Tethered chains in diblock copolymer structures

We study polymer chains tethered to flat semicrystalline diblock copolymer interfaces, tethered chains at spherical micellar interfaces, and mixed tethered chain layers in the bulk using small angle X-ray (SAXS) and neutron scattering (SANS), and theoretical self-consistent mean field (SCF) calculations. In dilute solution, semicrystalline diblocks form thin platelet structures consisting of a chain-folded crystalline domain between solvated layers of the amorphous block chains. Theoretical predictions from an SCF theory are compared with SAXS and SANS measurements from poly(ethylene oxide)-polystyrene (PEO/PS) and polyethylene poly(ethyl propylene) (PE/PEP) diblock copolymer solutions. The SCF predictions for the crystalline domain thickness are good for systems with short crystalline blocks or strong enthalpic interactions between the two blocks. The SANS intensity from the tethered chain structure of a PE/PEP diblock is consistent with both SCF calculations and SAXS measurements. Tethered chains at spherical interfaces have different properties arising from the increased volume available to the polymer chain as it extends away from the interface. We adapt the SCF theory for a curved geometry and propose a modified Derjaguin approximation to calculate the interaction potential between spheres with tethered chain layers. Variations in the interaction potentials with curvature are related to changes in the tethered layer structure. The range of the interaction potential generally correlates with the layer thickness predicted from scaling theory. The form of the interaction potentials represents an improvement over previously proposed functions for the interaction potentials. We calculate interaction potentials which quantitatively fit experimental data from diblock copolymer micellar suspensions. Diblock copolymers in the melt undergo microphase separation into ordered domains due to the unfavorable interactions between the two blocks and the constraint of the chemical bond joining the two blocks. We use SAXS and transmission electron microscopy to study the effect of very short diblocks on long diblock copolymer morphologies using polystyrene-polyisoprene (PS/PI) diblocks. The addition of small amounts of the short diblock (2-5 vol%) results in decreases in the domain spacing. As the short diblock concentration increases, we observe the structural transition between the long-ranged order of the pure long diblock and the disordered structure of the short diblock.