tilt angle was found to increase with increasing Tc. In the cylindrical morphology, the relationships between the tilt angle and the Tc for different samples, that have almost the same confine size, are nearly identical. In the lamellar morphology, the temperature range where the PEO chains have a tilted orientation decreased with increasing confinement size. In the HPL morphology, confinement comes not only from the PS layer, but also from the "cages" of PS cylinders in the PEO layer. The Tc-dependent PEO chain orientation in the crystals is thus different from those in the case of lamellar confinement. In general, the Tc-dependant crystal orientations not only critically depend on the PEO-block nucleation density and crystal sizes, the confinement size also plays an important role. |
