Nanostructured materials basing on diblock copolymers have got a soaring interest due to their opportunity to exploit the microphase/nanophase separation behavior for developing materials with nanostructures in bulk and films or at surfaces. Nanotechnology with block copolymers (BCP) has therefore become one of the most innovative fields of polymer science. The work was directed to the development of nanostructured surfaces based on the phase separation of poly(pentylmethacrylate-b-methylmethacrylate) diblock copolymers (PPMA/PMMA). Following steps
- BCP synthesis and chemical characterization,
- phase separation in solid state (bulk) including mean field calculations,
- morphology and phase separation in thin films by combination of advanced physical methods
had to be intensively investigated. PPMA/PMMA with preferably lamellar and cylindrical structure were synthesized and subsequently tagged with functional groups for later incorporation of inorganic nanoobjects. The synthesis was performed by sequential living anionic polymerization of PMA and MMA. Polydispersities PDI of BCP with different molar masses and compositions were low as expected.
The phase separation behavior was estimated using the phase diagram obtained by mean field calculation based on an approach (Leibler, Benoit). Low PDI of BCP could be included into the calculation of the spinodals. The experimentally observed phase behavior was compared to the predicted one and a good correlation was found. Most of BCP were phase separated and did not show an order-disorder transition in T-SAXS, thus reflecting the high tendency of phase separation despite the chemical similarity of the blocks. Most of the samples formed a well-pronounced lamellar structure. Only a few ones in a quite narrow compositional region showed cylindrical structures. SAXS periodicities d corresponded to the total molar mass of BCP. Introduction of functionalities did not significantly change both, the type of morphology as well as the d-value. The wide range of lamellar structures in PPMA/PMMA compared to other types of BCP and the absence of bicontinuous structures may be explained by the chemical similarity of both blocks.
Thin films of PPMA/PMMA with cylindrical and lamellar bulk morphology on silicon wafer with film thickness between 25 and 120 nm and very low roughness were obtained by dip coating into weakly concentrated polymer solutions. The laterally demixed morphologies were examined by AFM and GISAXS. Film morphologies depended on the chemical composition of BCP (as in the bulk) as well as the molar mass. Very thin films with a thickness in the range or below dbulk indeed showed standing cylinders or standing lamellae often arranged in a wavy structure, but lateral to the surface. Thicker films with thickness higher than dbulk gave “lying” cylinders or lamellae arranged parallel to the surface. The periodicities of nanostructures in thin films were comparable to the periodicities obtained in bulk samples. |