Control of morphology orientation in thin films of PS-b-PEO diblock copolymers and PS-b-PEO/resorcinol molecular complexes

One of the main limits in the use of block copolymers for nanotechnological applications lies in the poor control over the alignment of the nanoscopic domains. The self-assembling behavior of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) has been modified by stoichiometric complexation of the ethylene oxide units with resorcinol and a simple procedure to prepare nanostructured films with normally oriented cylinders is reported. By direct spin coating of a series of complexated PS-b-PEO samples with different molecular weight and composition, films with the same morphology and orientation (i.e., normally oriented packed cylinders) have been obtained, also when different nanostructures and alignments were expected on the basis of the volume fraction composition and self-assembling behavior of pure copolymers. Tuning of the cylinder diameters in the range from 20 to 50 nm was possible by varying the length of the PEO block. The effects of resorcinol complexation have been studied by differential scanning calorimetry and X-ray diffraction and the morphologies of PS-b-PEO and PS-b-PEO/resorcinol films have been monitored by atomic force microscopy and electron microscopies. DSC and XRD analyses demonstrate that resorcinol significantly influences the crystallization behavior of the PEO block. The varied interfacial and surface energies of the PEO domains and the overall reduction of the crystalline phase in PS-b-PEO/resorcinol films appear to be strictly related to the morphological changes occurring by complexation.